Probability: One or Many?

The article deals with the interpretation of probability. There is no doubt that irrespective of its philosophical meaning probability can be applied to all sorts of problems by virtue of its mathematical properties alone. However, it is the philosophical significance of probability that has fostered endless debate. More than three and a half centuries after the “official” birth of probability with the work of Blaise Pascal and Pierre Fermat, the dispute on the interpretation of probability is far from being settled. One can distinguish at least four interpretations: frequentism, propensionism, logicism and subjectivism, each of which admits of a number of variants. Against the tendency to claim that the natural sciences call for a strongly objective, realistic notion of probability, and that the subjective interpretation is at most applicable to the social sciences, it will be argued that, on closer inspection, subjectivism has the resources to cover all uses of probability, in the natural as well as the social sciences. This conclusion is substantiated by some ideas borrowed from the writings of Frank Ramsey, Bruno de Finetti and Harold Jeffreys, ideas that have been overlooked by the otherwise extensive literature on these authors.