Clarence Irving Lewis (1883–1964) was born in Stoneham, Massachusetts, and graduated from Harvard (1906), where his teachers included William James and Josiah Royce — the former’s pragmatism and the latter’s absolute idealism would permanently mark his philosophy. He taught at the University of California, Berkeley from 1911 to 1920, before returning to Harvard, where he remained until his retirement in 1953 as Edgar Pierce Professor of Philosophy. His work joins two fields that at first glance seem distant — formal logic and epistemology — around a single concern: how concepts and deductive systems, though conventional in origin, can still organize experience objectively.

Dissatisfied with the material implication of Russell and Whitehead’s logic — which declares any conditional true whenever its antecedent is false or its consequent true, generating the so-called “paradoxes of material implication” — Lewis proposed in A Survey of Symbolic Logic (1918) the concept of strict implication: “p strictly implies q” holds when it is impossible for p to be true and q false, that is, when the implication captures a relation of necessity rather than a mere factual distribution of truth-values. In Symbolic Logic (1932), co-written with C. H. (Cooper Harold) Langford, this intuition was developed into a hierarchy of five successively stronger modal systems, the S1 through S5 systems, which would become the starting point of modern modal logic.

In epistemology, Lewis developed in Mind and the World Order (1929) his conceptual pragmatism: knowledge results from the encounter between an immediate sense datum — “the given” — and conceptual categories the mind applies to that datum to constitute objects of experience. Unlike traditional apriorism, for Lewis the a priori principles (logical, categorial) are not necessary truths about the world but stipulations expressing relations of meaning within a conceptual scheme — and can therefore, in principle, be pragmatically revised if they cease to serve the organization of experience well: this is his pragmatic a priori. In An Analysis of Knowledge and Valuation (1946), his mature epistemological work, he deepened the analysis of the sense datum, defined as immediate, incorrigible, and at the same time ineffable — describable only through an expressive language that must not be confused with objective judgments about the world.

Key Concepts

  • Strict implication: a logical relation according to which “p strictly implies q” means it is impossible for p to be true and q false, proposed as an alternative to material implication in order to avoid the latter’s paradoxes.
  • S1–S5 systems: a hierarchy of modal logic systems, presented with C. H. Langford in Symbolic Logic (1932), formalizing notions of necessity and possibility and marking the founding moment of twentieth-century modal logic.
  • Conceptual pragmatism: the thesis that knowledge arises from applying conceptual categories — conventional but not arbitrary — to an immediate sense datum, with the choice among competing conceptual schemes being a pragmatic matter.
  • The given: the immediate sensory element of experience, prior to any conceptual interpretation — certain and incorrigible, yet ineffable in purely objective terms.
  • Pragmatic a priori: a reformulation of the Kantian notion of the a priori: logical and categorial principles do not describe necessities of the world but express relations of meaning within an adopted conceptual scheme, and can be revised for pragmatic reasons.

Influenced by

  • William James — pragmatism as philosophical method and attention to concrete experience as the criterion of meaning
  • Josiah Royce — absolute idealism and reflection on the categorial structure of knowledge; both were Lewis’s teachers at Harvard
  • Kant — the distinction between sense datum and conceptual form, reworked by Lewis as the basis of conceptual pragmatism
  • Russell and Whitehead — the symbolic logic of the Principia Mathematica, whose material implication Lewis criticized as the starting point for his own modal logic
  • Peirce — the American pragmatist tradition on meaning and scientific method

Influenced

  • Quine — his student at Harvard, who developed his critique of the analytic-synthetic dualism in direct dialogue with Lewis’s conceptual pragmatism
  • Nelson Goodman and Roderick Chisholm — Lewis’s students at Harvard, who both extended and criticized his epistemological program
  • Wilfrid Sellars — whose critique of the “myth of the given” takes direct aim at Lewis’s notion of the sense datum
  • Ruth Barcan Marcus and Saul Kripke — developed possible-worlds semantics for the modal systems that originated in Lewis’s S1–S5
  • Twentieth-century analytic epistemology of justified true belief, which inherits from Lewis the foundationalism of the given as the basis of justification

Works

A Survey of Symbolic Logic (1918); Mind and the World Order: Outline of a Theory of Knowledge (1929); Symbolic Logic (with C. H. Langford, 1932); An Analysis of Knowledge and Valuation (1946); The Ground and Nature of the Right (1955); Our Social Inheritance (1957).

See also

William James, Russell, Kant, Quine, Peirce