Colloquium Lecture: Katie Elliott (Brandeis University), "The Principal Principle: What is it? Who cares?"

Abstract: The “Principal Principle” is David Lewis’s attempt to characterize the epistemic role of objective chance.  Despite being my very favorite topic in philosophy, the principle is no longer frequently discussed.  One problem is that key terms in the principle are left undefined.  Another is that the principle is framed inside of a Bayesian approach to epistemology that should be more controversial than the principle itself.  Perhaps worst of all, the principle invokes a notorious metaphysical posit—chance—which many philosophers still hope to be able to do without.  Even Lewis eventually gave up on the Principal Principle, partly thanks to work on the “New Principle” by Edward Hall. 

My own view is that the Principal Principle is motivated by a deep and important insight into the epistemology of empirical reasoning.  The goal of my talk is to say what that insight is and why it’s important, but without mentioning any weird stuff like “probabilities” or “chances” until necessary.