An Adamite Derivation of the Principles of the Calculus of Probability

Abstract

If Adam was a rational man even before he had garnered much experience of the world, and if the ability to reason probabilistically is an essential part of rationality (as Bishop Butler maintained when he wrote that “But, to us, probability is the very guide of life,”¹), then Adam must at least tacitly have known the Principles of the Calculus of Probability. Specifically, Adam must have known that the epistemic concept of probability — probability in the sense of “reasonable degree of belief” — satisfies these Principles, for it is the epistemic concept, rather than the frequency concept or the propensity concept, which enters into rational assessments about uncertain outcomes.² But what warrant did Adam have for either an explicit or a tacit assertion that epistemic probability satisfies the Principles of the Calculus of Probability?

This paper is based upon a lecture given at the University of Pittsburgh in January 1982. A similar thesis is developed independently by Bas van Fraassen in “Calibration: A Frequency Justification for Personal Probability,” in Physics, Philosophy, and Psychoanalysis: Essays in Honor of Adolf Grünbaum, ed. by R. S. Cohen and L. Laudan (D. Reidel: Dordrecht and Boston, 1983). I dedicate the paper to Wesley C. Salmon, because he explored with penetration and devotion the epistemic applicability of the frequency concept of probability.