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.