1883 – 1964
Clarence Irving Lewis (1883–1964) was an American philosopher at Harvard University and a founding figure of conceptual pragmatism. He made foundational contributions to modal logic and epistemology, developing the logic of strict implication as an alternative to material implication and arguing that knowledge is shaped by a priori conceptual frameworks applied to sensory experience.
Developed the system of strict implication, a rigorous formal treatment of modal logic predating Kripke semantics
Founded conceptual pragmatism, synthesizing Kantian apriorism with Peircean pragmatism in Mind and the World Order (1929)
Introduced the distinction between the a priori conceptual framework and the given in experience
Authored An Analysis of Knowledge and Valuation (1946), a landmark work in epistemology and value theory
Wrote A Survey of Symbolic Logic (1918), an early comprehensive treatment of formal logic in English