CHANCE, CREDENCE, AND THE PRINCIPAL PRINCIPLE

Any adequate theory of chance must accommodate some version of David L ewis's 'Principal Principle', and Lewis has argued forcibly that belie vers in primitive propensities have a problem in explaining what makes the Principle true. But Lewis can only derive (a revised version of) the Principle from his own Humean theory by putting constraints on ind uctive rationality which cannot be given a Humean rationale.