The New York Times memorialized him as "a leading authority on symbolic logic and on the philosophic concepts of knowledge and value.
His father was a skilled worker in a shoe factory, and Lewis grew up in relatively humble circumstances.
[9] In 1905, Harvard College awarded Lewis the Bachelor of Arts cum laude after a mere three years of study, during which time he supported himself with part-time jobs.
Lewis restated this criticism in his reviews[citation needed] of both editions of Principia Mathematica.
[15] Lewis's strict implication is now a historical curiosity, but the formal modal logic in which he grounded that notion is the ancestor of all modern work on the subject.
At the time of its publication, it included the only discussion in English of the logical writings of Charles Sanders Peirce.
[16] This book followed Russell's 1900 monograph on Leibnitz, and in later editions he removed a section that seemed similar to it.
[14] Around 1930, with the introduction of logical empiricism to America by German and Austrian philosophers fleeing Europe under Nazi Germany, American philosophy went through a turning point.
This new doctrine, with its emphasis on scientific models of knowledge and on the logical analysis of meaning, soon became dominant, challenging American philosophers such as Lewis who held a naturalistic or pragmatic approach.
[19] Reflecting on the differences between pragmatism and positivism, Lewis devised the notion of cognitive structure, concluding that any significant knowledge must come from experience.
Concepts, according to Lewis' explanation of Peirce, are abstractions in which the experience is to be considered, rather than any "factual" or "immediate" truth.
Furthermore, according to Lewis' interpretation of Peirce, knowledge of something requires that the verifying experience itself be actually experienced as well.
Lewis firmly objected to the positivist interpretation of value statements as being merely "expressive", devoid of any cognitive content.
In his 1946 essay Logical Positivism and Pragmatism Lewis set out both his concept of sense meaning, and his thesis that valuation is a form of empirical cognition.
Lewis argued that there is a deep difference between the seemingly similar concepts of pragmatic meaning and the logical-positivist requirement of verification.
Thus, according to Lewis, the positivist view precisely omits the necessary empirical meaning as it would be called by the pragmatist.
Lewis argues against the logical positivist who shut their eyes to precisely that which properly confirms a sentence, namely the content of experience.
[22] Lewis was an early exponent of coherentism, particularly as supported by probability observations such as those advocated by Thomas Bayes.
[23] He was the first to employ the term "qualia", popularized by his doctoral student Nelson Goodman, in its generally agreed modern sense.
From 1946 until his death, he wrote many drafts of chapters of a proposed treatise on ethics, which he did not live to complete.
Lewis's work has been relatively neglected in recent years, even though he set out his ideas at length.
He can be understood as both a late pragmatist and an early analytic philosopher, and had students of the calibre of Brand Blanshard, Nelson Goodman, and Roderick Chisholm.
[28] Ten lectures and short articles that Lewis produced in the 1950s were collected and edited by John Lange in 1969.