 So Bayes’ Theorem works by expressing posterior credences in terms of some prior credences \(\Cr(H_i)\) and some prior conditional credences \(\Cr(E \mid H_i)\). The latter, called likelihoods, are subjective opinions, but they can be replaced by objective chances thanks to the Principal Principle. So this principle is often taken to be an important way to reduce some subjective factors in the Bayesian account of scientific inference. For discussions of other subjective factors, see  section 4.1.