 Clarence Irving (C.I.) Lewis was perhaps the most important American academic philosopher active in the 1930s and 1940s. He made major contributions in epistemology and logic, and, to a lesser degree, ethics. Lewis was also a key figure in the rise of analytic philosophy in the United States, both through the development and influence of his own writings and through his influence, direct and indirect, on graduate students at Harvard, including some of the leading analytic philosophers of the last half of the 20th century.