His work was instrumental in the development of logical positivism and linguistic analysis. Ludwig Wittgenstein's book Logische- Philosophische Abhandlung (Tractatus Logico-Philosophicus) (1922) is based upon notes he took as a soldier in World War I and written while on a leave of absence.
Wittgenstein believed that, in this book, he had solved all philosophical problems and as a result after the war he decided to abandon philosophy and went to teach at a grammar school in Austria.
In TractatusLudwig Wittgenstein argues that our world is composed of facts, pictured by thoughts, which are in turn expressed by propositions of a logically structured language. Thus, a world made up of atomic facts is described by a language of atomic propositions in a one-to-one correspondence. Everything beyond this is literally nonsense, including metaphysics, ethics, religion, and aesthetics, and this formed one of the basic doctrines of logical positivism. He writes: "Whereof one cannot speak, thereof one must be silent."
Aside from a single article, Tractatus was the only thing he published during his life, but it was enough to solidify his reputation and position in Western philosophy. Later work, published posthumously in the Philosophical Investigations (1953), argued that ordinary language is constructed less strictly and tightly than he had written in Tractatus, and that communicating a clear picture of reality is often not important in linguistic success. Wittgenstein came to believe that he had oversimplified the way language works, and so tried to construct a new explanation.
This new explanation was that language is essentially a social instrument which is constantly being developed to serve an ever-changing set of purposes. Thus, instead of a "picture," language is described as being more of a "tool" or a "game." This allows for a more tolerant position regarding religion than his earlier writings did because Wittgenstein did not believe that there existed any privileged position from which a language game could be evaluated or criticized.