Richard Jeffrey

American philosopher who developed Jeffrey conditionalization — Bayesian updating for uncertain observations — and defended radical probabilism, the view that probability is always subjective.

Jeffrey conditionalization: extends Bayesian updating to cases where the observation doesn't make any proposition certain but merely shifts its probability — a more realistic model of learning from experience. Radical probabilism: there are no logical constraints on prior probabilities beyond coherence. The Logic of Decision: decision theory for uncertain beliefs.