On Certainty

On Certainty (German: Über Gewissheit, original spelling German: Über Gewißheit) is a philosophical book composed from the notes written by Ludwig Wittgenstein just prior to his death. Some of the notes were left at the home of G. E. M. Anscombe, who later compiled the notes into a book.

The book's concerns are largely epistemological, its main theme being that there are some things which must be exempt from doubt in order for human practices to be possible (i.e. 'doubt' being a practice as well). The book takes as its starting point the 'here is one hand' argument made by G. E. Moore and examines the place of claims to know in our knowledge.

Another important point is his claim that all doubt is embedded into underlying beliefs and therefore that the most radical forms of doubt must be rejected since they form a contradiction within the system that expressed them. Wittgenstein also provides a novel refutation of various forms of philosophical skepticism. The book was published posthumously in 1969 from notebooks written in the last two years of his life.