# Rationality Never Travels Across the Mind

*Every description of rationality is already a reinterpretation.*

Theoretical rationality treats a coherent preference structure and a consistent decision rule — uniquely held at each mind — as interpersonally portable. Behavioral economics conditions that prior without discarding it. The residual step converts that local serviceability into a standing, transferable thesis.

## Reinterpretation is the medium of the description

Any mind that articulates, receives, or evaluates a statement about what counts as rational is already performing the reinterpretation. The process is the medium of the description itself.

## Theoretical rationality treats the structure as portable

Theoretical rationality begins from a different premise. It posits a coherent set of preferences and a consistent decision rule — typically expected-utility maximization or game-theoretic equilibrium — and treats that structure as interpersonally portable. Once the premise is granted, the rationality registered by one idealized agent can be aggregated, compared, and prescribed across agents as if their internal maps of value, risk, and constraint were interchangeable. [The rational choice postulate is the original sin](../the-rational-choice-postulate-is-the-original-sin/) is that freeze installed as micro-foundation: consistency and intersubjective uniformity treated as solid enough to ground aggregation while choice continues only under private premises.

Historical illustration makes the premise’s failure concrete. Von Neumann’s formal arguments for nuclear first strikes followed rigorously from the model, yet the decision-makers who received them experienced the recommendation as alien and refused it. What one mind registers as rational arrives in another already rewritten. [Price as utterance, understanding as trade](../price-as-utterance-understanding-as-trade/) is that non-arrival under ordinary exchange: a print or a sentence is residue; force is only how another mind re-traces it.

## Behavioral economics conditions the prior

Behavioral economics stands in a relationship to this theoretical prior. It treats the standard rational-choice apparatus as the organizing structure and performs a sequence of Bayesian updates upon it. Observed departures — loss aversion, probability weighting, present bias, fairness constraints — are absorbed as revised parameters or additional terms. The prior is never challenged; it is conditioned so that the posterior model yields improved descriptive fit. The result is a refined calculus that remains inside the original optimization framework. The adjustment improves local explainability with limited improvement in predictive power. The portable calculus remains the description of agency.

## The judgment of accuracy reenacts the theoretical move

Even a judgment that the relationship is accurate or not reenacts the original theoretical move. Such a judgment claims an external vantage from which the relationship between behavioral economics and theoretical rationality can be assessed as correct across minds. That vantage is itself another local reinterpretation. [Self-image speaks as if from nowhere](../self-image-speaks-as-if-from-nowhere/) is that stand: a re-projection occupied as detached exterior. The description is retained for its local usefulness — serviceable inside a particular exchange and a particular set of examples. The residual step converts that local serviceability into a standing, transferable thesis. [When observation becomes performance](../when-observation-becomes-performance/) is that conversion under virtue costume: a first-person reference packaged as portable product.