Name given by David Lewis to a principle connecting together subjective or personal degrees of confidence or credence, with objective chances. The principle states that for any reasonable way of forming degrees of belief, given the information (based on data and the best theory of the way the world works) that the objective chance of an event is x, and given no further, inadmissible evidence, then the degree of belief in the occurrence of the event should equal x. Inadmissible evidence is difficult to define, but would include unnatural sources, such as peeks into the future. Lewis held that the principle encapsulated all that was clear about the metaphysical notion of objective chance. This could seem like a vindication of a notion of objective chance, or a constructivist account of its role as an imaginary focus for the activities connected with changing credences. Constructivists or expressivists might similarly hold that all that is known about objective value is that, if it were given (by one’s best theory of values) that the objective value of something was (for instance) high, and given nothing else, then the strength of one’s admiration of the object should be similarly high.