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Ludwig Wittgenstein wrote a series of interconnected remarks on the concept of certainty from April, 1950, until April 27, 1951, two days before his death. Although he did not live to edit this work, which was published in 1969, his observations constitute a remarkably coherent discussion of what is arguably the central problem of epistemology: the question of whether, in what sense, and by what methods it may be possible to attain absolute certainty in knowledge.

The quest for certainty is a legacy of French philosopher René Descartes’s seventeenth century rationalist philosophy. Philosophers have long sought to answer arguments brought by skepticism that knowledge, let alone certain or absolutely certain knowledge, is impossible. The problem of arriving at certain knowledge is carried forward by philosopher G. E. Moore’s essays, including “A Defence of Common Sense” (1923), “Proof of an External World” (1939), and “Certainty” (1943). In these essays, Moore tries to argue that there are items of commonsense knowledge, ultimately justified by immediate sense experience, that can be known without possibility of doubt and that can thereby constitute the foundations for all other knowledge. Wittgenstein regards Moore’s treatment of certainty as among his most important contributions to philosophy, yet he seems to appreciate the essays more as a statement of ordinary ways of thinking about the nature of certainty than for the philosophical conclusions Moore attempts to derive. Without defending skepticism, Wittgenstein mounts a devastating critique of Moore’s attempt to gain certain knowledge for commonsense beliefs.

In a numbered series of reflections, Wittgenstein explores the implications and limitations of the concept of certainty. The problems of epistemology are a mainstay for most philosophers but an unusual topic for Wittgenstein. In his early masterwork, “Logisch-philosophische Abhandlung” (1921; best known by the bilingual German and English edition title of Tractatus Logico-Philosophicus, 1922, 1961), Wittgenstein explicitly separates the theory of knowledge from philosophy properly understood. There he writes: “Psychology is no nearer related to philosophy, than is any other natural science./ The theory of knowledge is the philosophy of psychology.” (4.1121) Indeed, Wittgenstein does not address the traditional questions of epistemology outside On Certainty.

Psychological and Absolute Certainty

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The book begins with Wittgenstein’s admission that if we can grant Moore that we can know in holding up a hand before us that here is one hand, then everything else in Moore’s argument for a commonsense theory of knowledge follows. This single example, amplified by a few digressions into related knowledge claims, provides the primary focus for Wittgenstein’s criticism. Wittgenstein distinguishes between psychological certainty, as expressed in Moore’s confident assertion of the existence of his hand, and epistemic certainty as objectively incorrigible or incontrovertible belief. Wittgenstein maintains that psychological certainty is irrelevant to the truth of what we claim to know. We participate in systems of beliefs, in which different kinds of propositions play different kinds of roles. To declare one’s certainty in the truth of a particular selection of beliefs in such a system is to identify those judgments as being among a privileged set that are held fixed in our epistemic activity as not subject to revision. Wittgenstein explains: “Even if the most trustworthy of men assures me that he knows things are thus and so, this by itself cannot satisfy me that he does know. Only that he believes he knows. That is why Moore’s assurance that he knows . . . does not interest us. The propositions, however, which Moore retails as examples of such known truths are indeed interesting. Not because anyone knows their truth, or believes he knows them,...

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Belief Systems

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Wittgenstein describes the entire system of beliefs that a person may accept as being made up of different kinds of propositions in various categories and with varying purposes. He articulates a polarity principle as part of the philosophical grammar of epistemic terminology, whereby it makes no sense to speak of a belief as capable of doubt except by contrast with other beliefs that are certain: “If you tried to doubt everything you would not get as far as doubting anything. The game of doubting itself presupposes certainty.” (115) Within a belief system, some propositions may gain or lose credibility relative to other propositions about which are we are not prepared to entertain doubts. Beliefs that we are not prepared to doubt in a complex system of beliefs are those we designate in ordinary language-games as certain, as one of the main nonphilosophical uses of the word. This is the source of the mistaken philosophical idea that Moore among others in the history of philosophy tried to develop that we might also be able to attribute absolute certainty to special propositions in an even higher philosophical sense that would make them immune from any imaginable skepticism.

Wittgenstein captures the relation between the fixed and fluid propositions in an entire system of beliefs in one of his characteristically vivid metaphors, when he writes in 343: “If I want the door to turn, the hinges must stay put.” The unquestioned, and in that sense...

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An Answer to Skeptics

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On Certainty attracted a wide philosophical audience. It was received as a sequel to Wittgenstein’s Philosophische Untersuchungen/Philosophical Investigations (1953, bilingual German and English edition) and Remarks on the Foundations of Mathematics, (1956, bilingual German and English edition), and as an unconventional contribution to epistemology in its own right. Wittgenstein’s remarks on knowledge are extraordinarily rich in their variety of valuable observations about the nature and conditions of belief, certainty, and doubt.

Avrum Stroll, in his Moore and Wittgenstein on Certainty (1994), says of the “small but growing coterie of scholars” who have written book-length studies of Wittgenstein’s text (to say nothing of the scores of articles in anthologies and essays in professional philosophical journals) that “they have . . . come to realize that there is more to On Certainty than merely a commentary on Moore.” He adds: “They now realize that it contains a novel approach to the problem of certitude and to the sceptical challenges that any defender of certitude must face.” Wittgenstein’s treatment of the philosophical grammar of epistemic vocabulary in ordinary language-games in which knowledge and certainty are legitimately attributed to beliefs, by contrast with problematic uses of the same terminology by philosophers, continues to inspire Wittgenstein scholars to consider, interpret, and apply his penetrating investigations of the concept of certainty.


(Student Guide to World Philosophy)

Additional Reading

Fann, K. T., ed. Ludwig Wittgenstein: The Man and His Philosophy. New York: Dell, 1967. A collection of articles by friends, students, and scholars of Ludwig Wittgenstein. Included are articles on Wittgenstein as a person, a teacher, and a philosopher, and treatments of various aspects of Wittgenstein’s philosophical work.

Hacker, P. M. S. Wittgenstein. New York: Routledge, 1999. An excellent biographical introduction to the thoughts of the philosopher, clearly presented and requiring no special background. Bibliography.

Hacker, P. M. S. Wittgenstein’s Place in Twentieth-Century Analytic Philosophy. Oxford: Blackwell, 1996. A monumental work by a leading authority of Wittgenstein. This book thoroughly treats philosophical history before, during, and after the time of Wittgenstein.

Hallett, Garth L. Essentialism: A Wittgensteinian Critique. Albany: State University of New York Press, 1991. Strictly speaking, this book is an application of Wittgenstein’s later thought rather than an introduction to it, but Hallett is so faithful to Wittgenstein’s philosophy that the book is in fact a good guide to a correct understanding of it.

Hodges, Michael, and John Lachs. Thinking in the Ruins: Wittgenstein and Santayana on Contingency....

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