A Closer Look at the 'New' Principle

Published: British Journal for the Philosophy of Science 46, 545–561, 1995

Abstract: David Lewis, Michael Thau and Ned Hall have argued that the Principal Principle -- an inferential rule underlying much of our reasoning about probability -- is inadequate in certain respects, and that something called the "New Principle" ought to take its place. This paper argues that the Principle Principal need not be discarded. On the contrary, Lewis et al. can get everything they need -- including the New Principle -- from the Principal Principle itself, while avoiding the problems that originally caused them to abandon that principle. In the course of the discussion, the application of the Principal Principle to conditional probabilities is examined.

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