Ladd, George Trumbull, 1842–1921, American philosopher, b. Painesville, Ohio, grad. Western Reserve Univ., 1864, and Andover Theological Seminary, 1869. He taught at Yale from 1881 until his retirement in 1906. Influenced by Hermann Lotze, he worked primarily in experimental psychology and founded the psychology laboratory at Yale. His books include Elements of Physiological Psychology (1887, rev. ed. 1911) and Knowledge, Life, and Reality (1909).