Unknown Probabilities, Bayesianism, and De Finetti’s Representation Theorem

Abstract

In the development of the theory of subjective probability and in discussions about it an important role has been played by de Finetti’s representation theorem and by a number of related results presented in de Finetti’s classic monograph.¹ This theorem, together with the notion of exchangeability (among its aliases there are the terms equivalence, permutability, and symmetry), was originally put forward by Bruno de Finetti as a solution to a problem to which his subjectivistic interpretation of probability had led him. Although this theorem is mentioned in many expositions of the theory of subjective probability, there are not many satisfactory discussions of its significance available to philosophers. (The best one, and almost the only one, is Braithwaite’s paper ‘On Unknown Probabilities’.²) The purpose of the present paper is not to present any new results but rather to call attention to certain philosophical issues connected with it that apparently are not as fully appreciated as they ought to be.