Ludwig Wittgenstein was an Austrian philosopher who lived from 1889 to 1951 and is considered to have been the greatest philosopher of the 20th century. He was the resident professor of philosophy at Cambridge University in England from 1939 to 1947. Two contemporary philosophical movements are credited to him — logical positivism and ordinary language philosophy.
Wittgenstein was born into a wealthy Austrian family. From an early age, he was involved in philosophy, and many scholars divide his contributions to the field into two or three distinct periods, depending on his age. He published very little, but two writings of his gained exceptional notoriety.
His early years are epitomized in the 75 page Tractatus Logico-Philosophicus, which is Latin for Logical-Philosophical Treatise, written in 1921 at the age of 32. It was a ambitious attempt by Wittgenstein to reconcile apriorism, belief based on arguments or principles, with atomism, the reduction of all psychological events to simple elements. An attempt to discover the logic behind language and its relationship with reality, it is considered to be one of the most important philosophical publications of the period. The publishing of Tractatus was so monumental that many in the field felt it had brought an end to philosophy by resolving its key problems for all time.
The second period of his life was one of mostly inactivity in terms of publishing. During the 18 years that Wittgenstein taught at Cambridge, his lectures were often characterized by agonizing over how he had got everything wrong in the writing of Tractatus. His teaching methods transfixed his students, as he was able to answer some profound questions that they posed, and completely ignored others. He spent his entire career at Cambridge reworking his notes from Tractatus to produce a second publication. His class notes from the period have themselves been compiled as the Blue Book, which has been widely distributed and represents a key turning point in his philosophical outlook.
Wittgenstein's philosophical investigations led him to believe that there was an inherent flaw in Tractatus. In 1936, he initiated work on a plan to fix it, which eventually led to the production of Philosophical Investigations. This new masterpiece by Wittgenstein was completed in 1948, only three years before his death, and it was published initially in 1953 posthumously. It also received a wider circulation publication in 1999, and is now considered one of the most important books in 20th century philosophy.
Philosophical Investigations is 693 pages long and composed of three distinct styles of writing, the first constituting the bulk of the book and the second added by his editors. Much of the work explains how his original ideas in Tractatus were based on ideals of language that don't exist in the real world, instead of the commonplace use of language. His final contributions to the work that took place from 1946 until his death in 1951 are considered a third distinct phase of his thinking on philosophy, where he most seriously dealt with issues of epistemology, or the limits of human knowledge.