Sport pertains to any form of competitive physical activity or game that aims to use, maintain or improve physical ability and skills while providing enjoyment to participants and, in some cases, entertainment to spectators. Sports can, through casual or organized participation, improve one's physical health. Hundreds of sports exist, from those between single contestants, through to those with hundreds of simultaneous participants, either in teams or competing as individuals. In certain sports such as racing, many contestants may compete, simultaneously or consecutively, with one winner; in others, the contest is between two sides, each attempting to exceed the other. Some sports allow a tie or draw, in which there is no single winner; others provide tie-breaking methods to ensure one winner and one loser. A number of contests may be arranged in a tournament producing a champion. Many sports leagues make an annual champion by arranging games in a regular sports season, followed in some cases by playoffs.Sport is generally recognised as system of activities based in physical athleticism or physical dexterity, with major competitions such as the Olympic Games admitting only sports meeting this definition. Other organisations, such as the Council of Europe, preclude activities without a physical element from classification as sports. However, a number of competitive, but non-physical, activities claim recognition as mind sports. The International Olympic Committee recognises both chess and bridge as bona fide sports, and SportAccord, the international sports federation association, recognises five non-physical sports: bridge, chess, draughts, Go and xiangqi, and limits the number of mind games which can be admitted as sports.Sport is usually governed by a set of rules or customs, which serve to ensure fair competition, and allow consistent adjudication of the winner. Winning can be determined by physical events such as scoring goals or crossing a line first. It can also be determined by judges who are scoring elements of the sporting performance, including objective or subjective measures such as technical performance or artistic impression.Records of performance are often kept, and for popular sports, this information may be widely announced or reported in sport news. Sport is also a major source of entertainment for non-participants, with spectator sport drawing large crowds to sport venues, and reaching wider audiences through broadcasting. Sport betting is in some cases severely regulated, and in some cases is central to the sport.According to A.T. Kearney, a consultancy, the global sporting industry is worth up to $620 billion as of 2013. The world's most accessible and practised sport is running, while association football is the most popular spectator sport. The precise definition of what separates a sport from other leisure activities varies between sources. The closest to an international agreement on a definition is provided by SportAccord, which is the association for all the largest international sports federations, and is therefore the de facto representative of international sport.SportAccord uses the following criteria, determining that a sport should:  have an element of competition  be in no way harmful to any living creature  not rely on equipment provided by a single supplier   not rely on any luck element specifically designed into the sport.They also recognise that sport can be primarily physical, primarily mind, predominantly motorised, primarily co-ordination, or primarily animal-supported.The inclusion of mind sports within sport definitions has not been universally accepted, leading to legal challenges from governing bodies in regards to being denied funding available to sports. Whilst SportAccord recognises a small number of mind sports, it is not open to admitting any further mind sports.There has been an increase in the application of the term sport to a wider set of non-physical challenges such as video games, also called esports, especially due to the large scale of participation and organised competition, but these are not widely recognised by mainstream sports organisations. According to Council of Europe, European Sports Charter, article 2.i, 'Sport' means all forms of physical activity which, through casual or organised participation, aim at expressing or improving physical fitness and mental well-being, forming social relationships or obtaining results in competition at all levels.Competition100m race record holder Usain Bolt and other runners, Moscow, 2013.There are opposing views on the necessity of competition as a defining element of a sport, with almost all professional sports involving competition, and governing bodies requiring competition as a prerequisite of recognition by the International Olympic Committee or SportAccord.Other bodies advocate widening the definition of sport to include all physical activity. For instance, the Council of Europe include all forms of physical exercise, including those competed just for fun.In order to widen participation, and reduce the impact of losing on less able participants, there has been an introduction of non-competitive physical activity to traditionally competitive events such as school sports days, although moves like this are often controversial.In competitive events, participants are graded or classified based on their result and often divided into groups of comparable performance,. The measurement of the result may be objective or subjective, and corrected with handicaps or penalties. In a race, for example, the time to complete the course is an objective measurement. In gymnastics or diving the result is decided by a panel of judges, and therefore subjective. There are many shades of judging between boxing and mixed martial arts, where victory is assigned by judges if neither competitor has lost at the end of the match time.HistoryMain article: History of sportRoman bronze reduction of Myron's Discobolos, 2nd century AD.Artifacts and structures suggest sport in China as early as 2000 BC. Gymnastics appears to have been popular in China's ancient past. Monuments to the Pharaohs indicate that a number of sports, including swimming and fishing, were well-developed and regulated several thousands of years ago in ancient Egypt. Other Egyptian sports included javelin throwing, high jump, and wrestling. Ancient Persian sports such as the traditional Iranian martial art of Zoorkhaneh had a close connection to warfare skills. Among other sports that originated in ancient Persia are polo and jousting.Motorised sports have appeared since the advent of the modern age.Swimmers perform squats as warm-up exercise prior to entering the pool in a U.S. military base, 2011A wide range of sports were already established by the time of Ancient Greece and the military culture and the development of sport in Greece influenced one another considerably. Sport became such a prominent part of their culture that the Greeks created the Olympic Games, which in ancient times were held every four years in a small village in the Peloponnesus called Olympia.Sports have been increasingly organised and regulated from the time of the ancient Olympics up to the present century. Industrialisation has brought increased leisure time, letting people attend and follow spectator sports and participate in athletic activities. These trends continued with the advent of mass media and global communication. Professionalism became prevalent, further adding to the increase in sport's popularity, as sports fans followed the exploits of professional athletes – all while enjoying the exercise and competition associated with amateur participation in sports. Since the turn of the 21st century, there has been increasing debate about whether transgender sports persons should be able to participate in sport events that conform with their post-transition gender identity.Fair playSportsmanshipMain article: SportsmanshipSee also: Gamesmanship and Winning isn't everything; it's the only thingSportsmanship is an attitude that strives for fair play, courtesy toward teammates and opponents, ethical behaviour and integrity, and grace in victory or defeat.Sportsmanship expresses an aspiration or ethos that the activity will be enjoyed for its own sake. The well-known sentiment by sports journalist Grantland Rice, that it's not that you won or lost but how you played the game, and the modern Olympic creed expressed by its founder Pierre de Coubertin: The most important thing... is not winning but taking part are typical expressions of this sentiment.CheatingSee also: Match fixing and cheatingKey principles of sport include that the result should not be predetermined, and that both sides should have equal opportunity to win. Rules are in place to ensure fair play, but participants can break these rules in order to gain advantage.Participants may cheat in order to unfairly increase their chance of winning, or in order to achieve other advantages such as financial gains. The widespread existence of gambling on the results of sports fixtures creates a motivation for match fixing, where a participant or participants deliberately work to ensure a given outcome rather than simply playing to win.Doping and drugsMain article: Use of performance-enhancing drugs in sportThe competitive nature of sport encourages some participants to attempt to enhance their performance through the use of medicines, or through other means such as increasing the volume of blood in their bodies through artificial means.All sports recognised by the IOC or SportAccord are required to implement a testing programme, looking for a list of banned drugs, with suspensions or bans being placed on participants who test positive for banned substances.ViolenceViolence in sports involves crossing the line between fair competition and intentional aggressive violence. Athletes, coaches, fans, and parents sometimes unleash violent behaviour on people or property, in misguided shows of loyalty, dominance, anger, or celebration. Rioting or hooliganism by fans in particular is a problem at some national and international sporting contests.ParticipationGender participationInternational level female athletes at ISTAF Berlin, 2006	This section needs expansion. You can help by adding to it. See also: Women's sports, Women's professional sports, and Women's sports in the United StatesFemale participation in sports continues to rise alongside the opportunity for involvement and the value of sports for child development and physical fitness. Despite increases in female participation during the last three decades, a gap persists in the enrolment figures between male and female players in sports-related teams. Female players account for 39% of the total participation in US interscholastic athletics.Youth participation	This section needs expansion. You can help by adding to it. See also: College sportYouth sport presents children with opportunities for fun, socialisation, forming peer relationships, physical fitness, and athletic scholarships. Activists for education and the war on drugs encourage youth sport as a means to increase educational participation and to fight the illegal drug trade. According to the Center for Injury Research and Policy at Nationwide Children's Hospital, the biggest risk for youth sport is death or serious injury including concussion. These risks come from running, basketball, association football, volleyball, gridiron, gymnastics, and ice hockey. Youth sport in the US is a $15 billion industry including equipment up to private coaching.Disabled participationA runner gives a friendly tap on the shoulder to a wheelchair racer during the Marathon International de Paris in 2014.See also: Disabled sportsDisabled sports also adaptive sports or parasports, are sports played by persons with a disability, including physical and intellectual disabilities. As many of these are based on existing sports modified to meet the needs of persons with a disability, they are sometimes referred to as adapted sports. However, not all disabled sports are adapted; several sports that have been specifically created for persons with a disability have no equivalent in able-bodied sports.Spectator involvementSpectators at the 1906 unofficial Olympic GamesMain article: Spectator sportThe competition element of sport, along with the aesthetic appeal of some sports, result in the popularity of people attending to watch sport being played. This has led to the specific phenomenon of spectator sport.Both amateur and professional sports attract spectators, both in person at the sport venue, and through broadcast media including radio, television and internet broadcast. Both attendance in person and viewing remotely can incur a sometimes substantial charge, such as an entrance ticket, or pay-per-view television broadcast.It is common for popular sports to attract large broadcast audiences, leading to rival broadcasters bidding large amounts of money for the rights to show certain fixtures. The football World Cup attracts a global television audience of hundreds of millions; the 2006 final alone attracted an estimated worldwide audience of well over 700 million and the 2011 Cricket World Cup Final attracted an estimated audience of 135 million in India alone.In the United States, the championship game of the NFL, the Super Bowl, has become one of the most watched television broadcasts of the year. Super Bowl Sunday is a de facto national holiday in America; the viewership being so great that in 2015, advertising space was reported as being sold at $4.5m for a 30-second slot.Amateur and professionalWomen's volleyball team of a U.S. university.See also: professional sport and amateur sportSport can be undertaken on an amateur, professional or semi-professional basis, depending on whether participants are incentivised for participation. Amateur participation in sport at lower levels is often called grassroots sport.The popularity of spectator sport as a recreation for non-participants has led to sport becoming a major business in its own right, and this has incentivised a high paying professional sport culture, where high performing participants are rewarded with pay far in excess of average wages, which can run into millions of dollars.Some sports, or individual competitions within a sport, retain a policy of allowing only amateur sport. The Olympic Games started with a principle of amateur competition with those who practised a sport professionally considered to have an unfair advantage over those who practised it merely as a hobby. From 1971, Olympic athletes were allowed to receive compensation and sponsorship, and from 1986, the IOC decided to make all professional athletes eligible for the Olympics, with the exceptions of boxing, and wrestling.TechnologyThese lights at the Melbourne Cricket Ground indicate the decision the third umpire makes following a review.Technology plays an important part in modern sport. With it being a necessary part of some sports, it is used in others to improve performance. Some sports also use it to allow off-field decision making.Sports science is a widespread academic discipline, and can be applied to areas including athlete performance, such as the use of video analysis to fine-tune technique, or to equipment, such as improved running shoes or competitive swimwear. Sports engineering emerged as a discipline in 1998 with an increasing focus not just on materials design but also the use of technology in sport, from analytics and big data to wearable technology. In order to control the impact of technology on fair play, governing bodies frequently have specific rules that are set to control the impact of technical advantage between participants. For example, in 2010, full-body, non-textile swimsuits were banned by FINA, as they were enhancing swimmers' performances.The increase in technology has also allowed many decisions in sports matches to be taken, or reviewed, off-field, with another official using instant replays to make decisions. In some sports, players can now challenge decisions made by officials. In Association football, goal-line technology makes decisions on whether a ball has crossed the goal line or not. The technology is not compulsory, but was used in the 2014 FIFA World Cup in Brazil, and the 2015 FIFA Women's World Cup in Canada, as well as in the Premier League from 2013–14, and the Bundesliga from 2015–16. In the NFL, a referee can ask for a review from the replay booth, or a head coach can issue a challenge to review the play using replays. The final decision rests with the referee. A video referee can also use replays to help decision-making in rugby. In international cricket, an umpire can ask the Third umpire for a decision, and the third umpire makes the final decision. Since 2008, a decision review system for players to review decisions has been introduced and used in ICC-run tournaments, and optionally in other matches. Depending on the host broadcaster, a number of different technologies are used during an umpire or player review, including instant replays, Hawk-Eye, Hot Spot and Real Time Snickometer. Hawk-Eye is also used in tennis to challenge umpiring decisions.Sports and educationResearch suggests that sports have the capacity to connect youth to positive adult role models and provide positive development opportunities, as well as promote the learning and application of life skills. In recent years the use of sport to reduce crime, as well as to prevent violent extremism and radicalization, has become more widespread, especially as a tool to improve self-esteem, enhance social bonds and provide participants with a feeling of purpose.There is no high-quality evidence that shows the effectiveness of interventions to increase sports participation of the community in sports such as mass media campaigns, educational sessions, and policy changes. There is also no high-quality studies that investigate the effect of such interventions in promoting healthy behavior change in the community.PoliticsMain article: Politics and sports	This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Benito Mussolini used the 1934 FIFA World Cup, which was held in Italy, to showcase Fascist Italy. Adolf Hitler also used the 1936 Summer Olympics held in Berlin, and the 1936 Winter Olympics held in Garmisch-Partenkirchen, to promote the Nazi ideology of the superiority of the Aryan race, and inferiority of the Jews and other undesirables. Germany used the Olympics to give off a peaceful image while secretly preparing for war.When apartheid was the official policy in South Africa, many sports people, particularly in rugby union, adopted the conscientious approach that they should not appear in competitive sports there. Some feel this was an effective contribution to the eventual demolition of the policy of apartheid, others feel that it may have prolonged and reinforced its worst effects.In the history of Ireland, Gaelic sports were connected with cultural nationalism. Until the mid-20th century a person could have been banned from playing Gaelic football, hurling, or other sports administered by the Gaelic Athletic Association if she/he played or supported Association football, or other games seen to be of British origin. Until recently the GAA continued to ban the playing of football and rugby union at Gaelic venues. This ban, also known as Rule 42, is still enforced, but was modified to allow football and rugby to be played in Croke Park while Lansdowne Road was redeveloped into Aviva Stadium. Until recently, under Rule 21, the GAA also banned members of the British security forces and members of the RUC from playing Gaelic games, but the advent of the Good Friday Agreement in 1998 led to the eventual removal of the ban.Nationalism is often evident in the pursuit of sport, or in its reporting: people compete in national teams, or commentators and audiences can adopt a partisan view. On occasion, such tensions can lead to violent confrontation among players or spectators within and beyond the sporting venue, as in the Football War. These trends are seen by many as contrary to the fundamental ethos of sport being carried on for its own sake and for the enjoyment of its participants.Sport and politics collided in the 1972 Olympics in Munich. Masked men entered the hotel of the Israeli Olympic team and killed many of their men. This was known as the Munich massacre.A study of US elections has shown that the result of sports events can affect the results. A study published in the Proceedings of the National Academy of Sciences showed that when the home team wins the game before the election, the incumbent candidates can increase their share of the vote by 1.5 percent. A loss had the opposite effect, and the effect is greater for higher-profile teams or unexpected wins and losses. Also, when Washington Redskins win their final game before an election, then the incumbent President is more likely to win, and if the Redskins lose, then the opposition candidate is more likely to win; this has become known as the Redskins Rule.As a means of controlling and subduing populationsÉtienne de La Boétie, in his essay Discourse on Voluntary Servitude describes athletic spectacles as means for tyrants to control their subjects by distracting them.  Do not imagine that there is any bird more easily caught by decoy, nor any fish sooner fixed on the hook by wormy bait, than are all these poor fools neatly tricked into servitude by the slightest feather passed, so to speak, before their mouths. Truly it is a marvellous thing that they let themselves be caught so quickly at the slightest tickling of their fancy. Plays, farces, spectacles, gladiators, strange beasts, medals, pictures, and other such opiates, these were for ancient peoples the bait toward slavery, the price of their liberty, the instruments of tyranny. By these practices and enticements the ancient dictators so successfully lulled their subjects under the yoke, that the stupefied peoples, fascinated by the pastimes and vain pleasures flashed before their eyes, learned subservience as naïvely, but not so creditably, as little children learn to read by looking at bright picture books.Religious viewsThe foot race was one of the events dedicated to Zeus. Panathenaic amphora, Kleophrades painter, circa 500 BC, Louvre museum.Sport was an important form of worship in Ancient Greek religion. The ancient Olympic Games, called the Olympiad, were held in honour of the head deity, Zeus, and featured various forms of religious dedication to him and other gods. As many Greeks travelled to see the games, this combination of religion and sport also served as a way of uniting them.The practice of athletic competitions has been criticised by some Christian thinkers as a form of idolatry, in which human beings extol themselves, adore themselves, sacrifice themselves and reward themselves. Sports are seen by these critics as a manifestation of collective pride and national self-deification in which feats of human power are idolized at the expense of divine worship.Tertullian condemns the athletic performances of his day, insisting the entire apparatus of the shows is based upon idolatry. The shows, says Tertullian, excite passions foreign to the calm temperament cultivated by the Christian:  God has enjoined us to deal calmly, gently, quietly, and peacefully with the Holy Spirit, because these things are alone in keeping with the goodness of His nature, with His tenderness and sensitiveness.... Well, how shall this be made to accord with the shows? For the show always leads to spiritual agitation, since where there is pleasure, there is keenness of feeling giving pleasure its zest; and where there is keenness of feeling, there is rivalry giving in turn its zest to that. Then, too, where you have rivalry, you have rage, bitterness, wrath and grief, with all bad things which flow from them – the whole entirely out of keeping with the religion of Christ.Christian clerics in the Wesleyan-Holiness movement oppose the viewing of or participation in professional sports, believing that professional sports leagues profane the Sabbath as in the modern era, certain associations hold games on the Lord's Day. They also criticize professional sports for its fostering of a commitment that competes with a Christian's primary commitment to God in opposition to 1 Corinthians 7:35, what they perceive to be a lack of modesty in the players' and cheerleaders' uniforms, its association with violence in opposition to Hebrews 7:26, what they perceive to be the extensive use of profanity among many players that contravenes Colossians 3:8–10, and the frequent presence of gambling, as well as alcohol and other drugs at sporting events, which go against a commitment to teetotalism. A society is a group of individuals involved in persistent social interaction, or a large social group sharing the same spatial or social territory, typically subject to the same political authority and dominant cultural expectations. Societies are characterized by patterns of relationships between individuals who share a distinctive culture and institutions; a given society may be described as the sum total of such relationships among its constituent of members. In the social sciences, a larger society often exhibits stratification or dominance patterns in subgroups.Societies construct patterns of behavior by deeming certain actions or concepts as acceptable or unacceptable. These patterns of behavior within a given society are known as societal norms. Societies, and their norms, undergo gradual and perpetual changes.Insofar as it is collaborative, a society can enable its members to benefit in ways that would otherwise be difficult on an individual basis; both individual and social benefits can thus be distinguished, or in many cases found to overlap. A society can also consist of like-minded people governed by their own norms and values within a dominant, larger society. This is sometimes referred to as a subculture, a term used extensively within criminology, and also applied to distinctive subsections of a larger society.More broadly, and especially within structuralist thought, a society may be illustrated as an economic, social, industrial or cultural infrastructure, made up of, yet distinct from, a varied collection of individuals. In this regard society can mean the objective relationships people have with the material world and with other people, rather than other people beyond the individual and their familiar social environment. Society, in general, addresses the fact that an individual has rather limited means as an autonomous unit. The great apes have always been more or less social animals, so Robinson Crusoe-like situations are either fictions or unusual corner cases to the ubiquity of social context for humans, who fall between presocial and eusocial in the spectrum of animal ethology.Cultural relativism as a widespread approach or ethic has largely replaced notions of primitive, better/worse, or progress in relation to cultures.According to anthropologist Maurice Godelier, one critical novelty in society, in contrast to humanity's closest biological relatives, is the parental role assumed by the males, which supposedly would be absent in our nearest relatives for whom paternity is not generally determinable.In political scienceSocieties may also be structured politically. In order of increasing size and complexity, there are bands, tribes, chiefdoms, and state societies. These structures may have varying degrees of political power, depending on the cultural, geographical, and historical environments that these societies must contend with. Thus, a more isolated society with the same level of technology and culture as other societies is more likely to survive than one in close proximity to others that may encroach on their resources. A society that is unable to offer an effective response to other societies it competes with will usually be subsumed into the culture of the competing society.In sociologyThe social group enables its members to benefit in ways that would not otherwise be possible on an individual basis. Both individual and social goals can thus be distinguished and considered. Ant social ethology.Sociologist Peter L. Berger defines society as...a human product, and nothing but a human product, that yet continuously acts upon its producers. According to him, society was created by humans, but this creation turns back and creates or molds humans every day.Canis lupus social ethologySociologist Gerhard Lenski differentiates societies based on their level of technology, communication, and economy: hunters and gatherers, simple agricultural, advanced agricultural, industrial, and special. This is similar to the system earlier developed by anthropologists Morton H. Fried, a conflict theorist, and Elman Service, an integration theorist, who have produced a system of classification for societies in all human cultures based on the evolution of social inequality and the role of the state. This system of classification contains four categories:  Hunter-gatherer bands. Then came the agricultural society.  Tribal societies in which there are some limited instances of social rank and prestige.  Stratified structures led by chieftains.  Civilizations, with complex social hierarchies and organized, institutional governments.In addition to this there are:  Humanity, humankind, upon which rest all the elements of society, including society's beliefs.  Virtual society, a society based on online identity, which is evolving in the information age.Over time, some cultures have progressed toward more complex forms of organization and control. This cultural evolution has a profound effect on patterns of community. Hunter-gatherer tribes settled around seasonal food stocks to become agrarian villages. Villages grew to become towns and cities. Cities turned into city-states and nation-states.Many societies distribute largess at the behest of some individual or some larger group of people. This type of generosity can be seen in all known cultures; typically, prestige accrues to the generous individual or group. Conversely, members of a society may also shun or scapegoat any members of the society who violate its norms. Mechanisms such as gift-giving, joking relationships and scapegoating, which may be seen in various types of human groupings, tend to be institutionalized within a society. Social evolution as a phenomenon carries with it certain elements that could be detrimental to the population it serves.Some societies bestow status on an individual or group of people when that individual or group performs an admired or desired action. This type of recognition is bestowed in the form of a name, title, manner of dress, or monetary reward. In many societies, adult male or female status is subject to a ritual or process of this type. Altruistic action in the interests of the larger group is seen in virtually all societies. The phenomena of community action, shunning, scapegoating, generosity, shared risk, and reward is common to many forms of society.TypesSocieties are social groups that differ according to subsistence strategies, the ways that humans use technology to provide needs for themselves. Although humans have established many types of societies throughout history, anthropologists tend to classify different societies according to the degree to which different groups within a society have unequal access to advantages such as resources, prestige, or power. Virtually all societies have developed some degree of inequality among their people through the process of social stratification, the division of members of a society into levels with unequal wealth, prestige, or power. Sociologists place societies in three broad categories: pre-industrial, industrial, and postindustrial.Pre-industrialMain article: Pre-industrial societyIn a pre-industrial society, food production, which is carried out through the use of human and animal labor, is the main economic activity. These societies can be subdivided according to their level of technology and their method of producing food. These subdivisions are hunting and gathering, pastoral, horticultural, agricultural, and feudal.Hunting and gatheringMain article: Hunter-gatherer societySan people in Botswana start a fire by hand.The main form of food production in such societies is the daily collection of wild plants and the hunting of wild animals. Hunter-gatherers move around constantly in search of food. As a result, they do not build permanent villages or create a wide variety of artifacts, and usually only form small groups such as bands and tribes. However, some hunting and gathering societies in areas with abundant resources lived in larger groups and formed complex hierarchical social structures such as chiefdom. The need for mobility also limits the size of these societies. They generally consist of fewer than 60 people and rarely exceed 100. Statuses within the tribe are relatively equal, and decisions are reached through general agreement. The ties that bind the tribe are more complex than those of the bands. Leadership is personal—charismatic—and used for special purposes only in tribal society. There are no political offices containing real power, and a chief is merely a person of influence, a sort of adviser; therefore, tribal consolidations for collective action are not governmental. The family forms the main social unit, with most members being related by birth or marriage. This type of organization requires the family to carry out most social functions, including production and education.PastoralMain article: Pastoral societyPastoralism is a slightly more efficient form of subsistence. Rather than searching for food on a daily basis, members of a pastoral society rely on domesticated herd animals to meet their food needs. Pastoralists live a nomadic life, moving their herds from one pasture to another. Because their food supply is far more reliable, pastoral societies can support larger populations. Since there are food surpluses, fewer people are needed to produce food. As a result, the division of labor becomes more complex. For example, some people become craftworkers, producing tools, weapons, and jewelry, among other items of value. The production of goods encourages trade. This trade helps to create inequality, as some families acquire more goods than others do. These families often gain power through their increased wealth. The passing on of property from one generation to another helps to centralize wealth and power. Over time emerge hereditary chieftainships, the typical form of government in pastoral societies.HorticulturalMain article: Horticulturalist societyFruits and vegetables grown in garden plots that have been cleared from the jungle or forest provide the main source of food in a horticultural society. These societies have a level of technology and complexity similar to pastoral societies. Some horticultural groups use the slash-and-burn method to raise crops. The wild vegetation is cut and burned, and ashes are used as fertilizers. Horticulturists use human labor and simple tools to cultivate the land for one or more seasons. When the land becomes barren, horticulturists clear a new plot and leave the old plot to revert to its natural state. They may return to the original land several years later and begin the process again. By rotating their garden plots, horticulturists can stay in one area for a fairly long period of time. This allows them to build semipermanent or permanent villages. The size of a village's population depends on the amount of land available for farming; thus villages can range from as few as 30 people to as many as 2000.As with pastoral societies, surplus food leads to a more complex division of labor. Specialized roles in horticultural societies include craftspeople, shamans, and traders. This role specialization allows people to create a wide variety of artifacts. As in pastoral societies, surplus food can lead to inequalities in wealth and power within horticultural political systems, developed because of the settled nature of horticultural life.AgrarianMain article: Agrarian societyPloughing with oxen in the 15th centuryAgrarian societies use agricultural technological advances to cultivate crops over a large area. Sociologists use the phrase agricultural revolution to refer to the technological changes that occurred as long as 8,500 years ago that led to cultivating crops and raising farm animals. Increases in food supplies then led to larger populations than in earlier communities. This meant a greater surplus, which resulted in towns that became centers of trade supporting various rulers, educators, craftspeople, merchants, and religious leaders who did not have to worry about locating nourishment.Greater degrees of social stratification appeared in agrarian societies. For example, women previously had higher social status because they shared labor more equally with men. In hunting and gathering societies, women even gathered more food than men. However, as food stores improved and women took on lesser roles in providing food for the family, they increasingly became subordinate to men. As villages and towns expanded into neighboring areas, conflicts with other communities inevitably occurred. Farmers provided warriors with food in exchange for protection against invasion by enemies. A system of rulers with high social status also appeared. This nobility organized warriors to protect the society from invasion. In this way, the nobility managed to extract goods from lesser members of society.Cleric, knight and peasant; an example of feudal societiesFeudalMain article: Feudal societyFeudalism was a form of society based on ownership of land. Unlike today's farmers, vassals under feudalism were bound to cultivating their lord's land. In exchange for military protection, the lords exploited the peasants into providing food, crops, crafts, homage, and other services to the landowner. The estates of the realm system of feudalism was often multigenerational; the families of peasants may have cultivated their lord's land for generations.IndustrialMain article: Industrial societiesBetween the 15th and 16th centuries, a new economic system emerged that began to replace feudalism. Capitalism is marked by open competition in a free market, in which the means of production are privately owned. Europe's exploration of the Americas served as one impetus for the development of capitalism. The introduction of foreign metals, silks, and spices stimulated great commercial activity in European societies.Industrial societies rely heavily on machines powered by fuels for the production of goods. This produced further dramatic increases in efficiency. The increased efficiency of production of the industrial revolution produced an even greater surplus than before. Now the surplus was not just agricultural goods, but also manufactured goods. This larger surplus caused all of the changes discussed earlier in the domestication revolution to become even more pronounced.Once again, the population boomed. Increased productivity made more goods available to everyone. However, inequality became even greater than before. The breakup of agricultural-based feudal societies caused many people to leave the land and seek employment in cities. This created a great surplus of labor and gave capitalists plenty of laborers who could be hired for extremely low wages.Post-industrialMain article: Post-industrial societySee also: Information revolutionPost-industrial societies are societies dominated by information, services, and high technology more than the production of goods. Advanced industrial societies are now seeing a shift toward an increase in service sectors over manufacturing and production. The United States is the first country to have over half of its workforce employed in service industries. Service industries include government, research, education, health, sales, law, and banking.Contemporary usageThe term society is currently used to cover both a number of political and scientific connotations as well as a variety of associations.WesternMain article: Western worldThe development of the Western world has brought with it the emerging concepts of Western culture, politics, and ideas, often referred to simply as Western society. Geographically, it covers at the very least the countries of Western Europe, North America, Australia, and New Zealand. It sometimes also includes Eastern Europe, South America, and Israel.The cultures and lifestyles of all of these stem from Western Europe. They all enjoy relatively strong economies and stable governments, allow freedom of religion, have chosen democracy as a form of governance, favor capitalism and international trade, are heavily influenced by Judeo-Christian values, and have some form of political and military alliance or cooperation.InformationWorld Summit on the Information Society, GenevaMain article: Information societyAlthough the concept of information society has been under discussion since the 1930s, in the modern world it is almost always applied to the manner in which information technologies have impacted society and culture. It, therefore, covers the effects of computers and telecommunications on the home, the workplace, schools, government, and various communities and organizations, as well as the emergence of new social forms in cyberspace.One of the European Union's areas of interest is the information society. Here policies are directed towards promoting an open and competitive digital economy, research into information and communication technologies, as well as their application to improve social inclusion, public services, and quality of life.The International Telecommunication Union's World Summit on the Information Society in Geneva and Tunis has led to a number of policy and application areas where action is envisaged.KnowledgeMain article: Knowledge societyThe Seoul Cyworld control roomAs the access to electronic information resources increased at the beginning of the 21st century, special attention was extended from the information society to the knowledge society. An analysis by the Irish government stated, The capacity to manipulate, store and transmit large quantities of information cheaply has increased at a staggering rate over recent years. The digitisation of information and the associated pervasiveness of the Internet are facilitating a new intensity in the application of knowledge to economic activity, to the extent that it has become the predominant factor in the creation of wealth. As much as 70 to 80 percent of economic growth is now said to be due to new and better knowledge.Other usesSustainable development.svgAbout this imageScheme of sustainable development:at the confluence of three constituent parts. People of many nations united by common political and cultural traditions, beliefs, or values are sometimes also said to form a society. When used in this context, the term is employed as a means of contrasting two or more societies whose members represent alternative conflicting and competing worldviews.Some academic, professional, and scientific associations describe themselves as societies.In some countries, e.g. the United States, France, and Latin America, the term society' is used in commerce to denote a partnership between investors or the start of a business. In the United Kingdom, partnerships are not called societies, but co-operatives or mutuals are often known as societies. The earliest roots of science can be traced to Ancient Egypt and Mesopotamia in around 3000 to 1200 BCE. Their contributions to mathematics, astronomy, and medicine entered and shaped Greek natural philosophy of classical antiquity, whereby formal attempts were made to provide explanations of events in the physical world based on natural causes. After the fall of the Western Roman Empire, knowledge of Greek conceptions of the world deteriorated in Western Europe during the early centuries of the Middle Ages, but was preserved in the Muslim world during the Islamic Golden Age. The recovery and assimilation of Greek works and Islamic inquiries into Western Europe from the 10th to 13th century revived natural philosophy, which was later transformed by the Scientific Revolution that began in the 16th century as new ideas and discoveries departed from previous Greek conceptions and traditions. The scientific method soon played a greater role in knowledge creation and it was not until the 19th century that many of the institutional and professional features of science began to take shape; along with the changing of natural philosophy to natural science.Modern science is typically divided into three major branches that consist of the natural sciences, which study nature in the broadest sense; the social sciences, which study individuals and societies; and the formal sciences, which deal with symbols governed by rules. There is disagreement, however, on whether the formal sciences actually constitute a science as they do not rely on empirical evidence. Disciplines that use existing scientific knowledge for practical purposes, such as engineering and medicine, are described as applied sciences.New knowledge in science is advanced by research from scientists who are motivated by curiosity about the world and a desire to solve problems. Contemporary scientific research is highly collaborative and is usually done by teams in academic and research institutions, government agencies, and companies. The practical impact of their work has led to the emergence of science policies that seek to influence the scientific enterprise by prioritizing the development of commercial products, armaments, health care, public infrastructure, and environmental protection. Science in a broad sense existed before the modern era and in many historical civilizations. Modern science is distinct in its approach and successful in its results, so it now defines what science is in the strictest sense of the term. Science in its original sense was a word for a type of knowledge, rather than a specialized word for the pursuit of such knowledge. In particular, it was the type of knowledge that people can communicate to each other and share. For example, knowledge about the working of natural things was gathered long before recorded history and led to the development of complex abstract thought. This is shown by the construction of complex calendars, techniques for making poisonous plants edible, public works at a national scale, such as those which harnessed the floodplain of the Yangtse with reservoirs, dams, and dikes, and buildings such as the Pyramids. However, no consistent conscious distinction was made between knowledge of such things, which are true in every community, and other types of communal knowledge, such as mythologies and legal systems. Metallurgy was known in prehistory, and the Vinča culture was the earliest known producer of bronze-like alloys. It is thought that early experimentation with heating and mixing of substances over time developed into alchemy.Earliest rootsFurther information: History of science in early culturesClay models of animal livers dating between the nineteenth and eighteenth centuries BCE, found in the royal palace in Mari, SyriaThe earliest roots of science can be traced to Ancient Egypt and Mesopotamia in around 3000 to 1200 BCE. Although the words and concepts of science and nature were not part of the conceptual landscape at the time, the ancient Egyptians and Mesopotamians made contributions that would later find a place in Greek and medieval science: mathematics, astronomy, and medicine. Starting in around 3000 BCE, the ancient Egyptians developed a numbering system that was decimal in character and had orientated their knowledge of geometry to solving practical problems such as those of surveyors and builders. They even developed an official calendar that contained twelve months, thirty days each, and five days at the end of the year. Based on the medical papyri written in the 2500-1200 BCE, the ancient Egyptians believed that disease was mainly caused by the invasion of bodies by evil forces or spirits. Thus, in addition to drug treatments, healing therapies would involve prayer, incantation, and ritual.The ancient Mesopotamians used knowledge about the properties of various natural chemicals for manufacturing pottery, faience, glass, soap, metals, lime plaster, and waterproofing; they also studied animal physiology, anatomy, and behavior for divinatory purposes and made extensive records of the movements of astronomical objects for their study of astrology. The Mesopotamians had intense interest in medicine and the earliest medical prescriptions appear in Sumerian during the Third Dynasty of Ur. Nonetheless, the Mesopotamians seem to have had little interest in gathering information about the natural world for the mere sake of gathering information and mainly only studied scientific subjects which had obvious practical applications or immediate relevance to their religious system.Classical antiquityFurther information: History of science in classical antiquity and Nature In classical antiquity, there is no real ancient analog of a modern scientist. Instead, well-educated, usually upper-class, and almost universally male individuals performed various investigations into nature whenever they could afford the time. Before the invention or discovery of the concept of nature by the Pre-Socratic philosophers, the same words tend to be used to describe the natural way in which a plant grows, and the way in which, for example, one tribe worships a particular god. For this reason, it is claimed that these men were the first philosophers in the strict sense, and also the first people to clearly distinguish nature and convention.: 209 Natural philosophy, the precursor of natural science, was thereby distinguished as the knowledge of nature and things which are true for every community, and the name of the specialized pursuit of such knowledge was philosophy – the realm of the first philosopher-physicists. They were mainly speculators or theorists, particularly interested in astronomy. In contrast, trying to use knowledge of nature to imitate nature was seen by classical scientists as a more appropriate interest for artisans of lower social class.The universe as conceived of by Aristotle and Ptolemy from Peter Apian's 1524 work Cosmographia. The Earth is composed of four elements: earth, water, fire and air. The Earth does not move or rotate. It is surrounded by concentric spheres containing the planets, the sun, the stars, and heaven.The early Greek philosophers of the Milesian school, which was founded by Thales of Miletus and later continued by his successors Anaximander and Anaximenes, were the first to attempt to explain natural phenomena without relying on the supernatural. The Pythagoreans developed a complex number philosophy: 467–68 and contributed significantly to the development of mathematical science.: 465 The theory of atoms was developed by the Greek philosopher Leucippus and his student Democritus. The Greek doctor Hippocrates established the tradition of systematic medical science and is known as The Father of Medicine.A turning point in the history of early philosophical science was Socrates' example of applying philosophy to the study of human matters, including human nature, the nature of political communities, and human knowledge itself. The Socratic method as documented by Plato's dialogues is a dialectic method of hypothesis elimination: better hypotheses are found by steadily identifying and eliminating those that lead to contradictions. This was a reaction to the Sophist emphasis on rhetoric. The Socratic method searches for general, commonly held truths that shape beliefs and scrutinizes them to determine their consistency with other beliefs. Socrates criticized the older type of study of physics as too purely speculative and lacking in self-criticism. Socrates was later, in the words of his Apology, accused of corrupting the youth of Athens because he did not believe in the gods the state believes in, but in other new spiritual beings. Socrates refuted these claims, but was sentenced to death.: 30e Aristotle later created a systematic programme of teleological philosophy: Motion and change is described as the actualization of potentials already in things, according to what types of things they are. In his physics, the Sun goes around the Earth, and many things have it as part of their nature that they are for humans. Each thing has a formal cause, a final cause, and a role in a cosmic order with an unmoved mover. The Socratics also insisted that philosophy should be used to consider the practical question of the best way to live for a human being. Aristotle maintained that man knows a thing scientifically when he possesses a conviction arrived at in a certain way, and when the first principles on which that conviction rests are known to him with certainty.The Greek astronomer Aristarchus of Samos was the first to propose a heliocentric model of the universe, with the Sun at the center and all the planets orbiting it. Aristarchus's model was widely rejected because it was believed to violate the laws of physics. The inventor and mathematician Archimedes of Syracuse made major contributions to the beginnings of calculus and has sometimes been credited as its inventor, although his proto-calculus lacked several defining features. Pliny the Elder was a Roman writer and polymath, who wrote the seminal encyclopedia Natural History, dealing with history, geography, medicine, astronomy, earth science, botany, and zoology. Other scientists or proto-scientists in Antiquity were Theophrastus, Euclid, Herophilos, Hipparchus, Ptolemy, and Galen.Medieval scienceFurther information: Byzantine science, Science in the medieval Islamic world, and European science in the Middle AgesDe potentiis anime sensitive, Gregor Reisch Margarita philosophica. Medieval science postulated a ventricle of the brain as the location for our common sense,: 189 where the forms from our sensory systems commingled.Because of the collapse of the Western Roman Empire due to the Migration Period an intellectual decline took place in the western part of Europe in the 400s. In contrast, the Byzantine Empire resisted the attacks from invaders, and preserved and improved upon the learning. John Philoponus, a Byzantine scholar in the 500s, questioned Aristotle's teaching of physics, noting its flaws.: pp.307, 311, 363, 402 John Philoponus' criticism of Aristotelian principles of physics served as an inspiration to medieval scholars as well as to Galileo Galilei who ten centuries later, during the Scientific Revolution, extensively cited Philoponus in his works while making the case for why Aristotelian physics was flawed.During late antiquity and the early Middle Ages, the Aristotelian approach to inquiries on natural phenomena was used. Aristotle's four causes prescribed that the question why should be answered in four ways in order to explain things scientifically. Some ancient knowledge was lost, or in some cases kept in obscurity, during the fall of the Western Roman Empire and periodic political struggles. However, the general fields of science and much of the general knowledge from the ancient world remained preserved through the works of the early Latin encyclopedists like Isidore of Seville. However, Aristotle's original texts were eventually lost in Western Europe, and only one text by Plato was widely known, the Timaeus, which was the only Platonic dialogue, and one of the few original works of classical natural philosophy, available to Latin readers in the early Middle Ages. Another original work that gained influence in this period was Ptolemy's Almagest, which contains a geocentric description of the solar system.During late antiquity, in the Byzantine empire many Greek classical texts were preserved. Many Syriac translations were done by groups such as the Nestorians and Monophysites. They played a role when they translated Greek classical texts into Arabic under the Caliphate, during which many types of classical learning were preserved and in some cases improved upon. In addition, the neighboring Sassanid Empire established the medical Academy of Gondeshapur where Greek, Syriac, and Persian physicians established the most important medical center of the ancient world during the 6th and 7th centuries.The House of Wisdom was established in Abbasid-era Baghdad, Iraq, where the Islamic study of Aristotelianism flourished. Al-Kindi was the first of the Muslim Peripatetic philosophers, and is known for his efforts to introduce Greek and Hellenistic philosophy to the Arab world. The Islamic Golden Age flourished from this time until the Mongol invasions of the 13th century. Ibn al-Haytham, as well as his predecessor Ibn Sahl, was familiar with Ptolemy's Optics, and used experiments as a means to gain knowledge.: 463–65 Alhazen disproved Ptolemy's theory of vision, but did not make any corresponding changes to Aristotle's metaphysics. Furthermore, doctors and alchemists such as the Persians Avicenna and Al-Razi also greatly developed the science of Medicine with the former writing the Canon of Medicine, a medical encyclopedia used until the 18th century and the latter discovering multiple compounds like alcohol. Avicenna's canon is considered to be one of the most important publications in medicine and they both contributed significantly to the practice of experimental medicine, using clinical trials and experiments to back their claims.In Classical antiquity, Greek and Roman taboos had meant that dissection was usually banned in ancient times, but in Middle Ages it changed: medical teachers and students at Bologna began to open human bodies, and Mondino de Luzzi produced the first known anatomy textbook based on human dissection.By the eleventh century, most of Europe had become Christian; stronger monarchies emerged; borders were restored; technological developments and agricultural innovations were made which increased the food supply and population. In addition, classical Greek texts started to be translated from Arabic and Greek into Latin, giving a higher level of scientific discussion in Western Europe.By 1088, the first university in Europe had emerged from its clerical beginnings. Demand for Latin translations grew; western Europeans began collecting texts written not only in Latin, but also Latin translations from Greek, Arabic, and Hebrew. Manuscript copies of Alhazen's Book of Optics also propagated across Europe before 1240,: Intro. p. xx as evidenced by its incorporation into Vitello's Perspectiva. Avicenna's Canon was translated into Latin. In particular, the texts of Aristotle, Ptolemy, and Euclid, preserved in the Houses of Wisdom and also in the Byzantine Empire, were sought amongst Catholic scholars. The influx of ancient texts caused the Renaissance of the 12th century and the flourishing of a synthesis of Catholicism and Aristotelianism known as Scholasticism in western Europe, which became a new geographic center of science. An experiment in this period would be understood as a careful process of observing, describing, and classifying. One prominent scientist in this era was Roger Bacon. Scholasticism had a strong focus on revelation and dialectic reasoning, and gradually fell out of favour over the next centuries, as alchemy's focus on experiments that include direct observation and meticulous documentation slowly increased in importance.Renaissance and early modern scienceFurther information: Scientific RevolutionAstronomy became more accurate after Tycho Brahe devised his scientific instruments for measuring angles between two celestial bodies, before the invention of the telescope. Brahe's observations were the basis for Kepler's laws.New developments in optics played a role in the inception of the Renaissance, both by challenging long-held metaphysical ideas on perception, as well as by contributing to the improvement and development of technology such as the camera obscura and the telescope. Before what we now know as the Renaissance started, Roger Bacon, Vitello, and John Peckham each built up a scholastic ontology upon a causal chain beginning with sensation, perception, and finally apperception of the individual and universal forms of Aristotle. A model of vision later known as perspectivism was exploited and studied by the artists of the Renaissance. This theory uses only three of Aristotle's four causes: formal, material, and final.In the sixteenth century, Copernicus formulated a heliocentric model of the solar system unlike the geocentric model of Ptolemy's Almagest. This was based on a theorem that the orbital periods of the planets are longer as their orbs are farther from the centre of motion, which he found not to agree with Ptolemy's model.Kepler and others challenged the notion that the only function of the eye is perception, and shifted the main focus in optics from the eye to the propagation of light.: 102 Kepler modelled the eye as a water-filled glass sphere with an aperture in front of it to model the entrance pupil. He found that all the light from a single point of the scene was imaged at a single point at the back of the glass sphere. The optical chain ends on the retina at the back of the eye. Kepler is best known, however, for improving Copernicus' heliocentric model through the discovery of Kepler's laws of planetary motion. Kepler did not reject Aristotelian metaphysics and described his work as a search for the Harmony of the Spheres.Galileo made innovative use of experiment and mathematics. However, he became persecuted after Pope Urban VIII blessed Galileo to write about the Copernican system. Galileo had used arguments from the Pope and put them in the voice of the simpleton in the work Dialogue Concerning the Two Chief World Systems, which greatly offended Urban VIII.In Northern Europe, the new technology of the printing press was widely used to publish many arguments, including some that disagreed widely with contemporary ideas of nature. René Descartes and Francis Bacon published philosophical arguments in favor of a new type of non-Aristotelian science. Descartes emphasized individual thought and argued that mathematics rather than geometry should be used in order to study nature. Bacon emphasized the importance of experiment over contemplation. Bacon further questioned the Aristotelian concepts of formal cause and final cause, and promoted the idea that science should study the laws of simple natures, such as heat, rather than assuming that there is any specific nature, or formal cause, of each complex type of thing. This new science began to see itself as describing laws of nature. This updated approach to studies in nature was seen as mechanistic. Bacon also argued that science should aim for the first time at practical inventions for the improvement of all human life.Age of EnlightenmentIsaac Newton's copy of Principia from 1687. Newton made seminal contributions to classical mechanics, gravity, and optics. Newton also shares credit with Gottfried Leibniz for the development of calculus.As a precursor to the Age of Enlightenment, Isaac Newton and Gottfried Wilhelm Leibniz succeeded in developing a new physics, now referred to as classical mechanics, which could be confirmed by experiment and explained using mathematics, Philosophiæ Naturalis Principia Mathematica). Leibniz also incorporated terms from Aristotelian physics, but now being used in a new non-teleological way, for example, energy and potential. This implied a shift in the view of objects: Where Aristotle had noted that objects have certain innate goals that can be actualized, objects were now regarded as devoid of innate goals. In the style of Francis Bacon, Leibniz assumed that different types of things all work according to the same general laws of nature, with no special formal or final causes for each type of thing. It is during this period that the word science gradually became more commonly used to refer to a type of pursuit of a type of knowledge, especially knowledge of nature – coming close in meaning to the old term natural philosophy.During this time, the declared purpose and value of science became producing wealth and inventions that would improve human lives, in the materialistic sense of having more food, clothing, and other things. In Bacon's words, the real and legitimate goal of sciences is the endowment of human life with new inventions and riches, and he discouraged scientists from pursuing intangible philosophical or spiritual ideas, which he believed contributed little to human happiness beyond the fume of subtle, sublime, or pleasing speculation.Science during the Enlightenment was dominated by scientific societies and academies, which had largely replaced universities as centres of scientific research and development. Societies and academies were also the backbones of the maturation of the scientific profession. Another important development was the popularization of science among an increasingly literate population. Philosophes introduced the public to many scientific theories, most notably through the Encyclopédie and the popularization of Newtonianism by Voltaire as well as by Émilie du Châtelet, the French translator of Newton's Principia.Some historians have marked the 18th century as a drab period in the history of science; however, the century saw significant advancements in the practice of medicine, mathematics, and physics; the development of biological taxonomy; a new understanding of magnetism and electricity; and the maturation of chemistry as a discipline, which established the foundations of modern chemistry.Enlightenment philosophers chose a short history of scientific predecessors – Galileo, Boyle, and Newton principally – as the guides and guarantors of their applications of the singular concept of nature and natural law to every physical and social field of the day. In this respect, the lessons of history and the social structures built upon it could be discarded.Ideas on human nature, society, and economics also evolved during the Enlightenment. Hume and other Scottish Enlightenment thinkers developed a science of man, which was expressed historically in works by authors including James Burnett, Adam Ferguson, John Millar and William Robertson, all of whom merged a scientific study of how humans behaved in ancient and primitive cultures with a strong awareness of the determining forces of modernity. Modern sociology largely originated from this movement. In 1776, Adam Smith published The Wealth of Nations, which is often considered the first work on modern economics.19th centuryThe first diagram of an evolutionary tree made by Charles Darwin in 1837, which eventually led to his most famous work, On the Origin of Species, in 1859.The nineteenth century is a particularly important period in the history of science since during this era many distinguishing characteristics of contemporary modern science began to take shape such as: transformation of the life and physical sciences, frequent use of precision instruments, emergence of terms like biologist, physicist, scientist; slowly moving away from antiquated labels like natural philosophy and natural history, increased professionalization of those studying nature lead to reduction in amateur naturalists, scientists gained cultural authority over many dimensions of society, economic expansion and industrialization of numerous countries, thriving of popular science writings and emergence of science journals.Early in the 19th century, John Dalton suggested the modern atomic theory, based on Democritus's original idea of indivisible particles called atoms.Both John Herschel and William Whewell systematized methodology: the latter coined the term scientist.During the mid-19th century, Charles Darwin and Alfred Russel Wallace independently proposed the theory of evolution by natural selection in 1858, which explained how different plants and animals originated and evolved. Their theory was set out in detail in Darwin's book On the Origin of Species, which was published in 1859. Separately, Gregor Mendel presented his paper, Versuche über Pflanzenhybriden, in 1865, which outlined the principles of biological inheritance, serving as the basis for modern genetics.The laws of conservation of energy, conservation of momentum and conservation of mass suggested a highly stable universe where there could be little loss of resources. With the advent of the steam engine and the industrial revolution, there was, however, an increased understanding that all forms of energy as defined in physics were not equally useful: they did not have the same energy quality. This realization led to the development of the laws of thermodynamics, in which the free energy of the universe is seen as constantly declining: the entropy of a closed universe increases over time.The electromagnetic theory was also established in the 19th century by the works of Hans Christian Ørsted, André-Marie Ampère, Michael Faraday, James Clerk Maxwell, Oliver Heaviside, and Heinrich Hertz. The new theory raised questions that could not easily be answered using Newton's framework. The phenomena that would allow the deconstruction of the atom were discovered in the last decade of the 19th century: the discovery of X-rays inspired the discovery of radioactivity. In the next year came the discovery of the first subatomic particle, the electron.During the late 19th century, psychology emerged as a separate discipline from philosophy when Wilhelm Wundt founded the first laboratory for psychological research in 1879.20th centuryThe DNA double helix is a molecule that encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses.Albert Einstein's theory of relativity and the development of quantum mechanics led to the replacement of classical mechanics with a new physics which contains two parts that describe different types of events in nature.In the first half of the century, the development of antibiotics and artificial fertilizers made global human population growth possible. At the same time, the structure of the atom and its nucleus was discovered, leading to the release of atomic energy. In addition, the extensive use of technological innovation stimulated by the wars of this century led to revolutions in transportation, the development of ICBMs, a space race, and a nuclear arms race.Evolution became a unified theory in the early 20th-century when the modern synthesis reconciled Darwinian evolution with classical genetics. The molecular structure of DNA was discovered by James Watson and Francis Crick in 1953.The discovery of the cosmic microwave background radiation in 1964 led to a rejection of the Steady State theory of the universe in favor of the Big Bang theory of Georges Lemaître.The development of spaceflight in the second half of the century allowed the first astronomical measurements done on or near other objects in space, including six manned landings on the Moon. Space telescopes lead to numerous discoveries in astronomy and cosmology.Widespread use of integrated circuits in the last quarter of the 20th century combined with communications satellites led to a revolution in information technology and the rise of the global internet and mobile computing, including smartphones. The need for mass systematization of long, intertwined causal chains and large amounts of data led to the rise of the fields of systems theory and computer-assisted scientific modelling, which are partly based on the Aristotelian paradigm.Harmful environmental issues such as ozone depletion, acidification, eutrophication and climate change came to the public's attention in the same period, and caused the onset of environmental science and environmental technology.21st centuryA simulated event in the CMS detector of the Large Hadron Collider, featuring a possible appearance of the Higgs bosonThe Human Genome Project was completed in 2003, determining the sequence of nucleotide base pairs that make up human DNA, and identifying and mapping all of the genes of the human genome. Induced pluripotent stem cells were developed in 2006, a technology allowing adult cells to be transformed into stem cells capable of giving rise to any cell type found in the body, potentially of huge importance to the field of regenerative medicine.With the discovery of the Higgs boson in 2012, the last particle predicted by the Standard Model of particle physics was found. In 2015, gravitational waves, predicted by general relativity a century before, were first observed.In 2019, the Event Horizon Telescope Observatory announced its first results in simultaneous press conferences around the world on April 10, 2019. Press conferences presented the first direct image of a black hole, where the supermassive black hole appeared in the heart of the galaxy Messier 87, which is 55 million light-years away from Earth. The scientific findings are presented in a series of six papers published in The Astrophysical Journal.Branches of scienceThe scale of the Universe mapped to branches of science and showing how one system is built atop the next through the hierarchy of the sciencesModern science is commonly divided into three major branches: natural science, social science, and formal science. Each of these branches comprises various specialized yet overlapping scientific disciplines that often possess their own nomenclature and expertise. Both natural and social sciences are empirical sciences, as their knowledge is based on empirical observations and is capable of being tested for its validity by other researchers working under the same conditions.There are also closely related disciplines that use science, such as engineering and medicine, which are sometimes described as applied sciences. The relationships between the branches of science are summarized by the following table.	ScienceEmpirical sciences Formal scienceNatural science Social scienceBasic Physics, chemistry, biology, earth science, and space science Anthropology, economics, political science, human geography, psychology, and sociology Logic, mathematics, and statisticsApplied Engineering, agricultural science, medicine, and materials science Business administration, public policy, marketing, law, pedagogy, and international development Computer scienceNatural scienceFurther information: Outline of natural scienceNatural science is the study of the physical world. It can be divided into two main branches: life science and physical science. These two branches may be further divided into more specialized disciplines. For example, physical science can be subdivided into physics, chemistry, astronomy, and earth science. Modern natural science is the successor to the natural philosophy that began in Ancient Greece. Galileo, Descartes, Bacon, and Newton debated the benefits of using approaches which were more mathematical and more experimental in a methodical way. Still, philosophical perspectives, conjectures, and presuppositions, often overlooked, remain necessary in natural science. Systematic data collection, including discovery science, succeeded natural history, which emerged in the 16th century by describing and classifying plants, animals, minerals, and so on. Today, natural history suggests observational descriptions aimed at popular audiences.Social scienceFurther information: Outline of social scienceIn economics, the supply and demand model describes how prices vary in a market economy as a result of a balance between product availability and consumer demand.Social science is the study of human behavior and functioning of societies. It has many disciplines that include, but are not limited to anthropology, economics, history, human geography, political science, psychology, and sociology. In the social sciences, there are many competing theoretical perspectives, many of which are extended through competing research programs such as the functionalists, conflict theorists, and interactionists in sociology. Due to the limitations of conducting controlled experiments involving large groups of individuals or complex situations, social scientists may adopt other research methods such as the historical method, case studies, and cross-cultural studies. Moreover, if quantitative information is available, social scientists may rely on statistical approaches to better understand social relationships and processes.Formal scienceFurther information: Outline of formal scienceFormal science is an area of study that generates knowledge using formal systems. It includes mathematics, systems theory, and theoretical computer science. The formal sciences share similarities with the other two branches by relying on objective, careful, and systematic study of an area of knowledge. They are, however, different from the empirical sciences as they rely exclusively on deductive reasoning, without the need for empirical evidence, to verify their abstract concepts. The formal sciences are therefore a priori disciplines and because of this, there is disagreement on whether they actually constitute a science. Nevertheless, the formal sciences play an important role in the empirical sciences. Calculus, for example, was initially invented to understand motion in physics. Natural and social sciences that rely heavily on mathematical applications include mathematical physics, mathematical chemistry, mathematical biology, mathematical finance, and mathematical economics.Applied scienceFurther information: Outline of applied scienceLouis Pasteur's pasteurization experiment illustrates that the spoilage of liquid is caused by particles in the air rather than the liquid itself. Pasteur also discovered the principles of vaccination and fermentation.Applied science is the use of the scientific method and knowledge to attain practical goals and includes a broad range of disciplines such as engineering and medicine. Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. Engineering itself encompasses a range of more specialized fields of engineering, each with a more specific emphasis on particular areas of applied mathematics, science, and types of application. Medicine is the practice of caring for patients by maintaining and restoring health through the prevention, diagnosis, and treatment of injury or disease. Contemporary medicine applies biomedical sciences, medical research, genetics, and medical technology to prevent, diagnose, and treat injury and disease, typically through the use of medications, medical devices, surgery, and non-pharmacological interventions. The applied sciences are often contrasted with the basic sciences, which are focused on advancing scientific theories and laws that explain and predict events in the natural world.Scientific researchFurther information: ResearchScientific research can be labeled as either basic or applied research. Basic research is the search for knowledge and applied research is the search for solutions to practical problems using this knowledge. Although some scientific research is applied research into specific problems, a great deal of our understanding comes from the curiosity-driven undertaking of basic research. This leads to options for technological advances that were not planned or sometimes even imaginable. This point was made by Michael Faraday when allegedly in response to the question what is the use of basic research? he responded: Sir, what is the use of a new-born child?. For example, research into the effects of red light on the human eye's rod cells did not seem to have any practical purpose; eventually, the discovery that our night vision is not troubled by red light would lead search and rescue teams to adopt red light in the cockpits of jets and helicopters. Finally, even basic research can take unexpected turns, and there is some sense in which the scientific method is built to harness luck.Scientific methodThe scientific method originated with Aristotle's idea that knowledge came from careful observation, and was brought into modern form by Galileo's collection of empirical evidence.Scientific research involves using the scientific method, which seeks to objectively explain the events of nature in a reproducible way. An explanatory thought experiment or hypothesis is put forward as explanation using principles such as parsimony and are generally expected to seek consilience – fitting well with other accepted facts related to the phenomena. This new explanation is used to make falsifiable predictions that are testable by experiment or observation. The predictions are to be posted before a confirming experiment or observation is sought, as proof that no tampering has occurred. Disproof of a prediction is evidence of progress. This is done partly through observation of natural phenomena, but also through experimentation that tries to simulate natural events under controlled conditions as appropriate to the discipline. Experimentation is especially important in science to help establish causal relationships.When a hypothesis proves unsatisfactory, it is either modified or discarded. If the hypothesis survived testing, it may become adopted into the framework of a scientific theory, a logically reasoned, self-consistent model or framework for describing the behavior of certain natural phenomena. A theory typically describes the behavior of much broader sets of phenomena than a hypothesis; commonly, a large number of hypotheses can be logically bound together by a single theory. Thus a theory is a hypothesis explaining various other hypotheses. In that vein, theories are formulated according to most of the same scientific principles as hypotheses. In addition to testing hypotheses, scientists may also generate a model, an attempt to describe or depict the phenomenon in terms of a logical, physical or mathematical representation and to generate new hypotheses that can be tested, based on observable phenomena.While performing experiments to test hypotheses, scientists may have a preference for one outcome over another, and so it is important to ensure that science as a whole can eliminate this bias. This can be achieved by careful experimental design, transparency, and a thorough peer review process of the experimental results as well as any conclusions. After the results of an experiment are announced or published, it is normal practice for independent researchers to double-check how the research was performed, and to follow up by performing similar experiments to determine how dependable the results might be. Taken in its entirety, the scientific method allows for highly creative problem solving while minimizing any effects of subjective bias on the part of its users.VerifiabilityJohn Ziman points out that intersubjective verifiability is fundamental to the creation of all scientific knowledge. Ziman shows how scientists can identify patterns to each other across centuries; he refers to this ability as perceptual consensibility. He then makes consensibility, leading to consensus, the touchstone of reliable knowledge.Role of mathematicsCalculus, the mathematics of continuous change, underpins many of the sciences.Mathematics is essential in the formation of hypotheses, theories, and laws in the natural and social sciences. For example, it is used in quantitative scientific modeling, which can generate new hypotheses and predictions to be tested. It is also used extensively in observing and collecting measurements. Statistics, a branch of mathematics, is used to summarize and analyze data, which allow scientists to assess the reliability and variability of their experimental results.Computational science applies computing power to simulate real-world situations, enabling a better understanding of scientific problems than formal mathematics alone can achieve. The use of machine learning is becoming a central feature of computational contributions to science for example in agent-based computational economics, random forests, topic modelling and various forms of prediction. According to the Society for Industrial and Applied Mathematics, computation is now as important as theory and experiment in advancing scientific knowledge. However, machines alone rarely advance knowledge as they require human guidance and capacity to reason; and they can introduce bias against certain social groups or sometimes underperform compared to humans. Thus, machine learning is often used in science as prediction in the service of estimation.Philosophy of scienceFurther information: Philosophy of scienceScientists usually take for granted a set of basic assumptions that are needed to justify the scientific method: that there is an objective reality shared by all rational observers; that this objective reality is governed by natural laws; that these laws can be discovered by means of systematic observation and experimentation. The philosophy of science seeks a deep understanding of what these underlying assumptions mean and whether they are valid.The belief that scientific theories should and do represent metaphysical reality is known as realism. It can be contrasted with anti-realism, the view that the success of science does not depend on it being accurate about unobservable entities such as electrons. One form of anti-realism is idealism, the belief that the mind or consciousness is the most basic essence, and that each mind generates its own reality. In an idealistic world view, what is true for one mind need not be true for other minds.There are different schools of thought in the philosophy of science. The most popular position is empiricism, which holds that knowledge is created by a process involving observation and that scientific theories are the result of generalizations from such observations. Empiricism generally encompasses inductivism, a position that tries to explain the way general theories can be justified by the finite number of observations humans can make and hence the finite amount of empirical evidence available to confirm scientific theories. This is necessary because the number of predictions those theories make is infinite, which means that they cannot be known from the finite amount of evidence using deductive logic only. Many versions of empiricism exist, with the predominant ones being Bayesianism and the hypothetico-deductive method.The Horse in Motion falsifies the flying gallop. Karl Popper, best known for his work on empirical falsification, proposed replacing verifiability with conjecture and refutation as the landmark of scientific theories.Empiricism has stood in contrast to rationalism, the position originally associated with Descartes, which holds that knowledge is created by the human intellect, not by observation. Critical rationalism is a contrasting 20th-century approach to science, first defined by Austrian-British philosopher Karl Popper. Popper rejected the way that empiricism describes the connection between theory and observation. He claimed that theories are not generated by observation, but that observation is made in the light of theories and that the only way a theory can be affected by observation is when it comes in conflict with it. Popper proposed replacing verifiability with falsifiability as the landmark of scientific theories and replacing induction with falsification as the empirical method. Popper further claimed that there is actually only one universal method, not specific to science: the negative method of criticism, trial and error. It covers all products of the human mind, including science, mathematics, philosophy, and art.Another approach, instrumentalism, emphasizes the utility of theories as instruments for explaining and predicting phenomena. It views scientific theories as black boxes with only their input and output being relevant. Consequences, theoretical entities, and logical structure are claimed to be something that should simply be ignored and that scientists should not make a fuss about. Close to instrumentalism is constructive empiricism, according to which the main criterion for the success of a scientific theory is whether what it says about observable entities is true.For Kuhn, the addition of epicycles in Ptolemaic astronomy was normal science within a paradigm, whereas the Copernican revolution was a paradigm shift.Thomas Kuhn argued that the process of observation and evaluation takes place within a paradigm, a logically consistent portrait of the world that is consistent with observations made from its framing. He characterized normal science as the process of observation and puzzle solving which takes place within a paradigm, whereas revolutionary science occurs when one paradigm overtakes another in a paradigm shift. Each paradigm has its own distinct questions, aims, and interpretations. The choice between paradigms involves setting two or more portraits against the world and deciding which likeness is most promising. A paradigm shift occurs when a significant number of observational anomalies arise in the old paradigm and a new paradigm makes sense of them. That is, the choice of a new paradigm is based on observations, even though those observations are made against the background of the old paradigm. For Kuhn, acceptance or rejection of a paradigm is a social process as much as a logical process. Kuhn's position, however, is not one of relativism.Finally, another approach often cited in debates of scientific skepticism against controversial movements like creation science is methodological naturalism. Its main point is that a difference between natural and supernatural explanations should be made and that science should be restricted methodologically to natural explanations. That the restriction is merely methodological means that science should not consider supernatural explanations itself, but should not claim them to be wrong either. Instead, supernatural explanations should be left a matter of personal belief outside the scope of science. Methodological naturalism maintains that proper science requires strict adherence to empirical study and independent verification as a process for properly developing and evaluating explanations for observable phenomena. The absence of these standards, arguments from authority, biased observational studies and other common fallacies are frequently cited by supporters of methodological naturalism as characteristic of the non-science they criticize.Certainty and scienceA scientific theory is empirical and is always open to falsification if new evidence is presented. That is, no theory is ever considered strictly certain as science accepts the concept of fallibilism. The philosopher of science Karl Popper sharply distinguished truth from certainty. He wrote that scientific knowledge consists in the search for truth, but it is not the search for certainty... All human knowledge is fallible and therefore uncertain.New scientific knowledge rarely results in vast changes in our understanding. According to psychologist Keith Stanovich, it may be the media's overuse of words like breakthrough that leads the public to imagine that science is constantly proving everything it thought was true to be false. While there are such famous cases as the theory of relativity that required a complete reconceptualization, these are extreme exceptions. Knowledge in science is gained by a gradual synthesis of information from different experiments by various researchers across different branches of science; it is more like a climb than a leap. Theories vary in the extent to which they have been tested and verified, as well as their acceptance in the scientific community. For example, heliocentric theory, the theory of evolution, relativity theory, and germ theory still bear the name theory even though, in practice, they are considered factual. Philosopher Barry Stroud adds that, although the best definition for knowledge is contested, being skeptical and entertaining the possibility that one is incorrect is compatible with being correct. Therefore, scientists adhering to proper scientific approaches will doubt themselves even once they possess the truth. The fallibilist C. S. Peirce argued that inquiry is the struggle to resolve actual doubt and that merely quarrelsome, verbal, or hyperbolic doubt is fruitless – but also that the inquirer should try to attain genuine doubt rather than resting uncritically on common sense. He held that the successful sciences trust not to any single chain of inference but to the cable of multiple and various arguments intimately connected.Stanovich also asserts that science avoids searching for a magic bullet; it avoids the single-cause fallacy. This means a scientist would not ask merely What is the cause of..., but rather What are the most significant causes of.... This is especially the case in the more macroscopic fields of science. Research often analyzes few factors at once, but these are always added to the long list of factors that are most important to consider. For example, knowing the details of only a person's genetics, or their history and upbringing, or the current situation may not explain a behavior, but a deep understanding of all these variables combined can be very predictive.Scientific literatureCover of the first volume of the scientific journal Science in 1880Scientific research is published in an enormous range of scientific literature. Scientific journals communicate and document the results of research carried out in universities and various other research institutions, serving as an archival record of science. The first scientific journals, Journal des Sçavans followed by the Philosophical Transactions, began publication in 1665. Since that time the total number of active periodicals has steadily increased. In 1981, one estimate for the number of scientific and technical journals in publication was 11,500. The United States National Library of Medicine currently indexes 5,516 journals that contain articles on topics related to the life sciences. Although the journals are in 39 languages, 91 percent of the indexed articles are published in English.Most scientific journals cover a single scientific field and publish the research within that field; the research is normally expressed in the form of a scientific paper. Science has become so pervasive in modern societies that it is generally considered necessary to communicate the achievements, news, and ambitions of scientists to a wider populace.Science magazines such as New Scientist, Science & Vie, and Scientific American cater to the needs of a much wider readership and provide a non-technical summary of popular areas of research, including notable discoveries and advances in certain fields of research. Science books engage the interest of many more people. Tangentially, the science fiction genre, primarily fantastic in nature, engages the public imagination and transmits the ideas, if not the methods, of science.Recent efforts to intensify or develop links between science and non-scientific disciplines such as literature or more specifically, poetry, include the Creative Writing Science resource developed through the Royal Literary Fund.Practical impactsDiscoveries in fundamental science can be world-changing. For example:  Research Impact  Static electricity and magnetism   Electric current 	All electric appliances, dynamos, electric power stations, modern electronics, including electric lighting, television, electric heating, transcranial magnetic stimulation, deep brain stimulation, magnetic tape, loudspeaker, and the compass and lightning rod.  Diffraction 	Optics, hence fiber optic cable, modern intercontinental communications, and cable TV and internet.  Germ theory 	Hygiene, leading to decreased transmission of infectious diseases; antibodies, leading to techniques for disease diagnosis and targeted anticancer therapies.  Vaccination 	Leading to the elimination of most infectious diseases from developed countries and the worldwide eradication of smallpox.  Photovoltaic effect 	Solar cells, hence solar power, solar powered watches, calculators and other devices.  The strange orbit of Mercury and other research  leading to special and general relativity 	Satellite-based technology such as GPS, satnav and satellite communications.  Radio waves 	Radio had become used in innumerable ways beyond its better-known areas of telephony, and broadcast television and radio entertainment. Other uses included – emergency services, radar, medicine, astronomy, wireless communications, geophysics, and networking. Radio waves also led researchers to adjacent frequencies such as microwaves, used worldwide for heating and cooking food.  Radioactivity and antimatter 	Cancer treatment, Radiometric dating, nuclear reactors and weapons, mineral exploration, PET scans, and medical research.  X-rays 	Medical imaging, including computed tomography.  Crystallography and quantum mechanics 	Semiconductor devices, hence modern computing and telecommunications including the integration with wireless devices: the mobile phone, LED lamps and lasers.  Plastics 	Starting with Bakelite, many types of artificial polymers for numerous applications in industry and daily life.  Antibiotics 	Salvarsan, Penicillin, doxycycline, etc.  Nuclear magnetic resonance 	Nuclear magnetic resonance spectroscopy, magnetic resonance imaging, functional magnetic resonance imaging. ChallengesReplication crisisFurther information: MetascienceThe replication crisis is an ongoing methodological crisis primarily affecting parts of the social and life sciences in which scholars have found that the results of many scientific studies are difficult or impossible to replicate or reproduce on subsequent investigation, either by independent researchers or by the original researchers themselves. The crisis has long-standing roots; the phrase was coined in the early 2010s as part of a growing awareness of the problem. The replication crisis represents an important body of research in metascience, which aims to improve the quality of all scientific research while reducing waste.Fringe science, pseudoscience, and junk scienceAn area of study or speculation that masquerades as science in an attempt to claim a legitimacy that it would not otherwise be able to achieve is sometimes referred to as pseudoscience, fringe science, or junk science. Physicist Richard Feynman coined the term cargo cult science for cases in which researchers believe they are doing science because their activities have the outward appearance of science but actually lack the kind of utter honesty that allows their results to be rigorously evaluated. Various types of commercial advertising, ranging from hype to fraud, may fall into these categories. Science has been described as the most important tool for separating valid claims from invalid ones.There can also be an element of political or ideological bias on all sides of scientific debates. Sometimes, research may be characterized as bad science, research that may be well-intended but is actually incorrect, obsolete, incomplete, or over-simplified expositions of scientific ideas. The term scientific misconduct refers to situations such as where researchers have intentionally misrepresented their published data or have purposely given credit for a discovery to the wrong person.Scientific communityThe scientific community is a group of all interacting scientists, along with their respective societies and institutions.ScientistsGerman-born scientist Albert Einstein developed the theory of relativity. He also won the Nobel Prize in Physics in 1921 for his explanation of the photoelectric effect.Scientists are individuals who conduct scientific research to advance knowledge in an area of interest. The term scientist was coined by William Whewell in 1833. In modern times, many professional scientists are trained in an academic setting and upon completion, attain an academic degree, with the highest degree being a doctorate such as a Doctor of Philosophy. Many scientists pursue careers in various sectors of the economy such as academia, industry, government, and nonprofit organizations.Scientists exhibit a strong curiosity about reality, with some scientists having a desire to apply scientific knowledge for the benefit of health, nations, environment, or industries. Other motivations include recognition by their peers and prestige. The Nobel Prize, a widely regarded prestigious award, is awarded annually to those who have achieved scientific advances in the fields of medicine, physics, chemistry, and economics.Women in scienceFurther information: Women in science and Women in STEM fieldsMarie Curie was the first person to be awarded two Nobel Prizes: Physics in 1903 and Chemistry in 1911.Science has historically been a male-dominated field, with some notable exceptions. Women faced considerable discrimination in science, much as they did in other areas of male-dominated societies, such as frequently being passed over for job opportunities and denied credit for their work. For example, Christine Ladd was able to enter a Ph.D. program as C. Ladd; Christine Kitty Ladd completed the requirements in 1882, but was awarded her degree only in 1926, after a career which spanned the algebra of logic, color vision, and psychology. Her work preceded notable researchers like Ludwig Wittgenstein and Charles Sanders Peirce. The achievements of women in science have been attributed to the defiance of their traditional role as laborers within the domestic sphere.In the late 20th century, active recruitment of women and elimination of institutional discrimination on the basis of sex greatly increased the number of women scientists, but large gender disparities remain in some fields; in the early 21st century over half of the new biologists were female, while 80% of PhDs in physics are given to men. In the early part of the 21st century, women in the United States earned 50.3% of bachelor's degrees, 45.6% of master's degrees, and 40.7% of PhDs in science and engineering fields. They earned more than half of the degrees in psychology, social sciences, and biology but earned less than half the degrees in the physical sciences, earth sciences, mathematics, engineering, and computer science. Lifestyle choice also plays a major role in female engagement in science; women with young children are 28% less likely to take tenure-track positions due to work-life balance issues, and female graduate students' interest in careers in research declines dramatically over the course of graduate school, whereas that of their male colleagues remains unchanged.Learned societiesPhysicists in front of the Royal Society building in London Learned societies for the communication and promotion of scientific thought and experimentation have existed since the Renaissance. Many scientists belong to a learned society that promotes their respective scientific discipline, profession, or group of related disciplines. Membership may be open to all, may require possession of some scientific credentials, or may be an honor conferred by election. Most scientific societies are non-profit organizations, and many are professional associations. Their activities typically include holding regular conferences for the presentation and discussion of new research results and publishing or sponsoring academic journals in their discipline. Some also act as professional bodies, regulating the activities of their members in the public interest or the collective interest of the membership. Scholars in the sociology of science argue that learned societies are of key importance and their formation assists in the emergence and development of new disciplines or professions.The professionalization of science, begun in the 19th century, was partly enabled by the creation of distinguished academy of sciences in a number of countries such as the Italian Accademia dei Lincei in 1603, the British Royal Society in 1660, the French Académie des Sciences in 1666, the American National Academy of Sciences in 1863, the German Kaiser Wilhelm Institute in 1911, and the Chinese Academy of Sciences in 1928. International scientific organizations, such as the International Council for Science, have since been formed to promote cooperation between the scientific communities of different nations.Science and the publicScience and society redirects here. For the academic journal, see Science & Society. For the study of science as a social activity, see Sociology of scientific knowledge.Science policyFurther information: History of science policy and Economics of scienceThe United Nations Global Science-Policy-Business Forum on the Environment in Nairobi, Kenya Science policy is an area of public policy concerned with the policies that affect the conduct of the scientific enterprise, including research funding, often in pursuance of other national policy goals such as technological innovation to promote commercial product development, weapons development, health care, and environmental monitoring. Science policy also refers to the act of applying scientific knowledge and consensus to the development of public policies. Science policy thus deals with the entire domain of issues that involve the natural sciences. In accordance with public policy being concerned about the well-being of its citizens, science policy's goal is to consider how science and technology can best serve the public.State policy has influenced the funding of public works and science for thousands of years, particularly within civilizations with highly organized governments such as imperial China and the Roman Empire. Prominent historical examples include the Great Wall of China, completed over the course of two millennia through the state support of several dynasties, and the Grand Canal of the Yangtze River, an immense feat of hydraulic engineering begun by Sunshu Ao, Ximen Bao, and Shi Chi. This construction dates from the 6th century BCE under the Sui Dynasty and is still in use today. In China, such state-supported infrastructure and scientific research projects date at least from the time of the Mohists, who inspired the study of logic during the period of the Hundred Schools of Thought and the study of defensive fortifications like the Great Wall of China during the Warring States period.Public policy can directly affect the funding of capital equipment and intellectual infrastructure for industrial research by providing tax incentives to those organizations that fund research. Vannevar Bush, director of the Office of Scientific Research and Development for the United States government, the forerunner of the National Science Foundation, wrote in July 1945 that Science is a proper concern of government.Funding of scienceFurther information: Funding of scienceThe Commonwealth Scientific and Industrial Research Organisation Main Entomology Building in AustraliaScientific research is often funded through a competitive process in which potential research projects are evaluated and only the most promising receive funding. Such processes, which are run by government, corporations, or foundations, allocate scarce funds. Total research funding in most developed countries is between 1.5% and 3% of GDP. In the OECD, around two-thirds of research and development in scientific and technical fields is carried out by industry, and 20% and 10% respectively by universities and government. The government funding proportion in certain industries is higher, and it dominates research in social science and humanities. Similarly, with some exceptions government provides the bulk of the funds for basic scientific research. Many governments have dedicated agencies to support scientific research. Prominent scientific organizations include the National Science Foundation in the United States, the National Scientific and Technical Research Council in Argentina, Commonwealth Scientific and Industrial Research Organisation in Australia, Centre national de la recherche scientifique in France, the Max Planck Society and Deutsche Forschungsgemeinschaft in Germany, and CSIC in Spain. In commercial research and development, all but the most research-oriented corporations focus more heavily on near-term commercialisation possibilities rather than blue-sky ideas or technologies.Public awareness of scienceFurther information: Public awareness of science, Science outreach, and Science communicationDinosaur exhibit in the Houston Museum of Natural ScienceThe public awareness of science relates to the attitudes, behaviors, opinions, and activities that make up the relations between science and the general public. It integrates various themes and activities such as science communication, science museums, science festivals, science fairs, citizen science, and science in popular culture. Social scientists have devised various metrics to measure the public understanding of science such as factual knowledge, self-reported knowledge, and structural knowledge.Science journalismFurther information: Science journalismThe mass media face a number of pressures that can prevent them from accurately depicting competing scientific claims in terms of their credibility within the scientific community as a whole. Determining how much weight to give different sides in a scientific debate may require considerable expertise regarding the matter. Few journalists have real scientific knowledge, and even beat reporters who know a great deal about certain scientific issues may be ignorant about other scientific issues that they are suddenly asked to cover.Politicization of scienceAcademic studies of scientific agreement on human-caused global warming: A 2019 study found scientific consensus to be at 100%, and a 2021 study concluded that it exceeded 99%.Scientific consensus contrasts with the politically correlated opinions over this issue, particularly in the United States.Politicization of science occurs when government, business, or advocacy groups use legal or economic pressure to influence the findings of scientific research or the way it is disseminated, reported, or interpreted. Many factors can act as facets of the politicization of science such as populist anti-intellectualism, perceived threats to religious beliefs, postmodernist subjectivism, and fear for business interests. Politicization of science is usually accomplished when scientific information is presented in a way that emphasizes the uncertainty associated with the scientific evidence. Tactics such as shifting conversation, failing to acknowledge facts, and capitalizing on doubt of scientific consensus have been used to gain more attention for views that have been undermined by scientific evidence. Examples of issues that have involved the politicization of science include the global warming controversy, health effects of pesticides, and health effects of tobacco. Music is the art of arranging sounds in time through the elements of melody, harmony, rhythm, and timbre. It is one of the universal cultural aspects of all human societies. General definitions of music include common elements such as pitch, rhythm, dynamics, and the sonic qualities of timbre and texture. Different styles or types of music may emphasize, de-emphasize or omit some of these elements. Music is performed with a vast range of instruments and vocal techniques ranging from singing to rapping; there are solely instrumental pieces, solely vocal pieces and pieces that combine singing and instruments. The word derives from Greek μουσική of the Muses).In its most general form, the activities describing music as an art form or cultural activity include the creation of works of music, the criticism of music, the study of the history of music, and the aesthetic examination of music. Ancient Greek and Indian philosophers defined music in two parts: melodies, as tones ordered horizontally, and harmonies as tones ordered vertically. Common sayings such as the harmony of the spheres and it is music to my ears point to the notion that music is often ordered and pleasant to listen to. However, 20th-century composer John Cage thought that any sound can be music, saying, for example, There is no noise, only sound.The creation, performance, significance, and even the definition of music vary according to culture and social context. Indeed, throughout history, some new forms or styles of music have been criticized as not being music, including Beethoven's Grosse Fuge string quartet in 1825, early jazz in the beginning of the 1900s and hardcore punk in the 1980s. There are many types of music, including popular music, traditional music, art music, music written for religious ceremonies, and work songs such as chanteys. Music ranges from strictly organized compositions—such as Classical music symphonies from the 1700s and 1800s—through to spontaneously played improvisational music such as jazz, and avant-garde styles of chance-based contemporary music from the 20th and 21st centuries.Music can be divided into genres and genres can be further divided into subgenres, although the dividing lines and relationships between music genres are often subtle, sometimes open to personal interpretation, and occasionally controversial. For example, it can be hard to draw the line between some early 1980s hard rock and heavy metal. Within the arts, music may be classified as a performing art, a fine art, or as an auditory art. Music may be played or sung and heard live at a rock concert or orchestra performance, heard live as part of a dramatic work, or it may be recorded and listened to on a radio, MP3 player, CD player, smartphone or as film score or TV show.In many cultures, music is an important part of people's way of life, as it plays a key role in religious rituals, rite of passage ceremonies, social activities and cultural activities ranging from amateur karaoke singing to playing in an amateur funk band or singing in a community choir. People may make music as a hobby, like a teen playing cello in a youth orchestra, or work as a professional musician or singer. The music industry includes the individuals who create new songs and musical pieces, individuals who perform music, individuals who record music, individuals who organize concert tours, and individuals who sell recordings, sheet music, and scores to customers. Even once a song or piece has been performed, music critics, music journalists, and music scholars may assess and evaluate the piece and its performance. Music is composed and performed for many purposes, ranging from aesthetic pleasure, religious or ceremonial purposes, or as an entertainment product for the marketplace. When music was only available through sheet music scores, such as during the Classical and Romantic eras, music lovers would buy the sheet music of their favourite pieces and songs so that they could perform them at home on the piano. With the advent of the phonograph, records of popular songs, rather than sheet music became the dominant way that music lovers would enjoy their favourite songs. With the advent of home tape recorders in the 1980s and digital music in the 1990s, music lovers could make tapes or playlists of their favourite songs and take them with them on a portable cassette player or MP3 player. Some music lovers create mix tapes of their favourite songs, which serve as a self-portrait, a gesture of friendship, prescription for an ideal party... an environment consisting solely of what is most ardently loved.Amateur musicians can compose or perform music for their own pleasure, and derive their income elsewhere. Professional musicians are employed by a range of institutions and organisations, including armed forces, churches and synagogues, symphony orchestras, broadcasting or film production companies, and music schools. Professional musicians sometimes work as freelancers or session musicians, seeking contracts and engagements in a variety of settings. There are often many links between amateur and professional musicians. Beginning amateur musicians take lessons with professional musicians. In community settings, advanced amateur musicians perform with professional musicians in a variety of ensembles such as community concert bands and community orchestras.A distinction is often made between music performed for a live audience and music that is performed in a studio so that it can be recorded and distributed through the music retail system or the broadcasting system. However, there are also many cases where a live performance in front of an audience is also recorded and distributed. Live concert recordings are popular in both classical music and in popular music forms such as rock, where illegally taped live concerts are prized by music lovers. In the jam band scene, live, improvised jam sessions are preferred to studio recordings.CompositionMain article: Musical compositionPeople composing music in 2013 using electronic keyboards and computers.French Baroque music composer Michel Richard Delalande, pen in hand.Composition is the act or practice of creating a song, an instrumental music piece, a work with both singing and instruments, or another type of music. In many cultures, including Western classical music, the act of composing also includes the creation of music notation, such as a sheet music score, which is then performed by the composer or by other singers or musicians. In popular music and traditional music, the act of composing, which is typically called songwriting, may involve the creation of a basic outline of the song, called the lead sheet, which sets out the melody, lyrics and chord progression. In classical music, the composer typically orchestrates his or her own compositions, but in musical theatre and in pop music, songwriters may hire an arranger to do the orchestration. In some cases, a songwriter may not use notation at all, and instead, compose the song in her mind and then play or record it from memory. In jazz and popular music, notable recordings by influential performers are given the weight that written scores play in classical music.Even when music is notated relatively precisely, as in classical music, there are many decisions that a performer has to make, because notation does not specify all of the elements of music precisely. The process of deciding how to perform music that has been previously composed and notated is termed interpretation. Different performers' interpretations of the same work of music can vary widely, in terms of the tempos that are chosen and the playing or singing style or phrasing of the melodies. Composers and songwriters who present their own music are interpreting their songs, just as much as those who perform the music of others. The standard body of choices and techniques present at a given time and a given place is referred to as performance practice, whereas interpretation is generally used to mean the individual choices of a performer.Although a musical composition often uses musical notation and has a single author, this is not always the case. A work of music can have multiple composers, which often occurs in popular music when a band collaborates to write a song, or in musical theatre, when one person writes the melodies, a second person writes the lyrics, and a third person orchestrates the songs. In some styles of music, such as the blues, a composer/songwriter may create, perform and record new songs or pieces without ever writing them down in music notation. A piece of music can also be composed with words, images, or computer programs that explain or notate how the singer or musician should create musical sounds. Examples range from avant-garde music that uses graphic notation, to text compositions such as Aus den sieben Tagen, to computer programs that select sounds for musical pieces. Music that makes heavy use of randomness and chance is called aleatoric music, and is associated with contemporary composers active in the 20th century, such as John Cage, Morton Feldman, and Witold Lutosławski. A more commonly known example of chance-based music is the sound of wind chimes jingling in a breeze.The study of composition has traditionally been dominated by examination of methods and practice of Western classical music, but the definition of composition is broad enough to include the creation of popular music and traditional music songs and instrumental pieces as well as spontaneously improvised works like those of free jazz performers and African percussionists such as Ewe drummers.NotationMain article: Musical notationSheet music is a written representation of music. Homorhythmic arrangement of the traditional Adeste Fideles in standard two-staff format for mixed voices.Menu0:00In the 2000s, music notation typically means the written expression of music notes and rhythms on paper using symbols. When music is written down, the pitches and rhythm of the music, such as the notes of a melody, are notated. Music notation also often provides instructions on how to perform the music. For example, the sheet music for a song may state that the song is a slow blues or a fast swing, which indicates the tempo and the genre. To read music notation, a person must have an understanding of music theory, harmony and the performance practice associated with a particular song or piece's genre.Written notation varies with the style and period of music. In the 2000s, notated music is produced as sheet music or, for individuals with computer scorewriter programs, as an image on a computer screen. In ancient times, music notation was put onto stone or clay tablets. To perform music from notation, a singer or instrumentalist requires an understanding of the rhythmic and pitch elements embodied in the symbols and the performance practice that is associated with a piece of music or a genre. In genres requiring musical improvisation, the performer often plays from music where only the chord changes and form of the song are written, requiring the performer to have a great understanding of the music's structure, harmony and the styles of a particular genre.In Western art music, the most common types of written notation are scores, which include all the music parts of an ensemble piece, and parts, which are the music notation for the individual performers or singers. In popular music, jazz, and blues, the standard musical notation is the lead sheet, which notates the melody, chords, lyrics, and structure of the music. Fake books are also used in jazz; they may consist of lead sheets or simply chord charts, which permit rhythm section members to improvise an accompaniment part to jazz songs. Scores and parts are also used in popular music and jazz, particularly in large ensembles such as jazz big bands. In popular music, guitarists and electric bass players often read music notated in tablature, which indicates the location of the notes to be played on the instrument using a diagram of the guitar or bass fingerboard. Tablature was also used in the Baroque era to notate music for the lute, a stringed, fretted instrument.ImprovisationImprovisation plays a central role in jazz; musicians learn progressions using scale and chord tones Main article: Musical improvisationMusical improvisation is the creation of spontaneous music, often within a pre-existing harmonic framework or chord progression. Improvisers use the notes of the chord, various scales that are associated with each chord, and chromatic ornaments and passing tones which may be neither chord tones nor from the typical scales associated with a chord. Musical improvisation can be done with or without preparation. Improvisation is a major part of some types of music, such as blues, jazz, and jazz fusion, in which instrumental performers improvise solos, melody lines, and accompaniment parts.In the Western art music tradition, improvisation was an important skill during the Baroque era and during the Classical era. In the Baroque era, performers improvised ornaments, and basso continuo keyboard players improvised chord voicings based on figured bass notation. As well, the top soloists were expected to be able to improvise pieces such as preludes. In the Classical era, solo performers and singers improvised virtuoso cadenzas during concerts.However, in the 20th and early 21st century, as common practice Western art music performance became institutionalized in symphony orchestras, opera houses, and ballets, improvisation has played a smaller role, as more and more music was notated in scores and parts for musicians to play. At the same time, some 20th and 21st century art music composers have increasingly included improvisation in their creative work. In Indian classical music, improvisation is a core component and an essential criterion of performances.TheoryMain article: Music theoryMusic theory encompasses the nature and mechanics of music. It often involves identifying patterns that govern composers' techniques and examining the language and notation of music. In a grand sense, music theory distills and analyzes the parameters or elements of music – rhythm, harmony, melody, structure, form, and texture. Broadly, music theory may include any statement, belief, or conception of or about music. People who study these properties are known as music theorists, and they typically work as professors in colleges, universities, and music conservatories. Some have applied acoustics, human physiology, and psychology to the explanation of how and why music is perceived. Music theorists publish their research in music theory journals and university press books.ElementsMain article: History of musicGlobe icon.	The examples and perspective in this section may not represent a worldwide view of the subject. You may improve this section, discuss the issue on the talk page, or create a new section, as appropriate. 	This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.Find sources: Music – news · newspapers · books · scholar · JSTOR Main article: Elements of musicMusic has many different fundamentals or elements. Depending on the definition of element being used, these can include pitch, beat or pulse, tempo, rhythm, melody, harmony, texture, style, allocation of voices, timbre or color, dynamics, expression, articulation, form, and structure. The elements of music feature prominently in the music curriculums of Australia, the UK, and the US. All three curriculums identify pitch, dynamics, timbre, and texture as elements, but the other identified elements of music are far from universally agreed upon. Below is a list of the three official versions of the elements of music:  Australia: pitch, timbre, texture, dynamics and expression, rhythm, form and structure.  UK: pitch, timbre, texture, dynamics, duration, tempo, structure.  USA: pitch, timbre, texture, dynamics, rhythm, form, harmony, style/articulation.In relation to the UK curriculum, in 2013 the term: appropriate musical notations was added to their list of elements and the title of the list was changed from the elements of music to the inter-related dimensions of music. The inter-related dimensions of music are listed as: pitch, duration, dynamics, tempo, timbre, texture, structure, and appropriate musical notations.The phrase the elements of music is used in a number of different contexts. The two most common contexts can be differentiated by describing them as the rudimentary elements of music and the perceptual elements of music.RudimentaryIn the 1800s, the phrases the elements of music and the rudiments of music were used interchangeably. The elements described in these documents refer to aspects of music that are needed in order to become a musician, Recent writers such as Espie Estrella seem to be using the phrase elements of music in a similar manner. A definition which most accurately reflects this usage is: the rudimentary principles of an art, science, etc.: the elements of grammar. The UK's curriculum switch to the inter-related dimensions of music seems to be a move back to using the rudimentary elements of music.PerceptualSince the emergence of the study of psychoacoustics in the 1930s, most lists of elements of music have related more to how we hear music than how we learn to play it or study it. C.E. Seashore, in his book Psychology of Music, identified four psychological attributes of sound. These were: pitch, loudness, time, and timbre. He did not call them the elements of music but referred to them as elemental components. Nonetheless, these elemental components link precisely with four of the most common musical elements: Pitch and timbre match exactly, loudness links with dynamics, and time links with the time-based elements of rhythm, duration, and tempo. This usage of the phrase the elements of music links more closely with Webster's New 20th Century Dictionary definition of an element as: a substance which cannot be divided into a simpler form by known methods and educational institutions' lists of elements generally align with this definition as well.Although writers of lists of rudimentary elements of music can vary their lists depending on their personal priorities, the perceptual elements of music should consist of an established list of discrete elements which can be independently manipulated to achieve an intended musical effect. It seems at this stage that there is still research to be done in this area.A slightly different way of approaching the identification of the elements of music, is to identify the elements of sound as: pitch, duration, loudness, timbre, sonic texture and spatial location, and then to define the elements of music as: sound, structure, and artistic intent.DescriptionsPitch and melodyPitch is an aspect of a sound that we can hear, reflecting whether one musical sound, note, or tone is higher or lower than another musical sound, note, or tone. We can talk about the highness or lowness of pitch in the more general sense, such as the way a listener hears a piercingly high piccolo note or whistling tone as higher in pitch than a deep thump of a bass drum. We also talk about pitch in the precise sense associated with musical melodies, basslines and chords. Precise pitch can only be determined in sounds that have a frequency that is clear and stable enough to distinguish from noise. For example, it is much easier for listeners to discern the pitch of a single note played on a piano than to try to discern the pitch of a crash cymbal that is struck.The melody to the traditional song Pop Goes the WeaselMenu0:00A melody is a series of pitches sounding in succession, often in a rising and falling pattern. The notes of a melody are typically created using pitch systems such as scales or modes. Melodies also often contain notes from the chords used in the song. The melodies in simple folk songs and traditional songs may use only the notes of a single scale, the scale associated with the tonic note or key of a given song. For example, a folk song in the key of C may have a melody that uses only the notes of the C major scale. A low, deep musical line played by bass instruments such as double bass, electric bass, or tuba is called a bassline.Harmony and chordsWhen musicians play three or more different notes at the same time, this creates a chord. In Western music, including classical music, pop music, rock music, and many related styles, the most common chords are triads– three notes usually played at the same time. The most commonly used chords are the major chord and the minor chord. An example of a major chord is the three pitches C, E and G. An example of a minor chord is the three pitches A, C, and E..Harmony refers to the vertical sounds of pitches in music, which means pitches that are played or sung together at the same time to create a chord. Usually, this means the notes are played at the same time, although harmony may also be implied by a melody that outlines a harmonic structure. In music written using the system of major-minor tonality, which includes most classical music written from 1600 to 1900 and most Western pop, rock, and traditional music, the key of a piece determines the scale used, which centres around the home note or tonic of the key. Simple classical pieces and many pop and traditional music songs are written so that all the music is in a single key. More complex Classical, pop, and traditional music songs and pieces may have two keys. Classical music from the Romantic era often contains multiple keys, as does jazz, especially Bebop jazz from the 1940s, in which the key or home note of a song may change every four bars or even every two bars.RhythmRhythm is the arrangement of sounds and silences in time. Meter animates time in regular pulse groupings, called measures or bars, which in Western classical, popular, and traditional music often group notes in sets of two, three, or four. Meters are made easier to hear because songs and pieces often place an emphasis on the first beat of each grouping. Notable exceptions exist, such as the backbeat used in much Western pop and rock, in which a song that uses a measure that consists of four beats will have accents on beats two and four, which are typically performed by the drummer on the snare drum, a loud and distinctive-sounding percussion instrument. In pop and rock, the rhythm parts of a song are played by the rhythm section, which includes chord-playing instruments, a bass instrument and a drum kit player.TextureMusical texture is the overall sound of a piece of music or song. The texture of a piece or song is determined by how the melodic, rhythmic, and harmonic materials are combined in a composition, thus determining the overall nature of the sound in a piece. Texture is often described in regard to the density, or thickness, and range, or width, between lowest and highest pitches, in relative terms as well as more specifically distinguished according to the number of voices, or parts, and the relationship between these voices. For example, a thick texture contains many 'layers' of instruments. One of these layers could be a string section or another brass. The thickness also is affected by the amount and the richness of the instruments. Texture is commonly described according to the number of and relationship between parts or lines of music:  monophony: a single melody with neither instrumental accompaniment nor a harmony part. A mother singing a lullaby to her baby would be an example.  heterophony: two or more instruments or singers playing/singing the same melody, but with each performer slightly varying the rhythm or speed of the melody or adding different ornaments to the melody. Two bluegrass fiddlers playing the same traditional fiddle tune together will typically each vary the melody by some degree and each add different ornaments.  polyphony: multiple independent melody lines that interweave together, which are sung or played at the same time. Choral music written in the Renaissance music era was typically written in this style. A round, which is a song such as Row, Row, Row Your Boat, which different groups of singers all start to sing at a different time, is an example of polyphony.  homophony: a clear melody supported by chordal accompaniment. Most Western popular music songs from the 19th century onward are written in this texture.Music that contains a large number of independent parts is generally said to have a thicker or denser texture than a work with few parts.Timbre or tone colorTimbre, sometimes called color or tone color is the quality or sound of a voice or instrument. Timbre is what makes a particular musical sound different from another, even when they have the same pitch and loudness. For example, a 440 Hz A note sounds different when it is played on oboe, piano, violin, or electric guitar. Even if different players of the same instrument play the same note, their notes might sound different due to differences in instrumental technique, different types of accessories or strings made out of different materials for string players. Even two instrumentalists playing the same note on the same instrument may sound different due to different ways of playing the instrument.The physical characteristics of sound that determine the perception of timbre include the spectrum, envelope, and overtones of a note or musical sound. For electric instruments developed in the 20th century, such as electric guitar, electric bass and electric piano, the performer can also change the tone by adjusting equalizer controls, tone controls on the instrument, and by using electronic effects units such as distortion pedals. The tone of the electric Hammond organ is controlled by adjusting drawbars.ExpressionSingers add expression to the melodies they sing using many methods, including changing the tone of their singing, adding vibrato to certain notes, and emphasizing important words in the lyrics.Expressive qualities are those elements in music that create change in music without changing the main pitches or substantially changing the rhythms of the melody and its accompaniment. Performers, including singers and instrumentalists, can add musical expression to a song or piece by adding phrasing, by adding effects such as vibrato, dynamics, tempo fluctuations, by adding pauses or fermatas on a cadence, and by changing the articulation of the notes.Expression is achieved through the manipulation of pitch, volume, duration, timbre and sometimes even texture. Expression therefore can be seen as a manipulation of all elements in order to convey an indication of mood, spirit, character etc. and as such cannot be included as a unique perceptual element of music, although it can be considered an important rudimentary element of music.FormSee also: Strophic form, Binary form, Ternary form, Rondo form, Variation, and Musical developmentSheet music notation for the chorus of the Christmas song Jingle BellsMenu0:00In music, form describes the overall structure or plan of a song or piece of music, and it describes the layout of a composition as divided into sections. In the early 20th century, Tin Pan Alley songs and Broadway musical songs were often in AABA 32 bar form, in which the A sections repeated the same eight bar melody and the B section provided a contrasting melody or harmony for eight bars. From the 1960s onward, Western pop and rock songs are often in verse-chorus form, which is based around a sequence of verse and chorus sections, with new lyrics for most verses and repeating lyrics for the choruses. Popular music often makes use of strophic form, sometimes in conjunction with the twelve bar blues.In the tenth edition of The Oxford Companion to Music, Percy Scholes defines musical form as a series of strategies designed to find a successful mean between the opposite extremes of unrelieved repetition and unrelieved alteration. Examples of common forms of Western music include the fugue, the invention, sonata-allegro, canon, strophic, theme and variations, and rondo.Scholes states that European classical music had only six stand-alone forms: simple binary, simple ternary, compound binary, rondo, air with variations, and fugue Where a piece cannot readily be broken down into sectional units, it is said to be through-composed. Such is often the case with a fantasia, prelude, rhapsody, etude, symphonic poem, Bagatelle, impromptu, etc. Professor Charles Keil classified forms and formal detail as sectional, developmental, or variational.Analysis of stylesFunk places most of its emphasis on rhythm and groove, with entire songs based around a vamp on a single chord. Pictured are the influential funk musicians George Clinton and Parliament-Funkadelic in 2006.Some styles of music place an emphasis on certain of these fundamentals, while others place less emphasis on certain elements. To give one example, while Bebop-era jazz makes use of very complex chords, including altered dominants and challenging chord progressions, with chords changing two or more times per bar and keys changing several times in a tune, funk places most of its emphasis on rhythm and groove, with entire songs based around a vamp on a single chord. While Romantic era classical music from the mid- to late-1800s makes great use of dramatic changes of dynamics, from whispering pianissimo sections to thunderous fortissimo sections, some entire Baroque dance suites for harpsichord from the early 1700s may use a single dynamic. To give another example, while some art music pieces, such as symphonies are very long, some pop songs are just a few minutes long.HistoryMain article: History of musicGlobe icon.	The examples and perspective in this section may not represent a worldwide view of the subject. You may improve this section, discuss the issue on the talk page, or create a new section, as appropriate. PrehistoryPrehistoric music can only be theorized based on findings from paleolithic archaeology sites. Flutes are often discovered, carved from bones in which lateral holes have been pierced; these are thought to have been blown at one end like the Japanese shakuhachi. The Divje Babe flute, carved from a cave bear femur, is thought to be at least 40,000 years old, though there is considerable debate surrounding whether it is truly a musical instrument or an object formed by animals. Instruments such as the seven-holed flute and various types of stringed instruments, such as the Ravanahatha, have been recovered from the Indus Valley Civilization archaeological sites. India has one of the oldest musical traditions in the world—references to Indian classical music are found in the Vedas, ancient scriptures of the Hindu tradition. The earliest and largest collection of prehistoric musical instruments was found in China and dates back to between 7000 and 6600 BC. The Hurrian Hymn to Nikkal, found on clay tablets that date back to approximately 1400 BC, is the oldest surviving notated work of music.Ancient EgyptMain article: Music of EgyptMusicians of Amun, Tomb of Nakht, 18th Dynasty, Western ThebesThe earliest material and representational evidence of Egyptian musical instruments dates to the Predynastic period, but the evidence is more securely attested in the Old Kingdom when harps, flutes and double clarinets were played. Percussion instruments, lyres and lutes were added to orchestras by the Middle Kingdom. Cymbals frequently accompanied music and dance, much as they still do in Egypt today. Egyptian folk music, including the traditional Sufi dhikr rituals, are the closest contemporary music genre to ancient Egyptian music, having preserved many of its features, rhythms and instruments.Asian culturesIndian women dressed in regional attire playing a variety of musical instruments popular in different parts of IndiaGangubai HangalDurgaAsian music covers a vast swath of music cultures surveyed in the articles on Arabia, Central Asia, East Asia, South Asia, and Southeast Asia. Several have traditions reaching into antiquity.Indian classical music is one of the oldest musical traditions in the world. The Indus Valley civilization has sculptures that show dance and old musical instruments, like the seven holed flute. Various types of stringed instruments and drums have been recovered from Harappa and Mohenjo Daro by excavations carried out by Sir Mortimer Wheeler. The Rigveda has elements of present Indian music, with a musical notation to denote the metre and the mode of chanting. Indian classical music is monophonic, and based on a single melody line or raga rhythmically organized through talas. Silappadhikaram by Ilango Adigal provides information about how new scales can be formed by modal shifting of the tonic from an existing scale. Present day Hindi music was influenced by Persian traditional music and Afghan Mughals. Carnatic music, popular in the southern states, is largely devotional; the majority of the songs are addressed to the Hindu deities. There are also many songs emphasising love and other social issues.Chinese classical music, the traditional art or court music of China, has a history stretching over around three thousand years. It has its own unique systems of musical notation, as well as musical tuning and pitch, musical instruments and styles or musical genres. Chinese music is pentatonic-diatonic, having a scale of twelve notes to an octave as does European-influenced music.Ancient Greece	Epitaph of Seikilos Menu0:00Melody sung in an approximation of Koine Greek pronunciation and in modern popular vocal style.Problems playing this file? See media help.Music was an important part of social and cultural life in ancient Greece, in fact it was one of the main subjects taught to children. Musical education was considered to be important for the development of an individual's soul. Musicians and singers played a prominent role in Greek theater and the ones who received a musical education were seen as nobles and in perfect harmony Mixed-gender choruses performed for entertainment, celebration, and spiritual ceremonies. Holy Ancient Greek music will be considered an example of perfection and purity. Instruments included the double-reed aulos and a plucked string instrument, the lyre, principally the special kind called a kithara. Music was an important part of education, and boys were taught music starting at age six. Greek musical literacy created a flowering of music development. Greek music theory included the Greek musical modes, that eventually became the basis for Western religious and classical music. Later, influences from the Roman Empire, Eastern Europe, and the Byzantine Empire changed Greek music. The Seikilos epitaph is the oldest surviving example of a complete musical composition, including musical notation, from anywhere in the world. The oldest surviving work written on the subject of music theory is Harmonika Stoicheia by Aristoxenus.Western classical	This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. Middle AgesLéonin or PérotinBreves dies hominisMusical notation from a Catholic Missal, c. 1310–1320The medieval era, which took place during the Middle Ages, started with the introduction of monophonic chanting into Roman Catholic Church services. Musical notation was used since Ancient times in Greek culture, but in the Middle Ages, notation was first introduced by the Catholic church so that the chant melodies could be written down, to facilitate the use of the same melodies for religious music across the entire Catholic empire. The only European Medieval repertory that has been found in written form from before 800 is the monophonic liturgical plainsong chant of the Roman Catholic Church, the central tradition of which was called Gregorian chant. Alongside these traditions of sacred and church music there existed a vibrant tradition of secular song. Examples of composers from this period are Léonin, Pérotin, Guillaume de Machaut, and Walther von der Vogelweide.RenaissanceT.L. de VictoriaAmicus meusAllegory of Music, by Filippino LippiRenaissance music was more focused on secular themes, such as courtly love. Around 1450, the printing press was invented, which made printed sheet music much less expensive and easier to mass-produce. The increased availability of sheet music helped to spread musical styles more quickly and across a larger area. Musicians and singers often worked for the church, courts and towns. Church choirs grew in size, and the church remained an important patron of music. By the middle of the 15th century, composers wrote richly polyphonic sacred music, in which different melody lines were interwoven simultaneously. Prominent composers from this era include Guillaume Dufay, Giovanni Pierluigi da Palestrina, Thomas Morley, and Orlande de Lassus. As musical activity shifted from the church to the aristocratic courts, kings, queens and princes competed for the finest composers. Many leading important composers came from the Netherlands, Belgium, and northern France. They are called the Franco-Flemish composers. They held important positions throughout Europe, especially in Italy. Other countries with vibrant musical activity included Germany, England, and Spain.BaroqueJ.S. BachToccata and FugueThe Baroque era of music took place from 1600 to 1750, as the Baroque artistic style flourished across Europe; and during this time, music expanded in its range and complexity. Baroque music began when the first operas were written. During the Baroque era, polyphonic contrapuntal music, in which multiple, simultaneous independent melody lines were used, remained important. German Baroque composers wrote for small ensembles including strings, brass, and woodwinds, as well as for choirs and keyboard instruments such as pipe organ, harpsichord, and clavichord. During this period several major music forms were defined that lasted into later periods when they were expanded and evolved further, including the fugue, the invention, the sonata, and the concerto. The late Baroque style was polyphonically complex and richly ornamented. Important composers from the Baroque era include Johann Sebastian Bach, George Frideric Handel, Georg Philipp Telemann and Antonio Lucio Vivaldi.ClassicismW.A. MozartSymphony 40 G minorWolfgang Amadeus Mozart was a child prodigy virtuoso performer on the piano and violin. Even before he became a celebrated composer, he was widely known as a gifted performer and improviser.The music of the Classical period aimed to imitate what were seen as the key elements of the art and philosophy of Ancient Greece and Rome: the ideals of balance, proportion and disciplined expression.. Music from the Classical period has a lighter, clearer and considerably simpler texture than the Baroque music which preceded it. The main style was homophony, where a prominent melody and a subordinate chordal accompaniment part are clearly distinct. Classical instrumental melodies tended to be almost voicelike and singable. New genres were developed, and the fortepiano, the forerunner to the modern piano, replaced the Baroque era harpsichord and pipe organ as the main keyboard instrument.Importance was given to instrumental music. It was dominated by further development of musical forms initially defined in the Baroque period: the sonata, the concerto, and the symphony. Others main kinds were the trio, string quartet, serenade and divertimento. The sonata was the most important and developed form. Although Baroque composers also wrote sonatas, the Classical style of sonata is completely distinct. All of the main instrumental forms of the Classical era, from string quartets to symphonies and concertos, were based on the structure of the sonata. The instruments used chamber music and orchestra became more standardized. In place of the basso continuo group of the Baroque era, which consisted of harpsichord, organ or lute along with a number of bass instruments selected at the discretion of the group leader, Classical chamber groups used specified, standardized instruments. The Baroque era improvised chord-playing of the continuo keyboardist or lute player was gradually phased out between 1750 and 1800.One of the most important changes made in the Classical period was the development of public concerts. The aristocracy still played a significant role in the sponsorship of concerts and compositions, but it was now possible for composers to survive without being permanent employees of queens or princes. The increasing popularity of classical music led to a growth in the number and types of orchestras. The expansion of orchestral concerts necessitated the building of large public performance spaces. Symphonic music including symphonies, musical accompaniment to ballet and mixed vocal/instrumental genres such as opera and oratorio became more popular.The best known composers of Classicism are Carl Philipp Emanuel Bach, Christoph Willibald Gluck, Johann Christian Bach, Joseph Haydn, Wolfgang Amadeus Mozart, Ludwig van Beethoven and Franz Schubert. Beethoven and Schubert are also considered to be composers in the later part of the Classical era, as it began to move towards Romanticism.RomanticismThe piano was the centrepiece of social activity for middle-class urbanites in the 19th century. The man at the piano is composer Franz Schubert.R. WagnerDie WalküreRomantic music from the 19th century had many elements in common with the Romantic styles in literature and painting of the era. Romanticism was an artistic, literary, and intellectual movement was characterized by its emphasis on emotion and individualism as well as glorification of all the past and nature. Romantic music expanded beyond the rigid styles and forms of the Classical era into more passionate, dramatic expressive pieces and songs. Romantic composers such as Wagner and Brahms attempted to increase emotional expression and power in their music to describe deeper truths or human feelings. With symphonic tone poems, composers tried to tell stories and evoke images or landscapes using instrumental music. Some composers promoted nationalistic pride with patriotic orchestral music inspired by folk music. The emotional and expressive qualities of music came to take precedence over tradition.Romantic composers grew in idiosyncrasy, and went further in the syncretism of exploring different art-forms in a musical context,, history, or nature itself. Romantic love or longing was a prevalent theme in many works composed during this period. In some cases, the formal structures from the classical period continued to be used, but these forms were expanded and altered. In many cases, new approaches were explored for existing genres, forms, and functions. Also, new forms were created that were deemed better suited to the new subject matter. Composers continued to develop opera and ballet music, exploring new styles and themes.In the years after 1800, the music developed by Ludwig van Beethoven and Franz Schubert introduced a more dramatic, expressive style. In Beethoven's case, short motifs, developed organically, came to replace melody as the most significant compositional unit. Later Romantic composers such as Pyotr Ilyich Tchaikovsky, Antonín Dvořák, and Gustav Mahler used more unusual chords and more dissonance to create dramatic tension. They generated complex and often much longer musical works. During the late Romantic period, composers explored dramatic chromatic alterations of tonality, such as extended chords and altered chords, which created new sound colours. The late 19th century saw a dramatic expansion in the size of the orchestra, and the industrial revolution helped to create better instruments, creating a more powerful sound. Public concerts became an important part of well-to-do urban society. It also saw a new diversity in theatre music, including operetta, and musical comedy and other forms of musical theatre.20th and 21st centuryMain article: 20th-century musicIn the 19th century, one of the key ways that new compositions became known to the public was by the sales of sheet music, which middle class amateur music lovers would perform at home on their piano or other common instruments, such as violin. With 20th-century music, the invention of new electric technologies such as radio broadcasting and the mass market availability of gramophone records meant that sound recordings of songs and pieces heard by listeners became the main way to learn about new songs and pieces. There was a vast increase in music listening as the radio gained popularity and phonographs were used to replay and distribute music, because whereas in the 19th century, the focus on sheet music restricted access to new music to the middle class and upper-class people who could read music and who owned pianos and instruments, in the 20th century, anyone with a radio or record player could hear operas, symphonies and big bands right in their own living room. This allowed lower-income people, who would never be able to afford an opera or symphony concert ticket to hear this music. It also meant that people could hear music from different parts of the country, or even different parts of the world, even if they could not afford to travel to these locations. This helped to spread musical styles.The focus of art music in the 20th century was characterized by exploration of new rhythms, styles, and sounds. The horrors of World War I influenced many of the arts, including music, and some composers began exploring darker, harsher sounds. Traditional music styles such as jazz and folk music were used by composers as a source of ideas for classical music. Igor Stravinsky, Arnold Schoenberg, and John Cage were all influential composers in 20th-century art music. The invention of sound recording and the ability to edit music gave rise to new subgenre of classical music, including the acousmatic and Musique concrète schools of electronic composition. Sound recording was also a major influence on the development of popular music genres, because it enabled recordings of songs and bands to be widely distributed. The introduction of the multitrack recording system had a major influence on rock music, because it could do much more than record a band's performance. Using a multitrack system, a band and their music producer could overdub many layers of instrument tracks and vocals, creating new sounds that would not be possible in a live performance.Jazz evolved and became an important genre of music over the course of the 20th century, and during the second half of that century, rock music did the same. Jazz is an American musical artform that originated in the beginning of the 20th century in African American communities in the Southern United States from a confluence of African and European music traditions. The style's West African pedigree is evident in its use of blue notes, improvisation, polyrhythms, syncopation, and the swung note.Rock music is a genre of popular music that developed in the 1960s from 1950s rock and roll, rockabilly, blues, and country music. The sound of rock often revolves around the electric guitar or acoustic guitar, and it uses a strong back beat laid down by a rhythm section. Along with the guitar or keyboards, saxophone and blues-style harmonica are used as soloing instruments. In its purest form, it has three chords, a strong, insistent back beat, and a catchy melody. The traditional rhythm section for popular music is rhythm guitar, electric bass guitar, drums. Some bands also have keyboard instruments such as organ, piano, or, since the 1970s, analog synthesizers. In the 1980s, pop musicians began using digital synthesizers, such as the DX-7 synthesizer, electronic drum machines such as the TR-808 and synth bass devices or synth bass keyboards. In the 1990s, an increasingly large range of computerized hardware musical devices and instruments and software were used. In the 2020s, soft synths and computer music apps make it possible for bedroom producers to create and record some types of music, such as electronic dance music in their own home, adding sampled and digital instruments and editing the recording digitally. In the 1990s, some bands in genres such as nu metal began including DJs in their bands. DJs create music by manipulating recorded music on record players or CD players, using a DJ mixer.Innovation in music technology continued into the 21st century, including the development of isomorphic keyboards and Dynamic Tonality.Performance	This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. Chinese Naxi musiciansAssyrians playing zurna and Davul, instruments that go back thousands of years.Performance is the physical expression of music, which occurs when a song is sung or when a piano piece, electric guitar melody, symphony, drum beat or other musical part is played by musicians. In classical music, a musical work is written in music notation by a composer and then it is performed once the composer is satisfied with its structure and instrumentation. However, as it gets performed, the interpretation of a song or piece can evolve and change. In classical music, instrumental performers, singers or conductors may gradually make changes to the phrasing or tempo of a piece. In popular and traditional music, the performers have a lot more freedom to make changes to the form of a song or piece. As such, in popular and traditional music styles, even when a band plays a cover song, they can make changes to it such as adding a guitar solo to or inserting an introduction.A performance can either be planned out and rehearsed —which is the norm in classical music, with jazz big bands and many popular music styles–or improvised over a chord progression, which is the norm in small jazz and blues groups. Rehearsals of orchestras, concert bands and choirs are led by a conductor. Rock, blues and jazz bands are usually led by the bandleader. A rehearsal is a structured repetition of a song or piece by the performers until it can be sung or played correctly and, if it is a song or piece for more than one musician, until the parts are together from a rhythmic and tuning perspective. Improvisation is the creation of a musical idea–a melody or other musical line–created on the spot, often based on scales or pre-existing melodic riffs.Many cultures have strong traditions of solo performance, such as in Indian classical music, and in the Western art-music tradition. Other cultures, such as in Bali, include strong traditions of group performance. All cultures include a mixture of both, and performance may range from improvised solo playing to highly planned and organised performances such as the modern classical concert, religious processions, classical music festivals or music competitions. Chamber music, which is music for a small ensemble with only a few of each type of instrument, is often seen as more intimate than large symphonic works.Oral and aural traditionMany types of music, such as traditional blues and folk music were not written down in sheet music; instead, they were originally preserved in the memory of performers, and the songs were handed down orally, from one musician or singer to another, or aurally, in which a performer learns a song by ear. When the composer of a song or piece is no longer known, this music is often classified as traditional or as a folk song. Different musical traditions have different attitudes towards how and where to make changes to the original source material, from quite strict, to those that demand improvisation or modification to the music. A culture's history and stories may also be passed on by ear through song.OrnamentationTrill sign—a rapid alternation between two notes.Menu0:00In music, an ornament consists of added notes that provide decoration to a melody, bassline or other musical part. The detail included explicitly in the music notation varies between genres and historical periods. In general, art music notation from the 17th through the 19th centuries required performers to have a great deal of contextual knowledge about performing styles. For example, in the 17th and 18th centuries, music notated for solo performers typically indicated a simple, unadorned melody. Performers were expected to know how to add stylistically appropriate ornaments to add interest to the music, such as trills and turns. Different styles of music use different ornaments. A Baroque flute player might add mordents, which are short notes that are played before the main melody note, either above or below the main melody note. A blues guitarist playing electric guitar might use string bending to add expression; a heavy metal guitar player might use hammer-ons and pull-offs.In the 19th century, art music for solo performers may give a general instruction such as to perform the music expressively, without describing in detail how the performer should do this. The performer was expected to know how to use tempo changes, accentuation, and pauses to obtain this expressive performance style. In the 20th century, art music notation often became more explicit and used a range of markings and annotations to indicate to performers how they should play or sing the piece. In popular music and traditional music styles, performers are expected to know what types of ornaments are stylistically appropriate for a given song or piece, and performers typically add them in an improvised fashion. One exception is note-for-note solos, in which some players precisely recreate a famous version of a solo, such as a guitar solo.Philosophy and aestheticsFurther information: Aesthetics of musicPainting by Boldini of a woman playing the pianoPhilosophy of music is a subfield of philosophy. The philosophy of music is the study of fundamental questions regarding music. The philosophical study of music has many connections with philosophical questions in metaphysics and aesthetics. Some basic questions in the philosophy of music are:  What is the definition of music?   What is the relationship between music and mind?  What does music history reveal to us about the world?  What is the connection between music and emotions?  What is meaning in relation to music?In ancient times, such as with the Ancient Greeks, the aesthetics of music explored the mathematical and cosmological dimensions of rhythmic and harmonic organization. In the 18th century, focus shifted to the experience of hearing music, and thus to questions about its beauty and human enjoyment of music. The origin of this philosophic shift is sometimes attributed to Alexander Gottlieb Baumgarten in the 18th century, followed by Immanuel Kant. Through their writing, the ancient term 'aesthetics', meaning sensory perception, received its present-day connotation. In the 2000s, philosophers have tended to emphasize issues besides beauty and enjoyment. For example, music's capacity to express emotion has been a central issue.In the 20th century, important contributions were made by Peter Kivy, Jerrold Levinson, Roger Scruton, and Stephen Davies. However, many musicians, music critics, and other non-philosophers have contributed to the aesthetics of music. In the 19th century, a significant debate arose between Eduard Hanslick, a music critic and musicologist, and composer Richard Wagner regarding whether music can express meaning. Harry Partch and some other musicologists, such as Kyle Gann, have studied and tried to popularize microtonal music and the usage of alternate musical scales. Also many modern composers like La Monte Young, Rhys Chatham and Glenn Branca paid much attention to a scale called just intonation.It is often thought that music has the ability to affect our emotions, intellect, and psychology; it can assuage our loneliness or incite our passions. The philosopher Plato suggests in The Republic that music has a direct effect on the soul. Therefore, he proposes that in the ideal regime music would be closely regulated by the state. In Ancient China, the philosopher Confucius believed that music and rituals or rites are interconnected and harmonious with nature; he stated that music was the harmonization of heaven and earth, while the order was brought by the rites order, making them extremely crucial functions in society.There has been a strong tendency in the aesthetics of music to emphasize the paramount importance of compositional structure; however, other issues concerning the aesthetics of music include lyricism, harmony, hypnotism, emotiveness, temporal dynamics, resonance, playfulness, and color.PsychologyModern music psychology aims to explain and understand musical behavior and experience. Research in this field and its subfields are primarily empirical; their knowledge tends to advance on the basis of interpretations of data collected by systematic observation of and interaction with human participants. In addition to its focus on fundamental perceptions and cognitive processes, music psychology is a field of research with practical relevance for many areas, including music performance, composition, education, criticism, and therapy, as well as investigations of human aptitude, skill, intelligence, creativity, and social behavior.NeuroscienceMain article: Neuroscience of musicThe primary auditory cortex is one of the main areas associated with superior pitch resolution.Cognitive neuroscience of music is the scientific study of brain-based mechanisms involved in the cognitive processes underlying music. These behaviours include music listening, performing, composing, reading, writing, and ancillary activities. It also is increasingly concerned with the brain basis for musical aesthetics and musical emotion. The field is distinguished by its reliance on direct observations of the brain, using such techniques as functional magnetic resonance imaging, transcranial magnetic stimulation, magnetoencephalography, electroencephalography, and positron emission tomography.Cognitive musicologyCognitive musicology is a branch of cognitive science concerned with computationally modeling musical knowledge with the goal of understanding both music and cognition. The use of computer models provides an exacting, interactive medium in which to formulate and test theories and has roots in artificial intelligence and cognitive science.This interdisciplinary field investigates topics such as the parallels between language and music in the brain. Biologically inspired models of computation are often included in research, such as neural networks and evolutionary programs. This field seeks to model how musical knowledge is represented, stored, perceived, performed, and generated. By using a well-structured computer environment, the systematic structures of these cognitive phenomena can be investigated.PsychoacousticsFurther information: HearingPsychoacoustics is the scientific study of sound perception. More specifically, it is the branch of science studying the psychological and physiological responses associated with sound. It can be further categorized as a branch of psychophysics.Evolutionary musicologyEvolutionary musicology concerns the origins of music, the question of animal song, selection pressures underlying music evolution, and music evolution and human evolution. It seeks to understand music perception and activity in the context of evolutionary theory. Charles Darwin speculated that music may have held an adaptive advantage and functioned as a protolanguage, a view which has spawned several competing theories of music evolution. An alternate view sees music as a by-product of linguistic evolution; a type of auditory cheesecake that pleases the senses without providing any adaptive function. This view has been directly countered by numerous music researchers.Cultural effectsMain article: Culture in music cognitionSee also: EthnomusicologyAn individual's culture or ethnicity plays a role in their music cognition, including their preferences, emotional reaction, and musical memory. Musical preferences are biased toward culturally familiar musical traditions beginning in infancy, and adults' classification of the emotion of a musical piece depends on both culturally specific and universal structural features. Additionally, individuals' musical memory abilities are greater for culturally familiar music than for culturally unfamiliar music.Sociological aspectsMain article: SociomusicologySong Dynasty painting, Night Revels of Han Xizai, showing Chinese musicians entertaining guests at a party in a 10th-century householdMany ethnographic studies demonstrate that music is a participatory, community-based activity. Music is experienced by individuals in a range of social settings ranging from being alone to attending a large concert, forming a music community, which cannot be understood as a function of individual will or accident; it includes both commercial and non-commercial participants with a shared set of common values. Musical performances take different forms in different cultures and socioeconomic milieus. In Europe and North America, there is often a divide between what types of music are viewed as a high culture and low culture. High culture types of music typically include Western art music such as Baroque, Classical, Romantic, and modern-era symphonies, concertos, and solo works, and are typically heard in formal concerts in concert halls and churches, with the audience sitting quietly in seats.Other types of music—including, but not limited to, jazz, blues, soul, and country—are often performed in bars, nightclubs, and theatres, where the audience may be able to drink, dance, and express themselves by cheering. Until the later 20th century, the division between high and low musical forms was widely accepted as a valid distinction that separated out better quality, more advanced art music from the popular styles of music heard in bars and dance halls.However, in the 1980s and 1990s, musicologists studying this perceived divide between high and low musical genres argued that this distinction is not based on the musical value or quality of the different types of music. Rather, they argued that this distinction was based largely on the socioeconomics standing or social class of the performers or audience of the different types of music. For example, whereas the audience for Classical symphony concerts typically have above-average incomes, the audience for a rap concert in an inner-city area may have below-average incomes. Even though the performers, audience, or venue where non-art music is performed may have a lower socioeconomic status, the music that is performed, such as blues, rap, punk, funk, or ska may be very complex and sophisticated.When composers introduce styles of music that break with convention, there can be a strong resistance from academic music experts and popular culture. Late-period Beethoven string quartets, Stravinsky ballet scores, serialism, bebop-era jazz, hip hop, punk rock, and electronica have all been considered non-music by some critics when they were first introduced. Such themes are examined in the sociology of music. The sociological study of music, sometimes called sociomusicology, is often pursued in departments of sociology, media studies, or music, and is closely related to the field of ethnomusicology.Role of women	This section possibly contains original research. Please improve it by verifying the claims made and adding inline citations. Statements consisting only of original research should be removed. Main article: Women in music19th-century composer and pianist Clara SchumannNavneet Aditya Waiba- Nepali Folk Singer. The only singer using authentic/original folk instruments and singing authentic unadulterated Nepali Folk songs.Women have played a major role in music throughout history, as composers, songwriters, instrumental performers, singers, conductors, music scholars, music educators, music critics/music journalists and other musical professions. As well, it describes music movements, events and genres related to women, women's issues and feminism. In the 2010s, while women comprise a significant proportion of popular music and classical music singers, and a significant proportion of songwriters, there are few women record producers, rock critics and rock instrumentalists. Although there have been a huge number of women composers in classical music, from the medieval period to the present day, women composers are significantly underrepresented in the commonly performed classical music repertoire, music history textbooks and music encyclopedias; for example, in the Concise Oxford History of Music, Clara Schumann is one of the only female composers who is mentioned.Women comprise a significant proportion of instrumental soloists in classical music and the percentage of women in orchestras is increasing. A 2015 article on concerto soloists in major Canadian orchestras, however, indicated that 84% of the soloists with the Orchestre Symphonique de Montreal were men. In 2012, women still made up just 6% of the top-ranked Vienna Philharmonic orchestra. Women are less common as instrumental players in popular music genres such as rock and heavy metal, although there have been a number of notable female instrumentalists and all-female bands. Women are particularly underrepresented in extreme metal genres. In the 1960s pop-music scene, ike most aspects of the...music business, songwriting was a male-dominated field. Though there were plenty of female singers on the radio, women...were primarily seen as consumers:... Singing was sometimes an acceptable pastime for a girl, but playing an instrument, writing songs, or producing records simply wasn't done. Young women...were not socialized to see themselves as people who create.Women are also underrepresented in orchestral conducting, music criticism/music journalism, music producing, and sound engineering. While women were discouraged from composing in the 19th century, and there are few women musicologists, women became involved in music education...to such a degree that women dominated during the later half of the 19th century and well into the 20th century.According to Jessica Duchen, a music writer for London's The Independent, women musicians in classical music are...too often judged for their appearances, rather than their talent and they face pressure...to look sexy onstage and in photos. Duchen states that while here are women musicians who refuse to play on their looks,...the ones who do tend to be more materially successful. According to the UK's Radio 3 editor, Edwina Wolstencroft, the music industry has long been open to having women in performance or entertainment roles, but women are much less likely to have positions of authority, such as being the conductor of an orchestra. In popular music, while there are many women singers recording songs, there are very few women behind the audio console acting as music producers, the individuals who direct and manage the recording process. One of the most recorded artists is Asha Bhosle, an Indian singer best known as a playback singer in Hindi cinema.Media and technologyFurther information: Computer music and Music technologyMusic production in the 2000s using a digital audio workstation with an electronic keyboard and a multi-monitor set-upThe music that composers and songwriters make can be heard through several media; the most traditional way is to hear it live, in the presence of the musicians, in an outdoor or indoor space such as an amphitheatre, concert hall, cabaret room, theatre, pub, or coffeehouse. Since the 20th century, live music can also be broadcast over the radio, television or the Internet, or recorded and listened to on a CD player or Mp3 player.Some musical styles focus on producing songs and pieces for a live performance, while others focus on producing a recording that mixes together sounds that were never played live. Even in essentially live styles such as rock, recording engineers often use the ability to edit, splice and mix to produce recordings that may be considered better than the actual live performance. For example, some singers record themselves singing a melody and then record multiple harmony parts using overdubbing, creating a sound that would be impossible to do live.Technology has had an influence on music since prehistoric times, when cave people used simple tools to bore holes into bone flutes 41,000 years ago. Technology continued to influence music throughout the history of music, as it enabled new instruments and music notation reproduction systems to be used, with one of the watershed moments in music notation being the invention of the printing press in the 1400s, which meant music scores no longer had to be hand copied. In the 19th century, music technology led to the development of a more powerful, louder piano and led to the development of new valves brass instruments.In the early 20th century, as talking pictures emerged in the early 20th century, with their prerecorded musical tracks, an increasing number of moviehouse orchestra musicians found themselves out of work. During the 1920s, live musical performances by orchestras, pianists, and theater organists were common at first-run theaters. With the coming of the talking motion pictures, those featured performances were largely eliminated. The American Federation of Musicians took out newspaper advertisements protesting the replacement of live musicians with mechanical playing devices. One 1929 ad that appeared in the Pittsburgh Press features an image of a can labeled Canned Music / Big Noise Brand / Guaranteed to Produce No Intellectual or Emotional Reaction WhateverSince legislation introduced to help protect performers, composers, publishers and producers, including the Audio Home Recording Act of 1992 in the United States, and the 1979 revised Berne Convention for the Protection of Literary and Artistic Works in the United Kingdom, recordings and live performances have also become more accessible through computers, devices and Internet in a form that is commonly known as Music-On-Demand.In many cultures, there is less distinction between performing and listening to music, since virtually everyone is involved in some sort of musical activity, often in a communal setting. In industrialized countries, listening to music through a recorded form, such as sound recording on record or radio became more common than experiencing live performance, roughly in the middle of the 20th century. By the 1980s, watching music videos was a popular way to listen to music, while also seeing the performers.Sometimes, live performances incorporate prerecorded sounds. For example, a disc jockey uses disc records for scratching, and some 20th-century works have a solo for an instrument or voice that is performed along with music that is prerecorded onto a tape. Some pop bands use recorded backing tracks. Computers and many keyboards can be programmed to produce and play Musical Instrument Digital Interface music. Audiences can also become performers by participating in karaoke, an activity of Japanese origin centered on a device that plays voice-eliminated versions of well-known songs. Most karaoke machines also have video screens that show lyrics to songs being performed; performers can follow the lyrics as they sing over the instrumental tracks.InternetThe advent of the Internet and widespread high-speed broadband access has transformed the experience of music, partly through the increased ease of access to recordings of music via streaming video and vastly increased choice of music for consumers. Chris Anderson, in his book The Long Tail: Why the Future of Business Is Selling Less of More, suggests that while the traditional economic model of supply and demand describes scarcity, the Internet retail model is based on abundance. Digital storage costs are low, so a company can afford to make its whole recording inventory available online, giving customers as much choice as possible. It has thus become economically viable to offer music recordings that very few people are interested in. Consumers' growing awareness of their increased choice results in a closer association between listening tastes and social identity, and the creation of thousands of niche markets.Another effect of the Internet arose with online communities and social media websites like YouTube and Facebook, a social networking service. These sites make it easier for aspiring singers and amateur bands to distribute videos of their songs, connect with other musicians, and gain audience interest. Professional musicians also use YouTube as a free publisher of promotional material. YouTube users, for example, no longer only download and listen to MP3s, but also actively create their own. According to Don Tapscott and Anthony D. Williams, in their book Wikinomics, there has been a shift from a traditional consumer role to what they call a prosumer role, a consumer who both creates content and consumes. Manifestations of this in music include the production of mashes, remixes, and music videos by fans.Business	This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. Music store selling various singles and albumsThe music industry refers to the businesses connected with the creation and sale of music. It consists of songwriters and composers who create new songs and musical pieces, music producers and sound engineers who record songs and pieces, record labels and publishers that distribute recorded music products and sheet music internationally and that often control the rights to those products. Some music labels are independent, while others are subsidiaries of larger corporate entities or international media groups. In the 2000s, the increasing popularity of listening to music as digital music files on MP3 players, iPods, or computers, and of trading music on file sharing websites or buying it online in the form of digital files had a major impact on the traditional music business. Many smaller independent CD stores went out of business as music buyers decreased their purchases of CDs, and many labels had lower CD sales. Some companies did well with the change to a digital format, though, such as Apple's iTunes, an online music store that sells digital files of songs over the Internet.Intellectual property lawsMain article: Royalty payment § Music royaltiesIn spite of some international copyright treaties, determining which music is in the public domain is complicated by the variety of national copyright laws that may be applicable. US copyright law formerly protected printed music published after 1923 for 28 years and with renewal for another 28 years, but the Copyright Act of 1976 made renewal automatic, and the Digital Millennium Copyright Act changed the calculation of the copyright term to 70 years after the death of the creator. Recorded sound falls under mechanical licensing, often covered by a confusing patchwork of state laws; most cover versions are licensed through the Harry Fox Agency. Performance rights may be obtained by either performers or the performance venue; the two major organizations for licensing are BMI and ASCAP. Two online sources for public domain music are IMSLP and Choral Public Domain Library.Education	This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. Non-professionalMain article: Music educationA Suzuki violin recital with students of varying agesThe incorporation of some music or singing training into general education from preschool to post secondary education is common in North America and Europe. Involvement in playing and singing music is thought to teach basic skills such as concentration, counting, listening, and cooperation while also promoting understanding of language, improving the ability to recall information, and creating an environment more conducive to learning in other areas. In elementary schools, children often learn to play instruments such as the recorder, sing in small choirs, and learn about the history of Western art music and traditional music. Some elementary school children also learn about popular music styles. In religious schools, children sing hymns and other religious music. In secondary schools, students may have the opportunity to perform in some types of musical ensembles, such as choirs, marching bands, concert bands, jazz bands, or orchestras. In some school systems, music lessons on how to play instruments may be provided. Some students also take private music lessons after school with a singing teacher or instrument teacher. Amateur musicians typically learn basic musical rudiments and beginner- to intermediate-level singing or instrument-playing techniques.At the university level, students in most arts and humanities programs can receive credit for taking a few music courses, which typically take the form of an overview course on the history of music, or a music appreciation course that focuses on listening to music and learning about different musical styles. In addition, most North American and European universities have some types of musical ensembles that students in arts and humanities are able to participate in, such as choirs, marching bands, concert bands, or orchestras. The study of Western art music is increasingly common outside of North America and Europe, such as the Indonesian Institute of the Arts in Yogyakarta, Indonesia, or the classical music programs that are available in Asian countries such as South Korea, Japan, and China. At the same time, Western universities and colleges are widening their curriculum to include music of non-Western cultures, such as the music of Africa or Bali.ProfessionalManhattan School of Music professor and professional double bass player Timothy Cobb teaching a bass lesson in the late 2000s. His bass has a low C extension with a metal machine with buttons for playing the pitches on the extension.People aiming to become professional musicians, singers, composers, songwriters, music teachers and practitioners of other music-related professions such as music history professors, sound engineers, and so on study in specialized post-secondary programs offered by colleges, universities and music conservatories. Some institutions that train individuals for careers in music offer training in a wide range of professions, as is the case with many of the top U.S. universities, which offer degrees in music performance, music history, music theory, music composition, music education and, in some cases, conducting. On the other hand, some small colleges may only offer training in a single profession.While most university and conservatory music programs focus on training students in classical music, there are a number of universities and colleges that train musicians for careers as jazz or popular music musicians and composers, with notable U.S. examples including the Manhattan School of Music and the Berklee College of Music. Two important schools in Canada which offer professional jazz training are McGill University and Humber College. Individuals aiming at careers in some types of music, such as heavy metal music, country music or blues are less likely to become professionals by completing degrees or diplomas in colleges or universities. Instead, they typically learn about their style of music by singing or playing in many bands, studying recordings available on CD, DVD and the Internet and working with already-established professionals in their style of music, either through informal mentoring or regular music lessons. Since the 2000s, the increasing popularity and availability of Internet forums and YouTube how-to videos have enabled many singers and musicians from metal, blues and similar genres to improve their skills. Many pop, rock and country singers train informally with vocal coaches and singing teachers.UndergraduateUndergraduate university degrees in music, including the Bachelor of Music, the Bachelor of Music Education, and the Bachelor of Arts typically take about four years to complete. These degrees provide students with a grounding in music theory and music history, and many students also study an instrument or learn singing technique as part of their program. Graduates of undergraduate music programs can seek employment or go on to further study in music graduate programs. Bachelor's degree graduates are also eligible to apply to some graduate programs and professional schools outside of music.GraduateGraduate music degrees include the Master of Music, the Master of Arts, the Doctor of Philosophy, and more recently, the Doctor of Musical Arts, or DMA. The Master of Music degree, which takes one to two years to complete, is typically awarded to students studying the performance of an instrument, education, voice or composition. The Master of Arts degree, which takes one to two years to complete and often requires a thesis, is typically awarded to students studying musicology, music history, music theory or ethnomusicology.The PhD, which is required for students who want to work as university professors in musicology, music history, or music theory, takes three to five years of study after the master's degree, during which time the student will complete advanced courses and undertake research for a dissertation. The DMA is a relatively new degree that was created to provide a credential for professional performers or composers that want to work as university professors in musical performance or composition. The DMA takes three to five years after a master's degree, and includes advanced courses, projects, and performances. In Medieval times, the study of music was one of the Quadrivium of the seven Liberal Arts and considered vital to higher learning. Within the quantitative Quadrivium, music, or more accurately harmonics, was the study of rational proportions.MusicologyMusicology, the academic study of the subject of music, is studied in universities and music conservatories. The earliest definitions from the 19th century defined three sub-disciplines of musicology: systematic musicology, historical musicology, and comparative musicology or ethnomusicology. In 2010-era scholarship, one is more likely to encounter a division of the discipline into music theory, music history, and ethnomusicology. Research in musicology has often been enriched by cross-disciplinary work, for example in the field of psychoacoustics. The study of music of non-Western cultures, and the cultural study of music, is called ethnomusicology. Students can pursue the undergraduate study of musicology, ethnomusicology, music history, and music theory through several different types of degrees, including bachelor's degrees, master's degrees and PhD degrees.Music theoryMusic theory is the study of music, generally in a highly technical manner outside of other disciplines. More broadly it refers to any study of music, usually related in some form with compositional concerns, and may include mathematics, physics, and anthropology. What is most commonly taught in beginning music theory classes are guidelines to write in the style of the common practice period, or tonal music. Theory, even of music of the common practice period, may take many other forms. Musical set theory is the application of mathematical set theory to music, first applied to atonal music. Speculative music theory, contrasted with analytic music theory, is devoted to the analysis and synthesis of music materials, for example tuning systems, generally as preparation for composition.ZoomusicologyZoomusicology is the study of the music of non-human animals, or the musical aspects of sounds produced by non-human animals. As George Herzog asked, do animals have music? François-Bernard Mâche's Musique, mythe, nature, ou les Dauphins d'Arion, a study of ornitho-musicology using a technique of Nicolas Ruwet's Langage, musique, poésie paradigmatic segmentation analysis, shows that bird songs are organised according to a repetition-transformation principle. Jean-Jacques Nattiez, argues that in the last analysis, it is a human being who decides what is and is not musical, even when the sound is not of human origin. If we acknowledge that sound is not organised and conceptualised merely by its producer, but by the mind that perceives it, then music is uniquely human.EthnomusicologyMain article: EthnomusicologyEthnomusicologist Frances Densmore recording Blackfoot chief Mountain Chief for the Bureau of American Ethnology In the West, much of the history of music that is taught deals with the Western civilization's art music, which is known as classical music. The history of music in non-Western cultures, which typically covers music from Africa and Asia is also taught in Western universities. This includes the documented classical traditions of Asian countries outside the influence of Western Europe, as well as the folk or indigenous music of various other cultures. Popular or folk styles of music in non-Western countries varied widely from culture to culture, and from period to period. Different cultures emphasised different instruments, techniques, singing styles and uses for music. Music has been used for entertainment, ceremonies, rituals, religious purposes and for practical and artistic communication. Non-Western music has also been used for propaganda purposes, as was the case with Chinese opera during the Cultural Revolution.There is a host of music classifications for non-Western music, many of which are caught up in the argument over the definition of music. Among the largest of these is the division between classical music, and popular music. Some genres do not fit neatly into one of these big two classifications,.As world cultures have come into greater global contact, their indigenous musical styles have often merged with other styles, which produces new styles. For example, the United States bluegrass style contains elements from Anglo-Irish, Scottish, Irish, German and African instrumental and vocal traditions, which were able to fuse in the United States' multi-ethnic melting pot society. Some types of world music contain a mixture of non-Western indigenous styles with Western pop music elements. Genres of music are determined as much by tradition and presentation as by the actual music. Some works, like George Gershwin's Rhapsody in Blue, are claimed by both jazz and classical music, while Gershwin's Porgy and Bess and Leonard Bernstein's West Side Story are claimed by both opera and the Broadway musical tradition. Many current music festivals for non-Western music include bands and singers from a particular musical genre, such as world music.Indian music, for example, is one of the oldest and longest living types of music, and is still widely heard and performed in South Asia, as well as internationally. Indian music has mainly three forms of classical music, Hindustani, Carnatic, and Dhrupad styles. It has also a large repertoire of styles, which involve only percussion music such as the talavadya performances famous in South India.TherapyA music therapist from a Blues in the Schools program plays harmonica with a US Navy sailor at a Naval Therapy Center.Music therapy is an interpersonal process in which a trained therapist uses music and all of its facets—physical, emotional, mental, social, aesthetic, and spiritual—to help clients to improve or maintain their health. In some instances, the client's needs are addressed directly through music; in others they are addressed through the relationships that develop between the client and therapist. Music therapy is used with individuals of all ages and with a variety of conditions, including: psychiatric disorders, medical problems, physical disabilities, sensory impairments, developmental disabilities, substance abuse issues, communication disorders, interpersonal problems, and aging. It is also used to improve learning, build self-esteem, reduce stress, support physical exercise, and facilitate a host of other health-related activities. Music therapists may encourage clients to sing, play instruments, create songs, or do other musical activities.One of the earliest mentions of music therapy was in Al-Farabi's treatise Meanings of the Intellect, which described the therapeutic effects of music on the soul. Music has long been used to help people deal with their emotions. In the 17th century, the scholar Robert Burton's The Anatomy of Melancholy argued that music and dance were critical in treating mental illness, especially melancholia. He noted that music has an excellent power...to expel many other diseases and he called it a sovereign remedy against despair and melancholy. He pointed out that in Antiquity, Canus, a Rhodian fiddler, used music to make a melancholy man merry,...a lover more enamoured, a religious man more devout. In the Ottoman Empire, mental illnesses were treated with music. In November 2006, Dr. Michael J. Crawford and his colleagues also found that music therapy helped schizophrenic patients.Albert Einstein had a lifelong love of music, once stating that life without playing music would be inconceivable to him. In some interviews Einstein even attributed much of his scientific intuition to music, with his son Hans recounting that whenever he felt that he had come to the end of the road or into a difficult situation in his work, he would take refuge in music, and that would usually resolve all his difficulties. Something in the music, according to Michele and Robert Root-Bernstein in Psychology Today, would guide his thoughts in new and creative directions. It has been said that Einstein considered Mozart's music to reveal a universal harmony that Einstein believed existed in the universe, as if the great Wolfgang Amadeus did not 'create' his beautifully clear music at all, but simply discovered it already made. This perspective parallels, remarkably, Einstein’s views on the ultimate simplicity of nature and its explanation and statement via essentially simple mathematical expressions. A review suggests that music may be effective for improving subjective sleep quality in adults with insomnia symptoms. Music is also being used in clinical rehabilitation of cognitive and motor disorders. Mathematics includes the study of such topics as numbers, formulas and related structures, shapes and spaces in which they are contained, and quantities and their changes. There is no general consensus about its exact scope or epistemological status.Most of mathematical activity consists of discovering and proving properties of abstract objects. These objects are either abstractions from nature, or abstract entities that are defined by their basic properties, called axioms. A proof consists of a succession of applications of some deductive rules to already known results, including previously proved theorems, axioms and some basic properties that are considered as true starting points of the theory under consideration. The result of a proof is called a theorem. Contrary to physical laws, the validity of a theorem does not rely on any experimentation but on the correctness of its reasoning.Mathematics is widely used in science for modeling phenomena. This enables the extraction of quantitative predictions from experimental laws. For example, the movement of planets can be predicted with high accuracy using Newton's law of gravitation combined with mathematical computation. The independence of mathematical truth from any experimentation implies that the accuracy of such predictions depends only on the adequacy of the model for describing the reality. So when some inaccurate predictions arise, it means that the model must be improved or changed, not that the mathematics is wrong. For example, the perihelion precession of Mercury cannot be explained by Newton's law of gravitation, but is accurately explained by Einstein's general relativity. This experimental validation of Einstein's theory shows that Newton's law of gravitation is only an approximation.Mathematics is essential in many fields, including natural sciences, engineering, medicine, finance, computer science and social sciences. Some areas of mathematics, such as statistics and game theory, are developed in direct correlation with their applications, and are often grouped under the name of applied mathematics. Other mathematical areas are developed independently from any application, but practical applications are often discovered later. A fitting example is the problem of integer factorization which goes back to Euclid but had no practical application before its use in the RSA cryptosystem.Mathematics has been a human activity from as far back as written records exist. However, the concept of a proof and its associated mathematical rigour first appeared in Greek mathematics, most notably in Euclid's Elements. Mathematics developed at a relatively slow pace until the Renaissance, when algebra and infinitesimal calculus were added to arithmetic and geometry as main areas of mathematics. Since then the interaction between mathematical innovations and scientific discoveries have led to a rapid increase in the rate of mathematical discoveries. At the end of the 19th century, the foundational crisis of mathematics led to the systematization of the axiomatic method. This, in turn, gave rise to a dramatic increase in the number of mathematics areas and their fields of applications; a witness of this is the Mathematics Subject Classification, which lists more than sixty first-level areas of mathematics. Before the Renaissance, mathematics was divided into two main areas, arithmetic, devoted to the manipulation of numbers, and geometry, devoted to the study of shapes. There was also some pseudo-science, such as numerology and astrology that were not clearly distinguished from mathematics.Around the Renaissance, two new main areas appeared. The introduction of mathematical notation led to algebra, which, roughly speaking, consists of the study and the manipulation of formulas. Calculus, a shorthand of infinitesimal calculus and integral calculus, is the study of continuous functions, which model the change of, and the relationship between varying quantities. This division into four main areas remained valid until the end of the 19th century, although some areas, such as celestial mechanics and solid mechanics, which were often considered as mathematics, are now considered as belonging to physics. Also, some subjects developed during this period predate mathematics areas, such as probability theory and combinatorics, which only later became regarded as autonomous areas of their own.At the end of the 19th century, the foundational crisis in mathematics and the resulting systematization of the axiomatic method led to an explosion in the amount of areas of mathematics. The Mathematics Subject Classification contains more than 60 first-level areas. Some of these areas correspond to the older division in four main areas. This is the case of 11:number theory and 51:Geometry. However, there are several other first-level areas that have geometry in their name or are commonly considered as belonging to geometry. Algebra and calculus do not appear as first-level areas, but are each split into several first-level areas. Other first-level areas did not exist at all before the 20th century or were not considered before as mathematics, such as 03:Mathematical logic and foundations.Number theoryMain article: Number theoryNumber theory started with the manipulation of numbers, that is, natural numbers, {displaystyle,} {displaystyle,} later expanded to integers {displaystyle } {displaystyle } and rational numbers. {displaystyle.} {displaystyle.} Number theory was formerly called arithmetic, but nowadays this term is mostly used for the methods of calculation with numbers.A specificity of number theory is that many problems that can be stated very elementarily are very difficult, and, when solved, have a solution that require very sophisticated methods coming from various parts of mathematics. A notable example is Fermat's Last theorem that was stated in 1637 by Pierre de Fermat and proved only in 1994 by Andrew Wiles, using, among other tools, algebraic geometry, category theory and homological algebra. Another example is Goldbach's conjecture, that asserts that every even integer greater than 2 is the sum of two prime numbers. Stated in 1742 by Christian Goldbach it remains unproven despite considerable effort.In view of the diversity of the studied problems and the solving methods, number theory is presently split in several subareas, which include analytic number theory, algebraic number theory, geometry of numbers, Diophantine equations and transcendence theory.GeometryMain article: GeometryGeometry is, with arithmetic, one of the oldest branches of mathematics. It started with empirical recipes concerning shapes, such as lines, angles and circles, which were developed mainly for the need of surveying and architecture.A fundamental innovation was the elaboration of proofs by ancient Greeks: it is not sufficient to verify by measurement that, say, two lengths are equal. Such a property must be proved by abstract reasoning from previously proven results and basic properties ). This principle, which is foundational for all mathematics, was elaborated for the sake of geometry, and was systematized by Euclid around 300 BC in his book Elements.The resulting Euclidean geometry is the study of shapes and their arrangements constructed from lines, planes and circles in the Euclidean plane and the Euclidean space.Euclidean geometry was developed without a change of methods or scope until the 17th century, when René Descartes introduced what is now called Cartesian coordinates. This was a major change of paradigm, since instead of defining real numbers as lengths of line segments, it allowed the representation of points using numbers, and for the use of algebra and later, calculus for solving geometrical problems. This split geometry in two parts that differ only by their methods, synthetic geometry, which uses purely geometrical methods, and analytic geometry, which uses coordinates systemically.Analytic geometry allows the study of new shapes, in particular curves that are not related to circles and lines; these curves are defined either as graph of functions, or by implicit equations, often polynomial equations. Analytic geometry makes it possible to consider spaces dimensions higher than three, which are no longer a model of the physical space.Geometry expanded quickly during the 19th century. A major event was the discovery of non-Euclidean geometries, which are geometries where the parallel postulate is abandoned. This is, besides Russel's paradox, one of the starting points of the foundational crisis of mathematics, by taking into question the truth of the aforementioned postulate. This aspect of the crisis was solved by systematizing the axiomatic method, and adopting that the truth of the chosen axioms is not a mathematical problem. In turn, the axiomatic method allows for the study of various geometries obtained either by changing the axioms or by considering properties that are invariant under specific transformations of the space. This results in a number of subareas and generalizations of geometry that include:  Projective geometry, introduced in the 16th century by Girard Desargues, it extends Euclidean geometry by adding points at infinity at which parallel lines intersect. This simplifies many aspects of classical geometry by avoiding to have a different treatment for intersecting and parallel lines.  Affine geometry, the study of properties relative to parallelism and independent from the concept of length.  Differential geometry, the study of curves, surfaces, and their generalizations, which are defined using differentiable functions  Manifold theory, the study of shapes that are not necessarily embedded in a larger space  Riemannian geometry, the study of distance properties in curved spaces  Algebraic geometry, the study of curves, surfaces,and their generalizations, which are defined using polynomials  Topology, the study of properties that are kept under continuous deformations    Algebraic topology, the use in topology of algebraic methods, mainly homological algebra  Discrete geometry, the study of finite configurations in geometry  Convex geometry, the study of convex sets, which takes its importance from its applications in optimization  Complex geometry, the geometry obtained by replacing real numbers with complex numbersExamples of shapes encountered in geometry  Pythagorean theorem  Conic Sections  Elliptic curve  Triangle on a paraboloid  Torus  FractalAlgebraMain article: AlgebraAlgebra may be viewed as the art of manipulating equations and formulas. Diophantus and Al-Khowarazmi were two main precursors of algebra. The first one solved some relations between unknown natural numbers by deducing new relations until getting the solution. The second one introduced systematic methods for transforming equations. The term algebra is derived from the Arabic word that he used for naming one of these methods in the title of his main treatise.The quadratic formula expresses concisely the solutions of all quadratic equationsAlgebra began to be a specific area only with François Viète, who introduced the use of letters for representing unknown or unspecified numbers. This allows describing consisely the operations that have to be done on the numbers represented by the variables.Until the 19th century, algebra consisted mainly of the study of linear equations that is called presently linear algebra, and polynomial equations in a single unknown, which were called algebraic equations. During the 19th century, variables began to represent other things than numbers, on which some operations can operate, which are often generalizations of arithmetic operations. For dealing with this, the concept of algebraic structure was introduced, which consist of a set whose elements are unspecified, of operations acting on the elements of the set, and rules that these operations must follow. So, the scope of algebra evolved for becoming essentially the study of algebraic structures. This object of algebra was called modern algebra or abstract algebra, the latter term being still used, mainly in an educational context, in opposition with elementary algebra which is concerned with the older way of manipulating formulas.Rubik's cube: the study of its possible moves is a concrete application of group theorySome types of algebraic structures have properties that are useful, and often fundamental, in many areas of mathematics. Their study are nowadays autonomous parts of algebra, which include:  group theory;  field theory;  vector spaces, whose study is essentially the same as linear algebra;  ring theory;  commutative algebra, which is the study of commutative rings, includes the study of polynomials, and is a foundational part of algebraic geometry;  homological algebra  Lie algebra and Lie group theory;  Boolean algebra, which is widely used for the study of the logical structure of computers.The study of types algebraic structures as mathematical objects is the object of universal algebra and category theory. The latter applies to every mathematical structure. At its origin, it was introduced, together with homological algebra for allowing the algebraic study of non-algebraic objects such as topological spaces; this particular area of application is called algebraic topology.Calculus and analysisMain articles: Calculus and Mathematical analysisCalculus, formerly called infinitesimal calculus, was introduced in the 17th century by Newton and Leibniz, independently and simultaneously. It is fundamentally the study of the relationship of two changing quantities, called variables, such that one depends on the other. Calculus was largely expanded in the 18th century by Euler, with the introduction of the concept of a function, and many other results. Presently calculus refers mainly to the elementary part of this theory, and analysis is commonly used for advanced parts.Analysis is further subdivided into real analysis, where variables represent real numbers and complex analysis where variables represent complex numbers. Presently there are many subareas of analysis, some being shared with other areas of mathematics; they include:  Multivariable calculus  Functional analysis, where variables represent varying functions;  Integration, measure theory and potential theory, all strongly related with Probability theory;  Ordinary differential equations;  Partial differential equations;  Numerical analysis, mainly devoted to the computation on computers of solutions of ordinary and partial differential equations that arise in many applications of mathematics.Discrete mathematicsMain article: Discrete mathematicsMathematical logic and set theoryMain articles: Mathematical logic and set theoryThese subjects belong to mathematics since the end of the 19th century. Before this period, sets were not considered as mathematical objects, and logic, although used for mathematical proofs, belonged to philosophy, and was not specifically studied by mathematicians.Before the study of infinite sets by Georg Cantor, mathematicians were reluctant to consider collections that are actually infinite, and considered infinity as the result of an endless enumeration. Cantor's work offended many mathematicians not only by considering actually infinite sets, but also by showing that this implies different sizes of infinity and the existence of mathematical objects that cannot be computed, and not even be explicitly described. This led to the controversy over Cantor's set theory.In the same period, it appeared in various areas of mathematics that the former intuitive definitions of the basic mathematical objects were insufficient for insuring mathematical rigour. Examples of such intuitive definitions are a set is a collection of objects, natural number is what is used for counting, a point is a shape with a zero length in every direction, a curve is a trace left by a moving point, etc.This is the origin of the foundational crisis of mathematics. It has been eventually solved in the mainstream of mathematics by systematize the axiomatic method inside a formalized set theory. Roughly speaking, each mathematical object is defined by the set of all similar objects and the properties that these objects must have. For example, in Peano arithmetic, the natural numbers are defined by zero is a number, each number as a unique successor, each number but zero has a unique predecessor, and some rules of reasoning. The nature of the objects defined this way is a philosophical problem that mathematicians leave to philosophers, even as many mathematicians have opinions on this nature, and use their opinion—sometimes called intuition—to guide their study and finding proofs.This approach allows considering logics, theorems, proofs, etc.) as mathematical objects, and to prove theorems about them. For example, Gödel's incompleteness theorems assert, roughly speaking that, in every theory that contains the natural numbers, there are theorems that are true, but not provable inside the theory.This approach of the foundations of the mathematics was challenged during the first half of the 20th century by mathematicians leaded by L. E. J. Brouwer who promoted an intuitionistic logic that excludes the law of excluded middle.These problems and debates led to a wide expansion of mathematical logic, with subareas such as model theory, proof theory, type theory, computability theory and computational complexity theory. Although these aspects of mathematical logic were introduced before the rise of computers, their use in compiler design, program certification, proof assistants and other aspects of computer science, contributed in turn to the expansion of these logical theories.Applied mathematicsMain article: Applied mathematicsApplied mathematics concerns itself with mathematical methods that are typically used in science, engineering, business, and industry. Thus, applied mathematics is a mathematical science with specialized knowledge. The term applied mathematics also describes the professional specialty in which mathematicians work on practical problems; as a profession focused on practical problems, applied mathematics focuses on the formulation, study, and use of mathematical models in science, engineering, and other areas of mathematical practice.In the past, practical applications have motivated the development of mathematical theories, which then became the subject of study in pure mathematics, where mathematics is developed primarily for its own sake. Thus, the activity of applied mathematics is vitally connected with research in pure mathematics.Statistics and other decision sciencesMain article: StatisticsApplied mathematics has significant overlap with the discipline of statistics, whose theory is formulated mathematically, especially with probability theory. Statisticians create data that makes sense with random sampling and with randomized experiments; the design of a statistical sample or experiment specifies the analysis of the data. When reconsidering data from experiments and samples or when analyzing data from observational studies, statisticians make sense of the data using the art of modelling and the theory of inference—with model selection and estimation; the estimated models and consequential predictions should be tested on new data.Statistical theory studies decision problems such as minimizing the risk of a statistical action, such as using a procedure in, for example, parameter estimation, hypothesis testing, and selecting the best. In these traditional areas of mathematical statistics, a statistical-decision problem is formulated by minimizing an objective function, like expected loss or cost, under specific constraints: For example, designing a survey often involves minimizing the cost of estimating a population mean with a given level of confidence. Because of its use of optimization, the mathematical theory of statistics shares concerns with other decision sciences, such as operations research, control theory, and mathematical economics.Computational mathematicsComputational mathematics proposes and studies methods for solving mathematical problems that are typically too large for human numerical capacity. Numerical analysis studies methods for problems in analysis using functional analysis and approximation theory; numerical analysis broadly includes the study of approximation and discretisation with special focus on rounding errors. Numerical analysis and, more broadly, scientific computing also study non-analytic topics of mathematical science, especially algorithmic-matrix-and-graph theory. Other areas of computational mathematics include computer algebra and symbolic computation.Arbitrary-gametree-solved.svg BernoullisLawDerivationDiagram.svg Composite trapezoidal rule illustration small.svg Maximum boxed.png Two red dice 01.svg Oldfaithful3.png Caesar3.svgGame theory Fluid dynamics Numerical analysis Optimization Probability theory Statistics CryptographyMarket Data Index NYA on 20050726 202628 UTC.png Gravitation space source.svg CH4-structure.svg Signal transduction pathways.svg GDP PPP Per Capita IMF 2008.svg Simple feedback control loop2.svgMathematical finance Mathematical physics Mathematical chemistry Mathematical biology Mathematical economics Control theoryHistoryMain article: History of mathematicsThe history of mathematics can be seen as an ever-increasing series of abstractions. Evolutionarily speaking, the first abstraction to ever take place, which is shared by many animals, was probably that of numbers: the realization that a collection of two apples and a collection of two oranges have something in common, namely the quantity of their members. As evidenced by tallies found on bone, in addition to recognizing how to count physical objects, prehistoric peoples may have also recognized how to count abstract quantities, like time—days, seasons, or years.The Babylonian mathematical tablet Plimpton 322, dated to 1800 BC.Evidence for more complex mathematics does not appear until around 3000 BC, when the Babylonians and Egyptians began using arithmetic, algebra, and geometry for taxation and other financial calculations, for building and construction, and for astronomy. The oldest mathematical texts from Mesopotamia and Egypt are from 2000 to 1800 BC. Many early texts mention Pythagorean triples and so, by inference, the Pythagorean theorem seems to be the most ancient and widespread mathematical concept after basic arithmetic and geometry. It is in Babylonian mathematics that elementary arithmetic first appear in the archaeological record. The Babylonians also possessed a place-value system and used a sexagesimal numeral system which is still in use today for measuring angles and time.Archimedes used the method of exhaustion to approximate the value of pi.Beginning in the 6th century BC with the Pythagoreans, with Greek mathematics the Ancient Greeks began a systematic study of mathematics as a subject in its own right. Around 300 BC, Euclid introduced the axiomatic method still used in mathematics today, consisting of definition, axiom, theorem, and proof. His book, Elements, is widely considered the most successful and influential textbook of all time. The greatest mathematician of antiquity is often held to be Archimedes of Syracuse. He developed formulas for calculating the surface area and volume of solids of revolution and used the method of exhaustion to calculate the area under the arc of a parabola with the summation of an infinite series, in a manner not too dissimilar from modern calculus. Other notable achievements of Greek mathematics are conic sections, trigonometry, and the beginnings of algebra.The numerals used in the Bakhshali manuscript, dated between the 2nd century BC and the 2nd century AD.The Hindu–Arabic numeral system and the rules for the use of its operations, in use throughout the world today, evolved over the course of the first millennium AD in India and were transmitted to the Western world via Islamic mathematics. Other notable developments of Indian mathematics include the modern definition and approximation of sine and cosine, and an early form of infinite series.A page from al-Khwārizmī's AlgebraLeonardo Fibonacci, the Italian mathematician who introduced the Hindu–Arabic numeral system invented between the 1st and 4th centuries by Indian mathematicians, to the Western World.During the Golden Age of Islam, especially during the 9th and 10th centuries, mathematics saw many important innovations building on Greek mathematics. The most notable achievement of Islamic mathematics was the development of algebra. Other achievements of the Islamic period include advances in spherical trigonometry and the addition of the decimal point to the Arabic numeral system. Many notable mathematicians from this period were Persian, such as Al-Khwarismi, Omar Khayyam and Sharaf al-Dīn al-Ṭūsī.During the early modern period, mathematics began to develop at an accelerating pace in Western Europe. The development of calculus by Isaac Newton and Gottfried Leibniz in the 17th century revolutionized mathematics. Leonhard Euler was the most notable mathematician of the 18th century, contributing numerous theorems and discoveries. Perhaps the foremost mathematician of the 19th century was the German mathematician Carl Gauss, who made numerous contributions to fields such as algebra, analysis, differential geometry, matrix theory, number theory, and statistics. In the early 20th century, Kurt Gödel transformed mathematics by publishing his incompleteness theorems, which show in part that any consistent axiomatic system—if powerful enough to describe arithmetic—will contain true propositions that cannot be proved.Mathematics has since been greatly extended, and there has been a fruitful interaction between mathematics and science, to the benefit of both. Mathematical discoveries continue to be made to this very day. According to Mikhail B. Sevryuk, in the January 2006 issue of the Bulletin of the American Mathematical Society, The number of papers and books included in the Mathematical Reviews database since 1940 is now more than 1.9 million, and more than 75 thousand items are added to the database each year. The overwhelming majority of works in this ocean contain new mathematical theorems and their proofs.EtymologyThe word mathematics comes from Ancient Greek máthēma, meaning that which is learnt, what one gets to know, hence also study and science. The word for mathematics came to have the narrower and more technical meaning mathematical study even in Classical times. Its adjective is mathēmatikós, meaning related to learning or studious, which likewise further came to mean mathematical. In particular, mathēmatikḗ tékhnē meant the mathematical art.Similarly, one of the two main schools of thought in Pythagoreanism was known as the mathēmatikoi —which at the time meant learners rather than mathematicians in the modern sense.In Latin, and in English until around 1700, the term mathematics more commonly meant astrology rather than mathematics; the meaning gradually changed to its present one from about 1500 to 1800. This has resulted in several mistranslations. For example, Saint Augustine's warning that Christians should beware of mathematici, meaning astrologers, is sometimes mistranslated as a condemnation of mathematicians.The apparent plural form in English, like the French plural form les mathématiques, goes back to the Latin neuter plural mathematica, based on the Greek plural ta mathēmatiká, used by Aristotle, and meaning roughly all things mathematical, although it is plausible that English borrowed only the adjective mathematic and formed the noun mathematics anew, after the pattern of physics and metaphysics, which were inherited from Greek. In English, the noun mathematics takes a singular verb. It is often shortened to maths or, in North America, math.Philosophy of mathematicsMain articles: Philosophy of mathematics and Definitions of mathematicsThere is no general consensus about the exact definition or epistemological status of mathematics. Aristotle defined mathematics as the science of quantity and this definition prevailed until the 18th century. However, Aristotle also noted a focus on quantity alone may not distinguish mathematics from sciences like physics; in his view, abstraction and studying quantity as a property separable in thought from real instances set mathematics apart.In the 19th century, when the study of mathematics increased in rigor and began to address abstract topics such as group theory and projective geometry, which have no clear-cut relation to quantity and measurement, mathematicians and philosophers began to propose a variety of new definitions.A great many professional mathematicians take no interest in a definition of mathematics, or consider it undefinable. There is not even consensus on whether mathematics is an art or a science. Some just say, Mathematics is what mathematicians do.Three leading typesThree leading types of definition of mathematics today are called logicist, intuitionist, and formalist, each reflecting a different philosophical school of thought. All have severe flaws, none has widespread acceptance, and no reconciliation seems possible.Logicist definitionsAn early definition of mathematics in terms of logic was that of Benjamin Peirce : the science that draws necessary conclusions. In the Principia Mathematica, Bertrand Russell and Alfred North Whitehead advanced the philosophical program known as logicism, and attempted to prove that all mathematical concepts, statements, and principles can be defined and proved entirely in terms of symbolic logic. An example of a logicist definition of mathematics is Russell's All Mathematics is Symbolic Logic.Intuitionist definitionsIntuitionist definitions, developing from the philosophy of mathematician L. E. J. Brouwer, identify mathematics with certain mental phenomena. An example of an intuitionist definition is Mathematics is the mental activity which consists in carrying out constructs one after the other. A peculiarity of intuitionism is that it rejects some mathematical ideas considered valid according to other definitions. In particular, while other philosophies of mathematics allow objects that can be proved to exist even though they cannot be constructed, intuitionism allows only mathematical objects that one can actually construct. Intuitionists also reject the law of excluded middle. While this stance does force them to reject one common version of proof by contradiction as a viable proof method, namely the inference of P {displaystyle P} P from ¬ P → ⊥ {displaystyle eg P	o �ot } {displaystyle eg P	o �ot }, they are still able to infer ¬ P {displaystyle eg P} eg P from P → ⊥ {displaystyle P	o �ot } P	o �ot. For them, ¬ {displaystyle eg } {displaystyle eg } is a strictly weaker statement than P {displaystyle P} P.Formalist definitionsFormalist definitions identify mathematics with its symbols and the rules for operating on them. Haskell Curry defined mathematics simply as the science of formal systems. A formal system is a set of symbols, or tokens, and some rules on how the tokens are to be combined into formulas. In formal systems, the word axiom has a special meaning different from the ordinary meaning of a self-evident truth, and is used to refer to a combination of tokens that is included in a given formal system without needing to be derived using the rules of the system.Mathematics as scienceCarl Friedrich Gauss, known as the prince of mathematiciansThe German mathematician Carl Friedrich Gauss referred to mathematics as the Queen of the Sciences. More recently, Marcus du Sautoy has called mathematics the Queen of Science... the main driving force behind scientific discovery. The philosopher Karl Popper observed that most mathematical theories are, like those of physics and biology, hypothetico-deductive: pure mathematics therefore turns out to be much closer to the natural sciences whose hypotheses are conjectures, than it seemed even recently. Popper also noted that I shall certainly admit a system as empirical or scientific only if it is capable of being tested by experience.Mathematics shares much in common with many fields in the physical sciences, notably the exploration of the logical consequences of assumptions. Intuition and experimentation also play a role in the formulation of conjectures in both mathematics and the sciences. Experimental mathematics continues to grow in importance within mathematics, and computation and simulation are playing an increasing role in both the sciences and mathematics.Several authors consider that mathematics is not a science because it does not rely on empirical evidence. The opinions of mathematicians on this matter are varied. Many mathematicians feel that to call their area a science is to downplay the importance of its aesthetic side, and its history in the traditional seven liberal arts; others feel that to ignore its connection to the sciences is to turn a blind eye to the fact that the interface between mathematics and its applications in science and engineering has driven much development in mathematics. One way this difference of viewpoint plays out is in the philosophical debate as to whether mathematics is created or discovered. In practice, mathematicians are typically grouped with scientists at the gross level but separated at finer levels. This is one of many issues considered in philosophy of mathematics.Inspiration, pure and applied mathematics, and aestheticsMain article: Mathematical beautyIsaac NewtonGottfried Wilhelm von LeibnizIsaac Newton and Gottfried Wilhelm Leibniz developed infinitesimal calculus.Mathematics arises from many different kinds of problems. At first these were found in commerce, land measurement, architecture and later astronomy; today, all sciences pose problems studied by mathematicians, and many problems arise within mathematics itself. For example, the physicist Richard Feynman invented the path integral formulation of quantum mechanics using a combination of mathematical reasoning and physical insight, and today's string theory, a still-developing scientific theory which attempts to unify the four fundamental forces of nature, continues to inspire new mathematics.Some mathematics is relevant only in the area that inspired it, and is applied to solve further problems in that area. But often mathematics inspired by one area proves useful in many areas, and joins the general stock of mathematical concepts. A distinction is often made between pure mathematics and applied mathematics. However pure mathematics topics often turn out to have applications, e.g. number theory in cryptography.This remarkable fact, that even the purest mathematics often turns out to have practical applications, is what the physicist Eugene Wigner has named the unreasonable effectiveness of mathematics. The philosopher of mathematics Mark Steiner has written extensively on this matter and acknowledges that the applicability of mathematics constitutes a challenge to naturalism. For the philosopher of mathematics Mary Leng, the fact that the physical world acts in accordance with the dictates of non-causal mathematical entities existing beyond the universe is a happy coincidence. On the other hand, for some anti-realists, connections, which are acquired among mathematical things, just mirror the connections acquiring among objects in the universe, so there is no happy coincidence.As in most areas of study, the explosion of knowledge in the scientific age has led to specialization: there are now hundreds of specialized areas in mathematics and the latest Mathematics Subject Classification runs to 46 pages. Several areas of applied mathematics have merged with related traditions outside of mathematics and become disciplines in their own right, including statistics, operations research, and computer science.For those who are mathematically inclined, there is often a definite aesthetic aspect to much of mathematics. Many mathematicians talk about the elegance of mathematics, its intrinsic aesthetics and inner beauty. Simplicity and generality are valued. There is beauty in a simple and elegant proof, such as Euclid's proof that there are infinitely many prime numbers, and in an elegant numerical method that speeds up calculation, such as the fast Fourier transform. G. H. Hardy in A Mathematician's Apology expressed the belief that these aesthetic considerations are, in themselves, sufficient to justify the study of pure mathematics. He identified criteria such as significance, unexpectedness, inevitability, and economy as factors that contribute to a mathematical aesthetic. Mathematical research often seeks critical features of a mathematical object. A theorem expressed as a characterization of an object by these features is the prize. Examples of particularly succinct and revelatory mathematical arguments have been published in Proofs from THE BOOK.The popularity of recreational mathematics is another sign of the pleasure many find in solving mathematical questions. At the other social extreme, philosophers continue to find problems in philosophy of mathematics, such as the nature of mathematical proof.Notation, language, and rigorMain article: Mathematical notationLeonhard Euler created and popularized much of the mathematical notation used today.Most of the mathematical notation in use today was not invented until the 16th century. Before that, mathematics was written out in words, limiting mathematical discovery. Euler was responsible for many of the notations in use today. Modern notation makes mathematics much easier for the professional, but beginners often find it daunting. According to Barbara Oakley, this can be attributed to the fact that mathematical ideas are both more abstract and more encrypted than those of natural language. Unlike natural language, where people can often equate a word with the physical object it corresponds to, mathematical symbols are abstract, lacking any physical analog. Mathematical symbols are also more highly encrypted than regular words, meaning a single symbol can encode a number of different operations or ideas.Mathematical language can be difficult to understand for beginners because even common terms, such as or and only, have a more precise meaning than they have in everyday speech, and other terms such as open and field refer to specific mathematical ideas, not covered by their laymen's meanings. Mathematical language also includes many technical terms such as homeomorphism and integrable that have no meaning outside of mathematics. Additionally, shorthand phrases such as iff for if and only if belong to mathematical jargon. There is a reason for special notation and technical vocabulary: mathematics requires more precision than everyday speech. Mathematicians refer to this precision of language and logic as rigor.Mathematical proof is fundamentally a matter of rigor. Mathematicians want their theorems to follow from axioms by means of systematic reasoning. This is to avoid mistaken theorems, based on fallible intuitions, of which many instances have occurred in the history of the subject. The level of rigor expected in mathematics has varied over time: the Greeks expected detailed arguments, but at the time of Isaac Newton the methods employed were less rigorous. Problems inherent in the definitions used by Newton would lead to a resurgence of careful analysis and formal proof in the 19th century. Misunderstanding the rigor is a notable cause for some of the common misconceptions of mathematics. Today, mathematicians continue to argue among themselves about computer-assisted proofs. Since large computations are hard to verify, such proofs may be erroneous if the used computer program is erroneous. On the other hand, proof assistants allow for the verification of all details that cannot be given in a hand-written proof, and provide certainty of the correctness of long proofs such as that of the Feit–Thompson theorem.Axioms in traditional thought were self-evident truths, but that conception is problematic. At a formal level, an axiom is just a string of symbols, which has an intrinsic meaning only in the context of all derivable formulas of an axiomatic system. It was the goal of Hilbert's program to put all of mathematics on a firm axiomatic basis, but according to Gödel's incompleteness theorem every axiomatic system has undecidable formulas; and so a final axiomatization of mathematics is impossible. Nonetheless, mathematics is often imagined to be nothing but set theory in some axiomatization, in the sense that every mathematical statement or proof could be cast into formulas within set theory.Mathematical awardsArguably the most prestigious award in mathematics is the Fields Medal, established in 1936 and awarded every four years to as many as four individuals. The Fields Medal is often considered a mathematical equivalent to the Nobel Prize.The Wolf Prize in Mathematics, instituted in 1978, recognizes lifetime achievement, and another major international award, the Abel Prize, was instituted in 2003. The Chern Medal was introduced in 2010 to recognize lifetime achievement. These accolades are awarded in recognition of a particular body of work, which may be innovational, or provide a solution to an outstanding problem in an established field.A famous list of 23 open problems, called Hilbert's problems, was compiled in 1900 by German mathematician David Hilbert. This list achieved great celebrity among mathematicians, and at least nine of the problems have now been solved. A new list of seven important problems, titled the Millennium Prize Problems, was published in 2000. Only one of them, the Riemann hypothesis, duplicates one of Hilbert's problems. A solution to any of these problems carries a 1 million dollar reward. Currently, only one of these problems, the Poincaré conjecture, has been solved. A language is a structured system of communication used by humans, based on speech and gesture, sign, or often writing. The structure of language is its grammar and the free components are its vocabulary. Many languages, including the most widely-spoken ones, have writing systems that enable sounds or signs to be recorded for later reactivation. Human language is unique among known systems of animal communication in that it is not dependent on a single mode of transmission, it is highly variable between cultures and across time, and affords a much wider range of expression than other systems. It has the properties of productivity and displacement, and relies on social convention and learning.Estimates of the number of human languages in the world vary between 5,000 and 7,000. However, any precise estimate depends on the arbitrary distinction between languages and dialect. Natural languages are spoken or signed, but any language can be encoded into secondary media using auditory, visual, or tactile stimuli – for example, in writing, whistling, signing, or braille. In other words, human language is modality-independent, but written or signed language is the way to inscribe or encode the natural human speech or gestures.Depending on philosophical perspectives regarding the definition of language and meaning, when used as a general concept, language may refer to the cognitive ability to learn and use systems of complex communication, or to describe the set of rules that makes up these systems, or the set of utterances that can be produced from those rules. All languages rely on the process of semiosis to relate signs to particular meanings. Oral, manual and tactile languages contain a phonological system that governs how symbols are used to form sequences known as words or morphemes, and a syntactic system that governs how words and morphemes are combined to form phrases and utterances.The scientific study of language is called linguistics. Critical examinations of languages, such as philosophy of language, the relationships between language and thought, etc., such as how words represent experience, have been debated at least since Gorgias and Plato in ancient Greek civilization. Thinkers such as Rousseau have debated that language originated from emotions, while others like Kant, have held that languages originated from rational and logical thought. Twentieth century philosophers such as Wittgenstein argued that philosophy is really the study of language itself. Major figures in contemporary linguistics of these times include Ferdinand de Saussure and Noam Chomsky.Language is thought to have gradually diverged from earlier primate communication systems when early hominins acquired the ability to form a theory of mind and shared intentionality. This development is sometimes thought to have coincided with an increase in brain volume, and many linguists see the structures of language as having evolved to serve specific communicative and social functions. Language is processed in many different locations in the human brain, but especially in Broca's and Wernicke's areas. Humans acquire language through social interaction in early childhood, and children generally speak fluently by approximately three years old. Language and culture are codependent. Therefore, in addition to its strictly communicative uses, language has social uses such as signifying group identity, social stratification, as well as use for social grooming and entertainment.Languages evolve and diversify over time, and the history of their evolution can be reconstructed by comparing modern languages to determine which traits their ancestral languages must have had in order for the later developmental stages to occur. A group of languages that descend from a common ancestor is known as a language family; in contrast, a language that has been demonstrated to not have any living or non-living relationship with another language is called a language isolate. There are also many unclassified languages whose relationships have not been established, and spurious languages may have not existed at all. Academic consensus holds that between 50% and 90% of languages spoken at the beginning of the 21st century will probably have become extinct by the year 2100. The English word language derives ultimately from Proto-Indo-European *dn̥ǵʰwéh₂s tongue, speech, language through Latin lingua, language; tongue, and Old French language. The word is sometimes used to refer to codes, ciphers, and other kinds of artificially constructed communication systems such as formally defined computer languages used for computer programming. Unlike conventional human languages, a formal language in this sense is a system of signs for encoding and decoding information. This article specifically concerns the properties of natural human language as it is studied in the discipline of linguistics.As an object of linguistic study, language has two primary meanings: an abstract concept, and a specific linguistic system, e.g. French. The Swiss linguist Ferdinand de Saussure, who defined the modern discipline of linguistics, first explicitly formulated the distinction using the French word language for language as a concept, langue as a specific instance of a language system, and parole for the concrete usage of speech in a particular language.When speaking of language as a general concept, definitions can be used which stress different aspects of the phenomenon. These definitions also entail different approaches and understandings of language, and they also inform different and often incompatible schools of linguistic theory. Debates about the nature and origin of language go back to the ancient world. Greek philosophers such as Gorgias and Plato debated the relation between words, concepts and reality. Gorgias argued that language could represent neither the objective experience nor human experience, and that communication and truth were therefore impossible. Plato maintained that communication is possible because language represents ideas and concepts that exist independently of, and prior to, language.During the Enlightenment and its debates about human origins, it became fashionable to speculate about the origin of language. Thinkers such as Rousseau and Herder argued that language had originated in the instinctive expression of emotions, and that it was originally closer to music and poetry than to the logical expression of rational thought. Rationalist philosophers such as Kant and Descartes held the opposite view. Around the turn of the 20th century, thinkers began to wonder about the role of language in shaping our experiences of the world – asking whether language simply reflects the objective structure of the world, or whether it creates concepts that it in turn impose on our experience of the objective world. This led to the question of whether philosophical problems are really firstly linguistic problems. The resurgence of the view that language plays a significant role in the creation and circulation of concepts, and that the study of philosophy is essentially the study of language, is associated with what has been called the linguistic turn and philosophers such as Wittgenstein in 20th-century philosophy. These debates about language in relation to meaning and reference, cognition and consciousness remain active today.Mental faculty, organ or instinctOne definition sees language primarily as the mental faculty that allows humans to undertake linguistic behaviour: to learn languages and to produce and understand utterances. This definition stresses the universality of language to all humans, and it emphasizes the biological basis for the human capacity for language as a unique development of the human brain. Proponents of the view that the drive to language acquisition is innate in humans argue that this is supported by the fact that all cognitively normal children raised in an environment where language is accessible will acquire language without formal instruction. Languages may even develop spontaneously in environments where people live or grow up together without a common language; for example, creole languages and spontaneously developed sign languages such as Nicaraguan Sign Language. This view, which can be traced back to the philosophers Kant and Descartes, understands language to be largely innate, for example, in Chomsky's theory of Universal Grammar, or American philosopher Jerry Fodor's extreme innatist theory. These kinds of definitions are often applied in studies of language within a cognitive science framework and in neurolinguistics.Formal symbolic systemAnother definition sees language as a formal system of signs governed by grammatical rules of combination to communicate meaning. This definition stresses that human languages can be described as closed structural systems consisting of rules that relate particular signs to particular meanings. This structuralist view of language was first introduced by Ferdinand de Saussure, and his structuralism remains foundational for many approaches to language.Some proponents of Saussure's view of language have advocated a formal approach which studies language structure by identifying its basic elements and then by presenting a formal account of the rules according to which the elements combine in order to form words and sentences. The main proponent of such a theory is Noam Chomsky, the originator of the generative theory of grammar, who has defined language as the construction of sentences that can be generated using transformational grammars. Chomsky considers these rules to be an innate feature of the human mind and to constitute the rudiments of what language is. By way of contrast, such transformational grammars are also commonly used in formal logic, in formal linguistics, and in applied computational linguistics. In the philosophy of language, the view of linguistic meaning as residing in the logical relations between propositions and reality was developed by philosophers such as Alfred Tarski, Bertrand Russell, and other formal logicians.Tool for communicationA conversation in American Sign LanguageYet another definition sees language as a system of communication that enables humans to exchange verbal or symbolic utterances. This definition stresses the social functions of language and the fact that humans use it to express themselves and to manipulate objects in their environment. Functional theories of grammar explain grammatical structures by their communicative functions, and understand the grammatical structures of language to be the result of an adaptive process by which grammar was tailored to serve the communicative needs of its users.This view of language is associated with the study of language in pragmatic, cognitive, and interactive frameworks, as well as in sociolinguistics and linguistic anthropology. Functionalist theories tend to study grammar as dynamic phenomena, as structures that are always in the process of changing as they are employed by their speakers. This view places importance on the study of linguistic typology, or the classification of languages according to structural features, as it can be shown that processes of grammaticalization tend to follow trajectories that are partly dependent on typology. In the philosophy of language, the view of pragmatics as being central to language and meaning is often associated with Wittgenstein's later works and with ordinary language philosophers such as J.L. Austin, Paul Grice, John Searle, and W.O. Quine.Distinctive features of human languageMain articles: Animal language and Great ape languageA number of features, many of which were described by Charles Hockett and called design features set human language apart from communication used by non-human animals.Communication systems used by other animals such as bees or apes are closed systems that consist of a finite, usually very limited, number of possible ideas that can be expressed. In contrast, human language is open-ended and productive, meaning that it allows humans to produce a vast range of utterances from a finite set of elements, and to create new words and sentences. This is possible because human language is based on a dual code, in which a finite number of elements which are meaningless in themselves can be combined to form an infinite number of larger units of meaning. However, one study has demonstrated that an Australian bird, the chestnut-crowned babbler, is capable of using the same acoustic elements in different arrangements to create two functionally distinct vocalizations. Additionally, pied babblers have demonstrated the ability to generate two functionally distinct vocalisations composed of the same sound type, which can only be distinguished by the number of repeated elements.Several species of animals have proved to be able to acquire forms of communication through social learning: for instance a bonobo named Kanzi learned to express itself using a set of symbolic lexigrams. Similarly, many species of birds and whales learn their songs by imitating other members of their species. However, while some animals may acquire large numbers of words and symbols, none have been able to learn as many different signs as are generally known by an average 4 year old human, nor have any acquired anything resembling the complex grammar of human language.Human languages differ from animal communication systems in that they employ grammatical and semantic categories, such as noun and verb, present and past, which may be used to express exceedingly complex meanings. It is distinguished by the property of recursivity: for example, a noun phrase can contain another noun phrase or a clause can contain another clause. Human language is the only known natural communication system whose adaptability may be referred to as modality independent. This means that it can be used not only for communication through one channel or medium, but through several. For example, spoken language uses the auditive modality, whereas sign languages and writing use the visual modality, and braille writing uses the tactile modality.Human language is unusual in being able to refer to abstract concepts and to imagined or hypothetical events as well as events that took place in the past or may happen in the future. This ability to refer to events that are not at the same time or place as the speech event is called displacement, and while some animal communication systems can use displacement, the degree to which it is used in human language is also considered unique.OriginMain articles: Origin of language and Origin of speechSee also: Proto-Human languageThe Tower of Babel by Pieter Bruegel the Elder. Oil on board, 1563.Humans have speculated about the origins of language throughout history. The Biblical myth of the Tower of Babel is one such account; other cultures have different stories of how language arose.Theories about the origin of language differ in regard to their basic assumptions about what language is. Some theories are based on the idea that language is so complex that one cannot imagine it simply appearing from nothing in its final form, but that it must have evolved from earlier pre-linguistic systems among our pre-human ancestors. These theories can be called continuity-based theories. The opposite viewpoint is that language is such a unique human trait that it cannot be compared to anything found among non-humans and that it must therefore have appeared suddenly in the transition from pre-hominids to early man. These theories can be defined as discontinuity-based. Similarly, theories based on the generative view of language pioneered by Noam Chomsky see language mostly as an innate faculty that is largely genetically encoded, whereas functionalist theories see it as a system that is largely cultural, learned through social interaction.Chomsky is one prominent proponent of a discontinuity-based theory of human language origins. He suggests that for scholars interested in the nature of language, talk about the evolution of the language capacity is beside the point. Chomsky proposes that perhaps some random mutation took place and it reorganized the brain, implanting a language organ in an otherwise primate brain. Though cautioning against taking this story literally, Chomsky insists that it may be closer to reality than many other fairy tales that are told about evolutionary processes, including language.Continuity-based theories are held by a majority of scholars, but they vary in how they envision this development. Those who see language as being mostly innate, for example psychologist Steven Pinker, hold the precedents to be animal cognition, whereas those who see language as a socially learned tool of communication, such as psychologist Michael Tomasello, see it as having developed from animal communication in primates: either gestural or vocal communication to assist in cooperation. Other continuity-based models see language as having developed from music, a view already espoused by Rousseau, Herder, Humboldt, and Charles Darwin. A prominent proponent of this view is archaeologist Steven Mithen. Stephen Anderson states that the age of spoken languages is estimated at 60,000 to 100,000 years and that:  Researchers on the evolutionary origin of language generally find it plausible to suggest that language was invented only once, and that all modern spoken languages are thus in some way related, even if that relation can no longer be recovered... because of limitations on the methods available for reconstruction.Because language emerged in the early prehistory of man, before the existence of any written records, its early development has left no historical traces, and it is believed that no comparable processes can be observed today. Theories that stress continuity often look at animals to see if, for example, primates display any traits that can be seen as analogous to what pre-human language must have been like. Early human fossils can be inspected for traces of physical adaptation to language use or pre-linguistic forms of symbolic behaviour. Among the signs in human fossils that may suggest linguistic abilities are: the size of the brain relative to body mass, the presence of a larynx capable of advanced sound production and the nature of tools and other manufactured artifacts.It was mostly undisputed that pre-human australopithecines did not have communication systems significantly different from those found in great apes in general. However, a 2017 study on Ardipithecus ramidus challenges this belief. Scholarly opinions vary as to the developments since the appearance of the genus Homo some 2.5 million years ago. Some scholars assume the development of primitive language-like systems as early as Homo habilis while others place the development of primitive symbolic communication only with Homo erectus or Homo heidelbergensis, and the development of language proper with anatomically modern Homo sapiens with the Upper Paleolithic revolution less than 100,000 years ago.StudyWilliam Jones discovered the family relation between Latin and Sanskrit, laying the ground for the discipline of historical linguistics.Main articles: Linguistics and History of linguisticsThe study of language, linguistics, has been developing into a science since the first grammatical descriptions of particular languages in India more than 2000 years ago, after the development of the Brahmi script. Modern linguistics is a science that concerns itself with all aspects of language, examining it from all of the theoretical viewpoints described above.SubdisciplinesThe academic study of language is conducted within many different disciplinary areas and from different theoretical angles, all of which inform modern approaches to linguistics. For example, descriptive linguistics examines the grammar of single languages, theoretical linguistics develops theories on how best to conceptualize and define the nature of language based on data from the various extant human languages, sociolinguistics studies how languages are used for social purposes informing in turn the study of the social functions of language and grammatical description, neurolinguistics studies how language is processed in the human brain and allows the experimental testing of theories, computational linguistics builds on theoretical and descriptive linguistics to construct computational models of language often aimed at processing natural language or at testing linguistic hypotheses, and historical linguistics relies on grammatical and lexical descriptions of languages to trace their individual histories and reconstruct trees of language families by using the comparative method.Early historyFerdinand de Saussure developed the structuralist approach to studying language.The formal study of language is often considered to have started in India with Pāṇini, the 5th century BC grammarian who formulated 3,959 rules of Sanskrit morphology. However, Sumerian scribes already studied the differences between Sumerian and Akkadian grammar around 1900 BC. Subsequent grammatical traditions developed in all of the ancient cultures that adopted writing.In the 17th century AD, the French Port-Royal Grammarians developed the idea that the grammars of all languages were a reflection of the universal basics of thought, and therefore that grammar was universal. In the 18th century, the first use of the comparative method by British philologist and expert on ancient India William Jones sparked the rise of comparative linguistics. The scientific study of language was broadened from Indo-European to language in general by Wilhelm von Humboldt. Early in the 20th century, Ferdinand de Saussure introduced the idea of language as a static system of interconnected units, defined through the oppositions between them.By introducing a distinction between diachronic and synchronic analyses of language, he laid the foundation of the modern discipline of linguistics. Saussure also introduced several basic dimensions of linguistic analysis that are still fundamental in many contemporary linguistic theories, such as the distinctions between syntagm and paradigm, and the Langue-parole distinction, distinguishing language as an abstract system, from language as a concrete manifestation of this system.Modern linguisticsNoam Chomsky is one of the most important linguistic theorists of the 20th century.In the 1960s, Noam Chomsky formulated the generative theory of language. According to this theory, the most basic form of language is a set of syntactic rules that is universal for all humans and which underlies the grammars of all human languages. This set of rules is called Universal Grammar; for Chomsky, describing it is the primary objective of the discipline of linguistics. Thus, he considered that the grammars of individual languages are only of importance to linguistics insofar as they allow us to deduce the universal underlying rules from which the observable linguistic variability is generated.In opposition to the formal theories of the generative school, functional theories of language propose that since language is fundamentally a tool, its structures are best analyzed and understood by reference to their functions. Formal theories of grammar seek to define the different elements of language and describe the way they relate to each other as systems of formal rules or operations, while functional theories seek to define the functions performed by language and then relate them to the linguistic elements that carry them out. The framework of cognitive linguistics interprets language in terms of the concepts which underlie its forms. Cognitive linguistics is primarily concerned with how the mind creates meaning through language.Physiological and neural architecture of language and speechSpeaking is the default modality for language in all cultures. The production of spoken language depends on sophisticated capacities for controlling the lips, tongue and other components of the vocal apparatus, the ability to acoustically decode speech sounds, and the neurological apparatus required for acquiring and producing language. The study of the genetic bases for human language is at an early stage: the only gene that has definitely been implicated in language production is FOXP2, which may cause a kind of congenital language disorder if affected by mutations.The brainMain articles: Neurolinguistics and Language processing in the brainLanguage Areas of the brain. The Angular Gyrus is represented in orange, Supramarginal Gyrus is represented in yellow, Broca's area is represented in blue, Wernicke's area is represented in green, and the Primary Auditory Cortex is represented in pink.The brain is the coordinating center of all linguistic activity; it controls both the production of linguistic cognition and of meaning and the mechanics of speech production. Nonetheless, our knowledge of the neurological bases for language is quite limited, though it has advanced considerably with the use of modern imaging techniques. The discipline of linguistics dedicated to studying the neurological aspects of language is called neurolinguistics.Early work in neurolinguistics involved the study of language in people with brain lesions, to see how lesions in specific areas affect language and speech. In this way, neuroscientists in the 19th century discovered that two areas in the brain are crucially implicated in language processing. The first area is Wernicke's area, which is in the posterior section of the superior temporal gyrus in the dominant cerebral hemisphere. People with a lesion in this area of the brain develop receptive aphasia, a condition in which there is a major impairment of language comprehension, while speech retains a natural-sounding rhythm and a relatively normal sentence structure. The second area is Broca's area, in the posterior inferior frontal gyrus of the dominant hemisphere. People with a lesion to this area develop expressive aphasia, meaning that they know what they want to say, they just cannot get it out. They are typically able to understand what is being said to them, but unable to speak fluently. Other symptoms that may be present in expressive aphasia include problems with word repetition. The condition affects both spoken and written language. Those with this aphasia also exhibit ungrammatical speech and show inability to use syntactic information to determine the meaning of sentences. Both expressive and receptive aphasia also affect the use of sign language, in analogous ways to how they affect speech, with expressive aphasia causing signers to sign slowly and with incorrect grammar, whereas a signer with receptive aphasia will sign fluently, but make little sense to others and have difficulties comprehending others' signs. This shows that the impairment is specific to the ability to use language, not to the physiology used for speech production.With technological advances in the late 20th century, neurolinguists have also incorporated non-invasive techniques such as functional magnetic resonance imaging and electrophysiology to study language processing in individuals without impairments.Anatomy of speechMain articles: Speech production, Phonetics, and Articulatory phoneticsThe human vocal tract.Spectrogram of American English vowels showing the formants f1 and f2File:Real-time MRI - Speaking.ogvPlay mediaReal time MRI scan of a person speaking in Mandarin ChineseSpoken language relies on human physical ability to produce sound, which is a longitudinal wave propagated through the air at a frequency capable of vibrating the ear drum. This ability depends on the physiology of the human speech organs. These organs consist of the lungs, the voice box, and the upper vocal tract – the throat, the mouth, and the nose. By controlling the different parts of the speech apparatus, the airstream can be manipulated to produce different speech sounds.The sound of speech can be analyzed into a combination of segmental and suprasegmental elements. The segmental elements are those that follow each other in sequences, which are usually represented by distinct letters in alphabetic scripts, such as the Roman script. In free flowing speech, there are no clear boundaries between one segment and the next, nor usually are there any audible pauses between them. Segments therefore are distinguished by their distinct sounds which are a result of their different articulations, and can be either vowels or consonants. Suprasegmental phenomena encompass such elements as stress, phonation type, voice timbre, and prosody or intonation, all of which may have effects across multiple segments.Consonants and vowel segments combine to form syllables, which in turn combine to form utterances; these can be distinguished phonetically as the space between two inhalations. Acoustically, these different segments are characterized by different formant structures, that are visible in a spectrogram of the recorded sound wave. Formants are the amplitude peaks in the frequency spectrum of a specific sound.Vowels are those sounds that have no audible friction caused by the narrowing or obstruction of some part of the upper vocal tract. They vary in quality according to the degree of lip aperture and the placement of the tongue within the oral cavity. Vowels are called close when the lips are relatively closed, as in the pronunciation of the vowel, or open when the lips are relatively open, as in the vowel. If the tongue is located towards the back of the mouth, the quality changes, creating vowels such as. The quality also changes depending on whether the lips are rounded as opposed to unrounded, creating distinctions such as that between  and.Consonants are those sounds that have audible friction or closure at some point within the upper vocal tract. Consonant sounds vary by place of articulation, i.e. the place in the vocal tract where the airflow is obstructed, commonly at the lips, teeth, alveolar ridge, palate, velum, uvula, or glottis. Each place of articulation produces a different set of consonant sounds, which are further distinguished by manner of articulation, or the kind of friction, whether full closure, in which case the consonant is called occlusive or stop, or different degrees of aperture creating fricatives and approximants. Consonants can also be either voiced or unvoiced, depending on whether the vocal cords are set in vibration by airflow during the production of the sound. Voicing is what separates English in bus from in buzz.Some speech sounds, both vowels and consonants, involve release of air flow through the nasal cavity, and these are called nasals or nasalized sounds. Other sounds are defined by the way the tongue moves within the mouth such as the l-sounds, and the r-sounds.By using these speech organs, humans can produce hundreds of distinct sounds: some appear very often in the world's languages, whereas others are much more common in certain language families, language areas, or even specific to a single language.ModalityHuman language is plastic in its choice of the mode used to convey it. Two modes of communication appear to be fundamental: oral and manual. It is common for oral language to be accompanied by gesture, and for sign language to be accompanied by mouthing. In addition, some language communities use both modes to convey lexical or grammatical meaning, each mode complementing the other. Such bimodal use of language is especially common in genres such as story-telling, but also occurs in mundane conversation. For instance, many Australian languages have a rich set of case suffixes that provide details about the instrument used to perform an action. Others lack such grammatical precision in the oral mode, but supplement it with gesture to convey that information in the sign mode. In Iwaidja, for example, 'he went out for fish using a torch' is spoken as simply he-hunted fish torch, but the word for 'torch' is accompanied by a gesture indicating that it was held. In another example, the ritual language Damin had a heavily reduced oral vocabulary of only a few hundred words, each of which was very general in meaning, but which were supplemented by gesture for greater precision.Secondary modes of language, by which a fundamental mode is conveyed in a different medium, include writing, sign, whistling and drumming. Tertiary modes – such as semaphore, Morse code and spelling alphabets – convey the secondary mode of writing in a different medium. For some extinct languages that are maintained for ritual or liturgical purposes, writing may be the primary mode, with speech secondary.StructureWhen described as a system of symbolic communication, language is traditionally seen as consisting of three parts: signs, meanings, and a code connecting signs with their meanings. The study of the process of semiosis, how signs and meanings are combined, used, and interpreted is called semiotics. Signs can be composed of sounds, gestures, letters, or symbols, depending on whether the language is spoken, signed, or written, and they can be combined into complex signs, such as words and phrases. When used in communication, a sign is encoded and transmitted by a sender through a channel to a receiver who decodes it.Ancient Tamil inscription at ThanjavurSome of the properties that define human language as opposed to other communication systems are: the arbitrariness of the linguistic sign, meaning that there is no predictable connection between a linguistic sign and its meaning; the duality of the linguistic system, meaning that linguistic structures are built by combining elements into larger structures that can be seen as layered, e.g. how sounds build words and words build phrases; the discreteness of the elements of language, meaning that the elements out of which linguistic signs are constructed are discrete units, e.g. sounds and words, that can be distinguished from each other and rearranged in different patterns; and the productivity of the linguistic system, meaning that the finite number of linguistic elements can be combined into a theoretically infinite number of combinations.The rules by which signs can be combined to form words and phrases are called syntax or grammar. The meaning that is connected to individual signs, morphemes, words, phrases, and texts is called semantics. The division of language into separate but connected systems of sign and meaning goes back to the first linguistic studies of de Saussure and is now used in almost all branches of linguistics.SemanticsMain articles: Semantics, Semiotics, and Meaning Languages express meaning by relating a sign form to a meaning, or its content. Sign forms must be something that can be perceived, for example, in sounds, images, or gestures, and then related to a specific meaning by social convention. Because the basic relation of meaning for most linguistic signs is based on social convention, linguistic signs can be considered arbitrary, in the sense that the convention is established socially and historically, rather than by means of a natural relation between a specific sign form and its meaning.Thus, languages must have a vocabulary of signs related to specific meaning. The English sign dog denotes, for example, a member of the species Canis familiaris. In a language, the array of arbitrary signs connected to specific meanings is called the lexicon, and a single sign connected to a meaning is called a lexeme. Not all meanings in a language are represented by single words. Often, semantic concepts are embedded in the morphology or syntax of the language in the form of grammatical categories.All languages contain the semantic structure of predication: a structure that predicates a property, state, or action. Traditionally, semantics has been understood to be the study of how speakers and interpreters assign truth values to statements, so that meaning is understood to be the process by which a predicate can be said to be true or false about an entity, e.g. ] or ]. Recently, this model of semantics has been complemented with more dynamic models of meaning that incorporate shared knowledge about the context in which a sign is interpreted into the production of meaning. Such models of meaning are explored in the field of pragmatics.Sounds and symbolsMain articles: Phonology and WritingA spectrogram showing the sound of the spoken English word man, which is written phonetically as. Note that in flowing speech, there is no clear division between segments, only a smooth transition as the vocal apparatus moves.The syllable wi in the Hangul scriptThe sign for wi in Korean Sign Language Depending on modality, language structure can be based on systems of sounds, gestures, or graphic or tactile symbols. The ways in which languages use sounds or signs to construct meaning are studied in phonology.Sounds as part of a linguistic system are called phonemes. Phonemes are abstract units of sound, defined as the smallest units in a language that can serve to distinguish between the meaning of a pair of minimally different words, a so-called minimal pair. In English, for example, the words bat and pat form a minimal pair, in which the distinction between /b/ and /p/ differentiates the two words, which have different meanings. However, each language contrasts sounds in different ways. For example, in a language that does not distinguish between voiced and unvoiced consonants, the sounds and  could be considered a single phoneme, and consequently, the two pronunciations would have the same meaning. Similarly, the English language does not distinguish phonemically between aspirated and non-aspirated pronunciations of consonants, as many other languages like Korean and Hindi do: the unaspirated /p/ in spin and the aspirated /p/ in pin are considered to be merely different ways of pronouncing the same phoneme, whereas in Mandarin Chinese, the same difference in pronunciation distinguishes between the words 'crouch' and 'eight'.All spoken languages have phonemes of at least two different categories, vowels and consonants, that can be combined to form syllables. As well as segments such as consonants and vowels, some languages also use sound in other ways to convey meaning. Many languages, for example, use stress, pitch, duration, and tone to distinguish meaning. Because these phenomena operate outside of the level of single segments, they are called suprasegmental. Some languages have only a few phonemes, for example, Rotokas and Pirahã language with 11 and 10 phonemes respectively, whereas languages like Taa may have as many as 141 phonemes. In sign languages, the equivalent to phonemes are defined by the basic elements of gestures, such as hand shape, orientation, location, and motion, which correspond to manners of articulation in spoken language.Writing systems represent language using visual symbols, which may or may not correspond to the sounds of spoken language. The Latin alphabet was originally based on the representation of single sounds, so that words were constructed from letters that generally denote a single consonant or vowel in the structure of the word. In syllabic scripts, such as the Inuktitut syllabary, each sign represents a whole syllable. In logographic scripts, each sign represents an entire word, and will generally bear no relation to the sound of that word in spoken language.Because all languages have a very large number of words, no purely logographic scripts are known to exist. Written language represents the way spoken sounds and words follow one after another by arranging symbols according to a pattern that follows a certain direction. The direction used in a writing system is entirely arbitrary and established by convention. Some writing systems use the horizontal axis, while others such as traditional Chinese writing use the vertical dimension. A few writing systems use opposite directions for alternating lines, and others, such as the ancient Maya script, can be written in either direction and rely on graphic cues to show the reader the direction of reading.In order to represent the sounds of the world's languages in writing, linguists have developed the International Phonetic Alphabet, designed to represent all of the discrete sounds that are known to contribute to meaning in human languages.GrammarMain article: GrammarGrammar is the study of how meaningful elements called morphemes within a language can be combined into utterances. Morphemes can either be free or bound. If they are free to be moved around within an utterance, they are usually called words, and if they are bound to other words or morphemes, they are called affixes. The way in which meaningful elements can be combined within a language is governed by rules. The study of the rules for the internal structure of words are called morphology. The rules of the internal structure of phrases and sentences are called syntax.Grammatical categoriesMain article: Grammatical categoryGrammar can be described as a system of categories and a set of rules that determine how categories combine to form different aspects of meaning. Languages differ widely in whether they are encoded through the use of categories or lexical units. However, several categories are so common as to be nearly universal. Such universal categories include the encoding of the grammatical relations of participants and predicates by grammatically distinguishing between their relations to a predicate, the encoding of temporal and spatial relations on predicates, and a system of grammatical person governing reference to and distinction between speakers and addressees and those about whom they are speaking.Word classesLanguages organize their parts of speech into classes according to their functions and positions relative to other parts. All languages, for instance, make a basic distinction between a group of words that prototypically denotes things and concepts and a group of words that prototypically denotes actions and events. The first group, which includes English words such as dog and song, are usually called nouns. The second, which includes think and sing, are called verbs. Another common category is the adjective: words that describe properties or qualities of nouns, such as red or big. Word classes can be open if new words can continuously be added to the class, or relatively closed if there is a fixed number of words in a class. In English, the class of pronouns is closed, whereas the class of adjectives is open, since an infinite number of adjectives can be constructed from verbs or nouns. In other languages such as Korean, the situation is the opposite, and new pronouns can be constructed, whereas the number of adjectives is fixed.Word classes also carry out differing functions in grammar. Prototypically, verbs are used to construct predicates, while nouns are used as arguments of predicates. In a sentence such as Sally runs, the predicate is runs, because it is the word that predicates a specific state about its argument Sally. Some verbs such as curse can take two arguments, e.g. Sally cursed John. A predicate that can only take a single argument is called intransitive, while a predicate that can take two arguments is called transitive.Many other word classes exist in different languages, such as conjunctions like and that serve to join two sentences, articles that introduce a noun, interjections such as wow!, or ideophones like splash that mimic the sound of some event. Some languages have positionals that describe the spatial position of an event or entity. Many languages have classifiers that identify countable nouns as belonging to a particular type or having a particular shape. For instance, in Japanese, the general noun classifier for humans is nin, and it is used for counting humans, whatever they are called:  san-nin no gakusei lit. 3 human-classifier of student — three studentsFor trees, it would be:  san-bon no ki lit. 3 classifier-for-long-objects of tree — three treesMorphologyIn linguistics, the study of the internal structure of complex words and the processes by which words are formed is called morphology. In most languages, it is possible to construct complex words that are built of several morphemes. For instance, the English word unexpected can be analyzed as being composed of the three morphemes un-, expect and -ed.Morphemes can be classified according to whether they are independent morphemes, so-called roots, or whether they can only co-occur attached to other morphemes. These bound morphemes or affixes can be classified according to their position in relation to the root: prefixes precede the root, suffixes follow the root, and infixes are inserted in the middle of a root. Affixes serve to modify or elaborate the meaning of the root. Some languages change the meaning of words by changing the phonological structure of a word, for example, the English word run, which in the past tense is ran. This process is called ablaut. Furthermore, morphology distinguishes between the process of inflection, which modifies or elaborates on a word, and the process of derivation, which creates a new word from an existing one. In English, the verb sing has the inflectional forms singing and sung, which are both verbs, and the derivational form singer, which is a noun derived from the verb with the agentive suffix -er.Languages differ widely in how much they rely on morphological processes of word formation. In some languages, for example, Chinese, there are no morphological processes, and all grammatical information is encoded syntactically by forming strings of single words. This type of morpho-syntax is often called isolating, or analytic, because there is almost a full correspondence between a single word and a single aspect of meaning. Most languages have words consisting of several morphemes, but they vary in the degree to which morphemes are discrete units. In many languages, notably in most Indo-European languages, single morphemes may have several distinct meanings that cannot be analyzed into smaller segments. For example, in Latin, the word bonus, or good, consists of the root bon-, meaning good, and the suffix -us, which indicates masculine gender, singular number, and nominative case. These languages are called fusional languages, because several meanings may be fused into a single morpheme. The opposite of fusional languages are agglutinative languages which construct words by stringing morphemes together in chains, but with each morpheme as a discrete semantic unit. An example of such a language is Turkish, where for example, the word evlerinizden, or from your houses, consists of the morphemes, ev-ler-iniz-den with the meanings house-plural-your-from. The languages that rely on morphology to the greatest extent are traditionally called polysynthetic languages. They may express the equivalent of an entire English sentence in a single word. For example, in Persian the single word nafahmidamesh means I didn't understand it consisting of morphemes na-fahm-id-am-esh with the meanings, negation.understand.past.I.it. As another example with more complexity, in the Yupik word tuntussuqatarniksatengqiggtuq, which means He had not yet said again that he was going to hunt reindeer, the word consists of the morphemes tuntu-ssur-qatar-ni-ksaite-ngqiggte-uq with the meanings, reindeer-hunt-future-say-negation-again-third.person.singular.indicative, and except for the morpheme tuntu none of the other morphemes can appear in isolation.Many languages use morphology to cross-reference words within a sentence. This is sometimes called agreement. For example, in many Indo-European languages, adjectives must cross-reference the noun they modify in terms of number, case, and gender, so that the Latin adjective bonus, or good, is inflected to agree with a noun that is masculine gender, singular number, and nominative case. In many polysynthetic languages, verbs cross-reference their subjects and objects. In these types of languages, a single verb may include information that would require an entire sentence in English. For example, in the Basque phrase ikusi nauzu, or you saw me, the past tense auxiliary verb n-au-zu agrees with both the subject expressed by the n- prefix, and with the object expressed by the – zu suffix. The sentence could be directly transliterated as see you-did-meSyntaxMain article: SyntaxIn addition to word classes, a sentence can be analyzed in terms of grammatical functions: The cat is the subject of the phrase, on the mat is a locative phrase, and sat is the core of the predicate.Another way in which languages convey meaning is through the order of words within a sentence. The grammatical rules for how to produce new sentences from words that are already known is called syntax. The syntactical rules of a language determine why a sentence in English such as I love you is meaningful, but *love you I is not. Syntactical rules determine how word order and sentence structure is constrained, and how those constraints contribute to meaning. For example, in English, the two sentences the slaves were cursing the master and the master was cursing the slaves mean different things, because the role of the grammatical subject is encoded by the noun being in front of the verb, and the role of object is encoded by the noun appearing after the verb. Conversely, in Latin, both Dominus servos vituperabat and Servos vituperabat dominus mean the master was reprimanding the slaves, because servos, or slaves, is in the accusative case, showing that they are the grammatical object of the sentence, and dominus, or master, is in the nominative case, showing that he is the subject.Latin uses morphology to express the distinction between subject and object, whereas English uses word order. Another example of how syntactic rules contribute to meaning is the rule of inverse word order in questions, which exists in many languages. This rule explains why when in English, the phrase John is talking to Lucy is turned into a question, it becomes Who is John talking to?, and not John is talking to who?. The latter example may be used as a way of placing special emphasis on who, thereby slightly altering the meaning of the question. Syntax also includes the rules for how complex sentences are structured by grouping words together in units, called phrases, that can occupy different places in a larger syntactic structure. Sentences can be described as consisting of phrases connected in a tree structure, connecting the phrases to each other at different levels. To the right is a graphic representation of the syntactic analysis of the English sentence the cat sat on the mat. The sentence is analyzed as being constituted by a noun phrase, a verb, and a prepositional phrase; the prepositional phrase is further divided into a preposition and a noun phrase, and the noun phrases consist of an article and a noun.The reason sentences can be seen as being composed of phrases is because each phrase would be moved around as a single element if syntactic operations were carried out. For example, the cat is one phrase, and on the mat is another, because they would be treated as single units if a decision was made to emphasize the location by moving forward the prepositional phrase: on the mat, the cat sat. There are many different formalist and functionalist frameworks that propose theories for describing syntactic structures, based on different assumptions about what language is and how it should be described. Each of them would analyze a sentence such as this in a different manner.Typology and universalsMain articles: Linguistic typology and Linguistic universalLanguages can be classified in relation to their grammatical types. Languages that belong to different families nonetheless often have features in common, and these shared features tend to correlate. For example, languages can be classified on the basis of their basic word order, the relative order of the verb, and its constituents in a normal indicative sentence. In English, the basic order is SVO : The snake bit the man, whereas for example, the corresponding sentence in the Australian language Gamilaraay would be d̪uyugu n̪ama d̪ayn yiːy, SOV. Word order type is relevant as a typological parameter, because basic word order type corresponds with other syntactic parameters, such as the relative order of nouns and adjectives, or of the use of prepositions or postpositions. Such correlations are called implicational universals. For example, most languages that are of the SOV type have postpositions rather than prepositions, and have adjectives before nouns.All languages structure sentences into Subject, Verb, and Object, but languages differ in the way they classify the relations between actors and actions. English uses the nominative-accusative word typology: in English transitive clauses, the subjects of both intransitive sentences and transitive sentences are treated in the same way, shown here by the nominative pronoun I. Some languages, called ergative, Gamilaraay among them, distinguish instead between Agents and Patients. In ergative languages, the single participant in an intransitive sentence, such as I run, is treated the same as the patient in a transitive sentence, giving the equivalent of me run. Only in transitive sentences would the equivalent of the pronoun I be used. In this way the semantic roles can map onto the grammatical relations in different ways, grouping an intransitive subject either with Agents or Patients or even making each of the three roles differently, which is called the tripartite type.The shared features of languages which belong to the same typological class type may have arisen completely independently. Their co-occurrence might be due to universal laws governing the structure of natural languages, language universals, or they might be the result of languages evolving convergent solutions to the recurring communicative problems that humans use language to solve.Social contexts of use and transmissionWall of Love on Montmartre in Paris: I love you in 250 languages, by calligraphist Fédéric Baron and artist Claire Kito While humans have the ability to learn any language, they only do so if they grow up in an environment in which language exists and is used by others. Language is therefore dependent on communities of speakers in which children learn language from their elders and peers and themselves transmit language to their own children. Languages are used by those who speak them to communicate and to solve a plethora of social tasks. Many aspects of language use can be seen to be adapted specifically to these purposes. Owing to the way in which language is transmitted between generations and within communities, language perpetually changes, diversifying into new languages or converging due to language contact. The process is similar to the process of evolution, where the process of descent with modification leads to the formation of a phylogenetic tree.However, languages differ from biological organisms in that they readily incorporate elements from other languages through the process of diffusion, as speakers of different languages come into contact. Humans also frequently speak more than one language, acquiring their first language or languages as children, or learning new languages as they grow up. Because of the increased language contact in the globalizing world, many small languages are becoming endangered as their speakers shift to other languages that afford the possibility to participate in larger and more influential speech communities.Usage and meaningMain article: PragmaticsWhen studying the way in which words and signs are used, it is often the case that words have different meanings, depending on the social context of use. An important example of this is the process called deixis, which describes the way in which certain words refer to entities through their relation between a specific point in time and space when the word is uttered. Such words are, for example, the word, I, now, and here. Signs also change their meanings over time, as the conventions governing their usage gradually change. The study of how the meaning of linguistic expressions changes depending on context is called pragmatics. Deixis is an important part of the way that we use language to point out entities in the world. Pragmatics is concerned with the ways in which language use is patterned and how these patterns contribute to meaning. For example, in all languages, linguistic expressions can be used not just to transmit information, but to perform actions. Certain actions are made only through language, but nonetheless have tangible effects, e.g. the act of naming, which creates a new name for some entity, or the act of pronouncing someone man and wife, which creates a social contract of marriage. These types of acts are called speech acts, although they can also be carried out through writing or hand signing.The form of linguistic expression often does not correspond to the meaning that it actually has in a social context. For example, if at a dinner table a person asks, Can you reach the salt?, that is, in fact, not a question about the length of the arms of the one being addressed, but a request to pass the salt across the table. This meaning is implied by the context in which it is spoken; these kinds of effects of meaning are called conversational implicatures. These social rules for which ways of using language are considered appropriate in certain situations and how utterances are to be understood in relation to their context vary between communities, and learning them is a large part of acquiring communicative competence in a language.AcquisitionMain articles: Language acquisition, Second-language acquisition, Second language, and Language educationAll healthy, normally developing human beings learn to use language. Children acquire the language or languages used around them: whichever languages they receive sufficient exposure to during childhood. The development is essentially the same for children acquiring sign or oral languages. This learning process is referred to as first-language acquisition, since unlike many other kinds of learning, it requires no direct teaching or specialized study. In The Descent of Man, naturalist Charles Darwin called this process an instinctive tendency to acquire an art.A lesson at Kituwah Academy, a school where English and the Cherokee language are mediums of instructionFirst language acquisition proceeds in a fairly regular sequence, though there is a wide degree of variation in the timing of particular stages among normally developing infants. Studies published in 2013 have indicated that unborn fetuses are capable of language acquisition to some degree. From birth, newborns respond more readily to human speech than to other sounds. Around one month of age, babies appear to be able to distinguish between different speech sounds. Around six months of age, a child will begin babbling, producing the speech sounds or handshapes of the languages used around them. Words appear around the age of 12 to 18 months; the average vocabulary of an eighteen-month-old child is around 50 words. A child's first utterances are holophrases, utterances that use just one word to communicate some idea. Several months after a child begins producing words, he or she will produce two-word utterances, and within a few more months will begin to produce telegraphic speech, or short sentences that are less grammatically complex than adult speech, but that do show regular syntactic structure. From roughly the age of three to five years, a child's ability to speak or sign is refined to the point that it resembles adult language.Acquisition of second and additional languages can come at any age, through exposure in daily life or courses. Children learning a second language are more likely to achieve native-like fluency than adults, but in general, it is very rare for someone speaking a second language to pass completely for a native speaker. An important difference between first language acquisition and additional language acquisition is that the process of additional language acquisition is influenced by languages that the learner already knows.CultureSee also: Culture and Speech communityArnold Lakhovsky, The Conversation Languages, understood as the particular set of speech norms of a particular community, are also a part of the larger culture of the community that speaks them. Languages differ not only in pronunciation, vocabulary, and grammar, but also through having different cultures of speaking. Humans use language as a way of signalling identity with one cultural group as well as difference from others. Even among speakers of one language, several different ways of using the language exist, and each is used to signal affiliation with particular subgroups within a larger culture. Linguists and anthropologists, particularly sociolinguists, ethnolinguists, and linguistic anthropologists have specialized in studying how ways of speaking vary between speech communities.Linguists use the term varieties to refer to the different ways of speaking a language. This term includes geographically or socioculturally defined dialects as well as the jargons or styles of subcultures. Linguistic anthropologists and sociologists of language define communicative style as the ways that language is used and understood within a particular culture.Because norms for language use are shared by members of a specific group, communicative style also becomes a way of displaying and constructing group identity. Linguistic differences may become salient markers of divisions between social groups, for example, speaking a language with a particular accent may imply membership of an ethnic minority or social class, one's area of origin, or status as a second language speaker. These kinds of differences are not part of the linguistic system, but are an important part of how people use language as a social tool for constructing groups.However, many languages also have grammatical conventions that signal the social position of the speaker in relation to others through the use of registers that are related to social hierarchies or divisions. In many languages, there are stylistic or even grammatical differences between the ways men and women speak, between age groups, or between social classes, just as some languages employ different words depending on who is listening. For example, in the Australian language Dyirbal, a married man must use a special set of words to refer to everyday items when speaking in the presence of his mother-in-law. Some cultures, for example, have elaborate systems of social deixis, or systems of signalling social distance through linguistic means. In English, social deixis is shown mostly through distinguishing between addressing some people by first name and others by surname, and in titles such as Mrs., boy, Doctor, or Your Honor, but in other languages, such systems may be highly complex and codified in the entire grammar and vocabulary of the language. For instance, in languages of east Asia such as Thai, Burmese, and Javanese, different words are used according to whether a speaker is addressing someone of higher or lower rank than oneself in a ranking system with animals and children ranking the lowest and gods and members of royalty as the highest.Writing, literacy and technologyMain articles: Writing and LiteracyAn inscription of Swampy Cree using Canadian Aboriginal syllabics, an abugida developed by Christian missionaries for Indigenous Canadian languagesThroughout history a number of different ways of representing language in graphic media have been invented. These are called writing systems.The use of writing has made language even more useful to humans. It makes it possible to store large amounts of information outside of the human body and retrieve it again, and it allows communication across physical distances and timespans that would otherwise be impossible. Many languages conventionally employ different genres, styles, and registers in written and spoken language, and in some communities, writing traditionally takes place in an entirely different language than the one spoken. There is some evidence that the use of writing also has effects on the cognitive development of humans, perhaps because acquiring literacy generally requires explicit and formal education.The invention of the first writing systems is roughly contemporary with the beginning of the Bronze Age in the late 4th millennium BC. The Sumerian archaic cuneiform script and the Egyptian hieroglyphs are generally considered to be the earliest writing systems, both emerging out of their ancestral proto-literate symbol systems from 3400 to 3200 BC with the earliest coherent texts from about 2600 BC. It is generally agreed that Sumerian writing was an independent invention; however, it is debated whether Egyptian writing was developed completely independently of Sumerian, or was a case of cultural diffusion. A similar debate exists for the Chinese script, which developed around 1200 BC. The pre-Columbian Mesoamerican writing systems are generally believed to have had independent origins.ChangeMain articles: Language change and GrammaticalizationThe first page of the poem Beowulf, written in Old English in the early medieval period. Although Old English is the direct ancestor of modern English, it is unintelligible to contemporary English speakers.All languages change as speakers adopt or invent new ways of speaking and pass them on to other members of their speech community. Language change happens at all levels from the phonological level to the levels of vocabulary, morphology, syntax, and discourse. Even though language change is often initially evaluated negatively by speakers of the language who often consider changes to be decay or a sign of slipping norms of language usage, it is natural and inevitable.Changes may affect specific sounds or the entire phonological system. Sound change can consist of the replacement of one speech sound or phonetic feature by another, the complete loss of the affected sound, or even the introduction of a new sound in a place where there had been none. Sound changes can be conditioned in which case a sound is changed only if it occurs in the vicinity of certain other sounds. Sound change is usually assumed to be regular, which means that it is expected to apply mechanically whenever its structural conditions are met, irrespective of any non-phonological factors. On the other hand, sound changes can sometimes be sporadic, affecting only one particular word or a few words, without any seeming regularity. Sometimes a simple change triggers a chain shift in which the entire phonological system is affected. This happened in the Germanic languages when the sound change known as Grimm's law affected all the stop consonants in the system. The original consonant *bʰ became /b/ in the Germanic languages, the previous *b in turn became /p/, and the previous *p became /f/. The same process applied to all stop consonants and explains why Italic languages such as Latin have p in words like pater and pisces, whereas Germanic languages, like English, have father and fish.Another example is the Great Vowel Shift in English, which is the reason that the spelling of English vowels do not correspond well to their current pronunciation. This is because the vowel shift brought the already established orthography out of synchronization with pronunciation. Another source of sound change is the erosion of words as pronunciation gradually becomes increasingly indistinct and shortens words, leaving out syllables or sounds. This kind of change caused Latin mea domina to eventually become the French madame and American English ma'am.Change also happens in the grammar of languages as discourse patterns such as idioms or particular constructions become grammaticalized. This frequently happens when words or morphemes erode and the grammatical system is unconsciously rearranged to compensate for the lost element. For example, in some varieties of Caribbean Spanish the final /s/ has eroded away. Since Standard Spanish uses final /s/ in the morpheme marking the second person subject you in verbs, the Caribbean varieties now have to express the second person using the pronoun tú. This means that the sentence what's your name is ¿como te llamas? in Standard Spanish, but in Caribbean Spanish. The simple sound change has affected both morphology and syntax. Another common cause of grammatical change is the gradual petrification of idioms into new grammatical forms, for example, the way the English going to construction lost its aspect of movement and in some varieties of English has almost become a full-fledged future tense.Language change may be motivated by language internal factors, such as changes in pronunciation motivated by certain sounds being difficult to distinguish aurally or to produce, or through patterns of change that cause some rare types of constructions to drift towards more common types. Other causes of language change are social, such as when certain pronunciations become emblematic of membership in certain groups, such as social classes, or with ideologies, and therefore are adopted by those who wish to identify with those groups or ideas. In this way, issues of identity and politics can have profound effects on language structure.ContactMain article: language contactOne important source of language change is contact and resulting diffusion of linguistic traits between languages. Language contact occurs when speakers of two or more languages or varieties interact on a regular basis. Multilingualism is likely to have been the norm throughout human history and most people in the modern world are multilingual. Before the rise of the concept of the ethno-national state, monolingualism was characteristic mainly of populations inhabiting small islands. But with the ideology that made one people, one state, and one language the most desirable political arrangement, monolingualism started to spread throughout the world. Nonetheless, there are only 250 countries in the world corresponding to some 6000 languages, which means that most countries are multilingual and most languages therefore exist in close contact with other languages.When speakers of different languages interact closely, it is typical for their languages to influence each other. Through sustained language contact over long periods, linguistic traits diffuse between languages, and languages belonging to different families may converge to become more similar. In areas where many languages are in close contact, this may lead to the formation of language areas in which unrelated languages share a number of linguistic features. A number of such language areas have been documented, among them, the Balkan language area, the Mesoamerican language area, and the Ethiopian language area. Also, larger areas such as South Asia, Europe, and Southeast Asia have sometimes been considered language areas, because of widespread diffusion of specific areal features.Language contact may also lead to a variety of other linguistic phenomena, including language convergence, borrowing, and relexification. In situations of extreme and sustained language contact, it may lead to the formation of new mixed languages that cannot be considered to belong to a single language family. One type of mixed language called pidgins occurs when adult speakers of two different languages interact on a regular basis, but in a situation where neither group learns to speak the language of the other group fluently. In such a case, they will often construct a communication form that has traits of both languages, but which has a simplified grammatical and phonological structure. The language comes to contain mostly the grammatical and phonological categories that exist in both languages. Pidgin languages are defined by not having any native speakers, but only being spoken by people who have another language as their first language. But if a Pidgin language becomes the main language of a speech community, then eventually children will grow up learning the pidgin as their first language. As the generation of child learners grow up, the pidgin will often be seen to change its structure and acquire a greater degree of complexity. This type of language is generally called a creole language. An example of such mixed languages is Tok Pisin, the official language of Papua New-Guinea, which originally arose as a Pidgin based on English and Austronesian languages; others are Kreyòl ayisyen, the French-based creole language spoken in Haiti, and Michif, a mixed language of Canada, based on the Native American language Cree and French.Linguistic diversitySee also: Lists of languages and List of languages by total number of speakersLanguage Native speakersMandarin 848Spanish 329 English 328Portuguese 250Arabic 221Hindi 182Bengali 181Russian 144Japanese 122Javanese 84.3SIL Ethnologue defines a living language as one that has at least one speaker for whom it is their first language. The exact number of known living languages varies from 6,000 to 7,000, depending on the precision of one's definition of language, and in particular, on how one defines the distinction between a language and a dialect. As of 2016, Ethnologue cataloged 7,097 living human languages. The Ethnologue establishes linguistic groups based on studies of mutual intelligibility, and therefore often includes more categories than more conservative classifications. For example, the Danish language that most scholars consider a single language with several dialects is classified as two distinct languages by the Ethnologue.According to the Ethnologue, 389 languages have more than a million speakers. These languages together account for 94% of the world's population, whereas 94% of the world's languages account for the remaining 6% of the global population.Languages and dialectsMain article: Dialect § Dialect or languageMulti-lingual sign outside the mayor's office in Novi Sad, written in the four official languages of the city: Serbian, Hungarian, Slovak, and Pannonian RusynThere is no clear distinction between a language and a dialect, notwithstanding a famous aphorism attributed to linguist Max Weinreich that a language is a dialect with an army and navy. For example, national boundaries frequently override linguistic difference in determining whether two linguistic varieties are languages or dialects. Hakka, Cantonese and Mandarin are, for example, often classified as dialects of Chinese, even though they are more different from each other than Swedish is from Norwegian. Before the Yugoslav civil war, Serbo-Croatian was generally considered a single language with two normative variants, but due to sociopolitical reasons, Croatian and Serbian are now often treated as separate languages and employ different writing systems. In other words, the distinction may hinge on political considerations as much as on cultural differences, distinctive writing systems, or degree of mutual intelligibility.Language families of the worldMain articles: Language family, Dialectology, Historical linguistics, and List of language familiesPrincipal language families of the world. For greater detail, see Distribution of languages in the world.The world's languages can be grouped into language families consisting of languages that can be shown to have common ancestry. Linguists recognize many hundreds of language families, although some of them can possibly be grouped into larger units as more evidence becomes available and in-depth studies are carried out. At present, there are also dozens of language isolates: languages that cannot be shown to be related to any other languages in the world. Among them are Basque, spoken in Europe, Zuni of New Mexico, Purépecha of Mexico, Ainu of Japan, Burushaski of Pakistan, and many others.The language family of the world that has the most speakers is the Indo-European languages, spoken by 46% of the world's population. This family includes major world languages like English, Spanish, French, German, Russian, and Hindustani. The Indo-European family achieved prevalence first during the Eurasian Migration Period, and subsequently through the European colonial expansion, which brought the Indo-European languages to a politically and often numerically dominant position in the Americas and much of Africa. The Sino-Tibetan languages are spoken by 20% of the world's population and include many of the languages of East Asia, including Hakka, Mandarin Chinese, Cantonese, and hundreds of smaller languages.Africa is home to a large number of language families, the largest of which is the Niger-Congo language family, which includes such languages as Swahili, Shona, and Yoruba. Speakers of the Niger-Congo languages account for 6.9% of the world's population. A similar number of people speak the Afroasiatic languages, which include the populous Semitic languages such as Arabic, Hebrew language, and the languages of the Sahara region, such as the Berber languages and Hausa.The Austronesian languages are spoken by 5.5% of the world's population and stretch from Madagascar to maritime Southeast Asia all the way to Oceania. It includes such languages as Malagasy, Māori, Samoan, and many of the indigenous languages of Indonesia and Taiwan. The Austronesian languages are considered to have originated in Taiwan around 3000 BC and spread through the Oceanic region through island-hopping, based on an advanced nautical technology. Other populous language families are the Dravidian languages of South Asia, the Turkic languages of Central Asia, the Austroasiatic, and Tai–Kadai languages of Southeast Asia.The areas of the world in which there is the greatest linguistic diversity, such as the Americas, Papua New Guinea, West Africa, and South-Asia, contain hundreds of small language families. These areas together account for the majority of the world's languages, though not the majority of speakers. In the Americas, some of the largest language families include the Quechumaran, Arawak, and Tupi-Guarani families of South America, the Uto-Aztecan, Oto-Manguean, and Mayan of Mesoamerica, and the Na-Dene, Iroquoian, and Algonquian language families of North America. In Australia, most indigenous languages belong to the Pama-Nyungan family, whereas New Guinea is home to a large number of small families and isolates, as well as a number of Austronesian languages.Language endangermentMain articles: Endangered language, Language loss, Language shift, and Language deathTogether, the eight countries in red contain more than 50% of the world's languages. The areas in blue are the most linguistically diverse in the world, and the locations of most of the world's endangered languages.Language endangerment occurs when a language is at risk of falling out of use as its speakers die out or shift to speaking another language. Language loss occurs when the language has no more native speakers, and becomes a dead language. If eventually no one speaks the language at all, it becomes an extinct language. While languages have always gone extinct throughout human history, they have been disappearing at an accelerated rate in the 20th and 21st centuries due to the processes of globalization and neo-colonialism, where the economically powerful languages dominate other languages.The more commonly spoken languages dominate the less commonly spoken languages, so the less commonly spoken languages eventually disappear from populations. Of the between 6,000 and 7,000 languages spoken as of 2010, between 50 and 90% of those are expected to have become extinct by the year 2100. The top 20 languages, those spoken by more than 50 million speakers each, are spoken by 50% of the world's population, whereas many of the other languages are spoken by small communities, most of them with less than 10,000 speakers.The United Nations Educational, Scientific and Cultural Organization operates with five levels of language endangerment: safe, vulnerable, definitely endangered, severely endangered, and critically endangered. Notwithstanding claims that the world would be better off if most adopted a single common lingua franca, such as English or Esperanto, there is a consensus that the loss of languages harms the cultural diversity of the world. It is a common belief, going back to the biblical narrative of the tower of Babel in the Old Testament, that linguistic diversity causes political conflict, but this is contradicted by the fact that many of the world's major episodes of violence have taken place in situations with low linguistic diversity, such as the Yugoslav and American Civil War, or the genocide of Rwanda, whereas many of the most stable political units have been highly multilingual.Many projects aim to prevent or slow this loss by revitalizing endangered languages and promoting education and literacy in minority languages. Across the world, many countries have enacted specific legislation to protect and stabilize the language of indigenous speech communities. A minority of linguists have argued that language loss is a natural process that should not be counteracted, and that documenting endangered languages for posterity is sufficient.The University of Waikato are using the Welsh language as a model for their Māori language revitalisation programme as they deem Welsh to be the world's leading example for the survival of languages. In 2019 a Hawaiian tv company Oiwi visited a Welsh language centre in Nant Gwrtheyrn, North Wales to help find ways of preserving their Ōlelo Hawaiʻi language. The natural environment or natural world encompasses all living and non-living things occurring naturally, meaning in this case not artificial. The term is most often applied to the Earth or some parts of Earth. This environment encompasses the interaction of all living species, climate, weather and natural resources that affect human survival and economic activity. The concept of the natural environment can be distinguished as components:  Complete ecological units that function as natural systems without massive civilized human intervention, including all vegetation, microorganisms, soil, rocks, atmosphere, and natural phenomena that occur within their boundaries and their nature.  Universal natural resources and physical phenomena that lack clear-cut boundaries, such as air, water, and climate, as well as energy, radiation, electric charge, and magnetism, not originating from civilized human actions.In contrast to the natural environment is the built environment. Built environments are where humans have fundamentally transformed landscapes such as urban settings and agricultural land conversion, the natural environment is greatly changed into a simplified human environment. Even acts which seem less extreme, such as building a mud hut or a photovoltaic system in the desert, the modified environment becomes an artificial one. Though many animals build things to provide a better environment for themselves, they are not human, hence beaver dams, and the works of mound-building termites, are thought of as natural.People cannot find absolutely natural environments on Earth, and naturalness usually varies in a continuum, from 100% natural in one extreme to 0% natural in the other. The massive environmental changes of humanity in the Anthropocene have fundamentally effected all natural environments: including from climate change, biodiversity loss and pollution from plastic and other chemicals in the air and water. More precisely, we can consider the different aspects or components of an environment, and see that their degree of naturalness is not uniform. If, for instance, in an agricultural field, the mineralogic composition and the structure of its soil are similar to those of an undisturbed forest soil, but the structure is quite different. Earth science generally recognizes four spheres, the lithosphere, the hydrosphere, the atmosphere, and the biosphere as correspondent to rocks, water, air, and life respectively. Some scientists include as part of the spheres of the Earth, the cryosphere as a distinct portion of the hydrosphere, as well as the pedosphere as an active and intermixed sphere. Earth science, is an all-embracing term for the sciences related to the planet Earth. There are four major disciplines in earth sciences, namely geography, geology, geophysics and geodesy. These major disciplines use physics, chemistry, biology, chronology and mathematics to build a qualitative and quantitative understanding of the principal areas or spheres of Earth.Geological activityMain article: GeologyThe Earth's crust, or lithosphere, is the outermost solid surface of the planet and is chemically and mechanically different from underlying mantle. It has been generated greatly by igneous processes in which magma cools and solidifies to form solid rock. Beneath the lithosphere lies the mantle which is heated by the decay of radioactive elements. The mantle though solid is in a state of rheic convection. This convection process causes the lithospheric plates to move, albeit slowly. The resulting process is known as plate tectonics. Volcanoes result primarily from the melting of subducted crust material or of rising mantle at mid-ocean ridges and mantle plumes.Water on EarthCoral reefs have significant marine biodiversity.Most water is found in various kinds of natural body of water.OceansMain article: OceanAn ocean is a major body of saline water, and a component of the hydrosphere. Approximately 71% of the surface of the Earth is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas. More than half of this area is over 3,000 meters deep. Average oceanic salinity is around 35 parts per thousand, and nearly all seawater has a salinity in the range of 30 to 38 ppt. Though generally recognized as several separate oceans, these waters comprise one global, interconnected body of salt water often referred to as the World Ocean or global ocean. The deep seabeds are more than half the Earth's surface, and are among the least-modified natural environments. The major oceanic divisions are defined in part by the continents, various archipelagos, and other criteria: these divisions are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Southern Ocean and the Arctic Ocean.RiversMain article: RiverA river is a natural watercourse, usually freshwater, flowing toward an ocean, a lake, a sea or another river. A few rivers simply flow into the ground and dry up completely without reaching another body of water.Rocky stream in the U.S. state of HawaiiThe water in a river is usually in a channel, made up of a stream bed between banks. In larger rivers there is often also a wider floodplain shaped by waters over-topping the channel. Flood plains may be very wide in relation to the size of the river channel. Rivers are a part of the hydrological cycle. Water within a river is generally collected from precipitation through surface runoff, groundwater recharge, springs, and the release of water stored in glaciers and snowpacks.Small rivers may also be called by several other names, including stream, creek and brook. Their current is confined within a bed and stream banks. Streams play an important corridor role in connecting fragmented habitats and thus in conserving biodiversity. The study of streams and waterways in general is known as surface hydrology.Further information: StreamLakesLácar Lake, of glacial origin, in the province of Neuquén, ArgentinaMain article: LakeA lake is a terrain feature, a body of water that is localized to the bottom of basin. A body of water is considered a lake when it is inland, is not part of an ocean, and is larger and deeper than a pond.A swamp area in Everglades National Park, Florida, US.Natural lakes on Earth are generally found in mountainous areas, rift zones, and areas with ongoing or recent glaciation. Other lakes are found in endorheic basins or along the courses of mature rivers. In some parts of the world, there are many lakes because of chaotic drainage patterns left over from the last Ice Age. All lakes are temporary over geologic time scales, as they will slowly fill in with sediments or spill out of the basin containing them.PondsMain article: PondA pond is a body of standing water, either natural or man-made, that is usually smaller than a lake. A wide variety of man-made bodies of water are classified as ponds, including water gardens designed for aesthetic ornamentation, fish ponds designed for commercial fish breeding, and solar ponds designed to store thermal energy. Ponds and lakes are distinguished from streams by their current speed. While currents in streams are easily observed, ponds and lakes possess thermally driven micro-currents and moderate wind driven currents. These features distinguish a pond from many other aquatic terrain features, such as stream pools and tide pools.Human impact on waterHumans impact the water in different ways such as modifying rivers, urbanization, and deforestation. These impact lake levels, groundwater conditions, water pollution, thermal pollution, and marine pollution. Humans modify rivers by using direct channel manipulation. We build dams and reservoirs and manipulate the direction of the rivers and water path. Dams can usefully create reservoirs and hydroelectric power. However, reservoirs and dams may negatively impact the environment and wildlife. Dams stop fish migration and the movement of organisms downstream. Urbanization affects the environment because of deforestation and changing lake levels, groundwater conditions, etc. Deforestation and urbanization go hand in hand. Deforestation may cause flooding, declining stream flow, and changes in riverside vegetation. The changing vegetation occurs because when trees cannot get adequate water they start to deteriorate, leading to a decreased food supply for the wildlife in an area.Atmosphere, climate and weatherAtmospheric gases scatter blue light more than other wavelengths, creating a blue halo when seen from space.A view of Earth's troposphere from an airplaneLightning is an atmospheric discharge of electricity accompanied by thunder, which occurs during thunderstorms and certain other natural conditions.The atmosphere of the Earth serves as a key factor in sustaining the planetary ecosystem. The thin layer of gases that envelops the Earth is held in place by the planet's gravity. Dry air consists of 78% nitrogen, 21% oxygen, 1% argon and other inert gases, and carbon dioxide. The remaining gases are often referred to as trace gases. The atmosphere includes greenhouse gases such as carbon dioxide, methane, nitrous oxide, and ozone. Filtered air includes trace amounts of many other chemical compounds. Air also contains a variable amount of water vapor and suspensions of water droplets and ice crystals seen as clouds. Many natural substances may be present in tiny amounts in an unfiltered air sample, including dust, pollen and spores, sea spray, volcanic ash, and meteoroids. Various industrial pollutants also may be present, such as chlorine, fluorine compounds, elemental mercury, and sulphur compounds such as sulphur dioxide.The ozone layer of the Earth's atmosphere plays an important role in reducing the amount of ultraviolet radiation that reaches the surface. As DNA is readily damaged by UV light, this serves to protect life at the surface. The atmosphere also retains heat during the night, thereby reducing the daily temperature extremes.Layers of the atmosphereMain article: Earth's atmospherePrincipal layersEarth's atmosphere can be divided into five main layers. These layers are mainly determined by whether temperature increases or decreases with altitude. From highest to lowest, these layers are:  Exosphere: The outermost layer of Earth's atmosphere extends from the exobase upward, mainly composed of hydrogen and helium.  Thermosphere: The top of the thermosphere is the bottom of the exosphere, called the exobase. Its height varies with solar activity and ranges from about 350–800 km. The International Space Station orbits in this layer, between 320 and 380 km.  Mesosphere: The mesosphere extends from the stratopause to 80–85 km. It is the layer where most meteors burn up upon entering the atmosphere.  Stratosphere: The stratosphere extends from the tropopause to about 51 km. The stratopause, which is the boundary between the stratosphere and mesosphere, typically is at 50 to 55 km.  Troposphere: The troposphere begins at the surface and extends to between 7 km at the poles and 17 km at the equator, with some variation due to weather. The troposphere is mostly heated by transfer of energy from the surface, so on average the lowest part of the troposphere is warmest and temperature decreases with altitude. The tropopause is the boundary between the troposphere and stratosphere.Other layersWithin the five principal layers determined by temperature there are several layers determined by other properties.  The ozone layer is contained within the stratosphere. It is mainly located in the lower portion of the stratosphere from about 15–35 km, though the thickness varies seasonally and geographically. About 90% of the ozone in our atmosphere is contained in the stratosphere.  The ionosphere, the part of the atmosphere that is ionized by solar radiation, stretches from 50 to 1,000 km and typically overlaps both the exosphere and the thermosphere. It forms the inner edge of the magnetosphere.  The homosphere and heterosphere: The homosphere includes the troposphere, stratosphere, and mesosphere. The upper part of the heterosphere is composed almost completely of hydrogen, the lightest element.  The planetary boundary layer is the part of the troposphere that is nearest the Earth's surface and is directly affected by it, mainly through turbulent diffusion.Effects of global warmingThe retreat of glaciers since 1850 of Aletsch Glacier in the Swiss Alps, due to global warmingMain article: Effects of global warmingThe dangers of global warming are being increasingly studied by a wide global consortium of scientists. These scientists are increasingly concerned about the potential long-term effects of global warming on our natural environment and on the planet. Of particular concern is how climate change and global warming caused by anthropogenic, or human-made releases of greenhouse gases, most notably carbon dioxide, can act interactively, and have adverse effects upon the planet, its natural environment and humans' existence. It is clear the planet is warming, and warming rapidly. This is due to the greenhouse effect, which is caused by greenhouse gases, which trap heat inside the Earth's atmosphere because of their more complex molecular structure which allows them to vibrate and in turn trap heat and release it back towards the Earth. This warming is also responsible for the extinction of natural habitats, which in turn leads to a reduction in wildlife population. The most recent report from the Intergovernmental Panel on Climate Change concluded that the earth will warm anywhere from 2.7 to almost 11 degrees Fahrenheit between 1990 and 2100. Efforts have been increasingly focused on the mitigation of greenhouse gases that are causing climatic changes, on developing adaptative strategies to global warming, to assist humans, other animal, and plant species, ecosystems, regions and nations in adjusting to the effects of global warming. Some examples of recent collaboration to address climate change and global warming include:Another view of the Aletsch Glacier in the Swiss Alps, which because of global warming has been decreasing  The United Nations Framework Convention Treaty and convention on Climate Change, to stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.  The Kyoto Protocol, which is the protocol to the international Framework Convention on Climate Change treaty, again with the objective of reducing greenhouse gases in an effort to prevent anthropogenic climate change.  The Western Climate Initiative, to identify, evaluate, and implement collective and cooperative ways to reduce greenhouse gases in the region, focusing on a market-based cap-and-trade system.A significantly profound challenge is to identify the natural environmental dynamics in contrast to environmental changes not within natural variances. A common solution is to adapt a static view neglecting natural variances to exist. Methodologically, this view could be defended when looking at processes which change slowly and short time series, while the problem arrives when fast processes turns essential in the object of the study.ClimateMap of world dividing climate zones, largely influenced by latitude. The zones, going from the equator upward are Tropical, Dry, Moderate, Continental and Polar. There are subzones within these zones.Worldwide climate classifications mapMain article: ClimateClimate looks at the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elements in a given region over long periods of time. Weather, on the other hand, is the present condition of these same elements over periods up to two weeks.Climates can be classified according to the average and typical ranges of different variables, most commonly temperature and precipitation. The most commonly used classification scheme is the one originally developed by Wladimir Köppen. The Thornthwaite system, in use since 1948, uses evapotranspiration as well as temperature and precipitation information to study animal species diversity and the potential impacts of climate changes.WeatherA rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines onto droplets of moisture in the Earth's atmosphere.Main article: WeatherWeather is a set of all the phenomena occurring in a given atmospheric area at a given time. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate is the term for the average atmospheric conditions over longer periods of time. When used without qualification, weather is understood to be the weather of Earth.Weather occurs due to density differences between one place and another. These differences can occur due to the sun angle at any particular spot, which varies by latitude from the tropics. The strong temperature contrast between polar and tropical air gives rise to the jet stream. Weather systems in the mid-latitudes, such as extratropical cyclones, are caused by instabilities of the jet stream flow. Because the Earth's axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year. On the Earth's surface, temperatures usually range ±40 °C annually. Over thousands of years, changes in the Earth's orbit have affected the amount and distribution of solar energy received by the Earth and influence long-term climateSurface temperature differences in turn cause pressure differences. Higher altitudes are cooler than lower altitudes due to differences in compressional heating. Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. The atmosphere is a chaotic system, and small changes to one part of the system can grow to have large effects on the system as a whole. Human attempts to control the weather have occurred throughout human history, and there is evidence that civilized human activity such as agriculture and industry has inadvertently modified weather patterns.LifeThere are many plant species on the planet.An example of the many animal species on the EarthMain articles: Life, Biology, and BiosphereEvidence suggests that life on Earth has existed for about 3.7 billion years. All known life forms share fundamental molecular mechanisms, and based on these observations, theories on the origin of life attempt to find a mechanism explaining the formation of a primordial single cell organism from which all life originates. There are many different hypotheses regarding the path that might have been taken from simple organic molecules via pre-cellular life to protocells and metabolism.Although there is no universal agreement on the definition of life, scientists generally accept that the biological manifestation of life is characterized by organization, metabolism, growth, adaptation, response to stimuli and reproduction. Life may also be said to be simply the characteristic state of organisms. In biology, the science of living organisms, life is the condition which distinguishes active organisms from inorganic matter, including the capacity for growth, functional activity and the continual change preceding death.A diverse variety of living organisms can be found in the biosphere on Earth, and properties common to these organisms—plants, animals, fungi, protists, archaea, and bacteria—are a carbon- and water-based cellular form with complex organization and heritable genetic information. Living organisms undergo metabolism, maintain homeostasis, possess a capacity to grow, respond to stimuli, reproduce and, through natural selection, adapt to their environment in successive generations. More complex living organisms can communicate through various means.EcosystemsRainforests often have a great deal of biodiversity with many plant and animal species. This is the Gambia River in Senegal's Niokolo-Koba National Park.Main article: EcosystemAn ecosystem is a natural unit consisting of all plants, animals and micro-organisms in an area functioning together with all of the non-living physical factors of the environment.Central to the ecosystem concept is the idea that living organisms are continually engaged in a highly interrelated set of relationships with every other element constituting the environment in which they exist. Eugene Odum, one of the founders of the science of ecology, stated: Any unit that includes all of the organisms in a given area interacting with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity, and material cycles within the system is an ecosystem.Old-growth forest and a creek on Larch Mountain, in the U.S. state of OregonThe human ecosystem concept is then grounded in the deconstruction of the human/nature dichotomy, and the emergent premise that all species are ecologically integrated with each other, as well as with the abiotic constituents of their biotope.A greater number or variety of species or biological diversity of an ecosystem may contribute to greater resilience of an ecosystem, because there are more species present at a location to respond to change and thus absorb or reduce its effects. This reduces the effect before the ecosystem's structure is fundamentally changed to a different state. This is not universally the case and there is no proven relationship between the species diversity of an ecosystem and its ability to provide goods and services on a sustainable level.The term ecosystem can also pertain to human-made environments, such as human ecosystems and human-influenced ecosystems, and can describe any situation where there is relationship between living organisms and their environment. Fewer areas on the surface of the earth today exist free from human contact, although some genuine wilderness areas continue to exist without any forms of human intervention.BiomesMap of terrestrial biomes classified by vegetationMain article: BiomeBiomes are terminologically similar to the concept of ecosystems, and are climatically and geographically defined areas of ecologically similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, often referred to as ecosystems. Biomes are defined on the basis of factors such as plant structures, leaf types, plant spacing, and climate. Unlike biogeographic realms, biomes are not defined by genetic, taxonomic, or historical similarities. Biomes are often identified with particular patterns of ecological succession and climax vegetation.Biogeochemical cyclesChloroplasts conduct photosynthesis and are found in plant cells and other eukaryotic organisms. These are chloroplasts visible in the cells of Plagiomnium affine — many-fruited thyme-moss.Main article: Biogeochemical cyclesGlobal biogeochemical cycles are critical to life, most notably those of water, oxygen, carbon, nitrogen and phosphorus.  The nitrogen cycle is the transformation of nitrogen and nitrogen-containing compounds in nature. It is a cycle which includes gaseous components.  The water cycle, is the continuous movement of water on, above, and below the surface of the Earth. Water can change states among liquid, vapour, and ice at various places in the water cycle. Although the balance of water on Earth remains fairly constant over time, individual water molecules can come and go.  The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth.  The oxygen cycle is the movement of oxygen within and between its three main reservoirs: the atmosphere, the biosphere, and the lithosphere. The main driving factor of the oxygen cycle is photosynthesis, which is responsible for the modern Earth's atmospheric composition and life.  The phosphorus cycle is the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. The atmosphere does not play a significant role in the movements of phosphorus, because phosphorus and phosphorus compounds are usually solids at the typical ranges of temperature and pressure found on Earth.WildernessA conifer forest in the Swiss Alps The Ahklun Mountains and the Togiak Wilderness within the Togiak National Wildlife Refuge in the U.S. state of AlaskaMain article: WildernessWilderness is generally defined as a natural environment on Earth that has not been significantly modified by human activity. The WILD Foundation goes into more detail, defining wilderness as: The most intact, undisturbed wild natural areas left on our planet – those last truly wild places that humans do not control and have not developed with roads, pipelines or other industrial infrastructure. Wilderness areas and protected parks are considered important for the survival of certain species, ecological studies, conservation, solitude, and recreation. Wilderness is deeply valued for cultural, spiritual, moral, and aesthetic reasons. Some nature writers believe wilderness areas are vital for the human spirit and creativity.The word, wilderness, derives from the notion of wildness; in other words that which is not controllable by humans. The word's etymology is from the Old English wildeornes, which in turn derives from wildeor meaning wild beast. From this point of view, it is the wildness of a place that makes it a wilderness. The mere presence or activity of people does not disqualify an area from being wilderness. Many ecosystems that are, or have been, inhabited or influenced by activities of people may still be considered wild. This way of looking at wilderness includes areas within which natural processes operate without very noticeable human interference.Wildlife includes all non-domesticated plants, animals and other organisms. Domesticating wild plant and animal species for human benefit has occurred many times all over the planet, and has a major impact on the environment, both positive and negative. Wildlife can be found in all ecosystems. Deserts, rain forests, plains, and other areas—including the most developed urban sites—all have distinct forms of wildlife. While the term in popular culture usually refers to animals that are untouched by civilized human factors, most scientists agree that wildlife around the world is impacted by human activities.A view of wilderness in EstoniaChallengesBefore flue-gas desulfurization was installed, the air-polluting emissions from this power plant in New Mexico contained excessive amounts of sulfur dioxide.Amazon rainforest in Brazil. The tropical rainforests of South America contain the largest diversity of species on Earth, including some that have evolved within the past few hundred thousand years.See also: List of environmental issues and World Scientists' Warning to HumanityIt is the common understanding of natural environment that underlies environmentalism — a broad political, social, and philosophical movement that advocates various actions and policies in the interest of protecting what nature remains in the natural environment, or restoring or expanding the role of nature in this environment. While true wilderness is increasingly rare, wild nature can be found in many locations previously inhabited by humans.Goals for the benefit of people and natural systems, commonly expressed by environmental scientists and environmentalists include:  Elimination of pollution and toxicants in air, water, soil, buildings, manufactured goods, and food.  Preservation of biodiversity and protection of endangered species.  Conservation and sustainable use of resources such as water, land, air, energy, raw materials, and natural resources.  Halting human-induced global warming, which represents pollution, a threat to biodiversity, and a threat to human populations.  Shifting from fossil fuels to renewable energy in electricity, heating and cooling, and transportation, which addresses pollution, global warming, and sustainability. This may include public transportation and distributed generation, which have benefits for traffic congestion and electric reliability.  Shifting from meat-intensive diets to largely plant-based diets in order to help mitigate biodiversity loss and climate change.  Establishment of nature reserves for recreational purposes and ecosystem preservation.  Sustainable and less polluting waste management including waste reduction, reuse, recycling, composting, waste-to-energy, and anaerobic digestion of sewage sludge.  Reducing profligate consumption and clamping down on illegal fishing and logging.  Slowing and stabilisation of human population growth.CriticismIn some cultures the term environment is meaningless because there is no separation between people and what they view as the natural world, or their surroundings. Specifically in the United States and Arabian countries many native cultures do not recognize the environment, or see themselves as environmentalists. Education is the process of facilitating learning, or the acquisition of knowledge, skills, values, morals, beliefs, habits, and personal development. Educational methods include teaching, training, storytelling, discussion and directed research. Education frequently takes place under the guidance of educators; however, learners can also educate themselves. Education can take place in formal or informal settings, and any experience that has a formative effect on the way one thinks, feels, or acts may be considered educational. The methodology of teaching is called pedagogy.Formal education is commonly divided formally into stages such as preschool or kindergarten, primary school, secondary school and then college, university, or apprenticeship. In most regions, education is compulsory up to a certain age.There are movements for education reforms, such as for improving quality and efficiency of education towards relevance in students' lives and efficient problem solving in modern or future society at large, or for evidence-based education methodologies. A right to education has been recognized by some governments and the United Nations. Global initiatives aim at achieving the Sustainable Development Goal 4, which promotes quality education for all. Education began in prehistory, as adults trained the young in the knowledge and skills deemed necessary in their society. In pre-literate societies, this was achieved orally and through imitation. Story-telling passed knowledge, values, and skills from one generation to the next. As cultures began to extend their knowledge beyond skills that could be readily learned through imitation, formal education developed. Schools existed in Egypt at the time of the Middle Kingdom.Matteo Ricci and Xu Guangqi in the Chinese edition of Euclid's Elements published in 1607Plato founded the Academy in Athens, the first institution of higher learning in Europe. The city of Alexandria in Egypt, established in 330 BCE, became the successor to Athens as the intellectual cradle of Ancient Greece. There, the great Library of Alexandria was built in the 3rd century BCE. European civilizations suffered a collapse of literacy and organization following the fall of Rome in CE 476.In China, Confucius, of the State of Lu, was the country's most influential ancient philosopher, whose educational outlook continues to influence the societies of China and neighbours like Korea, Japan, and Vietnam. Confucius gathered disciples and searched in vain for a ruler who would adopt his ideals for good governance, but his Analects were written down by followers and have continued to influence education in East Asia into the modern era.The Aztecs had schools for the noble youths called Calmecac where they would receive rigorous religious and military training. The Aztecs also had a well-developed theory about education, which has an equivalent word in Nahuatl called tlacahuapahualiztli. It means the art of raising or educating a person, or the art of strengthening or bringing up men. This was a broad conceptualization of education, which prescribed that it begins at home, supported by formal schooling, and reinforced by community living. Historians cite that formal education was mandatory for everyone regardless of social class and gender. There was also the word neixtlamachiliztli, which is the act of giving wisdom to the face. These concepts underscore a complex set of educational practices, which was oriented towards communicating to the next generation the experience and intellectual heritage of the past for the purpose of individual development and his integration into the community.After the Fall of Rome, the Catholic Church became the sole preserver of literate scholarship in Western Europe. The church established cathedral schools in the Early Middle Ages as centres of advanced education. Some of these establishments ultimately evolved into medieval universities and forebears of many of Europe's modern universities. During the High Middle Ages, Chartres Cathedral operated the famous and influential Chartres Cathedral School. The medieval universities of Western Christendom were well-integrated across all of Western Europe, encouraged freedom of inquiry, and produced a great variety of fine scholars and natural philosophers, including Thomas Aquinas of the University of Naples, Robert Grosseteste of the University of Oxford, an early expositor of a systematic method of scientific experimentation, and Saint Albert the Great, a pioneer of biological field research. Founded in 1088, the University of Bologne is considered the first, and the oldest continually operating university.Elsewhere during the Middle Ages, Islamic science and mathematics flourished under the Islamic caliphate which was established across the Middle East, extending from the Iberian Peninsula in the west to the Indus in the east and to the Almoravid Dynasty and Mali Empire in the south.The Renaissance in Europe ushered in a new age of scientific and intellectual inquiry and appreciation of ancient Greek and Roman civilizations. Around 1450, Johannes Gutenberg developed a printing press, which allowed works of literature to spread more quickly. The European Age of Empires saw European ideas of education in philosophy, religion, arts and sciences spread out across the globe. Missionaries and scholars also brought back new ideas from other civilizations – as with the Jesuit China missions who played a significant role in the transmission of knowledge, science, and culture between China and Europe, translating works from Europe like Euclid's Elements for Chinese scholars and the thoughts of Confucius for European audiences. The Enlightenment saw the emergence of a more secular educational outlook in Europe. Much of modern traditional Western and Eastern education is based on the Prussian education system.In most countries today, full-time education, whether at school or otherwise, is compulsory for all children up to a certain age. Due to this the proliferation of compulsory education, combined with population growth, UNESCO has calculated that in the next 30 years more people will receive formal education than in all of human history thus far.FormalFormal learning redirects here. For the subfield of formal epistemology and computer science, see Formal learning theory.Formal education occurs in a structured environment whose explicit purpose is teaching students. Usually, formal education takes place in a school environment with classrooms of multiple students learning together with a trained, certified teacher of the subject. Most school systems are designed around a set of values or ideals that govern all educational choices in that system. Such choices include curriculum, organizational models, design of the physical learning spaces, student-teacher interactions, methods of assessment, class size, educational activities, and more.The International Standard Classification of Education was created by UNESCO as a statistical base to compare education systems. In 1997, it defined 7 levels of education and 25 fields, though the fields were later separated out to form a different project. The current version ISCED 2011 has 9 rather than 7 levels, created by dividing the tertiary pre-doctorate level into three levels. It also extended the lowest level to cover a new sub-category of early childhood educational development programmes, which target children below the age of 3 years.Early childhoodMain article: Early childhood educationYoung children in a kindergarten in JapanEducation designed to support early development in preparation for participation in school and society. The programmes are designed for children below the age of 3. This is ISCED level 01. Preschools provide education from ages approximately three to seven, depending on the country when children enter primary education. The children now readily interact with their peers and the educator. These are also known as nursery schools and as kindergarten, except in the US, where the term kindergarten refers to the earliest levels of primary education. Kindergarten provides a child-centred, preschool curriculum for three- to seven-year-old children that aim at unfolding the child's physical, intellectual, and moral nature with balanced emphasis on each of them. This is ISCED level 02.PrimaryNepali village school studentsMain article: Primary educationThis is ISCED level 1. Primary education consists of the first four to seven years of formal, structured education. In general, primary education consists of six to eight years of schooling starting at the age of five to seven, although this varies between, and sometimes within, countries. Globally, in 2008, around 89% of children aged six to twelve were enrolled in primary education, and this proportion was rising. Under the Education For All programs driven by UNESCO, most countries have committed to achieving universal enrollment in primary education by 2015, and in many countries, it is compulsory. The division between primary and secondary education is quite arbitrary, but it generally occurs at about eleven or twelve years of age. Some education systems have separate middle schools, with the transition to the final stage of secondary education taking place at around the age of fifteen. Schools that provide primary education, are mostly referred to as primary schools or elementary schools. Primary schools are often subdivided into infant schools and junior schools.In India, for example, compulsory education spans over twelve years, with eight years of elementary education, five years of primary schooling and three years of upper primary schooling. Various states in the republic of India provide 12 years of compulsory school education based on a national curriculum framework designed by the National Council of Educational Research and Training.Secondary	This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.Find sources: Education – news · newspapers · books · scholar · JSTOR Main article: Secondary educationThis covers the two ISCED levels, ISCED 2: Lower Secondary Education and ISCED 3: Upper Secondary Education.In most contemporary educational systems of the world, secondary education comprises the formal education that occurs during adolescence. In the United States, Canada, and Australia, primary and secondary education together are sometimes referred to as K-12 education, and in New Zealand Year 1–13 is used. The purpose of secondary education can be to give common knowledge, to ensure literacy, to prepare for higher education, or to train directly in a profession.Secondary education in the United States did not emerge until 1910, with the rise of large corporations and advancing technology in factories, which required skilled workers. In order to meet this new job demand, high schools were created, with a curriculum focused on practical job skills that would better prepare students for white collar or skilled blue collar work. This proved beneficial for both employers and employees, since the improved human capital lowered costs for the employer, while skilled employees received higher wages.Secondary education has a longer history in Europe, where grammar schools or academies date from as early as the 6th century, in the form of public schools, fee-paying schools, or charitable educational foundations, which themselves date even further back.It spans the period between the typically universal compulsory, primary education to the optional, selective tertiary, postsecondary, or higher education of ISCED 5 and 6, and the ISCED 4 Further education or vocational school.A high-school senior classrooms in Calhan, Colorado, United StatesDepending on the system, schools for this period, or a part of it, may be called secondary or high schools, gymnasiums, lyceums, middle schools, colleges, or vocational schools. The exact meaning of any of these terms varies from one system to another. The exact boundary between primary and secondary education also varies from country to country and even within them but is generally around the seventh to the tenth year of schooling.LowerPrograms at ISCED level 2, lower secondary education are usually organized around a more subject-oriented curriculum; differing from primary education. Teachers typically have pedagogical training in the specific subjects and, more often than at ISCED level 1, a class of students will have several teachers, each with specialized knowledge of the subjects they teach. Programmes at ISCED level 2, aim to lay the foundation for lifelong learning and human development upon introducing theoretical concepts across a broad range of subjects which can be developed in future stages. Some education systems may offer vocational education programs during ISCED level 2 providing skills relevant to employment.UpperPrograms at ISCED level 3, or upper secondary education, are typically designed to complete the secondary education process. They lead to skills relevant to employment and the skill necessary to engage in tertiary courses. They offer students more varied, specialized and in-depth instruction. They are more differentiated, with range of options and learning streams.Community colleges offer another option at this transitional stage of education. They provide nonresidential junior college courses to people living in a particular area.Tertiary	This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Students in a laboratory, Saint Petersburg State Polytechnical UniversityMain articles: Tertiary education and Higher educationSee also: Adult educationUniversities often host prominent guest speakers for student audiences, e.g. First Lady of the United States Michelle Obama delivering remarks at Peking University, Beijing, ChinaHigher education, also called tertiary, third stage, or postsecondary education, is the non-compulsory educational level that follows the completion of a school such as a high school or secondary school. Tertiary education is normally taken to include undergraduate and postgraduate education, as well as vocational education and training. Colleges and universities mainly provide tertiary education. Collectively, these are sometimes known as tertiary institutions. Individuals who complete tertiary education generally receive certificates, diplomas, or academic degrees.The ISCED distinguishes 4 levels of tertiary education. ISCED 6 is equivalent to a first degree, ISCED 7 is equivalent to a masters or an advanced professional qualification and ISCED 8 is an advanced research qualification, usually concluding with the submission and defence of a substantive dissertation of publishable quality based on original research. The category ISCED 5 is reserved for short-cycle courses of requiring degree level study.Higher education typically involves work towards a degree-level or foundation degree qualification. In most developed countries, a high proportion of the population now enter higher education at some time in their lives. Higher education is therefore very important to national economies, both as a significant industry in its own right and as a source of trained and educated personnel for the rest of the economy.University education includes teaching, research, and social services activities, and it includes both the undergraduate level and the graduate level. Some universities are composed of several colleges.One type of university education is a liberal arts education, which can be defined as a college or university curriculum aimed at imparting broad general knowledge and developing general intellectual capacities, in contrast to a professional, vocational, or technical curriculum. Although what is known today as liberal arts education began in Europe, the term liberal arts college is more commonly associated with institutions in the United States such as Williams College or Barnard College.VocationalCarpentry is normally learned through apprenticeship with an experienced carpenterMain article: Vocational educationVocational education is a form of education focused on direct and practical training for a specific trade or craft. Vocational education may come in the form of an apprenticeship or internship as well as institutions teaching courses such as carpentry, agriculture, engineering, medicine, architecture and the arts. Post 16 education, adult education and further education involve continued study, but a level no different from that found at upper secondary, and are grouped together as ISCED 4, post-secondary non-tertiary education.SpecialMain article: Special educationIn the past, those who were disabled were often not eligible for public education. Children with disabilities were repeatedly denied an education by physicians or special tutors. These early physicians set the foundation for special education today. They focused on individualized instruction and functional skills. In its early years, special education was only provided to people with severe disabilities, but more recently it has been opened to anyone who has experienced difficulty learning.Unconventional formsAlternativeGlobe icon.	The examples and perspective in this section deal primarily with US and do not represent a worldwide view of the subject. You may improve this section, discuss the issue on the talk page, or create a new section, as appropriate. Main article: Alternative educationWhile considered alternative today, most alternative systems have existed since ancient times. After the public school system was widely developed beginning in the 19th century, some parents found reasons to be discontented with the new system. Alternative education developed in part as a reaction to perceived limitations and failings of traditional education. A broad range of educational approaches emerged, including alternative schools, self learning, homeschooling, and unschooling. Example alternative schools include Montessori schools, Waldorf schools, Friends schools, Sands School, Summerhill School, Walden's Path, The Peepal Grove School, Sudbury Valley School, Krishnamurti schools, and open classroom schools.Charter schools are another example of alternative education, which have in the recent years grown in numbers in the US and gained greater importance in its public education system.In time, some ideas from these experiments and paradigm challenges may be adopted as the norm in education, just as Friedrich Fröbel's approach to early childhood education in 19th-century Germany has been incorporated into contemporary kindergarten classrooms. Other influential writers and thinkers have included the Swiss humanitarian Johann Heinrich Pestalozzi; the American transcendentalists Amos Bronson Alcott, Ralph Waldo Emerson, and Henry David Thoreau; the founders of progressive education, John Dewey and Francis Parker; and educational pioneers such as Maria Montessori and Rudolf Steiner, and more recently John Caldwell Holt, Paul Goodman, Frederick Mayer, George Dennison, and Ivan Illich.IndigenousNa Schoolyard.Teaching indigenous knowledge, models, and methods in Yanyuan County, Sichuan, ChinaMain article: Indigenous educationIndigenous education refers to the inclusion of indigenous knowledge, models, methods, and content within formal and non-formal educational systems. Often in a post-colonial context, the growing recognition and use of indigenous education methods can be a response to the erosion and loss of indigenous knowledge and language through the processes of colonialism. Furthermore, it can enable indigenous communities to reclaim and revalue their languages and cultures, and in so doing, improve the educational success of indigenous students.Informal learningMain article: Informal learningInformal learning is one of three forms of learning defined by the Organisation for Economic Co-operation and Development. Informal learning occurs in a variety of places, such as at home, work, and through daily interactions and shared relationships among members of society. For many learners, this includes language acquisition, cultural norms, and manners.A volunteer reads aloud to children in LaosIn informal learning, there is often a reference person, a peer or expert, to guide the learner. If learners have a personal interest in what they are informally being taught, learners tend to expand their existing knowledge and conceive new ideas about the topic being learned. For example, a museum is traditionally considered an informal learning environment, as there is room for free choice, a diverse and potentially non-standardized range of topics, flexible structures, socially rich interaction, and no externally imposed assessments.While informal learning often takes place outside educational establishments and does not follow a specified curriculum, it can also occur within educational settings and even during formal learning situations. Educators can structure their lessons to directly utilize their students informal learning skills within the education setting.In the late 19th century, education through play began to be recognized as making an important contribution to child development. In the early 20th century, the concept was broadened to include young adults but the emphasis was on physical activities. L.P. Jacks, also an early proponent of lifelong learning, described education through recreation: A master in the art of living draws no sharp distinction between his work and his play, his labour, and his leisure, his mind and his body, his education and his recreation. He hardly knows which is which. He simply pursues his vision of excellence through whatever he is doing and leaves others to determine whether he is working or playing. To himself, he always seems to be doing both. Enough for him that he does it well. Education through recreation is the opportunity to learn in a seamless fashion through all of life's activities. The concept has been revived by the University of Western Ontario to teach anatomy to medical students.Self-directed learningMain article: AutodidacticismAutodidacticism is self-directed learning. One may become an autodidact at nearly any point in one's life. Notable autodidacts include Abraham Lincoln, Srinivasa Ramanujan, Michael Faraday, Charles Darwin, Thomas Alva Edison, Tadao Ando, George Bernard Shaw, Frank Zappa, and Leonardo da Vinci.Evidence-basedMain article: Evidence-based educationEvidence-based education is the use of well designed scientific studies to determine which education methods work best. It consists of evidence-based teaching and evidence-based learning. Evidence-based learning methods such as spaced repetition can increase rate of learning. The evidence-based education movement has its roots in the larger movement towards evidence-based-practices.Open learning and electronic technologyMain articles: Open education and Educational technologyChildren computing by David ShankboneMany large university institutions are now starting to offer free or almost free full courses, through open education, such as Harvard, MIT and Berkeley teaming up to form edX. Other universities offering open education are prestigious private universities such as Stanford, Princeton, Duke, Johns Hopkins, the University of Pennsylvania, and Caltech, as well as notable public universities including Tsinghua, Peking, Edinburgh, University of Michigan, and University of Virginia.Open education has been called the biggest change in the way people learn since the printing press. Despite favourable studies on effectiveness, many people may still desire to choose traditional campus education for social and cultural reasons.Many open universities are working to have the ability to offer students standardized testing and traditional degrees and credentials.The conventional merit-system degree is currently not as common in open education as it is in campus universities, although some open universities do already offer conventional degrees such as the Open University in the United Kingdom. Presently, many of the major open education sources offer their own form of certificate.Out of 182 colleges surveyed in 2009 nearly half said tuition for online courses was higher than for campus-based ones.A 2010 meta-analysis found that online and blended educational approaches had better outcomes than methods that used solely face-to-face interaction.Public schoolingBeijing Normal University, which is governed directly by the Chinese Ministry of Education, is an example of collaboration between different entities in the education sectorThe education sector or education system is a group of institutions whose primary purpose is to provide education to children and young people in educational settings. It involves a wide range of people. These institutions can vary according to different contexts.Schools deliver education, with support from the rest of the education system through various elements such as education policies and guidelines – to which school policies can refer – curricula and learning materials, as well as pre- and in-service teacher training programmes. The school environment – both physical and psychological – is also guided by school policies that should ensure the well-being of students when they are in school. The Organisation for Economic Co-operation and Development has found that schools tend to perform best when principals have full authority and responsibility for ensuring that students are proficient in core subjects upon graduation. They must also seek feedback from students for quality-assurance and improvement. Governments should limit themselves to monitoring student proficiency.The education sector is fully integrated into society, through interactions with numerous stakeholders and other sectors. These include parents, local communities, religious leaders, NGOs, stakeholders involved in health, child protection, justice and law enforcement, media and political leadership.The shape, methodologies, taught material – the curriculum – of formal education is decided by political decision makers along with federal agencies such as the state education agency in the United States.Development goalsWorld map indicating Education Index Joseph Chimombo pointed out education's role as a policy instrument, capable of instilling social change and economic advancement in developing countries by giving communities the opportunity to take control of their destinies. The 2030 Agenda for Sustainable Development, adopted by the United Nations General Assembly in September 2015, calls for a new vision to address the environmental, social and economic concerns facing the world today. The Agenda includes 17 Sustainable Development Goals, including SDG 4 on education.Since 1909, the percentage of children in the developing world attending school has increased. Before then, a small minority of boys attended school. By the start of the twenty-first century, the majority of children in most regions of the world attended some form of school. By 2016, over 91 percent of children are enrolled in formal primary schooling. However, a learning crisis has emerged across the globe, due to the fact that a large proportion of students enrolled in school are not learning. A World Bank study found that 53 percent of children in low- and middle-income countries cannot read and understand a simple story by the end of primary school. While schooling has increased rapidly over the last few decades, learning has not followed suit.Universal Primary Education was one of the eight international Millennium Development Goals, towards which progress has been made in the past decade, though barriers still remain. Securing charitable funding from prospective donors is one particularly persistent problem. Researchers at the Overseas Development Institute have indicated that the main obstacles to funding for education include conflicting donor priorities, an immature aid architecture, and a lack of evidence and advocacy for the issue. Additionally, Transparency International has identified corruption in the education sector as a major stumbling block to achieving Universal Primary Education in Africa. Furthermore, demand in the developing world for improved educational access is not as high as foreigners have expected. Indigenous governments are reluctant to take on the ongoing costs involved. There is also economic pressure from some parents, who prefer their children to earn money in the short term rather than work towards the long-term benefits of education.A study conducted by the UNESCO International Institute for Educational Planning indicates that stronger capacities in educational planning and management may have an important spill-over effect on the system as a whole. Sustainable capacity development requires complex interventions at the institutional, organizational and individual levels that could be based on some foundational principles:  national leadership and ownership should be the touchstone of any intervention;  strategies must be context relevant and context specific;  plans should employ an integrated set of complementary interventions, though implementation may need to proceed in steps;  partners should commit to a long-term investment in capacity development while working towards some short-term achievements;  outside intervention should be conditional on an impact assessment of national capacities at various levels;  a certain percentage of students should be removed for improvisation of academics.InternationalisationNearly every country now has universal primary education.Similarities – in systems or even in ideas – that schools share internationally have led to an increase in international student exchanges. The European Socrates-Erasmus Programme facilitates exchanges across European universities. The Soros Foundation provides many opportunities for students from central Asia and eastern Europe. Programs such as the International Baccalaureate have contributed to the internationalization of education. The global campus online, led by American universities, allows free access to class materials and lecture files recorded during the actual classes.The Programme for International Student Assessment and the International Association for the Evaluation of Educational Achievement objectively monitor and compare the proficiency of students from a wide range of different nations.The internationalization of education is sometimes equated by critics with the westernization of education. These critics say that the internationalization of education leads to the erosion of local education systems and indigenous values and norms, which are replaced with Western systems and cultural and ideological values and orientation.Technology in developing countriesThe OLPC laptop being introduced to children in HaitiMain article: Education and technologyTechnology plays an increasingly significant role in improving access to education for people living in impoverished areas and developing countries. However, lack of technological advancement is still causing barriers with regards to quality and access to education in developing countries. Charities like One Laptop per Child are dedicated to providing infrastructures through which the disadvantaged may access educational materials.The OLPC foundation, a group out of MIT Media Lab and supported by several major corporations, has a stated mission to develop a $100 laptop for delivering educational software. The laptops were widely available as of 2008. They are sold at cost or given away based on donations.In Africa, the New Partnership for Africa's Development has launched an e-school program to provide all 600,000 primary and high schools with computer equipment, learning materials and internet access within 10 years. An International Development Agency project called nabuur.com, started with the support of former American President Bill Clinton, uses the Internet to allow co-operation by individuals on issues of social development.India is developing technologies that will bypass land-based telephone and Internet infrastructure to deliver distance learning directly to its students. In 2004, the Indian Space Research Organisation launched EDUSAT, a communications satellite providing access to educational materials that can reach more of the country's population at a greatly reduced cost.Funding in developing countriesA survey of literature of the research into low-cost private schools found that over 5-year period to July 2013, debate around LCPSs to achieving Education for All objectives was polarized and finding growing coverage in international policy. The polarization was due to disputes around whether the schools are affordable for the poor, reach disadvantaged groups, provide quality education, support or undermine equality, and are financially sustainable. The report examined the main challenges encountered by development organizations which support LCPSs. Surveys suggest these types of schools are expanding across Africa and Asia. This success is attributed to excess demand. These surveys found concern for:  Equity: This concern is widely found in the literature, suggesting the growth in low-cost private schooling may be exacerbating or perpetuating already existing inequalities in developing countries, between urban and rural populations, lower- and higher-income families, and between girls and boys. The report findings suggest that girls may be under represented and that LCPS are reaching low-income families in smaller numbers than higher-income families.  Quality and educational outcomes: It is difficult to generalize about the quality of private schools. While most achieve better results than government counterparts, even after their social background is taken into account, some studies find the opposite. Quality in terms of levels of teacher absence, teaching activity, and pupil to teacher ratios in some countries are better in LCPSs than in government schools.  Choice and affordability for the poor: Parents can choose private schools because of perceptions of better-quality teaching and facilities, and an English language instruction preference. Nevertheless, the concept of 'choice' does not apply in all contexts, or to all groups in society, partly because of limited affordability and other forms of exclusion, related to caste or social status.  Cost-effectiveness and financial sustainability: There is evidence that private schools operate at low cost by keeping teacher salaries low, and their financial situation may be precarious where they are reliant on fees from low-income households.The report showed some cases of successful voucher where there was an oversupply of quality private places and an efficient administrative authority and of subsidy programs. Evaluations of the effectiveness of international support to the sector are rare. Addressing regulatory ineffectiveness is a key challenge. Emerging approaches stress the importance of understanding the political economy of the market for LCPS, specifically how relationships of power and accountability between users, government, and private providers can produce better education outcomes for the poor.TheoryA class size experiment in the United States found that attending small classes for 3 or more years in the early grades increased high school graduation rates of students from low income families.Main article: Educational theoryFurther information: PedagogyPsychologyMain article: Educational psychologyEducational psychology is the study of how humans learn in educational settings, the effectiveness of educational interventions, the psychology of teaching, and the social psychology of schools as organizations. The terms educational psychology and school psychology are often used interchangeably. Educational psychology is concerned with the processes of educational attainment in the general population and in sub-populations such as gifted children and those with specific disabilities.Knowledge Day in Donetsk, Ukraine, 2013Educational psychology can in part be understood through its relationship with other disciplines. It is informed primarily by psychology, bearing a relationship to that discipline analogous to the relationship between medicine and biology. Educational psychology, in turn, informs a wide range of specialties within educational studies, including instructional design, educational technology, curriculum development, organizational learning, special education and classroom management. Educational psychology both draws from and contributes to cognitive science and the learning sciences. In universities, departments of educational psychology are usually housed within faculties of education, possibly accounting for the lack of representation of educational psychology content in introductory psychology textbooks.IntelligenceMain article: Intelligence and educationIntelligence is an important factor in how the individual responds to education. Those who have higher scores of intelligence-metrics tend to perform better at school and go on to higher levels of education. This effect is also observable in the opposite direction, in that education increases measurable intelligence. Studies have shown that while educational attainment is important in predicting intelligence in later life, intelligence at 53 is more closely correlated to intelligence at 8 years old than to educational attainment.Learning modalitiesMain article: Learning modalitiesThere has been much interest in learning modalities and styles over the last two decades. The most commonly employed learning modalities are:  Visual: learning based on observation and seeing what is being learned.  Auditory: learning based on listening to instructions/information.  Kinesthetic: learning based on movement, e.g. hands-on work and engaging in activities.Other commonly employed modalities include musical, interpersonal, verbal, logical, and intrapersonal.Dunn and Dunn focused on identifying relevant stimuli that may influence learning and manipulating the school environment, at about the same time as Joseph Renzulli recommended varying teaching strategies. Howard Gardner identified a wide range of modalities in his Multiple Intelligences theories. The Myers-Briggs Type Indicator and Keirsey Temperament Sorter, based on the works of Jung, focus on understanding how people's personality affects the way they interact personally, and how this affects the way individuals respond to each other within the learning environment. The work of David Kolb and Anthony Gregorc's Type Delineator follows a similar but more simplified approach.Some theories propose that all individuals benefit from a variety of learning modalities, while others suggest that individuals may have preferred learning styles, learning more easily through visual or kinesthetic experiences. A consequence of the latter theory is that effective teaching should present a variety of teaching methods which cover all three learning modalities so that different students have equal opportunities to learn in a way that is effective for them. Guy Claxton has questioned the extent that learning styles such as Visual, Auditory and Kinesthetic are helpful, particularly as they can have a tendency to label children and therefore restrict learning. Recent research has argued, there is no adequate evidence base to justify incorporating learning styles assessments into general educational practice.Mind, brain, and educationEducational neuroscience is an emerging scientific field that brings together researchers in cognitive neuroscience, developmental cognitive neuroscience, educational psychology, educational technology, education theory and other related disciplines to explore the interactions between biological processes and education. Researchers in educational neuroscience investigate the neural mechanisms of reading, numerical cognition, attention, and their attendant difficulties including dyslexia, dyscalculia, and ADHD as they relate to education. Several academic institutions around the world are beginning to devote resources to the establishment of educational neuroscience research.PhilosophyJohn Locke's work Some Thoughts Concerning Education was written in 1693 and still reflects traditional education priorities in the Western world.Main article: Philosophy of educationAs an academic field, philosophy of education is the philosophical study of education and its problems its central subject matter is education, and its methods are those of philosophy. The philosophy of education may be either the philosophy of the process of education or the philosophy of the discipline of education. That is, it may be part of the discipline in the sense of being concerned with the aims, forms, methods, or results of the process of educating or being educated; or it may be metadisciplinary in the sense of being concerned with the concepts, aims, and methods of the discipline. As such, it is both part of the field of education and a field of applied philosophy, drawing from fields of metaphysics, epistemology, axiology and the philosophical approaches to address questions in and about pedagogy, education policy, and curriculum, as well as the process of learning, to name a few. For example, it might study what constitutes upbringing and education, the values and norms revealed through upbringing and educational practices, the limits and legitimization of education as an academic discipline, and the relation between education theory and practice.PurposeThere is no broad consensus as to what education's chief aim or aims are or should be. Different places, and at different times, have used educational systems for different purposes. The Prussian education system in the 19th century, for example, wanted to turn boys and girls into adults who would serve the state's political goals.Some authors stress its value to the individual, emphasizing its potential for positively influencing students' personal development, promoting autonomy, forming a cultural identity or establishing a career or occupation. Other authors emphasize education's contributions to societal purposes, including good citizenship, shaping students into productive members of society, thereby promoting society's general economic development, and preserving cultural values.The purpose of education in a given time and place affects who is taught, what is taught, and how the education system behaves. For example, in the 21st century, many countries treat education as a positional good. In this competitive approach, people want their own students to get a better education than other students. This approach can lead to unfair treatment of some students, especially those from disadvantaged or marginalized groups. For example, in this system, a city's school system may draw school district boundaries so that nearly all the students in one school are from low-income families, and that nearly all the students in the neighboring schools come from more affluent families, even though concentrating low-income students in one school results in worse educational achievement for the entire school system.CurriculumMain articles: Curriculum, Curriculum theory, and List of academic disciplinesIn formal education, a curriculum is the set of courses and their content offered at a school or university. As an idea, curriculum stems from the Latin word for race course, referring to the course of deeds and experiences through which children grow to become mature adults. A curriculum is prescriptive and is based on a more general syllabus which merely specifies what topics must be understood and to what level to achieve a particular grade or standard.An academic discipline is a branch of knowledge which is formally taught, either at the university – or via some other such method. Each discipline usually has several sub-disciplines or branches, and distinguishing lines are often both arbitrary and ambiguous. Examples of broad areas of academic disciplines include the natural sciences, mathematics, computer science, social sciences, humanities and applied sciences.InstructionInstruction is the facilitation of another's learning. Instructors in primary and secondary institutions are often called teachers, and they direct the education of students and might draw on many subjects like reading, writing, mathematics, science and history. Instructors in post-secondary institutions might be called teachers, instructors, or professors, depending on the type of institution; and they primarily teach only their specific discipline. Studiesfrom the United States suggest that the quality of teachers is the single most important factor affecting student performance, and that countries which score highly on international tests have multiple policies in place to ensure that the teachers they employ are as effective as possible. With the passing of NCLB in the United States, teachers must be highly qualified.EconomicsMain article: Economics of educationIt has been argued that high rates of education are essential for countries to be able to achieve high levels of economic growth. Empirical analyses tend to support the theoretical prediction that poor countries should grow faster than rich countries because they can adopt cutting-edge technologies already tried and tested by rich countries. However, technology transfer requires knowledgeable managers and engineers who are able to operate new machines or production practices borrowed from the leader in order to close the gap through imitation. Therefore, a country's ability to learn from the leader is a function of its stock of human capital. Recent study of the determinants of aggregate economic growth have stressed the importance of fundamental economic institutions and the role of cognitive skills.At the level of the individual, there is a large literature, generally related to the work of Jacob Mincer, on how earnings are related to the schooling and other human capital. This work has motivated many studies, but is also controversial. The chief controversies revolve around how to interpret the impact of schooling. Some students who have indicated a high potential for learning, by testing with a high intelligence quotient, may not achieve their full academic potential, due to financial difficulties.Economists Samuel Bowles and Herbert Gintis argued in 1976 that there was a fundamental conflict in American schooling between the egalitarian goal of democratic participation and the inequalities implied by the continued profitability of capitalist production.DevelopmentComputer-supported group learningThe world is changing at an ever quickening rate, which means that a lot of knowledge becomes obsolete and inaccurate more quickly. The emphasis is therefore shifting to teaching the skills of learning: to picking up new knowledge quickly and in as agile a way as possible. Finnish schools have begun to move away from the regular subject-focused curricula, introducing instead developments like phenomenon-based learning, where students study concepts like climate change instead. There are also active educational interventions to implement programs and paths specific to non-traditional students, such as first generation students.Education is also becoming a commodity no longer reserved for children; adults need it too. Some governmental bodies, like the Finnish Innovation Fund Sitra in Finland, have proposed compulsory lifelong education.Studies found that automation is likely to eliminate nearly half the jobs in developed countries during roughly the next two decades. Automation is therefore considered to be a major factor in a race between education and technology. Automation technologies and their application may render certain currently taught skills and knowledge redundant while increasing the need for other curricula – such as material related to the application of automation. It has been argued that formal education is teaching workers the wrong things, and that deep reform is essential to facilitate the development of digital knowledge and technical skills, as well as nonroutine cognitive and noncognitive skills and that the formal state-organized education system – which is built on the Industrial Revolution model and focuses on IQ and memorization is losing relevance. FSchools were found rarely teach in forms of learning by doing, and many children above a certain age hate school in terms of the material and subjects being taught, with much of it being a waste of time that gets forgotten quickly and is useless in modern society. Moreover, the material currently being taught may not be taught in a highly time-efficient manner and analyzing educational issues over time and using relevant forms of student feedback in efficiency analysis were found to be important. Some research investigates how education can facilitate students' interest in topics – and jobs – that scientific research, data, economic players, financial markets, and other economic mechanisms consider important to contemporary and future human civilization and states. Research and data indicate future environmental conditions will be far more dangerous than currently believed, with a review concluding that the current challenges that humanity faces are enormous. The effective resolval of such challenges may require novel lesson plans tailored towards skills and knowledge found to be both required and reasonable to be taught at the respective age with the respective methodology despite novel technological computation and information retrieval technologies such as smartphones, mathematical software and the World Wide Web. Environmental education is not widely taught extensively or facilitated while being potentially important to the protection and generation of – often unquantified – economic value such as clean air that agents of the economy can breathe. Education is often considered to be a national investment which may not always optimize for cost-efficiency while optimizing only in terms of contemporary economic value metrics or evaluations such as of finance and GDP without consideration of economic values or priorizations beyond these tools such as minimized marine pollution and maximized climate change mitigation. Researchers found that there is a growing disconnect between humans and nature and that schools are not properly preparing students to become the scientists of tomorrow. They also find that critical thought, social responsibility, health and safety are often neglected. According to UNESCO, for a country to meet the basic needs of its people, the teaching of science is a strategic imperative.One example of a skill not commonly taught in formal education systems around the world but increasingly critical to both the individuals' lives and modern society at large is digital media literacy – the ability to access, analyze, evaluate, create, and act using all forms of modern ICTs, with scientists calling for inclusion of it in curricula as well as for adult education.Studies have shown that active learning rarely applied in schools is highly efficacious. Studies found that massive open online courses offer a pathway to employment that currently bypasses conventional universities and their degree programs while often being more relevant to contemporary economic activities and the students' interests. Such online courses are not commonly part of formal education but are typically both completed and selected entirely on behalf of the student, sometimes with the support of peers over online forums. In contrast, blended learning merges online education with forms of face‐to‐face communication and traditional class-based education in classrooms, revealing itself to have the general capacity for increasingly relevant, resource-efficient and effective approaches to education. Deploying, using, and managing various tools or platforms for education typically imply an increase in economic investment. Expenses for education are often large with many calling for further increases. Potential policies for the development of international open source educational software using latest technologies may minimize costs, hardware requirements, problem-resolval efforts and deployment-times while increasing robustness, security and functional features of the software.COVID-19 pandemicSee also: Impact of the COVID-19 pandemic on educationBeginning in early 2020, the COVID-19 pandemic disrupted education systems throughout the world, affecting nearly 1.6 billion learners in more than 190 countries. Closures of schools and other learning spaces have impacted 94 percent of the world's student population, up to 99 percent in low and lower-middle income countries. Many schools made alternative plans during the pandemic, leading to a variety of in-person, hybrid, and online-only plans, which led to challenges for many students, teachers, and families including children with learning disabilities and those learning in a language that is not their native one. As of September 30, 2020 there were 27 countries that had localized school closures. In the United States, an estimated 55.1 million students were forced to cease in-person instruction as of April 10, 2020. A switch to a virtual learning experience is particularly challenging for families that cannot afford the proper technology, such as laptops, printers, or a reliable Internet connection. When schools close, parents are often asked to facilitate the learning of children at home and can struggle to perform this task. This is especially true for parents with limited education and resources. Students who require special education found it difficult to progress through the curriculum without tools and support that they require. Polling suggests that schools that serve a majority of students of color are far less likely to have access to the technology needed for remote learning. Only 66% of Black households in the U.S. had home broadband service in 2019. Only 45% of Black Americans owned a desktop or laptop computer in 2015. Without access to the internet or a computer, Black parents are at a disadvantage in educating their children. The mental health of students has been greatly impacted due to the pandemic. It is estimated that three in ten participating in school at home have had their emotional and mental health negatively impacted. Similarly, the social lives of students have also been upended and this has been detrimental to the health of students worldwide which has also negatively impacted educational quality. This will be an issue for years to come. COVID-19 has shone a light on opportunity gaps and it will be up to educators and policymakers to direct the necessary resources to mitigating them in the coming years. A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as programs. These programs enable computers to perform a wide range of tasks. A computer system is a complete computer that includes the hardware, operating system, and peripheral equipment needed and used for full operation. This term may also refer to a group of computers that are linked and function together, such as a computer network or computer cluster.A broad range of industrial and consumer products use computers as control systems. Simple special-purpose devices like microwave ovens and remote controls are included, as are factory devices like industrial robots and computer-aided design, as well as general-purpose devices like personal computers and mobile devices like smartphones. Computers power the Internet, which links billions of other computers and users.Early computers were meant to be used only for calculations. Simple manual instruments like the abacus have aided people in doing calculations since ancient times. Early in the Industrial Revolution, some mechanical devices were built to automate long tedious tasks, such as guiding patterns for looms. More sophisticated electrical machines did specialized analog calculations in the early 20th century. The first digital electronic calculating machines were developed during World War II. The first semiconductor transistors in the late 1940s were followed by the silicon-based MOSFET and monolithic integrated circuit chip technologies in the late 1950s, leading to the microprocessor and the microcomputer revolution in the 1970s. The speed, power and versatility of computers have been increasing dramatically ever since then, with transistor counts increasing at a rapid pace, leading to the Digital Revolution during the late 20th to early 21st centuries.Conventionally, a modern computer consists of at least one processing element, typically a central processing unit in the form of a microprocessor, along with some type of computer memory, typically semiconductor memory chips. The processing element carries out arithmetic and logical operations, and a sequencing and control unit can change the order of operations in response to stored information. Peripheral devices include input devices, output devices, and input/output devices that perform both functions. Peripheral devices allow information to be retrieved from an external source and they enable the result of operations to be saved and retrieved. According to the Oxford English Dictionary, the first known use of computer was in a 1613 book called The Yong Mans Gleanings by the English writer Richard Brathwait: I haue read the truest computer of Times, and the best Arithmetician that euer breathed, and he reduceth thy dayes into a short number. This usage of the term referred to a human computer, a person who carried out calculations or computations. The word continued with the same meaning until the middle of the 20th century. During the latter part of this period women were often hired as computers because they could be paid less than their male counterparts. By 1943, most human computers were women.The Online Etymology Dictionary gives the first attested use of computer in the 1640s, meaning 'one who calculates'; this is an agent noun from compute. The Online Etymology Dictionary states that the use of the term to mean 'calculating machine' is from 1897. The Online Etymology Dictionary indicates that the modern use of the term, to mean 'programmable digital electronic computer' dates from 1945 under this name; theoretical from 1937, as Turing machine.HistoryMain articles: History of computing hardware and History of computingPre-20th centuryThe Ishango bone, a bone tool dating back to prehistoric Africa.Devices have been used to aid computation for thousands of years, mostly using one-to-one correspondence with fingers. The earliest counting device was probably a form of tally stick. Later record keeping aids throughout the Fertile Crescent included calculi which represented counts of items, probably livestock or grains, sealed in hollow unbaked clay containers. The use of counting rods is one example.The Chinese suanpan. The number represented on this abacus is 6,302,715,408.The abacus was initially used for arithmetic tasks. The Roman abacus was developed from devices used in Babylonia as early as 2400 BC. Since then, many other forms of reckoning boards or tables have been invented. In a medieval European counting house, a checkered cloth would be placed on a table, and markers moved around on it according to certain rules, as an aid to calculating sums of money.The Antikythera mechanism, dating back to ancient Greece circa 150–100 BC, is an early analog computing device.The Antikythera mechanism is believed to be the earliest mechanical analog computer, according to Derek J. de Solla Price. It was designed to calculate astronomical positions. It was discovered in 1901 in the Antikythera wreck off the Greek island of Antikythera, between Kythera and Crete, and has been dated to c. 100 BC. Devices of a level of complexity comparable to that of the Antikythera mechanism would not reappear until a thousand years later.Many mechanical aids to calculation and measurement were constructed for astronomical and navigation use. The planisphere was a star chart invented by Abū Rayhān al-Bīrūnī in the early 11th century. The astrolabe was invented in the Hellenistic world in either the 1st or 2nd centuries BC and is often attributed to Hipparchus. A combination of the planisphere and dioptra, the astrolabe was effectively an analog computer capable of working out several different kinds of problems in spherical astronomy. An astrolabe incorporating a mechanical calendar computer and gear-wheels was invented by Abi Bakr of Isfahan, Persia in 1235. Abū Rayhān al-Bīrūnī invented the first mechanical geared lunisolar calendar astrolabe, an early fixed-wired knowledge processing machine with a gear train and gear-wheels, c. 1000 AD.The sector, a calculating instrument used for solving problems in proportion, trigonometry, multiplication and division, and for various functions, such as squares and cube roots, was developed in the late 16th century and found application in gunnery, surveying and navigation.The planimeter was a manual instrument to calculate the area of a closed figure by tracing over it with a mechanical linkage.A slide rule.The slide rule was invented around 1620–1630 by the English clergyman William Oughtred, shortly after the publication of the concept of the logarithm. It is a hand-operated analog computer for doing multiplication and division. As slide rule development progressed, added scales provided reciprocals, squares and square roots, cubes and cube roots, as well as transcendental functions such as logarithms and exponentials, circular and hyperbolic trigonometry and other functions. Slide rules with special scales are still used for quick performance of routine calculations, such as the E6B circular slide rule used for time and distance calculations on light aircraft.In the 1770s, Pierre Jaquet-Droz, a Swiss watchmaker, built a mechanical doll that could write holding a quill pen. By switching the number and order of its internal wheels different letters, and hence different messages, could be produced. In effect, it could be mechanically programmed to read instructions. Along with two other complex machines, the doll is at the Musée d'Art et d'Histoire of Neuchâtel, Switzerland, and still operates.In 1831–1835, mathematician and engineer Giovanni Plana devised a Perpetual Calendar machine, which, though a system of pulleys and cylinders and over, could predict the perpetual calendar for every year from AD 0 to AD 4000, keeping track of leap years and varying day length. The tide-predicting machine invented by the Scottish scientist Sir William Thomson in 1872 was of great utility to navigation in shallow waters. It used a system of pulleys and wires to automatically calculate predicted tide levels for a set period at a particular location.The differential analyser, a mechanical analog computer designed to solve differential equations by integration, used wheel-and-disc mechanisms to perform the integration. In 1876, Sir William Thomson had already discussed the possible construction of such calculators, but he had been stymied by the limited output torque of the ball-and-disk integrators. In a differential analyzer, the output of one integrator drove the input of the next integrator, or a graphing output. The torque amplifier was the advance that allowed these machines to work. Starting in the 1920s, Vannevar Bush and others developed mechanical differential analyzers.First computerA portion of Babbage's Difference engine.Charles Babbage, an English mechanical engineer and polymath, originated the concept of a programmable computer. Considered the father of the computer, he conceptualized and invented the first mechanical computer in the early 19th century. After working on his revolutionary difference engine, designed to aid in navigational calculations, in 1833 he realized that a much more general design, an Analytical Engine, was possible. The input of programs and data was to be provided to the machine via punched cards, a method being used at the time to direct mechanical looms such as the Jacquard loom. For output, the machine would have a printer, a curve plotter and a bell. The machine would also be able to punch numbers onto cards to be read in later. The Engine incorporated an arithmetic logic unit, control flow in the form of conditional branching and loops, and integrated memory, making it the first design for a general-purpose computer that could be described in modern terms as Turing-complete.The machine was about a century ahead of its time. All the parts for his machine had to be made by hand – this was a major problem for a device with thousands of parts. Eventually, the project was dissolved with the decision of the British Government to cease funding. Babbage's failure to complete the analytical engine can be chiefly attributed to political and financial difficulties as well as his desire to develop an increasingly sophisticated computer and to move ahead faster than anyone else could follow. Nevertheless, his son, Henry Babbage, completed a simplified version of the analytical engine's computing unit in 1888. He gave a successful demonstration of its use in computing tables in 1906.Analog computersMain article: Analog computerSir William Thomson's third tide-predicting machine design, 1879–81During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for computation. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers. The first modern analog computer was a tide-predicting machine, invented by Sir William Thomson in 1872. The differential analyser, a mechanical analog computer designed to solve differential equations by integration using wheel-and-disc mechanisms, was conceptualized in 1876 by James Thomson, the elder brother of the more famous Sir William Thomson.The art of mechanical analog computing reached its zenith with the differential analyzer, built by H. L. Hazen and Vannevar Bush at MIT starting in 1927. This built on the mechanical integrators of James Thomson and the torque amplifiers invented by H. W. Nieman. A dozen of these devices were built before their obsolescence became obvious. By the 1950s, the success of digital electronic computers had spelled the end for most analog computing machines, but analog computers remained in use during the 1950s in some specialized applications such as education and aircraft.Digital computersElectromechanicalBy 1938, the United States Navy had developed an electromechanical analog computer small enough to use aboard a submarine. This was the Torpedo Data Computer, which used trigonometry to solve the problem of firing a torpedo at a moving target. During World War II similar devices were developed in other countries as well.Replica of Zuse's Z3, the first fully automatic, digital computer.Early digital computers were electromechanical; electric switches drove mechanical relays to perform the calculation. These devices had a low operating speed and were eventually superseded by much faster all-electric computers, originally using vacuum tubes. The Z2, created by German engineer Konrad Zuse in 1939, was one of the earliest examples of an electromechanical relay computer.In 1941, Zuse followed his earlier machine up with the Z3, the world's first working electromechanical programmable, fully automatic digital computer. The Z3 was built with 2000 relays, implementing a 22 bit word length that operated at a clock frequency of about 5–10 Hz. Program code was supplied on punched film while data could be stored in 64 words of memory or supplied from the keyboard. It was quite similar to modern machines in some respects, pioneering numerous advances such as floating-point numbers. Rather than the harder-to-implement decimal system, using a binary system meant that Zuse's machines were easier to build and potentially more reliable, given the technologies available at that time. The Z3 was not itself a universal computer but could be extended to be Turing complete.Vacuum tubes and digital electronic circuitsPurely electronic circuit elements soon replaced their mechanical and electromechanical equivalents, at the same time that digital calculation replaced analog. The engineer Tommy Flowers, working at the Post Office Research Station in London in the 1930s, began to explore the possible use of electronics for the telephone exchange. Experimental equipment that he built in 1934 went into operation five years later, converting a portion of the telephone exchange network into an electronic data processing system, using thousands of vacuum tubes. In the US, John Vincent Atanasoff and Clifford E. Berry of Iowa State University developed and tested the Atanasoff–Berry Computer in 1942, the first automatic electronic digital computer. This design was also all-electronic and used about 300 vacuum tubes, with capacitors fixed in a mechanically rotating drum for memory.Two women are seen by the Colossus computer.Colossus, the first electronic digital programmable computing device, was used to break German ciphers during World War II. It is seen here in use at Bletchley Park in 1943.During World War II, the British code-breakers at Bletchley Park achieved a number of successes at breaking encrypted German military communications. The German encryption machine, Enigma, was first attacked with the help of the electro-mechanical bombes which were often run by women. To crack the more sophisticated German Lorenz SZ 40/42 machine, used for high-level Army communications, Max Newman and his colleagues commissioned Flowers to build the Colossus. He spent eleven months from early February 1943 designing and building the first Colossus. After a functional test in December 1943, Colossus was shipped to Bletchley Park, where it was delivered on 18 January 1944 and attacked its first message on 5 February.Colossus was the world's first electronic digital programmable computer. It used a large number of valves. It had paper-tape input and was capable of being configured to perform a variety of boolean logical operations on its data, but it was not Turing-complete. Nine Mk II Colossi were built. Colossus Mark I contained 1,500 thermionic valves, but Mark II with 2,400 valves, was both five times faster and simpler to operate than Mark I, greatly speeding the decoding process.ENIAC was the first electronic, Turing-complete device, and performed ballistics trajectory calculations for the United States Army.The ENIAC was the first electronic programmable computer built in the U.S. Although the ENIAC was similar to the Colossus, it was much faster, more flexible, and it was Turing-complete. Like the Colossus, a program on the ENIAC was defined by the states of its patch cables and switches, a far cry from the stored program electronic machines that came later. Once a program was written, it had to be mechanically set into the machine with manual resetting of plugs and switches. The programmers of the ENIAC were six women, often known collectively as the ENIAC girls.It combined the high speed of electronics with the ability to be programmed for many complex problems. It could add or subtract 5000 times a second, a thousand times faster than any other machine. It also had modules to multiply, divide, and square root. High speed memory was limited to 20 words. Built under the direction of John Mauchly and J. Presper Eckert at the University of Pennsylvania, ENIAC's development and construction lasted from 1943 to full operation at the end of 1945. The machine was huge, weighing 30 tons, using 200 kilowatts of electric power and contained over 18,000 vacuum tubes, 1,500 relays, and hundreds of thousands of resistors, capacitors, and inductors.Modern computersConcept of modern computerThe principle of the modern computer was proposed by Alan Turing in his seminal 1936 paper, On Computable Numbers. Turing proposed a simple device that he called Universal Computing machine and that is now known as a universal Turing machine. He proved that such a machine is capable of computing anything that is computable by executing instructions stored on tape, allowing the machine to be programmable. The fundamental concept of Turing's design is the stored program, where all the instructions for computing are stored in memory. Von Neumann acknowledged that the central concept of the modern computer was due to this paper. Turing machines are to this day a central object of study in theory of computation. Except for the limitations imposed by their finite memory stores, modern computers are said to be Turing-complete, which is to say, they have algorithm execution capability equivalent to a universal Turing machine.Stored programsMain article: Stored-program computerThree tall racks containing electronic circuit boardsA section of the Manchester Baby, the first electronic stored-program computerEarly computing machines had fixed programs. Changing its function required the re-wiring and re-structuring of the machine. With the proposal of the stored-program computer this changed. A stored-program computer includes by design an instruction set and can store in memory a set of instructions that details the computation. The theoretical basis for the stored-program computer was laid by Alan Turing in his 1936 paper. In 1945, Turing joined the National Physical Laboratory and began work on developing an electronic stored-program digital computer. His 1945 report Proposed Electronic Calculator was the first specification for such a device. John von Neumann at the University of Pennsylvania also circulated his First Draft of a Report on the EDVAC in 1945.The Manchester Baby was the world's first stored-program computer. It was built at the University of Manchester in England by Frederic C. Williams, Tom Kilburn and Geoff Tootill, and ran its first program on 21 June 1948. It was designed as a testbed for the Williams tube, the first random-access digital storage device. Although the computer was considered small and primitive by the standards of its time, it was the first working machine to contain all of the elements essential to a modern electronic computer. As soon as the Baby had demonstrated the feasibility of its design, a project was initiated at the university to develop it into a more usable computer, the Manchester Mark 1. Grace Hopper was the first person to develop a compiler for programming language.The Mark 1 in turn quickly became the prototype for the Ferranti Mark 1, the world's first commercially available general-purpose computer. Built by Ferranti, it was delivered to the University of Manchester in February 1951. At least seven of these later machines were delivered between 1953 and 1957, one of them to Shell labs in Amsterdam. In October 1947, the directors of British catering company J. Lyons & Company decided to take an active role in promoting the commercial development of computers. The LEO I computer became operational in April 1951 and ran the world's first regular routine office computer job.TransistorsMain articles: Transistor and History of the transistorFurther information: Transistor computer and MOSFETBipolar junction transistor The concept of a field-effect transistor was proposed by Julius Edgar Lilienfeld in 1925. John Bardeen and Walter Brattain, while working under William Shockley at Bell Labs, built the first working transistor, the point-contact transistor, in 1947, which was followed by Shockley's bipolar junction transistor in 1948. From 1955 onwards, transistors replaced vacuum tubes in computer designs, giving rise to the second generation of computers. Compared to vacuum tubes, transistors have many advantages: they are smaller, and require less power than vacuum tubes, so give off less heat. Junction transistors were much more reliable than vacuum tubes and had longer, indefinite, service life. Transistorized computers could contain tens of thousands of binary logic circuits in a relatively compact space. However, early junction transistors were relatively bulky devices that were difficult to manufacture on a mass-production basis, which limited them to a number of specialised applications.At the University of Manchester, a team under the leadership of Tom Kilburn designed and built a machine using the newly developed transistors instead of valves. Their first transistorised computer and the first in the world, was operational by 1953, and a second version was completed there in April 1955. However, the machine did make use of valves to generate its 125 kHz clock waveforms and in the circuitry to read and write on its magnetic drum memory, so it was not the first completely transistorized computer. That distinction goes to the Harwell CADET of 1955, built by the electronics division of the Atomic Energy Research Establishment at Harwell.MOSFET, showing gate, body, source and drain terminals. The gate is separated from the body by an insulating layer.The metal–oxide–silicon field-effect transistor, also known as the MOS transistor, was invented by Mohamed M. Atalla and Dawon Kahng at Bell Labs in 1959. It was the first truly compact transistor that could be miniaturised and mass-produced for a wide range of uses. With its high scalability, and much lower power consumption and higher density than bipolar junction transistors, the MOSFET made it possible to build high-density integrated circuits. In addition to data processing, it also enabled the practical use of MOS transistors as memory cell storage elements, leading to the development of MOS semiconductor memory, which replaced earlier magnetic-core memory in computers. The MOSFET led to the microcomputer revolution, and became the driving force behind the computer revolution. The MOSFET is the most widely used transistor in computers, and is the fundamental building block of digital electronics.Integrated circuitsMain articles: Integrated circuit and Invention of the integrated circuitFurther information: Planar process and MicroprocessorThe next great advance in computing power came with the advent of the integrated circuit. The idea of the integrated circuit was first conceived by a radar scientist working for the Royal Radar Establishment of the Ministry of Defence, Geoffrey W.A. Dummer. Dummer presented the first public description of an integrated circuit at the Symposium on Progress in Quality Electronic Components in Washington, D.C. on 7 May 1952.The first working ICs were invented by Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor. Kilby recorded his initial ideas concerning the integrated circuit in July 1958, successfully demonstrating the first working integrated example on 12 September 1958. In his patent application of 6 February 1959, Kilby described his new device as a body of semiconductor material... wherein all the components of the electronic circuit are completely integrated. However, Kilby's invention was a hybrid integrated circuit, rather than a monolithic integrated circuit chip. Kilby's IC had external wire connections, which made it difficult to mass-produce.Noyce also came up with his own idea of an integrated circuit half a year later than Kilby. Noyce's invention was the first true monolithic IC chip. His chip solved many practical problems that Kilby's had not. Produced at Fairchild Semiconductor, it was made of silicon, whereas Kilby's chip was made of germanium. Noyce's monolithic IC was fabricated using the planar process, developed by his colleague Jean Hoerni in early 1959. In turn, the planar process was based on Mohamed M. Atalla's work on semiconductor surface passivation by silicon dioxide in the late 1950s.Modern monolithic ICs are predominantly MOS integrated circuits, built from MOSFETs. The earliest experimental MOS IC to be fabricated was a 16-transistor chip built by Fred Heiman and Steven Hofstein at RCA in 1962. General Microelectronics later introduced the first commercial MOS IC in 1964, developed by Robert Norman. Following the development of the self-aligned gate MOS transistor by Robert Kerwin, Donald Klein and John Sarace at Bell Labs in 1967, the first silicon-gate MOS IC with self-aligned gates was developed by Federico Faggin at Fairchild Semiconductor in 1968. The MOSFET has since become the most critical device component in modern ICs.The development of the MOS integrated circuit led to the invention of the microprocessor, and heralded an explosion in the commercial and personal use of computers. While the subject of exactly which device was the first microprocessor is contentious, partly due to lack of agreement on the exact definition of the term microprocessor, it is largely undisputed that the first single-chip microprocessor was the Intel 4004, designed and realized by Federico Faggin with his silicon-gate MOS IC technology, along with Ted Hoff, Masatoshi Shima and Stanley Mazor at Intel. In the early 1970s, MOS IC technology enabled the integration of more than 10,000 transistors on a single chip.System on a Chip are complete computers on a microchip the size of a coin. They may or may not have integrated RAM and flash memory. If not integrated, the RAM is usually placed directly above or below the SoC, and the flash memory is usually placed right next to the SoC, this all done to improve data transfer speeds, as the data signals don't have to travel long distances. Since ENIAC in 1945, computers have advanced enormously, with modern SoCs being the size of a coin while also being hundreds of thousands of times more powerful than ENIAC, integrating billions of transistors, and consuming only a few watts of power.Mobile computersThe first mobile computers were heavy and ran from mains power. The 50 lb IBM 5100 was an early example. Later portables such as the Osborne 1 and Compaq Portable were considerably lighter but still needed to be plugged in. The first laptops, such as the Grid Compass, removed this requirement by incorporating batteries – and with the continued miniaturization of computing resources and advancements in portable battery life, portable computers grew in popularity in the 2000s. The same developments allowed manufacturers to integrate computing resources into cellular mobile phones by the early 2000s.These smartphones and tablets run on a variety of operating systems and recently became the dominant computing device on the market. These are powered by System on a Chip, which are complete computers on a microchip the size of a coin. Art is a wide range of human activities that involve creative imagination and an aim to express technical proficiency, beauty, emotional power, or conceptual ideas.There is no generally agreed definition of what constitutes art, and ideas have changed over time. The three classical branches of visual art are painting, sculpture, and architecture. Theatre, dance, and other performing arts, as well as literature, music, film and other media such as interactive media, are included in a broader definition of the arts. Until the 17th century, art referred to any skill or mastery and was not differentiated from crafts or sciences. In modern usage after the 17th century, where aesthetic considerations are paramount, the fine arts are separated and distinguished from acquired skills in general, such as the decorative or applied arts.The nature of art and related concepts, such as creativity and interpretation, are explored in a branch of philosophy known as aesthetics. The resulting artworks are studied in the professional fields of art criticism and the history of art. In the perspective of the history of art, artistic works have existed for almost as long as humankind: from early pre-historic art to contemporary art; however, some theorists feel that the typical concept of artistic works fits less well outside modern Western societies. One early sense of the definition of art is closely related to the older Latin meaning, which roughly translates to skill or craft, as associated with words such as artisan. English words derived from this meaning include artifact, artificial, artifice, medical arts, and military arts. However, there are many other colloquial uses of the word, all with some relation to its etymology.20th-century bottle, Twa peoples, Rwanda, Artistic works may serve practical functions, in addition to their decorative value.Over time, philosophers like Plato, Aristotle, Socrates and Kant, among others, questioned the meaning of art. Several dialogues in Plato tackle questions about art: Socrates says that poetry is inspired by the muses, and is not rational. He speaks approvingly of this, and other forms of divine madness in the Phaedrus, and yet in the Republic wants to outlaw Homer's great poetic art, and laughter as well. In Ion, Socrates gives no hint of the disapproval of Homer that he expresses in the Republic. The dialogue Ion suggests that Homer's Iliad functioned in the ancient Greek world as the Bible does today in the modern Christian world: as divinely inspired literary art that can provide moral guidance, if only it can be properly interpreted.With regards to the literary art and the musical arts, Aristotle considered epic poetry, tragedy, comedy, Dithyrambic poetry and music to be mimetic or imitative art, each varying in imitation by medium, object, and manner. For example, music imitates with the media of rhythm and harmony, whereas dance imitates with rhythm alone, and poetry with language. The forms also differ in their object of imitation. Comedy, for instance, is a dramatic imitation of men worse than average; whereas tragedy imitates men slightly better than average. Lastly, the forms differ in their manner of imitation—through narrative or character, through change or no change, and through drama or no drama. Aristotle believed that imitation is natural to mankind and constitutes one of mankind's advantages over animals.The more recent and specific sense of the word art as an abbreviation for creative art or fine art emerged in the early 17th century. Fine art refers to a skill used to express the artist's creativity, or to engage the audience's aesthetic sensibilities, or to draw the audience towards consideration of more refined or finer work of art.Within this latter sense, the word art may refer to several things: a study of a creative skill, a process of using the creative skill, a product of the creative skill, or the audience's experience with the creative skill. The creative arts are a collection of disciplines which produce artworks that are compelled by a personal drive and convey a message, mood, or symbolism for the perceiver to interpret. Art is something that stimulates an individual's thoughts, emotions, beliefs, or ideas through the senses. Works of art can be explicitly made for this purpose or interpreted on the basis of images or objects. For some scholars, such as Kant, the sciences and the arts could be distinguished by taking science as representing the domain of knowledge and the arts as representing the domain of the freedom of artistic expression.Often, if the skill is being used in a common or practical way, people will consider it a craft instead of art. Likewise, if the skill is being used in a commercial or industrial way, it may be considered commercial art instead of fine art. On the other hand, crafts and design are sometimes considered applied art. Some art followers have argued that the difference between fine art and applied art has more to do with value judgments made about the art than any clear definitional difference. However, even fine art often has goals beyond pure creativity and self-expression. The purpose of works of art may be to communicate ideas, such as in politically, spiritually, or philosophically motivated art; to create a sense of beauty; to explore the nature of perception; for pleasure; or to generate strong emotions. The purpose may also be seemingly nonexistent.The nature of art has been described by philosopher Richard Wollheim as one of the most elusive of the traditional problems of human culture. Art has been defined as a vehicle for the expression or communication of emotions and ideas, a means for exploring and appreciating formal elements for their own sake, and as mimesis or representation. Art as mimesis has deep roots in the philosophy of Aristotle. Leo Tolstoy identified art as a use of indirect means to communicate from one person to another. Benedetto Croce and R. G. Collingwood advanced the idealist view that art expresses emotions, and that the work of art therefore essentially exists in the mind of the creator. The theory of art as form has its roots in the philosophy of Kant, and was developed in the early 20th century by Roger Fry and Clive Bell. More recently, thinkers influenced by Martin Heidegger have interpreted art as the means by which a community develops for itself a medium for self-expression and interpretation. George Dickie has offered an institutional theory of art that defines a work of art as any artifact upon which a qualified person or persons acting on behalf of the social institution commonly referred to as the art world has conferred the status of candidate for appreciation. Larry Shiner has described fine art as not an essence or a fate but something we have made. Art as we have generally understood it is a European invention barely two hundred years old.Art may be characterized in terms of mimesis, narrative, expression, communication of emotion, or other qualities. During the Romantic period, art came to be seen as a special faculty of the human mind to be classified with religion and science.HistoryMain article: History of artVenus of Willendorf, circa 24,000–22,000 BPBack of a Renaissance oval basin or dish, in the Metropolitan Museum of ArtA shell engraved by Homo erectus was determined to be between 430,000 and 540,000 years old. A set of eight 130,000 years old white-tailed eagle talons bear cut marks and abrasion that indicate manipulation by neanderthals, possibly for using it as jewelry. A series of tiny, drilled snail shells about 75,000 years old—were discovered in a South African cave. Containers that may have been used to hold paints have been found dating as far back as 100,000 years.Sculptures, cave paintings, rock paintings and petroglyphs from the Upper Paleolithic dating to roughly 40,000 years ago have been found, but the precise meaning of such art is often disputed because so little is known about the cultures that produced them.Cave painting of a horse from the Lascaux caves, circa 16,000 BPMany great traditions in art have a foundation in the art of one of the great ancient civilizations: Ancient Egypt, Mesopotamia, Persia, India, China, Ancient Greece, Rome, as well as Inca, Maya, and Olmec. Each of these centers of early civilization developed a unique and characteristic style in its art. Because of the size and duration of these civilizations, more of their art works have survived and more of their influence has been transmitted to other cultures and later times. Some also have provided the first records of how artists worked. For example, this period of Greek art saw a veneration of the human physical form and the development of equivalent skills to show musculature, poise, beauty, and anatomically correct proportions.In Byzantine and Medieval art of the Western Middle Ages, much art focused on the expression of subjects about Biblical and religious culture, and used styles that showed the higher glory of a heavenly world, such as the use of gold in the background of paintings, or glass in mosaics or windows, which also presented figures in idealized, patterned forms. Nevertheless, a classical realist tradition persisted in small Byzantine works, and realism steadily grew in the art of Catholic Europe.Renaissance art had a greatly increased emphasis on the realistic depiction of the material world, and the place of humans in it, reflected in the corporeality of the human body, and development of a systematic method of graphical perspective to depict recession in a three-dimensional picture space.The stylized signature of Sultan Mahmud II of the Ottoman Empire was written in Islamic calligraphy. It reads Mahmud Khan son of Abdulhamid is forever victorious.The Great Mosque of Kairouan in Tunisia, also called the Mosque of Uqba, is one of the finest, most significant and best preserved artistic and architectural examples of early great mosques. Dated in its present state from the 9th century, it is the ancestor and model of all the mosques in the western Islamic lands.In the east, Islamic art's rejection of iconography led to emphasis on geometric patterns, calligraphy, and architecture. Further east, religion dominated artistic styles and forms too. India and Tibet saw emphasis on painted sculptures and dance, while religious painting borrowed many conventions from sculpture and tended to bright contrasting colors with emphasis on outlines. China saw the flourishing of many art forms: jade carving, bronzework, pottery, poetry, calligraphy, music, painting, drama, fiction, etc. Chinese styles vary greatly from era to era and each one is traditionally named after the ruling dynasty. So, for example, Tang dynasty paintings are monochromatic and sparse, emphasizing idealized landscapes, but Ming dynasty paintings are busy and colorful, and focus on telling stories via setting and composition. Japan names its styles after imperial dynasties too, and also saw much interplay between the styles of calligraphy and painting. Woodblock printing became important in Japan after the 17th century.Painting by Song dynasty artist Ma Lin, circa 1250. 24.8 × 25.2 cmThe western Age of Enlightenment in the 18th century saw artistic depictions of physical and rational certainties of the clockwork universe, as well as politically revolutionary visions of a post-monarchist world, such as Blake's portrayal of Newton as a divine geometer, or David's propagandistic paintings. This led to Romantic rejections of this in favor of pictures of the emotional side and individuality of humans, exemplified in the novels of Goethe. The late 19th century then saw a host of artistic movements, such as academic art, Symbolism, impressionism and fauvism among others.The history of 20th-century art is a narrative of endless possibilities and the search for new standards, each being torn down in succession by the next. Thus the parameters of Impressionism, Expressionism, Fauvism, Cubism, Dadaism, Surrealism, etc. cannot be maintained very much beyond the time of their invention. Increasing global interaction during this time saw an equivalent influence of other cultures into Western art. Thus, Japanese woodblock prints had an immense influence on impressionism and subsequent development. Later, African sculptures were taken up by Picasso and to some extent by Matisse. Similarly, in the 19th and 20th centuries the West has had huge impacts on Eastern art with originally western ideas like Communism and Post-Modernism exerting a powerful influence.Modernism, the idealistic search for truth, gave way in the latter half of the 20th century to a realization of its unattainability. Theodor W. Adorno said in 1970, It is now taken for granted that nothing which concerns art can be taken for granted any more: neither art itself, nor art in relationship to the whole, nor even the right of art to exist. Relativism was accepted as an unavoidable truth, which led to the period of contemporary art and postmodern criticism, where cultures of the world and of history are seen as changing forms, which can be appreciated and drawn from only with skepticism and irony. Furthermore, the separation of cultures is increasingly blurred and some argue it is now more appropriate to think in terms of a global culture, rather than of regional ones.In The Origin of the Work of Art, Martin Heidegger, a German philosopher and a seminal thinker, describes the essence of art in terms of the concepts of being and truth. He argues that art is not only a way of expressing the element of truth in a culture, but the means of creating it and providing a springboard from which that which is can be revealed. Works of art are not merely representations of the way things are, but actually produce a community's shared understanding. Each time a new artwork is added to any culture, the meaning of what it is to exist is inherently changed.Historically, art and artistic skills and ideas have often been spread through trade. An example of this is the Silk Road, where Hellenistic, Iranian, Indian and Chinese influences could mix. Greco Buddhist art is one of the most vivid examples of this interaction. The meeting of different cultures and worldviews also influenced artistic creation. An example of this is the multicultural port metropolis of Trieste at the beginning of the 20th century, where James Joyce met writers from Central Europe and the artistic development of New York City as a cultural melting pot.Forms, genres, media, and stylesNapoleon I on his Imperial Throne by Ingres, oil on canvasMain article: The artsThe creative arts are often divided into more specific categories, typically along perceptually distinguishable categories such as media, genre, styles, and form. Art form refers to the elements of art that are independent of its interpretation or significance. It covers the methods adopted by the artist and the physical composition of the artwork, primarily non-semantic aspects of the work, such as color, contour, dimension, medium, melody, space, texture, and value. Form may also include visual design principles, such as arrangement, balance, contrast, emphasis, harmony, proportion, proximity, and rhythm.In general there are three schools of philosophy regarding art, focusing respectively on form, content, and context. Extreme Formalism is the view that all aesthetic properties of art are formal. Philosophers almost universally reject this view and hold that the properties and aesthetics of art extend beyond materials, techniques, and form. Unfortunately, there is little consensus on terminology for these informal properties. Some authors refer to subject matter and content – i.e., denotations and connotations – while others prefer terms like meaning and significance.Extreme Intentionalism holds that authorial intent plays a decisive role in the meaning of a work of art, conveying the content or essential main idea, while all other interpretations can be discarded. It defines the subject as the persons or idea represented, and the content as the artist's experience of that subject. For example, the composition of Napoleon I on his Imperial Throne is partly borrowed from the Statue of Zeus at Olympia. As evidenced by the title, the subject is Napoleon, and the content is Ingres's representation of Napoleon as Emperor-God beyond time and space. Similarly to extreme formalism, philosophers typically reject extreme intentionalism, because art may have multiple ambiguous meanings and authorial intent may be unknowable and thus irrelevant. Its restrictive interpretation is socially unhealthy, philosophically unreal, and politically unwise.Finally, the developing theory of post-structuralism studies art's significance in a cultural context, such as the ideas, emotions, and reactions prompted by a work. The cultural context often reduces to the artist's techniques and intentions, in which case analysis proceeds along lines similar to formalism and intentionalism. However, in other cases historical and material conditions may predominate, such as religious and philosophical convictions, sociopolitical and economic structures, or even climate and geography. Art criticism continues to grow and develop alongside art.Skill and craftSee also: Conceptual art and artistic skillThe Creation of Adam, detail from Michelangelo's fresco in the Sistine Chapel Art can connote a sense of trained ability or mastery of a medium. Art can also simply refer to the developed and efficient use of a language to convey meaning with immediacy or depth. Art can be defined as an act of expressing feelings, thoughts, and observations.There is an understanding that is reached with the material as a result of handling it, which facilitates one's thought processes. A common view is that the epithet art, particular in its elevated sense, requires a certain level of creative expertise by the artist, whether this be a demonstration of technical ability, an originality in stylistic approach, or a combination of these two. Traditionally skill of execution was viewed as a quality inseparable from art and thus necessary for its success; for Leonardo da Vinci, art, neither more nor less than his other endeavors, was a manifestation of skill. Rembrandt's work, now praised for its ephemeral virtues, was most admired by his contemporaries for its virtuosity. At the turn of the 20th century, the adroit performances of John Singer Sargent were alternately admired and viewed with skepticism for their manual fluency, yet at nearly the same time the artist who would become the era's most recognized and peripatetic iconoclast, Pablo Picasso, was completing a traditional academic training at which he excelled.Detail of Leonardo da Vinci's Mona Lisa, c. 1503–1506, showing the painting technique of sfumatoA common contemporary criticism of some modern art occurs along the lines of objecting to the apparent lack of skill or ability required in the production of the artistic object. In conceptual art, Marcel Duchamp's Fountain is among the first examples of pieces wherein the artist used found objects and exercised no traditionally recognised set of skills. Tracey Emin's My Bed, or Damien Hirst's The Physical Impossibility of Death in the Mind of Someone Living follow this example and also manipulate the mass media. Emin slept in her bed before placing the result in a gallery as work of art. Hirst came up with the conceptual design for the artwork but has left most of the eventual creation of many works to employed artisans. Hirst's celebrity is founded entirely on his ability to produce shocking concepts. The actual production in many conceptual and contemporary works of art is a matter of assembly of found objects. However, there are many modernist and contemporary artists who continue to excel in the skills of drawing and painting and in creating hands-on works of art.PurposeA Navajo rug made circa 1880Mozarabic Beatus miniature. Spain, late 10th centuryArt has had a great number of different functions throughout its history, making its purpose difficult to abstract or quantify to any single concept. This does not imply that the purpose of Art is vague, but that it has had many unique, different reasons for being created. Some of these functions of Art are provided in the following outline. The different purposes of art may be grouped according to those that are non-motivated, and those that are motivated.Non-motivated functionsThe non-motivated purposes of art are those that are integral to being human, transcend the individual, or do not fulfill a specific external purpose. In this sense, Art, as creativity, is something humans must do by their very nature, and is therefore beyond utility.Basic human instinct for harmony, balance, rhythm. Art at this level is not an action or an object, but an internal appreciation of balance and harmony, and therefore an aspect of being human beyond utility.Imitation, then, is one instinct of our nature. Next, there is the instinct for 'harmony' and rhythm, meters being manifestly sections of rhythm. Persons, therefore, starting with this natural gift developed by degrees their special aptitudes, till their rude improvisations gave birth to Poetry. – AristotleExperience of the mysterious. Art provides a way to experience one's self in relation to the universe. This experience may often come unmotivated, as one appreciates art, music or poetry.The most beautiful thing we can experience is the mysterious. It is the source of all true art and science. – Albert EinsteinExpression of the imagination. Art provides a means to express the imagination in non-grammatic ways that are not tied to the formality of spoken or written language. Unlike words, which come in sequences and each of which have a definite meaning, art provides a range of forms, symbols and ideas with meanings that are malleable.Jupiter's eagle is not, like logical attributes of an object, the concept of the sublimity and majesty of creation, but rather something else—something that gives the imagination an incentive to spread its flight over a whole host of kindred representations that provoke more thought than admits of expression in a concept determined by words. They furnish an aesthetic idea, which serves the above rational idea as a substitute for logical presentation, but with the proper function, however, of animating the mind by opening out for it a prospect into a field of kindred representations stretching beyond its ken. – Immanuel KantRitualistic and symbolic functions. In many cultures, art is used in rituals, performances and dances as a decoration or symbol. While these often have no specific utilitarian purpose, anthropologists know that they often serve a purpose at the level of meaning within a particular culture. This meaning is not furnished by any one individual, but is often the result of many generations of change, and of a cosmological relationship within the culture.Most scholars who deal with rock paintings or objects recovered from prehistoric contexts that cannot be explained in utilitarian terms and are thus categorized as decorative, ritual or symbolic, are aware of the trap posed by the term 'art'. – Silva TomaskovaMotivated functionsMotivated purposes of art refer to intentional, conscious actions on the part of the artists or creator. These may be to bring about political change, to comment on an aspect of society, to convey a specific emotion or mood, to address personal psychology, to illustrate another discipline, to sell a product, or simply as a form of communication.Communication. Art, at its simplest, is a form of communication. As most forms of communication have an intent or goal directed toward another individual, this is a motivated purpose. Illustrative arts, such as scientific illustration, are a form of art as communication. Maps are another example. However, the content need not be scientific. Emotions, moods and feelings are also communicated through art. artefacts or images with symbolic meanings as a means of communication. – Steve MithenArt as entertainment. Art may seek to bring about a particular emotion or mood, for the purpose of relaxing or entertaining the viewer. This is often the function of the art industries of Motion Pictures and Video Games.The Avant-Garde. Art for political change. One of the defining functions of early 20th-century art has been to use visual images to bring about political change. Art movements that had this goal—Dadaism, Surrealism, Russian constructivism, and Abstract Expressionism, among others—are collectively referred to as the avant-garde arts.By contrast, the realistic attitude, inspired by positivism, from Saint Thomas Aquinas to Anatole France, clearly seems to me to be hostile to any intellectual or moral advancement. I loathe it, for it is made up of mediocrity, hate, and dull conceit. It is this attitude which today gives birth to these ridiculous books, these insulting plays. It constantly feeds on and derives strength from the newspapers and stultifies both science and art by assiduously flattering the lowest of tastes; clarity bordering on stupidity, a dog's life. – André Breton Art as a free zone, removed from the action of the social censure. Unlike the avant-garde movements, which wanted to erase cultural differences in order to produce new universal values, contemporary art has enhanced its tolerance towards cultural differences as well as its critical and liberating functions, becoming a more open place for research and experimentation.Art for social inquiry, subversion or anarchy. While similar to art for political change, subversive or deconstructivist art may seek to question aspects of society without any specific political goal. In this case, the function of art may be simply to criticize some aspect of society.Spray-paint graffiti on a wall in RomeGraffiti art and other types of street art are graphics and images that are spray-painted or stencilled on publicly viewable walls, buildings, buses, trains, and bridges, usually without permission. Certain art forms, such as graffiti, may also be illegal when they break laws.Art for social causes. Art can be used to raise awareness for a large variety of causes. A number of art activities were aimed at raising awareness of autism, cancer, human trafficking, and a variety of other topics, such as ocean conservation, human rights in Darfur, murdered and missing Aboriginal women, elder abuse, and pollution. Trashion, using trash to make fashion, practiced by artists such as Marina DeBris is one example of using art to raise awareness about pollution.Art for psychological and healing purposes. Art is also used by art therapists, psychotherapists and clinical psychologists as art therapy. The Diagnostic Drawing Series, for example, is used to determine the personality and emotional functioning of a patient. The end product is not the principal goal in this case, but rather a process of healing, through creative acts, is sought. The resultant piece of artwork may also offer insight into the troubles experienced by the subject and may suggest suitable approaches to be used in more conventional forms of psychiatric therapy.Art for propaganda, or commercialism. Art is often utilized as a form of propaganda, and thus can be used to subtly influence popular conceptions or mood. In a similar way, art that tries to sell a product also influences mood and emotion. In both cases, the purpose of art here is to subtly manipulate the viewer into a particular emotional or psychological response toward a particular idea or object.Art as a fitness indicator. It has been argued that the ability of the human brain by far exceeds what was needed for survival in the ancestral environment. One evolutionary psychology explanation for this is that the human brain and associated traits are the human equivalent of the peacock's tail. The purpose of the male peacock's extravagant tail has been argued to be to attract females. According to this theory superior execution of art was evolutionarily important because it attracted mates.The functions of art described above are not mutually exclusive, as many of them may overlap. For example, art for the purpose of entertainment may also seek to sell a product, i.e. the movie or video game.Public accessThe Metropolitan Museum of Art in Manhattan. Museums are important forums for the display of visual art.Since ancient times, much of the finest art has represented a deliberate display of wealth or power, often achieved by using massive scale and expensive materials. Much art has been commissioned by political rulers or religious establishments, with more modest versions only available to the most wealthy in society.Nevertheless, there have been many periods where art of very high quality was available, in terms of ownership, across large parts of society, above all in cheap media such as pottery, which persists in the ground, and perishable media such as textiles and wood. In many different cultures, the ceramics of indigenous peoples of the Americas are found in such a wide range of graves that they were clearly not restricted to a social elite, though other forms of art may have been. Reproductive methods such as moulds made mass-production easier, and were used to bring high-quality Ancient Roman pottery and Greek Tanagra figurines to a very wide market. Cylinder seals were both artistic and practical, and very widely used by what can be loosely called the middle class in the Ancient Near East. Once coins were widely used, these also became an art form that reached the widest range of society.Another important innovation came in the 15th century in Europe, when printmaking began with small woodcuts, mostly religious, that were often very small and hand-colored, and affordable even by peasants who glued them to the walls of their homes. Printed books were initially very expensive, but fell steadily in price until by the 19th century even the poorest could afford some with printed illustrations. Popular prints of many different sorts have decorated homes and other places for centuries.The Museum of Art in Basel, is the oldest public museum of art in the world.In 1661, the city of Basel, in Switzerland, opened the first public museum of art in the world, the Kunstmuseum Basel. Today, its collection is distinguished by an impressively wide historic span, from the early 15th century up to the immediate present. Its various areas of emphasis give it international standing as one of the most significant museums of its kind. These encompass: paintings and drawings by artists active in the Upper Rhine region between 1400 and 1600, and on the art of the 19th to 21st centuries.Public buildings and monuments, secular and religious, by their nature normally address the whole of society, and visitors as viewers, and display to the general public has long been an important factor in their design. Egyptian temples are typical in that the most largest and most lavish decoration was placed on the parts that could be seen by the general public, rather than the areas seen only by the priests. Many areas of royal palaces, castles and the houses of the social elite were often generally accessible, and large parts of the art collections of such people could often be seen, either by anybody, or by those able to pay a small price, or those wearing the correct clothes, regardless of who they were, as at the Palace of Versailles, where the appropriate extra accessories could be hired from shops outside.Special arrangements were made to allow the public to see many royal or private collections placed in galleries, as with the Orleans Collection mostly housed in a wing of the Palais Royal in Paris, which could be visited for most of the 18th century. In Italy the art tourism of the Grand Tour became a major industry from the Renaissance onwards, and governments and cities made efforts to make their key works accessible. The British Royal Collection remains distinct, but large donations such as the Old Royal Library were made from it to the British Museum, established in 1753. The Uffizi in Florence opened entirely as a gallery in 1765, though this function had been gradually taking the building over from the original civil servants' offices for a long time before. The building now occupied by the Prado in Madrid was built before the French Revolution for the public display of parts of the royal art collection, and similar royal galleries open to the public existed in Vienna, Munich and other capitals. The opening of the Musée du Louvre during the French Revolution as a public museum for much of the former French royal collection certainly marked an important stage in the development of public access to art, transferring ownership to a republican state, but was a continuation of trends already well established.Most modern public museums and art education programs for children in schools can be traced back to this impulse to have art available to everyone. However, museums do not only provide availability to art, but do also influence the way art is being perceived by the audience, as studies found. Thus, the museum itself is not only a blunt stage for the presentation of art, but plays an active and vital role in the overall perception of art in modern society.Museums in the United States tend to be gifts from the very rich to the masses. But despite all this, at least one of the important functions of art in the 21st century remains as a marker of wealth and social status.There have been attempts by artists to create art that can not be bought by the wealthy as a status object. One of the prime original motivators of much of the art of the late 1960s and 1970s was to create art that could not be bought and sold. It is necessary to present something more than mere objects said the major post war German artist Joseph Beuys. This time period saw the rise of such things as performance art, video art, and conceptual art. The idea was that if the artwork was a performance that would leave nothing behind, or was simply an idea, it could not be bought and sold. Democratic precepts revolving around the idea that a work of art is a commodity impelled the aesthetic innovation which germinated in the mid-1960s and was reaped throughout the 1970s. Artists broadly identified under the heading of Conceptual art... substituting performance and publishing activities for engagement with both the material and materialistic concerns of painted or sculptural form... endeavored to undermine the art object qua object.Versailles: Louis Le Vau opened up the interior court to create the expansive entrance cour d'honneur, later copied all over Europe.In the decades since, these ideas have been somewhat lost as the art market has learned to sell limited edition DVDs of video works, invitations to exclusive performance art pieces, and the objects left over from conceptual pieces. Many of these performances create works that are only understood by the elite who have been educated as to why an idea or video or piece of apparent garbage may be considered art. The marker of status becomes understanding the work instead of necessarily owning it, and the artwork remains an upper-class activity. With the widespread use of DVD recording technology in the early 2000s, artists, and the gallery system that derives its profits from the sale of artworks, gained an important means of controlling the sale of video and computer artworks in limited editions to collectors.ControversiesThéodore Géricault's Raft of the Medusa, circa 1820Art has long been controversial, that is to say disliked by some viewers, for a wide variety of reasons, though most pre-modern controversies are dimly recorded, or completely lost to a modern view. Iconoclasm is the destruction of art that is disliked for a variety of reasons, including religious ones. Aniconism is a general dislike of either all figurative images, or often just religious ones, and has been a thread in many major religions. It has been a crucial factor in the history of Islamic art, where depictions of Muhammad remain especially controversial. Much art has been disliked purely because it depicted or otherwise stood for unpopular rulers, parties or other groups. Artistic conventions have often been conservative and taken very seriously by art critics, though often much less so by a wider public. The iconographic content of art could cause controversy, as with late medieval depictions of the new motif of the Swoon of the Virgin in scenes of the Crucifixion of Jesus. The Last Judgment by Michelangelo was controversial for various reasons, including breaches of decorum through nudity and the Apollo-like pose of Christ.The content of much formal art through history was dictated by the patron or commissioner rather than just the artist, but with the advent of Romanticism, and economic changes in the production of art, the artists' vision became the usual determinant of the content of his art, increasing the incidence of controversies, though often reducing their significance. Strong incentives for perceived originality and publicity also encouraged artists to court controversy. Théodore Géricault's Raft of the Medusa, was in part a political commentary on a recent event. Édouard Manet's Le Déjeuner sur l'Herbe, was considered scandalous not because of the nude woman, but because she is seated next to men fully dressed in the clothing of the time, rather than in robes of the antique world. John Singer Sargent's Madame Pierre Gautreau, caused a controversy over the reddish pink used to color the woman's ear lobe, considered far too suggestive and supposedly ruining the high-society model's reputation. The gradual abandonment of naturalism and the depiction of realistic representations of the visual appearance of subjects in the 19th and 20th centuries led to a rolling controversy lasting for over a century.Performance by Joseph Beuys, 1978: Everyone an artist – On the way to the libertarian form of the social organism.In the 20th century, Pablo Picasso's Guernica used arresting cubist techniques and stark monochromatic oils, to depict the harrowing consequences of a contemporary bombing of a small, ancient Basque town. Leon Golub's Interrogation III, depicts a female nude, hooded detainee strapped to a chair, her legs open to reveal her sexual organs, surrounded by two tormentors dressed in everyday clothing. Andres Serrano's Piss Christ is a photograph of a crucifix, sacred to the Christian religion and representing Christ's sacrifice and final suffering, submerged in a glass of the artist's own urine. The resulting uproar led to comments in the United States Senate about public funding of the arts.TheoryMain article: AestheticsBefore Modernism, aesthetics in Western art was greatly concerned with achieving the appropriate balance between different aspects of realism or truth to nature and the ideal; ideas as to what the appropriate balance is have shifted to and fro over the centuries. This concern is largely absent in other traditions of art. The aesthetic theorist John Ruskin, who championed what he saw as the naturalism of J. M. W. Turner, saw art's role as the communication by artifice of an essential truth that could only be found in nature.The definition and evaluation of art has become especially problematic since the 20th century. Richard Wollheim distinguishes three approaches to assessing the aesthetic value of art: the Realist, whereby aesthetic quality is an absolute value independent of any human view; the Objectivist, whereby it is also an absolute value, but is dependent on general human experience; and the Relativist position, whereby it is not an absolute value, but depends on, and varies with, the human experience of different humans.Arrival of ModernismComposition with Red Blue and Yellow by Piet Mondrian The arrival of Modernism in the late 19th century lead to a radical break in the conception of the function of art, and then again in the late 20th century with the advent of postmodernism. Clement Greenberg's 1960 article Modernist Painting defines modern art as the use of characteristic methods of a discipline to criticize the discipline itself. Greenberg originally applied this idea to the Abstract Expressionist movement and used it as a way to understand and justify flat abstract painting:Realistic, naturalistic art had dissembled the medium, using art to conceal art; modernism used art to call attention to art. The limitations that constitute the medium of painting—the flat surface, the shape of the support, the properties of the pigment—were treated by the Old Masters as negative factors that could be acknowledged only implicitly or indirectly. Under Modernism these same limitations came to be regarded as positive factors, and were acknowledged openly.After Greenberg, several important art theorists emerged, such as Michael Fried, T. J. Clark, Rosalind Krauss, Linda Nochlin and Griselda Pollock among others. Though only originally intended as a way of understanding a specific set of artists, Greenberg's definition of modern art is important to many of the ideas of art within the various art movements of the 20th century and early 21st century.Pop artists like Andy Warhol became both noteworthy and influential through work including and possibly critiquing popular culture, as well as the art world. Artists of the 1980s, 1990s, and 2000s expanded this technique of self-criticism beyond high art to all cultural image-making, including fashion images, comics, billboards and pornography.Duchamp once proposed that art is any activity of any kind-everything. However, the way that only certain activities are classified today as art is a social construction. There is evidence that there may be an element of truth to this. In The Invention of Art: A Cultural History, Larry Shiner examines the construction of the modern system of the arts, i.e. fine art. He finds evidence that the older system of the arts before our modern system held art to be any skilled human activity; for example, Ancient Greek society did not possess the term art, but techne. Techne can be understood neither as art or craft, the reason being that the distinctions of art and craft are historical products that came later on in human history. Techne included painting, sculpting and music, but also cooking, medicine, horsemanship, geometry, carpentry, prophecy, and farming, etc.New Criticism and the intentional fallacyFollowing Duchamp during the first half of the 20th century, a significant shift to general aesthetic theory took place which attempted to apply aesthetic theory between various forms of art, including the literary arts and the visual arts, to each other. This resulted in the rise of the New Criticism school and debate concerning the intentional fallacy. At issue was the question of whether the aesthetic intentions of the artist in creating the work of art, whatever its specific form, should be associated with the criticism and evaluation of the final product of the work of art, or, if the work of art should be evaluated on its own merits independent of the intentions of the artist.In 1946, William K. Wimsatt and Monroe Beardsley published a classic and controversial New Critical essay entitled The Intentional Fallacy, in which they argued strongly against the relevance of an author's intention, or intended meaning in the analysis of a literary work. For Wimsatt and Beardsley, the words on the page were all that mattered; importation of meanings from outside the text was considered irrelevant, and potentially distracting.In another essay, The Affective Fallacy, which served as a kind of sister essay to The Intentional Fallacy Wimsatt and Beardsley also discounted the reader's personal/emotional reaction to a literary work as a valid means of analyzing a text. This fallacy would later be repudiated by theorists from the reader-response school of literary theory. Ironically, one of the leading theorists from this school, Stanley Fish, was himself trained by New Critics. Fish criticizes Wimsatt and Beardsley in his 1970 essay Literature in the Reader.As summarized by Gaut and Livingston in their essay The Creation of Art: Structuralist and post-structuralists theorists and critics were sharply critical of many aspects of New Criticism, beginning with the emphasis on aesthetic appreciation and the so-called autonomy of art, but they reiterated the attack on biographical criticisms' assumption that the artist's activities and experience were a privileged critical topic. These authors contend that: Anti-intentionalists, such as formalists, hold that the intentions involved in the making of art are irrelevant or peripheral to correctly interpreting art. So details of the act of creating a work, though possibly of interest in themselves, have no bearing on the correct interpretation of the work.Gaut and Livingston define the intentionalists as distinct from formalists stating that: Intentionalists, unlike formalists, hold that reference to intentions is essential in fixing the correct interpretation of works. They quote Richard Wollheim as stating that, The task of criticism is the reconstruction of the creative process, where the creative process must in turn be thought of as something not stopping short of, but terminating on, the work of art itself.Linguistic turn and its debateThe end of the 20th century fostered an extensive debate known as the linguistic turn controversy, or the innocent eye debate in the philosophy of art. This debate discussed the encounter of the work of art as being determined by the relative extent to which the conceptual encounter with the work of art dominates over the perceptual encounter with the work of art.Decisive for the linguistic turn debate in art history and the humanities were the works of yet another tradition, namely the structuralism of Ferdinand de Saussure and the ensuing movement of poststructuralism. In 1981, the artist Mark Tansey created a work of art titled The Innocent Eye as a criticism of the prevailing climate of disagreement in the philosophy of art during the closing decades of the 20th century. Influential theorists include Judith Butler, Luce Irigaray, Julia Kristeva, Michel Foucault and Jacques Derrida. The power of language, more specifically of certain rhetorical tropes, in art history and historical discourse was explored by Hayden White. The fact that language is not a transparent medium of thought had been stressed by a very different form of philosophy of language which originated in the works of Johann Georg Hamann and Wilhelm von Humboldt. Ernst Gombrich and Nelson Goodman in his book Languages of Art: An Approach to a Theory of Symbols came to hold that the conceptual encounter with the work of art predominated exclusively over the perceptual and visual encounter with the work of art during the 1960s and 1970s. He was challenged on the basis of research done by the Nobel prize winning psychologist Roger Sperry who maintained that the human visual encounter was not limited to concepts represented in language alone and that other forms of psychological representations of the work of art were equally defensible and demonstrable. Sperry's view eventually prevailed by the end of the 20th century with aesthetic philosophers such as Nick Zangwill strongly defending a return to moderate aesthetic formalism among other alternatives.Classification disputesMain article: Classificatory disputes about artThe original Fountain by Marcel Duchamp, 1917, photographed by Alfred Stieglitz at the 291 after the 1917 Society of Independent Artists exhibit. Stieglitz used a backdrop of The Warriors by Marsden Hartley to photograph the urinal. The exhibition entry tag can be clearly seen.Disputes as to whether or not to classify something as a work of art are referred to as classificatory disputes about art. Classificatory disputes in the 20th century have included cubist and impressionist paintings, Duchamp's Fountain, the movies, superlative imitations of banknotes, conceptual art, and video games. Philosopher David Novitz has argued that disagreement about the definition of art are rarely the heart of the problem. Rather, the passionate concerns and interests that humans vest in their social life are so much a part of all classificatory disputes about art. According to Novitz, classificatory disputes are more often disputes about societal values and where society is trying to go than they are about theory proper. For example, when the Daily Mail criticized Hirst's and Emin's work by arguing For 1,000 years art has been one of our great civilising forces. Today, pickled sheep and soiled beds threaten to make barbarians of us all they are not advancing a definition or theory about art, but questioning the value of Hirst's and Emin's work. In 1998, Arthur Danto, suggested a thought experiment showing that the status of an artifact as work of art results from the ideas a culture applies to it, rather than its inherent physical or perceptible qualities. Cultural interpretation is therefore constitutive of an object's arthood.Anti-art is a label for art that intentionally challenges the established parameters and values of art; it is term associated with Dadaism and attributed to Marcel Duchamp just before World War I, when he was making art from found objects. One of these, Fountain, an ordinary urinal, has achieved considerable prominence and influence on art. Anti-art is a feature of work by Situationist International, the lo-fi Mail art movement, and the Young British Artists, though it is a form still rejected by the Stuckists, who describe themselves as anti-anti-art.Architecture is often included as one of the visual arts; however, like the decorative arts, or advertising, it involves the creation of objects where the practical considerations of use are essential in a way that they usually are not in a painting, for example.Value judgmentAboriginal hollow log tombs. National Gallery, Canberra, Australia.Somewhat in relation to the above, the word art is also used to apply judgments of value, as in such expressions as that meal was a work of art, or the art of deception. It is this use of the word as a measure of high quality and high value that gives the term its flavor of subjectivity. Making judgments of value requires a basis for criticism. At the simplest level, a way to determine whether the impact of the object on the senses meets the criteria to be considered art is whether it is perceived to be attractive or repulsive. Though perception is always colored by experience, and is necessarily subjective, it is commonly understood that what is not somehow aesthetically satisfying cannot be art. However, good art is not always or even regularly aesthetically appealing to a majority of viewers. In other words, an artist's prime motivation need not be the pursuit of the aesthetic. Also, art often depicts terrible images made for social, moral, or thought-provoking reasons. For example, Francisco Goya's painting depicting the Spanish shootings of 3 May 1808 is a graphic depiction of a firing squad executing several pleading civilians. Yet at the same time, the horrific imagery demonstrates Goya's keen artistic ability in composition and execution and produces fitting social and political outrage. Thus, the debate continues as to what mode of aesthetic satisfaction, if any, is required to define 'art'.The assumption of new values or the rebellion against accepted notions of what is aesthetically superior need not occur concurrently with a complete abandonment of the pursuit of what is aesthetically appealing. Indeed, the reverse is often true, that the revision of what is popularly conceived of as being aesthetically appealing allows for a re-invigoration of aesthetic sensibility, and a new appreciation for the standards of art itself. Countless schools have proposed their own ways to define quality, yet they all seem to agree in at least one point: once their aesthetic choices are accepted, the value of the work of art is determined by its capacity to transcend the limits of its chosen medium to strike some universal chord by the rarity of the skill of the artist or in its accurate reflection in what is termed the zeitgeist. Art is often intended to appeal to and connect with human emotion. It can arouse aesthetic or moral feelings, and can be understood as a way of communicating these feelings. Artists express something so that their audience is aroused to some extent, but they do not have to do so consciously. Art may be considered an exploration of the human condition; that is, what it is to be human. By extension, it has been argued by Emily L. Spratt that the development of artificial intelligence, especially in regard to its uses with images, necessitates a re-evaluation of aesthetic theory in art history today and a reconsideration of the limits of human creativity.Art and lawAn essential legal issue are art forgeries, plagiarism, replicas and works that are strongly based on other works of art.The trade in works of art or the export from a country may be subject to legal regulations. Internationally there are also extensive efforts to protect the works of art created. The UN, UNESCO and Blue Shield International try to ensure effective protection at the national level and to intervene directly in the event of armed conflicts or disasters. This can particularly affect museums, archives, art collections and excavation sites. This should also secure the economic basis of a country, especially because works of art are often of tourist importance. The founding president of Blue Shield International, Karl von Habsburg, explained an additional connection between the destruction of cultural property and the cause of flight during a mission in Lebanon in April 2019: Cultural goods are part of the identity of the people who live in a certain place. If you destroy their culture, you also destroy their identity. Many people are uprooted, often no longer have any prospects and as a result flee from their homeland. Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in which their body consists of a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 micrometres to 33.6 metres. They have complex interactions with each other and their environments, forming intricate food webs. The scientific study of animals is known as zoology.Most living animal species are in Bilateria, a clade whose members have a bilaterally symmetric body plan. The Bilateria include the protostomes, containing invertebrates such as nematodes, arthropods, and molluscs, and the deuterostomes, containing the echinoderms and the chordates, the latter including the vertebrates. Life forms interpreted as early animals were present in the Ediacaran biota of the late Precambrian. Many modern animal phyla became clearly established in the fossil record as marine species during the Cambrian explosion, which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago.Historically, Aristotle divided animals into those with blood and those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between taxa.Humans make use of many animal species, such as for food, for materials, as pets, and as working animals including for transport. Dogs have been used in hunting, as have birds of prey, while many terrestrial and aquatic animals were hunted for sports. Nonhuman animals have appeared in art from the earliest times and are featured in mythology and religion. The word animal comes from the Latin animalis, meaning 'having breath', 'having soul' or 'living being'. The biological definition includes all members of the kingdom Animalia. In colloquial usage, the term animal is often used to refer only to nonhuman animals. Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and multicellular. Unlike plants and algae, which produce their own nutrients, animals are heterotrophic, feeding on organic material and digesting it internally. With very few exceptions, animals respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals, mussels, and barnacles, later become sessile. The blastula is a stage in embryonic development that is unique to animals, allowing cells to be differentiated into specialised tissues and organs. All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. During development, the animal extracellular matrix forms a relatively flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible. This may be calcified, forming structures such as shells, bones, and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, and so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, and desmosomes.With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues. These include muscles, which enable locomotion, and nerve tissues, which transmit signals and coordinate the body. Typically, there is also an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction. They produce haploid gametes by meiosis; the smaller, motile gametes are spermatozoa and the larger, non-motile gametes are ova. These fuse to form zygotes, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, and develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement. It first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm. In most cases, a third germ layer, the mesoderm, also develops between them. These germ layers then differentiate to form tissues and organs.Repeated instances of mating with a close relative during sexual reproduction generally leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding.Some animals are capable of asexual reproduction, which often results in a genetic clone of the parent. This may take place through fragmentation; budding, such as in Hydra and other cnidarians; or parthenogenesis, where fertile eggs are produced without mating, such as in aphids. Animals are categorised into ecological groups depending on how they obtain or consume organic material, including carnivores, herbivores, omnivores, detritivores, and parasites. Interactions between animals form complex food webs. In carnivorous or omnivorous species, predation is a consumer–resource interaction where a predator feeds on another organism. Selective pressures imposed on one another lead to an evolutionary arms race between predator and prey, resulting in various anti-predator adaptations. Almost all multicellular predators are animals. Some consumers use multiple methods; for example, in parasitoid wasps, the larvae feed on the hosts' living tissues, killing them in the process, but the adults primarily consume nectar from flowers. Other animals may have very specific feeding behaviours, such as hawksbill sea turtles primarily eating sponges.Hydrothermal vent mussels and shrimpsMost animals rely on the biomass and energy produced by plants through photosynthesis. Herbivores eat plant material directly, while carnivores, and other animals on higher trophic levels typically acquire it indirectly by eating other animals. Animals oxidize carbohydrates, lipids, proteins, and other biomolecules to unlock the chemical energy of molecular oxygen, which allows the animal to grow and to sustain biological processes such as locomotion. Animals living close to hydrothermal vents and cold seeps on the dark sea floor consume organic matter of archaea and bacteria produced in these locations through chemosynthesis.Animals originally evolved in the sea. Lineages of arthropods colonised land around the same time as land plants, probably between 510 and 471 million years ago during the Late Cambrian or Early Ordovician. Vertebrates such as the lobe-finned fish Tiktaalik started to move on to land in the late Devonian, about 375 million years ago. Animals occupy virtually all of earth's habitats and microhabitats, including salt water, hydrothermal vents, fresh water, hot springs, swamps, forests, pastures, deserts, air, and the interiors of animals, plants, fungi and rocks. Animals are however not particularly heat tolerant; very few of them can survive at constant temperatures above 50 °C. Only very few species of animals inhabit the most extreme cold deserts of continental Antarctica. The blue whale is the largest animal that has ever lived, weighing up to 190 tonnes and measuring up to 33.6 metres long. The largest extant terrestrial animal is the African bush elephant, weighing up to 12.25 tonnes and measuring up to 10.67 metres long. The largest terrestrial animals that ever lived were titanosaur sauropod dinosaurs such as Argentinosaurus, which may have weighed as much as 73 tonnes. Several animals are microscopic; some Myxozoa never grow larger than 20 µm, and one of the smallest species is no more than 8.5 µm when fully grown. The following table lists estimated numbers of described extant species for the animal groups with the largest numbers of species, along with their principal habitats, and free-living or parasitic ways of life. Species estimates shown here are based on numbers described scientifically; much larger estimates have been calculated based on various means of prediction, and these can vary wildly. For instance, around 25,000–27,000 species of nematodes have been described, while published estimates of the total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million. Using patterns within the taxonomic hierarchy, the total number of animal species—including those not yet described—was calculated to be about 7.77 million in 2011. The first fossils that might represent animals appear in the 665-million-year-old rocks of the Trezona Formation of South Australia. These fossils are interpreted as most probably being early sponges.Animals are found as long ago as the Ediacaran biota, towards the end of the Precambrian, and possibly somewhat earlier. It had long been doubted whether these life-forms included animals, but the discovery of the animal lipid cholesterol in fossils of Dickinsonia establishes their nature. Animals are thought to have originated under low-oxygen conditions, suggesting that they were capable of living entirely by anaerobic respiration, but as they became specialized for aerobic metabolism they became fully dependent on oxygen in their environments.Anomalocaris canadensis is one of the many animal species that emerged in the Cambrian explosion, starting some 542 million years ago, and found in the fossil beds of the Burgess shale.Many animal phyla first appear in the fossil record during the Cambrian explosion, starting about 542 million years ago, in beds such as the Burgess shale. Extant phyla in these rocks include molluscs, brachiopods, onychophorans, tardigrades, arthropods, echinoderms and hemichordates, along with numerous now-extinct forms such as the predatory Anomalocaris. The apparent suddenness of the event may however be an artefact of the fossil record, rather than showing that all these animals appeared simultaneously.Some palaeontologists have suggested that animals appeared much earlier than the Cambrian explosion, possibly as early as 1 billion years ago. Trace fossils such as tracks and burrows found in the Tonian period may indicate the presence of triploblastic worm-like animals, roughly as large and complex as earthworms. However, similar tracks are produced today by the giant single-celled protist Gromia sphaerica, so the Tonian trace fossils may not indicate early animal evolution. Around the same time, the layered mats of microorganisms called stromatolites decreased in diversity, perhaps due to grazing by newly evolved animals. Animals are monophyletic, meaning they are derived from a common ancestor. Animals are sister to the Choanoflagellata, with which they form the Choanozoa. The most basal animals, the Porifera, Ctenophora, Cnidaria, and Placozoa, have body plans that lack bilateral symmetry. Their relationships are still disputed; the sister group to all other animals could be the Porifera or the Ctenophora, both of which lack hox genes, important in body plan development.These genes are found in the Placozoa and the higher animals, the Bilateria. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago in the Precambrian. 25 of these are novel core gene groups, found only in animals; of those, 8 are for essential components of the Wnt and TGF-beta signalling pathways which may have enabled animals to become multicellular by providing a pattern for the body's system of axes, and another 7 are for transcription factors including homeodomain proteins involved in the control of development.The phylogenetic tree indicates approximately how many millions of years ago the lineages split. Several animal phyla lack bilateral symmetry. Among these, the sponges probably diverged first, representing the oldest animal phylum. Sponges lack the complex organization found in most other animal phyla; their cells are differentiated, but in most cases not organised into distinct tissues. They typically feed by drawing in water through pores.The Ctenophora and Cnidaria are radially symmetric and have digestive chambers with a single opening, which serves as both mouth and anus. Animals in both phyla have distinct tissues, but these are not organised into organs. They are diploblastic, having only two main germ layers, ectoderm and endoderm. The tiny placozoans are similar, but they do not have a permanent digestive chamber. The remaining animals, the great majority—comprising some 29 phyla and over a million species—form a clade, the Bilateria. The body is triploblastic, with three well-developed germ layers, and their tissues form distinct organs. The digestive chamber has two openings, a mouth and an anus, and there is an internal body cavity, a coelom or pseudocoelom. Animals with this bilaterally symmetric body plan and a tendency to move in one direction have a head end and a tail end as well as a back and a belly; therefore they also have a left side and a right side.Having a front end means that this part of the body encounters stimuli, such as food, favouring cephalisation, the development of a head with sense organs and a mouth. Many bilaterians have a combination of circular muscles that constrict the body, making it longer, and an opposing set of longitudinal muscles, that shorten the body; these enable soft-bodied animals with a hydrostatic skeleton to move by peristalsis. They also have a gut that extends through the basically cylindrical body from mouth to anus. Many bilaterian phyla have primary larvae which swim with cilia and have an apical organ containing sensory cells. However, there are exceptions to each of these characteristics; for example, adult echinoderms are radially symmetric, while some parasitic worms have extremely simplified body structures.Genetic studies have considerably changed zoologists' understanding of the relationships within the Bilateria. Most appear to belong to two major lineages, the protostomes and the deuterostomes. The basalmost bilaterians are the Xenacoelomorpha. Protostomes and deuterostomes differ in several ways. Early in development, deuterostome embryos undergo radial cleavage during cell division, while many protostomes undergo spiral cleavage. Animals from both groups possess a complete digestive tract, but in protostomes the first opening of the embryonic gut develops into the mouth, and the anus forms secondarily. In deuterostomes, the anus forms first while the mouth develops secondarily. Most protostomes have schizocoelous development, where cells simply fill in the interior of the gastrula to form the mesoderm. In deuterostomes, the mesoderm forms by enterocoelic pouching, through invagination of the endoderm.The main deuterostome phyla are the Echinodermata and the Chordata. Echinoderms are exclusively marine and include starfish, sea urchins, and sea cucumbers. The chordates are dominated by the vertebrates, which consist of fishes, amphibians, reptiles, birds, and mammals. The deuterostomes also include the Hemichordata. The Ecdysozoa are protostomes, named after their shared trait of ecdysis, growth by moulting. They include the largest animal phylum, the Arthropoda, which contains insects, spiders, crabs, and their kin. All of these have a body divided into repeating segments, typically with paired appendages. Two smaller phyla, the Onychophora and Tardigrada, are close relatives of the arthropods and share these traits. The ecdysozoans also include the Nematoda or roundworms, perhaps the second largest animal phylum. Roundworms are typically microscopic, and occur in nearly every environment where there is water; some are important parasites. Smaller phyla related to them are the Nematomorpha or horsehair worms, and the Kinorhyncha, Priapulida, and Loricifera. These groups have a reduced coelom, called a pseudocoelom. The Spiralia are a large group of protostomes that develop by spiral cleavage in the early embryo. The Spiralia's phylogeny has been disputed, but it contains a large clade, the superphylum Lophotrochozoa, and smaller groups of phyla such as the Rouphozoa which includes the gastrotrichs and the flatworms. All of these are grouped as the Platytrochozoa, which has a sister group, the Gnathifera, which includes the rotifers.The Lophotrochozoa includes the molluscs, annelids, brachiopods, nemerteans, bryozoa and entoprocts. The molluscs, the second-largest animal phylum by number of described species, includes snails, clams, and squids, while the annelids are the segmented worms, such as earthworms, lugworms, and leeches. These two groups have long been considered close relatives because they share trochophore larvae. In the classical era, Aristotle divided animals, based on his own observations, into those with blood and those without. The animals were then arranged on a scale from man down through the live-bearing tetrapods and other groups such as crustaceans down to spontaneously-generating creatures like sponges. Aristotle was uncertain whether sponges were animals, which in his system ought to have sensation, appetite, and locomotion, or plants, which did not: he knew that sponges could sense touch, and would contract if about to be pulled off their rocks, but that they were rooted like plants and never moved about.In 1758, Carl Linnaeus created the first hierarchical classification in his Systema Naturae. In his original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, the Chordata, while his Insecta and Vermes have been renamed or broken up. The process was begun in 1793 by Jean-Baptiste de Lamarck, who called the Vermes une espèce de chaos and split the group into three new phyla, worms, echinoderms, and polyps. By 1809, in his Philosophie Zoologique, Lamarck had created 9 phyla apart from vertebrates and molluscs, namely cirripedes, annelids, crustaceans, arachnids, insects, worms, radiates, polyps, and infusorians.In his 1817 Le Règne Animal, Georges Cuvier used comparative anatomy to group the animals into four embranchements, namely vertebrates, molluscs, articulated animals, and zoophytes. This division into four was followed by the embryologist Karl Ernst von Baer in 1828, the zoologist Louis Agassiz in 1857, and the comparative anatomist Richard Owen in 1860.In 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms: Metazoa and Protozoa, including a sixth animal phylum, sponges. The protozoa were later moved to the former kingdom Protista, leaving only the Metazoa as a synonym of Animalia. The human population exploits a large number of other animal species for food, both of domesticated livestock species in animal husbandry and, mainly at sea, by hunting wild species. Marine fish of many species are caught commercially for food. A smaller number of species are farmed commercially. Humans and their livestock make up more than 90% of the biomass of all terrestrial vertebrates, and almost as much as all insects combined.Invertebrates including cephalopods, crustaceans, and bivalve or gastropod molluscs are hunted or farmed for food. Chickens, cattle, sheep, pigs, and other animals are raised as livestock for meat across the world. Animal fibres such as wool are used to make textiles, while animal sinews have been used as lashings and bindings, and leather is widely used to make shoes and other items. Animals have been hunted and farmed for their fur to make items such as coats and hats. Dyestuffs including carmine, shellac, and kermes have been made from the bodies of insects. Working animals including cattle and horses have been used for work and transport from the first days of agriculture.Animals such as the fruit fly Drosophila melanogaster serve a major role in science as experimental models. Animals have been used to create vaccines since their discovery in the 18th century. Some medicines such as the cancer drug Yondelis are based on toxins or other molecules of animal origin. People have used hunting dogs to help chase down and retrieve animals, and birds of prey to catch birds and mammals, while tethered cormorants have been used to catch fish. Poison dart frogs have been used to poison the tips of blowpipe darts. A wide variety of animals are kept as pets, from invertebrates such as tarantulas and octopuses, insects including praying mantises, reptiles such as snakes and chameleons, and birds including canaries, parakeets, and parrots all finding a place. However, the most kept pet species are mammals, namely dogs, cats, and rabbits. There is a tension between the role of animals as companions to humans, and their existence as individuals with rights of their own. A wide variety of terrestrial and aquatic animals are hunted for sport. Animals have been the subjects of art from the earliest times, both historical, as in Ancient Egypt, and prehistoric, as in the cave paintings at Lascaux. Major animal paintings include Albrecht Dürer's 1515 The Rhinoceros, and George Stubbs's c. 1762 horse portrait Whistlejacket. Insects, birds and mammals play roles in literature and film, such as in giant bug movies. Animals including insects and mammals feature in mythology and religion. In both Japan and Europe, a butterfly was seen as the personification of a person's soul, while the scarab beetle was sacred in ancient Egypt. Among the mammals, cattle, deer, horses, lions, bats, bears, and wolves are the subjects of myths and worship. The signs of the Western and Chinese zodiacs are based on animals.