  While much more can be said about simple conditioning, Jeffrey conditioning and other forms of belief revision, these remarks should give the reader a sense of the importance of Bayes' Theorem in subjectivist accounts of learning and evidential support. Though a mathematical triviality, the Theorem's central insight — that a hypothesis is supported by any body of data it renders probable — lies at the heart of all subjectivist approaches to epistemology, statistics, and inductive logic.