A Subjectivist’s Guide to Objective Chance

Abstract

We subjectivists conceive of probability as the measure of reasonable partial belief. But we need not make war against other conceptions of probability, declaring that where subjective credence leaves off, there nonsense begins. Along with subjective credence we should believe also in objective chance. The practice and the analysis of science require both concepts. Neither can replace the other. Among the propositions that deserve our credence we find, for instance, the proposition that (as a matter of contingent fact about our world) any tritium atom that now exists has a certain chance of decaying within a year. Why should we subjectivists be less able than other folk to make sense of that?

I am grateful to several people for valuable discussions of this material; especially John Burgess, Nancy Cartwright, Richard Jeffrey, Peter Railton, and Brian Skyrms. I am also much indebted to Mellor (1971), which presents a view very close to mine; exactly how close I am not prepared to say.