C. I. Lewis

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Last Updated on May 5, 2015, by eNotes Editorial. Word Count: 2341

Article abstract: One of the leading American philosophers of his generation, Lewis responded to developments in logic and science by combining philosophical analysis with pragmatism. He also drew renewed attention to Kantian ethics.

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Early Life

Clarence Irving Lewis grew up in small Massachusetts towns and in the White Mountains of New Hampshire. Later he commented that mountains and deep woods had always had special meaning for him. His parents were orthodoxly religious. His father, who worked in a shoe factory, was quiet and thoughtful and had strong convictions concerning social betterment. He belonged to the Temperance movement, admired Fabian socialism, and joined the Knights of Labor. After involvement in a strike, he was blacklisted by the employers, losing both his job and his home. The family was condemned to years of meager existence.

To help his family, C. I. Lewis early began to undertake part-time and summer farm and factory work. When he was thirteen, he started to think speculatively about the cosmos, questioning the biblical account of it. He later described this as the period of the most intense and furious thinking he ever experienced, his native skepticism clashing explosively with his orthodox upbringing. When he was fifteen and doing summer farm work in the White Mountains, his employer, an elderly woman, encouraged him by revealing that she too had heretical thoughts and by listening at length to his. A year or two later, he began to read about the history of Greek philosophy and found that many of his speculations had been anticipated by the pre-Socratics.

Lewis received a solid education at the public high school of Haverhill and determined to go on to college. He entered Harvard in 1902. Tuition at that time was $150 per year; he had accumulated enough savings from his earlier work so that he was able to enter, and by continuing to do part-time work as a waiter and tutor, he was able to pay his way. He hastened to take his bachelor’s degree in three years, however, to minimize expense.

At Harvard, President Charles W. Eliot’s system of free electives was in place, and Lewis chose to study mainly philosophy. This was the golden age of Harvard philosophy, and his professors included philosophers and psychologists such as Josiah Royce, William James, Hugo Münsterburg, and later George Santayana and Ralph Barton Perry. It was Royce whom Lewis described as his own paradigm of a philosopher; Lewis admired what he called Royce’s ponderous cogency and respected Royce’s absolute idealism, though he did not accept it.

After completing his undergraduate program, Lewis found work as a teacher of English for three years. During this period he married his high-school sweetheart, and soon their first child was born. In 1908, Lewis returned to Harvard for graduate work in philosophy, again studying speedily in order to save money. He earned his doctoral degree in 1910, and in 1911 he secured a teaching position in philosophy at the University of California, Berkeley.

Life’s Work

At Harvard, Royce had encouraged Lewis to study new developments in symbolic and mathematical logic, and at Berkeley, Lewis began teaching in this area. Feeling the need for a better textbook, he set out to write A Survey of Symbolic Logic. This was a useful contribution at the time but in 1932 was superseded by Symbolic Logic, which Lewis wrote in collaboration with C. H. Langford. Both books devoted most of their space to presenting in accessible form results originated by others.

There is, however, one new contribution to logic that Lewis introduced in these books: the theory of what he called “strict implication.” This was in opposition to philosopher Bertrand Russell, who had studied the truth-functional conditional, which he had called “material implication.” A truth-functional conditional with false antecedent is true regardless of whether its consequent is true; Russell had confusingly expressed this point by saying that a false proposition implies any proposition. Lewis was incensed at this, because in the usual language of logic, to say that one proposition implies another is to say that the latter can validly be inferred from the former; however, it is not true in general that from a false proposition one may validly infer every proposition.

Lewis’s response was to introduce the notion of strict implication and to construct a formal system for it. Strict implication is the relation that holds between one proposition and another when, if the former is true, the latter must with logical necessity also be true. Lewis drew up sets of axioms for the theory of strict implication, employing also the correlative notion of possibility: a proposition being understood to be possible in this sense when and only when its negation is not logically impossible. In Lewis’s system, an impossible proposition does strictly imply any proposition, but no proposition strictly implies others merely because of its falsity. Lewis had begun the branch of logic that has come to be called “modal logic.”

In 1920, Lewis was called back to Harvard to join its philosophy faculty. He remained until his retirement in 1953. Lewis became an admired teacher at Harvard, noted for his eloquence in courses on the theory of knowledge and on Immanuel Kant’s philosophy. Tall and dignified, usually in a tweed suit, he had a mustache and often wore a pince-nez.

Lewis’s position as a significant American philosopher rests primarily on two large works, Mind and the World-Order and An Analysis of Knowledge and Valuation. Both books deal mainly with epistemological issues.

The earlier book is the more successful of the two because of its livelier style and its greater timeliness. The philosophical issue most prominent in this book is the nature of a priori knowledge, which had become a source of controversy in the 1920’s. Lewis was confident that there is an important distinction to be drawn between propositions such as those of logic and mathematics, which are knowable a priori without need of sensory evidence, and empirical propositions knowable only on the basis of sensory observation.

Rationalists had held that the human faculty of reason sees intellectually into the essential nature of reality, providing us with substantive information a priori; Kant had held that our faculty of sensibility provides us with pure intuitions that inform us a priori about the structure of space and time. Lewis rejected these views, holding that the mind cannot acquire information in such ways. Lewis’s view of a priori knowledge was that it is wholly analytic; it does not convey any substantive information but has to do only with the conceptual structures we create. We choose what concepts to employ in classifying the patterns of our experience. The set of concepts we choose to use changes and evolves over time. Whatever concepts we employ at a given time, there will be necessary truths about the relationships of their meanings, truths that we can know a priori merely by reflection on what we mean by our words or symbols.

Lewis went on to add that, in his view, a priori knowledge is made by mind and is capable of being altered. He called his view “conceptualistic pragmatism,” thereby suggesting linkage with the pragmatic philosophies of Charles Sanders Peirce, William James, and John Dewey. Lewis recognized that they did not share any clear common doctrine, but still, for Lewis, pragmatism stood for the idea that human activity can create truth. He thus seemed committed to the exciting but disturbing idea that any a priori truth can be altered by us if we choose to do so.

Much that Lewis had to say about a priori knowledge is impressive and plausible. There is an unresolved tension, though, between his insistence, on one hand, that a priori truths are necessarily true, and his insistence, on the other hand, that they are under our control. If it is a necessary truth that five plus seven equals twelve, then this sum cannot be otherwise, and if it cannot be otherwise, we cannot make it be otherwise.

Here it may be that Lewis was not distinguishing sufficiently between the truth that five plus seven equals twelve and the symbolism we use to convey this truth: 5 + 7 = 12. We could, of course, change our symbolic conventions, letting the numeral 5 stand for six and the numeral 7 stand for eight, in which case the expression “5 + 7 = 12” could convey something false rather than something true. Yet this would not mean that we had made five and seven no longer equal to twelve; it would mean only that we had altered our way of expressing this necessary, unalterable truth.

In An Analysis of Knowledge and Valuation, Lewis gives more emphasis to elaborating his theory of empirical knowledge. He introduces several distinctive notions of his own. He speaks of what he calls expressive statements, which he thinks of as worded in a private language one can use to formulate for oneself the indubitable content of one’s immediate sense experience. What he calls “terminating judgments” are predictions involving expressive statements. A terminating judgment says that if some specified sense experiences occur, and if one consciously acts in a certain way, then in all probability other specified sense experiences will occur. Such terminating judgments often can be decisively verified or falsified. Nonterminating judgments are complex logical combinations of innumerable terminating judgments; they can never be finally verified or falsified. Lewis’s view is that ordinary judgments about physical objects are nonterminating judgments.

This position looks rather like phenomenalism, that is, the reduction of talk about the external world to talk about immediate experience. Lewis does not want to dissolve the physical world into sense experience, however. For him, it is only what he calls the “intensional meaning” of ordinary judgments about physical objects that can be translated into complexes of expressive statements. Their denotational meaning he holds to be independent of the intensional meaning. Here Lewis seems committed to something like Kant’s distinction between phenomena and things-in-themselves. The view is puzzling, because we might have expected that the intensional meaning of a judgment would determine its denotation; it is not easy to see how denotation is to be understood if it is independent of intension.

The final section of An Analysis of Knowledge and Valuation deals with value judgments. Rejecting all noncognitivist theories, Lewis defends a form of naturalism, arguing that value judgments are a type of empirical judgment. There are immediate experiences of satisfaction of which we can be aware, and ordinary value judgments are empirical predictions that such experiences will arise in connection with specified objects.

In his last decade, Lewis devoted himself mainly to writing about ethics. His The Ground and Nature of the Right, Our Social Inheritance, and the posthumous Values and Imperatives belong to this period. He saw moral obligation as necessarily linked with value: One’s moral obligation is to do what will promote value. This view is akin to utilitarianism, but, contrary to the utilitarians, Lewis held that there are incommensurable kinds of good experiences, so we cannot establish what our moral obligations are merely by adding up the quantities of potential good that alternative actions would probably achieve. Lewis did not discuss the objection that utilitarianism is incompatible with justice, an objection that some later philosophers have emphasized.

Lewis advocated something like a Kantian categorical imperative: his principle that like cases should be judged the same way, or that one ought always to abide by universal rules applicable to everyone. He calls this a “rational principle” and presumably would have classified it as an analytic truth, although, as he states it, it seems rather substantive.


Lewis made an original contribution to logic by inventing modal logic. His work in epistemology helped spread in the United States a major new view of a priori knowledge as wholly analytic. His work on empirical knowledge and on value theory has been less widely influential, but his view of ethics contributed to a renewal of interest in Kantian ethical principles.

Additional Reading

Colella, E. Paul. C. I. Lewis and the Society Theory of Conceptualistic Pragmatism: The Individual and the Good Social Order. San Francisco: Mellen Research University Press, 1992. Examines the individual and the social order in Lewis’s version of pragmatism.

Gowans, Christopher W. “Two Concepts of the Given in C. I. Lewis: Realism and Foundationalism.” Journal of the History of Philosophy 27, no. 4 (October, 1989): 573-591. This essay examines realism and foundationalism in Lewis’s beliefs.

Luizzi, Vincet. A Naturalistic Theory of Justice: Critical Commentary on, and Selected Readings from, C. I. Lewis’ Ethics. Washington, D.C.: University Press of America, 1981. This volume looks at ethics and justice from Lewis’s point of view.

Quine, Willard V. “Truth by Convention.” Reprinted in Readings in Philosophical Analysis, edited by Herbert Feigl and Wilfred Sellars. New York: Appleton-Century-Crofts, 1949. Lewis’s younger colleague Quine examines the view that a priori statements are based on conventions of language.

Quine, Willard V. “Two Dogmas of Empiricism.” In From a Logical Point of View. Cambridge, Mass.: Harvard University Press, 1953. This famous article attacks the view, held by Lewis and many others, that there is a legitimate philosophical distinction between a priori and empirical statements.

Rosenthal, Sandra B. The Pragmatic a Priori: A Study in the Epistemology of C. I. Lewis. St. Louis: W. H. Green, 1976. This volume looks primarily at the epistemology of Lewis while emphasizing the pragmatic dimension.

Saydah, J. Roger. The Ethical Theory of Clarence Irving Lewis. Athens: Ohio University Press, 1969. This volume presents a detailed study of the ethical position held by Lewis.

Schilpp, Paul Arthur, ed. The Philosophy of C. I. Lewis. La Salle, Ill.: Open Court, 1968. Contains an autobiographical statement by Lewis, more than a dozen essays on his philosophy by others, his own fairly brief replies to those comments, and a bibliography of his writings.

West, Cornel. The American Evasion of Philosophy: A Genealogy of Pragmatism. Madison: University of Wisconsin Press, 1989. This readable survey of American pragmatism contains only a few references to Lewis because it emphasizes the social dimension. It is nevertheless helpful for placing Lewis in relation to other pragmatists.

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