Bayesian Coherentism and Rationality

Abstract

Abstract Rationality, although distinct from warrant, is a notion both interesting in its own right and important for a solid understanding of warrant. In this chapter, I first disambiguate at least five different forms of rationality, and, second, examine the relationship between Bayesianism and rationality (in its different forms or senses). Bayesians often claim that conformity to Bayesian constraints (such as coherence, changing belief by conditionalization or probability kinematics, or van Fraassen's Reflection) is necessary for rationality. Against this view, I argue that (1) none of the forms of rationality I distinguished requires coherence, and some of them in fact require incoherence, and that (2) changing belief by conditionalization (or by probability kinematics) is neither a sensible ideal for human cognizers nor a requirement for rationality. Finally, after a somewhat extended look at Reflection, I argue that (3) while van Fraassen surely has important and probably true things to say about what rational integrity requires with respect to one's commitments and intentions about belief change, it is nonetheless the case that rationality does not require that I conform to Reflection.