1 Noncomprehensive and Conditional Rationality © ProtoSociology www.protosociology.de/on-philosophy Noncomprehensive and Conditional Rationality Paul Weirich Rationality’s evaluations of beliefs, desires, and acts are variable in at least two ways. First, its evaluations have variable scope. For example, an act’s evalua- tion may assess the world that would be realized if the act were performed, or, less comprehensively, the act’s causal consequences. Second, rationality’s evaluations may be conditional. For example, an act’s evaluation may assess the act granting the agent’s beliefs and desires, however irrational they may be. Tis essay characterizes noncomprehensive and conditional evaluations. Ten it uses distinctions in types of evaluation to resolve puzzles about rational- ity’s evaluations. Te puzzles concern the principle that “ought” implies “can,” Newcomb’s problem, and the confict between actualism and possibilism. Te essay’s fnal section formulates a principle of detachment for a type of condi- tional rationality that grants mistakes the condition includes. 1. Noncomprehensive Rationality Rationality’s evaluations have variable scope. Some evaluate a decision taking for granted the agent’s beliefs and desires, whereas others evaluate it taking account of the agent’s beliefs and desires, in particular, those on which the decision rests. Taking beliefs and desires for granted yields an instrumental evaluation of the decision. Appraising the beliefs and desires grounding the decision, in the course of evaluating the decision, increases the evaluation’s comprehensiveness. It makes the evaluation more demanding than is a merely instrumental evaluation. A person who forgoes air travel because of an irratio- nal fear of fying decides in accordance with preferences but has defective pref- erences. Despite his decision’s instrumental rationality, his decision is irrational overall. It does not follow his preferences after their hypothetical correction for inexcusable, corrigible errors, and so revised to accord with reasonable beliefs and desires. Te person’s choice is rational taking his preferences for granted, yet irrational all things considered. A comprehensively rational decision is not only instrumentally rational but also is rationally grounded in beliefs and de- sires. It either rests on rational beliefs and desires or is equivalent to a decision that rests on rational beliefs and desires.