Tractatus Logico-Philosophicus

The Tractatus Logico-Philosophicus (Latin for "Logical-Philosophical Treatise") is the only book-length philosophical work published by the Austrian philosopher Ludwig Wittgenstein in his lifetime. It was an ambitious project: to identify the relationship between language and reality and to define the limits of science. It is recognized as a significant philosophical work of the twentieth century. G. E. Moore originally suggested the work's Latin title as homage to Tractatus Theologico-Politicus by Baruch Spinoza.

Wittgenstein wrote the notes for Tractatus while he was a soldier during World War I and completed it when a prisoner of war at Como and later Cassino in August 1918. It was first published in German in 1921 as Logisch-Philosophische Abhandlung. Tractatus was influential chiefly amongst the logical positivists of the Vienna Circle, such as Rudolf Carnap and Friedrich Waismann. Bertrand Russell's article "The Philosophy of Logical Atomism" is presented as a working out of ideas that he had learnt from Wittgenstein.

Tractatus employs a notoriously austere and succinct literary style. The work contains almost no arguments as such, but, rather, consists of declarative statements which are meant to be self-evident. The statements are hierarchically numbered, with seven basic propositions at the primary level (numbered 1–7), with each sub-level being a comment on or elaboration of the statement at the next higher level (e.g., 1, 1.1, 1.11, 1.12).

Wittgenstein's later works, notably the posthumously published Philosophical Investigations, criticised many of the ideas in Tractatus.