From Lewisian Chance to Humean Chance

Abstract This chapter introduces David Lewis’ highly influential views on objective chance, from his 1980 treatment of objective chance and the Principal Principle (PP) to his 1994 Humean Best System analysis of chance. Some unfortunate consequences of Lewis’ theory are discussed: (1) if the Best System of laws for the world has no probabilistic laws in it, then there are no objective chances in the world. (2) Physical determinism is incompatible with non-trivial objective chances. (3) Events in the past are “no longer chancy.” It is argued that a good account of chance can and should reject all three of these consequences. But two pillars of Lewis’ approach remain valid. First, his contention that the ability to demonstrably play the chance role captured by the PP is crucial for any account of the nature of objective chance. And second, his intuition that a Best System approach in which chance facts supervene on patterns in the Humean Mosaic is a promising approach vis-à-vis allowing such a demonstrable grounding of the PP.