THE COHERENCE ARGUMENT AGAINST CONDITIONALIZATION

I re-examine Coherence Arguments (Dutch Book Arguments, No Arbitrage A rguments) for diachronic constraints on Bayesian reasoning. I suggest to replace the usual game-theoretic coherence condition with a new dec ision-theoretic condition ('Diachronic Sure Thing Principle'). The new condition meets a large part of the standard objections against the C oherence Argument and frees it, in particular, from a commitment to ad ditive utilities. It also facilitates the proof of the Converse Dutch Book Theorem. I first apply the improved Coherence Argument to van Fra assen's (1984) Reflection principle. I then point out the failure of a Coherence Argument that is intended to support Conditionalization as a naive, universal, update rule. I also point out that Reflection is i ncompatible with the universal use of Conditionalization thus interpre ted. The Coherence Argument therefore defeats the naive view on Bayesi an learning that it was originally designed to justify.