Subjectivism, Objectivism and Objectivity in Bruno de Finetti’s Bayesianism

Abstract

The paper will focus on Bruno de Finetti’s position, which combines Bayesianism with a strictly subjective interpretation of probability. For de Finetti, probability is always subjective and expresses the degree of belief of the evaluating subject. His perspective does not accommodate a notion of “objective chance ” in the way other subjectivists, including Frank Ramsey, do. To de Finetti’s eyes, objectivism, namely the idea that probability depends entirely on some aspects of reality, is a distortion, and the same holds for the idea that there exists an absolute notion of objectivity, to be grounded on objective facts. For him there is no problem of objectivity beyond that of the evaluation of probabilities in a Bayesian framework. This is a complex procedure, which includes subjective elements as well as the consideration of objective elements like observed frequencies. 1. De Finetti’s subjectivism. Bruno de Finetti used to call his perspective “subjective Bayesianism ” (de Finetti 1969, p. 3), to stress that in his conception Bayes ’ scheme is assigned a central role, and that it goes hand in hand with a subjective view of probability. Inspired by what we would today call a radically “anti-realist” philosophy, de Finetti finds in the Bayesian approach a way of combining empiricism and pragmatism. The resulting position is not only incompatible with any perspective based on an objective notion of