Joseph Berkovitz (Toronto) gives a talk at the MCMP Colloquium (20 November, 2014) titled "On de Finetti's Instrumentalist Philosophy of Probability". Abstract: De Finetti is one of the founding fathers of the modern theory of subjective probability, where probabilities are coherent degrees of belief. De Finetti rejected the idea that subjective probabilities are supposed to be guesses, predictions or hypotheses about the corresponding objective probabilities. He argued that probabilities are inherently subjective, and that none of the objective interpretations of probability makes sense. While de Finetti’s theory has been influential in science and in philosophy, it has

encountered various objections. In particular, it has been argued that de Finetti’s concept of probability is too permissive, licensing degrees of belief that we would normally call ‘crazy’. Further, de Finetti is commonly conceived as giving an operational, behaviorist definition of degrees of belief and accordingly of probability. The claim is that degrees of belief are defined in terms of behaviors and behavioral dispositions in (hypothetical and actual) betting circumstances. Thus, the theory is said to inherit the difficulties embodied in operationalism and behaviorism. I argue that these and some other objections are unfounded as they overlook various central aspects of de Finetti’s philosophy of probability. I then propose a new interpretation of de Finetti’s theory that highlights these central aspects and explains how they are integral part of de Finetti’s instrumentalist philosophy of probability.