 We have just discussed the Principal Principle, which in a sense asks one to defer to a kind of expert (Gaifman 1986): the chance of an event \(E\) can be understood as an expert at predicting whether \(E\) will come out true. So, conditional on that expert’s saying so and so about \(E\), one’s opinion ought to defer to that expert. Construed that way, the Principal Principle is a kind of deference principle. There can be different deference principles, referring to different kinds of experts.