Lewis, Clarence Irving, 1883–1964, American philosopher, b. Stoneham, Mass., grad. Harvard (B.A., 1906; Ph.D., 1910). After teaching (1911–20) at the Univ. of California, he was professor of philosophy at Harvard from 1920 to 1953, when he became professor emeritus. Lewis's importance as a philosopher lies in his combination of symbolic logic with an essentially pragmatic epistemology. After studying logic under Josiah Royce, he developed his own system of symbolic logic in opposition to the Principia Mathematica of Bertrand Russell and Alfred North Whitehead. However, he soon began investigations in the field of epistemology. In his main work, Mind and the World-Order (1929), he developed a position according to which the choice between logical (and thus philosophical) systems must be based on pragmatic grounds. His other works include A Survey of Symbolic Logic (1918), Symbolic Logic (with C. H. Langford, 1932), An Analysis of Knowledge and Valuation (1946), Our Social Inheritance (1957), and The Ground and Nature of the Right (1955).
See his Collected Papers, ed. by J. D. Goheen and J. L. Mothershead (1970); J. R. Saydah, The Ethical Theory of Clarence Irving Lewis (1969).