 The Principal Principle/Direct Inference Principle. Let \(\Cr\) be one’s prior, i.e., the credence assignment that one has at the beginning of an inquiry. Let \(E\) be the event that such and such things will happen at a certain future time. Let \(A\) be a proposition that entails \(\Ch(E) = c\), which says that the chance for \(E\) to come out true is equal to \(c\). Then one’s prior \(\Cr\) ought to be such that \(\Cr(E \mid A) = c\), if \(A\) is an “ordinary” proposition in that it is logically equivalent to the conjunction of \(\Ch(E) = c\) with an “admissible” proposition.