Richard Jeffrey

Who was Richard Jeffrey?

Richard C. Jeffrey was an American philosopher, logician, and probability theorist. He was a native of Boston, Massachusetts.

Jeffrey served in the U.S. Navy during World War II. As a graduate student he studied under Rudolf Carnap, and Carl Hempel. He received his M.A. from the University of Chicago in 1952 and his Ph.D. from Princeton in 1957. After holding academic positions at MIT, City College of New York, Stanford University, and the University of Pennsylvania, he joined the faculty of Princeton University in 1974 and became a professor emeritus there in 1999. He was also a visiting professor at the University of California, Irvine.

As a philosopher, Jeffrey specialized in epistemology and decision theory. He is perhaps best known for defending and developing the Bayesian approach to probability—specifically, for inventing "Jeffrey conditioning", a way of modeling the change in the probability of a proposition in light of new evidence.