Having been a student of William James and Josiah Royce, C. I. Lewis carried on the tradition of Harvard pragmatism and became its foremost exponent. He made important contributions to logic, epistemology, and the theory of values, and had he lived to complete his book on ethics, he might well have made an important contribution to that field, as well. As a professor at Harvard from 1920 to 1953 he taught many of those who became the leading American philosophers of the generation after his; but his greatest influence was exerted through his writings, which included six books published during his lifetime and many articles.

The oldest of five children of Irving and Hannah Dearth Lewis, Clarence Irving Lewis was born in Stoneham, Massachusetts, on 12 April 1883. Irving Lewis was a socialist whose support of the Knights of Labor led to his being blacklisted from his trade as a shoemaker, leaving...