In Praise of a Modest Probabilism

Mark Kaplan
University of Wisconsin-Milwaukee

Orthodox Bayesians characteristically hold that

(1) for each person and each hypothesis she comprehends, there is a precise degree of confidence that person has in the truth of that hypothesis, and

(2) no person can be counted as rational unless the degree of confidence assignment she thus harbors satisfies the axioms of the probability calculus.

It is a picture of rational persons that many epistemologists have found hard to swallow. They have complained that its psychology is not credible, that its condition on rationality is too demanding, that its advice about what opinions to hold in case of ignorance is unsupportable.

I will argue that, powerful though these criticisms of orthodox Bayesianism are, there is available a kind of Bayesianism that escapes them. In so doing I will undertake to defend what is, perhaps, the most disorienting, and philosophically interesting, feature of the Bayesian approach to epistemology: its claim to find in decision theory a foundation for epistemological doctrines.