Hull spent the mature part of his career at Yale University, where he was recruited by the president and former-psychologist, James Rowland Angell. He performed research demonstrating that his theories could predict behavior. His most significant works were the Mathematico-Deductive Theory of Rote Learning (1940), and Principles of Behavior (1943), which established his analysis of animal learning and conditioning as the dominant learning theory of its time. Hull’s model is expressed in biological terms: Organisms suffer deprivation; deprivation creates needs; needs activate drives; drives activate behavior; behavior is goal directed; achieving the goal has survival value.