A More Robust Definition of Subjective Probability

The goal of choice-theoretic derivations of subjective probability is to separate a decisionmaker's underlying beliefs (subjective probabilities of events) from their preferences (attitudes toward risk). Classical derivations have all relied upon some form of the Marschak-Samuelson "Independence Axiom" or the Savage "Sure-Thing Principle, " which imply that preferences over lotteries conform to the expected utility hypothesis. This paper presents a choice-theoretic derivation of subjective probability in a Savage-type setting of purely subjective uncertainty, which neither assumes nor implies that the decisionmaker's preferences over lotteries necessarily conform to the expected utility hypothesis.