Ludwig Josef Johann Wittgenstein (April 26, 1889 - April 29, 1951) was an Austrian philosopher who worked primarily in logic, the philosophy of mathematics, the philosophy of mind, and the philosophy of language. From 1929-47, Wittgenstein taught at the University of Cambridge. During his lifetime he published just one slim book, the 75-page Tractatus Logico-Philosophicus (1921), one article, one book review and a children's dictionary. His manuscripts were edited and published posthumously. Philosophical Investigations appeared as a book in 1953 and by the end of the century it was considered an important modern classic. His philosophy is often divided into an early period, exemplified by the Tractatus, and a later period, articulated in the Philosophical Investigations. The early Wittgenstein was concerned with the logical relationship between propositions and the world and believed that by providing an account of the logic underlying this relationship, he had solved all philosophical problems. The later Wittgenstein rejected many of the assumptions of the Tractatus, arguing that the meaning of words is best understood as their use within a given language-game. His influence has been felt in nearly every field of the humanities and social sciences, yet there are diverging interpretations of his thought. He died in 1951 at the age of 62. No photographer credited, undated.