Name
Clarence Irving Lewis
Birth
April 12, 1883 (Stoneham, Massachusetts)
Death
February 3, 1964 (Cambridge, Massachusetts)
School/tradition
Analytic
Main interests
Epistemology, Logic, Ethics, Aesthetics
Notable ideas
Conceptual pragmatism, qualia
Influences
Josiah Royce, Ralph Barton Perry
Influenced
Nelson Goodman, Willard Van Orman Quine, Roderick Chisholm, Roderick Firth, W. K. Frankena,Robert Paul Wolff
Clarence Irving Lewis (April 12, 1883 Stoneham, Massachusetts - February 3, 1964 Cambridge, Massachusetts), usually cited as C. I. Lewis, was an American academic philosopher and the founder of conceptual pragmatism. First a noted logician, he later branched into epistemology, and during the last 20 years of his life, he wrote much on ethics.

Life
Lewis studied logic under his eventual Ph.D. thesis supervisor, Josiah Royce, and is arguably the founder of modern philosophical logic. In 1912, two years after the publication of the first volume of Principia Mathematica, Lewis began publishing articles taking exception to Principia' s pervasive use of material implication, more specifically, to Bertrand Russell's reading of a→b as "a implies b." Lewis restated this criticism in his reviews of both editions of PM. Lewis's reputation as a promising young logician was soon assured.
Material implication allows a true consequent to follow from a false antecedent. Lewis proposed to replace material implication with strict implication, such that a false antecedent can never strictly imply a true consequent. This strict implication was not primitive, but defined in terms of negation, conjunction, and a prefixed unary intensional modal operator, . Let X be a formula with a classical bivalent truth value. Then X can be read as "X is possibly true" (or false, as the case may be). Lewis then defined "A strictly implies B" as "~(A∧~B)". 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. Lewis's notation is still standard, but current practice usually takes its dual, ("necessity"), as primitive and as defined, in which case "A strictly implies B" is simply written as (A→B).
His first logic text, A Survey of Symbolic Logic (1918), went out of print after selling only several hundred copies. At the time of its publication, it included the only discussion in English of the logical writings of Leibniz and Charles Peirce. While the modal logic of A Survey was soon proved inconsistent, Lewis went on to devise the modal systems S1 to S5, and to set these out in Symbolic Logic (1932) as possible formal analyses of the alethic modalities. Lewis mildly preferred S2 over the others; the amended modal system of A Survey was S3. But it is S4 and S5 that have generated sustained interest, mathematical as well as philosophical, down to the present day. S4 and S5 are the beginning of what is now called normal modal logic. On Lewis's strict implication and his modal systems S1-S5, see Hughes and Cresswell (1996: chpt. 11).

Logic
This section follows Dayton (2004) closely. Around 1930, American philosophy began to experience a turning point because of the arrival of logical empiricism, brought by continental philosophers fleeing the Third Reich. This new doctrine challenged American philosophers of a naturalistic or pragmatic bent, such as Lewis. In any event, logical empiricism, with its emphasis on scientific models of knowledge and on the logical analysis of meaning, soon emerged as a, and perhaps the, dominant tendency in American philosophy.
While many saw Lewis as kin to the logical empiricists, he was never truly comfortable in such company because he declined to divorce experience from cognition. Positivism rejected value as lacking cognitive significance, also rejecting the analysis of experience in favor of physicalism. Both rejections struck him as regrettable. Indeed his growing awareness of the pragmatic tradition led him in the opposite direction. For Lewis, it is only within experience that anything can have significance for anything, and thus he came to see value as a way of representing the significance of knowledge for future conduct. These convictions led him to reflect on the differences between pragmatism and positivism, and on the cognitive structure of value experiences.
Lewis agreed that pragmatism committed one to the Peircean pragmatic test. But in a 1930 essay, "Pragmatism and Current Thought," he maintained that this commitment can be taken in either of two directions. One direction emphasises the subjectivity of experience. The other direction, and the one he took in 'his (1929), began with the Peirce's limitation of meaning to that which makes a verifiable difference in experience. Hence concepts are abstractions in which "the immediate is precisely that element which must be left out." But this claim must be properly understood. An operational account of concepts mainly eliminates the ineffable: "If your hours are felt as twice as long as mine, your pounds twice as heavy, that makes no difference, which can be tested, in our assignment of physical properties to things." Hence a concept is but a relational pattern. But it does not follow that one ought to discard the world as it is experienced:
"In one sense, that of connotation, a concept strictly comprises nothing but an abstract configuration of relations. In another sense, its denotation or empirical application, this meaning is vested in a process which characteristically begins with something given and ends with something done in the operation which translates a presented datum into an instrument of prediction and control."
Thus knowledge begins and ends in experience, keeping in mind that the beginning and ending experiences differ. Knowledge of something requires that the verifying experience be actually experienced. Thus for the pragmatist, verifiability as an operational definition (or test) of the empirical meaning of a statement requires that the speaker know how to apply the statement, and when not to apply it, and be able to trace the consequences of the statement in situations both real and hypothetical.
Lewis firmly objected to the positivist conception of value statements as devoid of cognitive content, as merely expressive. For a pragmatist, all judgements are implicitly value judgements. Lewis (1946) sets out both his conception of sense meaning, and his thesis that valuation is a form of empirical cognition.
In his essay "Logical Positivism and Pragmatism," Lewis revealed his disagreement with verificationism by comparing it unfavorably with his preferred pragmatic conception of empirical meaning. From the outset, he saw both pragmatism and logical positivism as forms of empiricism. At first glance, it would seem that the pragmatic conception of meaning, despite its different formulation and its focus on action, very much resembles the logical positivist verification requirement. Nevertheless, Lewis argued that there is a deep difference between the two: pragmatism ultimately grounds meaning on conceivable experience, while positivism reduces the relation between meaning and experience to a matter of logical form.
For Lewis, the positivist conception of meaning omits precisely what a pragmatist would count as empirical meaning. Specifying which observation sentences follow from a given sentence helps us determine the empirical meaning of the given sentence only if the observation sentences themselves have an already understood meaning in terms of the specific qualities of experience to which the predicates of the observation sentences refer. Thus Lewis saw the logical positivists as failing to distinguish between "linguistic" meaning, namely the logical relations among terms, and "empirical" meaning, namely the relation expressions have to experience. (In the well-known terminology of Carnap and Charles W. Morris, empirical meaning falls under pragmatics, linguistic meaning under semantics.) For Lewis, the logical positivist shuts his eyes to precisely that which properly confirms a sentence, namely the content of experience.

Pragmatist but no positivist
WikiProject Philosophy or the Philosophy Portal may be able to help recruit one. If a more appropriate WikiProject or portal exists, please adjust this template accordingly. Lewis (1929), Mind and the World Order, is now seen as one of the most important 20th century works in epistemology. Lewis is now included among the American pragmatists, a belated assessment that is the major theme of Murphey (2005).

Legacy

pragmatism
modal logic
Interior algebra