Clark L. Hull, in full Clark Leonard Hull (born May 24, 1884, Akron, N.Y., U.S.—died May 10, 1952, New Haven, Conn.), American psychologist known for his experimental studies on learning and for his attempt to give mathematical expression to psychological theory. He applied a deductive method of reasoning similar to that used in geometry, proposing that a series of postulates about psychology could be developed, from which logical conclusions could be deduced and tested. If a test failed, the postulate could be revised, and if the test then succeeded, the findings would be added to the body of psychological science.