Ludwig Josef Johann Wittgenstein (April 26, 1889 – April 29, 1951) was an Austrian philosopher who contributed several ground-breaking ideas to philosophy, primarily in the foundations of logic, the philosophy of mathematics, the philosophy of mind, and especially the philosophy of language.[1] His influence has been wide-ranging, placing him among the most significant philosophers of the 20th century, and he is regarded by some professionals as the most important philosopher since Immanuel Kant.

He served in the Austrian military and saw considerable combat through World War I. In 1918 he was captured by Italian forces near Monte Cassino and sat out the rest of the conflict as a prisoner.

Ludwig Wittgenstein was born in Vienna on April 26, 1889, to Karl and Leopoldine Wittgenstein. He was the youngest of eight children, born into one of the most prominent and wealthy families in the Austro-Hungarian empire. His father's parents, Hermann Christian and Fanny Wittgenstein, were born into Jewish families but later converted to Protestantism and moved from Saxony to Vienna in the 1850s. Ludwig's father, Karl Wittgenstein, became an industrialist and went on to make a fortune in iron and steel. Ludwig's mother Leopoldine, born Kalmus, was an aunt of the Nobel Prize laureate Friedrich von Hayek. Despite Karl's Protestantism, and the fact that Leopoldine's father was Jewish, the Wittgenstein children were baptized as Roman Catholics—the faith of their maternal grandmother—and Ludwig was given a Roman Catholic burial upon his death.

Ludwig grew up in a household that provided an exceptionally intense environment for artistic and intellectual achievement. His parents were both very musical and all their children were artistically and intellectually educated. The family was often visited by artists such as Johannes Brahms and Gustav Mahler. Ludwig's older brother Paul Wittgenstein went on to become a world-famous concert pianist, even after losing his right arm in World War I. Ludwig himself had absolute pitch, and his devotion to music remained vitally important to him throughout his life: he made frequent use of musical examples and metaphors in his philosophical writings, and was said to be unusually adept at whistling lengthy and detailed musical passages.

His family also had a history of intense self-criticism, to the point of depression and suicidal tendencies. Three of his four brothers committed suicide. The eldest of the brothers, Hans — an early musician who started composing at age four — killed himself in April 1902, in Havana, Cuba. The third son, Rudolf, followed in May 1904 in Berlin. Their brother Kurt shot himself at the end of World War I, in October 1918, when the Austrian troops he was commanding deserted en masse.

Until 1903, Ludwig was educated at home; after that, he began three years of schooling at the Realschule in Linz, a school emphasizing technical topics. Adolf Hitler was a student there at the same time, when both boys were 14 or 15 years old. Ludwig was interested in physics and wanted to study with Ludwig Boltzmann, whose collection of popular writings, including an inspiring essay about the hero and genius who would solve the problem of heavier-than-air flight ("On Aeronautics") was published during this time (1905). Boltzmann committed suicide in 1906, however.

In 1906, Wittgenstein began studying mechanical engineering in Berlin, and in 1908 he went to the University of Manchester to study for his doctorate in engineering, full of plans for aeronautical projects. During his research in Manchester, he became interested in the foundations of mathematics, particularly after reading Bertrand Russell's Principles of Mathematics and Gottlob Frege's Grundgesetze. In the summer of 1911 Wittgenstein visited Frege and, after having corresponded with him for some time, was advised by Frege to attend the University of Cambridge to study under Bertrand Russell.

In October 1911 Wittgenstein arrived unannounced at Russell's rooms in Trinity College and was soon attending his lectures and discussing philosophy with him at great length. He made a great impression on Russell and G. E. Moore and started to work on the foundations of logic and mathematical logic.

Russell was increasingly tired of philosophy and saw Wittgenstein as a successor who would carry on his work. During this period Wittgenstein's other major interests were music and travelling, often in the company of David Pinsent, an undergraduate who became a firm friend. He was also invited to join the Cambridge Apostles, an elite secret society which Russell and Moore had both belonged to as students.

In 1913 Wittgenstein inherited a large fortune when his father died. He donated some of it, initially anonymously, to Austrian artists and writers, including Rainer Maria Rilke and Georg Trakl. In 1914 he went to visit Trakl when the latter wanted to meet his benefactor, but Trakl died (an apparent suicide) days before Wittgenstein arrived.

Although he was invigorated by his study in Cambridge and his conversations with Russell, Wittgenstein came to feel that he could not get to the heart of his most fundamental questions while surrounded by other academics. In 1913 he retreated to the relative solitude of the remote village of Skjolden at the end of the Sognefjord in Norway. Here he rented the second floor of a house and stayed for the winter. The isolation from academia allowed him to devote himself entirely to his work, and he later saw this period as one of the most passionate and productive times of his life. While there he wrote a book entitled Logik, a ground-breaking work in the foundations of logic which was the immediate predecessor and source of much of the Tractatus Logico-Philosophicus.

The outbreak of World War I in the next year took him completely by surprise, as he was living a secluded life at the time. He volunteered for the Austro-Hungarian army, first serving on a ship and then in an artillery workshop. In 1916 he was sent as a member of a howitzer regiment to the Russian front, where he won several medals for bravery, then in the southern Tyrol, where he was taken as a prisoner of war by the Italian army in November 1918.

Throughout the war, Wittgenstein kept notebooks in which he frequently wrote philosophical and religious reflections alongside personal remarks. The notebooks reflect a profound change in his religious life: a militant atheist during his stint at Cambridge, Wittgenstein discovered Leo Tolstoy's The Gospel in Brief at a bookshop in Galicia. Wittgenstein's other religious influences includeSaint Augustine, Fyodor Dostoevsky and, most notably, Søren Kierkegaard, whom Wittgenstein referred to as "a saint".

Wittgenstein's work on Logik began to take on an ethical and religious significance. With this new concern with the ethical, combined with his earlier interest in logical analysis, and with key insights developed during the war (such as the so-called "picture theory" of propositions), Wittgenstein's work from Cambridge and Norway was transfigured into the material that eventually became the Tractatus. Towards the end of the war in 1918 Wittgenstein was promoted to reserve officer (lieutenant) and sent to northern Italy as part of an artillery regiment. On leave in the summer of 1918 he received a letter from David Pinsent's mother telling Wittgenstein that her son had been killed in an airplane accident. Suicidal, Wittgenstein went to stay with his uncle Paul, and completed the Tractatus, which he dedicated to Pinsent. In a letter to Mrs Pinsent Wittgenstein said "only in him did I find a real friend". The book was sent to publishers at this time, without success.

In October, Wittgenstein returned to the Italian front but was captured by the Italians shortly thereafter. While he was a prisoner of war, through the intervention of his Cambridge friends Russell, Keynes, and Pinsent, who had corresponded with him throughout the war via Switzerland, Wittgenstein managed to get access to books, prepare his manuscript, and send it back to England. Russell recognized it as a work of supreme philosophical importance and worked with Wittgenstein to get it published after his release in 1919. An English translation was prepared, first by Frank P. Ramsey and then by C. K. Ogden, with Wittgenstein's involvement. After some discussion of how best to translate the title, G. E. Moore suggested Tractatus Logico-Philosophicus, an allusion to Baruch Spinoza's Tractatus Theologico-Politicus. Russell wrote an introduction, lending the book his reputation as one of the foremost philosophers in the world.

However, difficulties remained. Wittgenstein had become personally disaffected with Russell and was displeased with Russell's introduction, which he thought evinced fundamental misunderstanding of the Tractatus. Wittgenstein grew frustrated as interested publishers proved difficult to find. To add insult to injury those publishers who were interested proved to be so mainly because of Russell's introduction. Finally Wilhelm Ostwald's journal Annalen der Naturphilosophie printed a German edition in 1921, and Routledge's Kegan Paul printed a bilingual edition with Russell's introduction and the Ramsey-Ogden translation in 1922.

By then Wittgenstein was a profoundly changed man. He had embraced the Christianity that he had previously opposed, faced harrowing combat in World War I, and crystallized his intellectual and emotional upheavals with the exhausting composition of the Tractatus. It was a work which transfigured all of his past work on logic into a radically new framework that he believed offered a definitive solution to all the problems of philosophy. These changes in Wittgenstein's inner and outer life left him both haunted and yet invigorated to follow a new, ascetic life. One of the most dramatic expressions of this change was his decision in 1919 to give away his portion of the family fortune that he had inherited when his father had died. The money was divided between his sisters Helene and Hermine and his brother Paul, and Wittgenstein insisted that they promise never to give it back.

Since Wittgenstein thought that the Tractatus had solved all the problems of philosophy, he left philosophy and returned to Austria to train as a primary school teacher. He was educated in the methods of the Austrian School Reform Movement which advocated the stimulation of the natural curiosity of children and their development as independent thinkers, instead of just letitbusng them memorize facts. Wittgenstein was enthusiastic about these ideas but ran into problems when he was appointed as an elementary teacher in the rural Austrian villages of Trattenbach, Puchberg-am-Schneeberg, and Otterthal. During his time as a schoolteacher Wittgenstein wrote a pronunciation and spelling dictionary for his own use in teaching students; it was published and well received by his colleagues.This would be the only book besides the Tractatus that Wittgenstein published in his lifetime.

Wittgenstein had unrealistic expectations of the rural children he autorbusght, and his teaching methods were intense and exacting — he had little patience with those children who had no aptitude for mathematics. However, he achieved good results with children attuned to his interests and style of teaching, especially boys. His severe disciplinary methods (often involving corporal punishment, not unusual at the time) — as well as a general suspicion amongst the villagers that he was somewhat mad — led to a long series of bitter disagreements with some of his students' parents, and eventually culminated in April 1926 in the collapse of an eleven year old boy whom Wittgenstein had struck on the head. The boy's father attempted to have Wittgenstein arrested, and despite being cleared of misconduct he resigned his position and returned to Vienna, feeling that he had failed as a school teacher.

After abandoning his work as a school teacher, Wittgenstein worked as a gardener's assistant in a monastery near Vienna. He considered becoming a monk, and went so far as to inquire about the requirements for joining an order. However, at the interview he was advised that he would not find in monastic life what he sought.

Two major developments helped to save Wittgenstein from this despairing state. The first was an invitation from his sister Margaret ("Gretl") Stonborough (who was painted by Gustav Klimt in 1905) to work on the design and construction of her new house. He worked with the architect, Paul Engelmann, and found the work intellectually absorbing, and exhausting.

Secondly, toward the end of his work on the house, Wittgenstein was contacted by Moritz Schlick, one of the leading figures of the newly formed Vienna Circle. The Tractatus had been tremendously influential to the development of the Vienna positivism and, although Schlick never succeeded in drawing Wittgenstein into the discussions of the Vienna Circle itself, he and some of his fellow circle members, especially Friedrich Waismann, met occasionally with Wittgenstein to discuss philosophical topics. Wittgenstein was frequently frustrated by these meetings — he believed that Schlick and his colleagues had fundamentally misunderstood the Tractatus, and at times would refuse to talk about it at all. (Much of the disagreements concerned the importance of religious life and the mystical; Wittgenstein considered these matters of a sort of wordless faith, whereas the positivists disdained them as useless. In one meeting Wittgenstein refused to discuss the Tractatus at all, and sat with his back to his guests while he read aloud from the poetry of Rabindranath Tagore.) Nevertheless, the contact with the Vienna Circle stimulated Wittgenstein intellectually and revived his interest in philosophy. He also met with Frank P. Ramsey, a young philosopher of mathematics who traveled several times from Cambridge to Austria to meet with Wittgenstein and the Vienna Circle. In the course of his conversations with the Vienna Circle and with Ramsey, Wittgenstein began to think that there might be some "grave mistakes" in his work as presented in the Tractatus — marking the beginning of a second career of ground-breaking philosophical work, which would occupy him for the rest of his life.

In 1929 he decided, at the urging of Ramsey and others, to return to Cambridge. He was met at the railway station by a crowd of England's greatest intellectuals, discovering rather to his horror that he was one of the most famed philosophers in the world.

Despite this fame he could not initially work at Cambridge as he did not have a degree, so he applied as an advanced undergraduate. Russell noted that his previous residency was in fact sufficient for a doctoral degree, and urged him to offer the Tractatus as a doctoral thesis, which he did in 1929. It was examined by Russell and Moore; at the end of the thesis defence, Wittgenstein clapped the two examiners on the shoulder and said, "Don't worry, I know you'll never understand it."Moore commented in the examiner's report: "In my opinion this is a work of genius; it is, in any case, up to the standards of a degree from Cambridge." Wittgenstein was appointed as a lecturer and was made a fellow of Trinity College.

Although Wittgenstein was involved in a relationship with Marguerite Respinger (a young Swiss woman he had met as a friend of the family), his plans to marry her were broken off in 1931 and he never married. Most of his romantic attachments were to young men. Wittgenstein had several long-term homoerotic attachments, including an infatuation with his friend David Pinsent and long-term relationships during his years in Cambridge with >Francis Skinner and possibly Ben Richards.

Wittgenstein's political sympathies lay on the left, and while he was opposed to Marxist theory, he described himself as a "communist at heart" and romanticized the life of labourers. In 1934, attracted by Keynes' description of Soviet life in Short View of Russia, he conceived the idea of emigrating to the Soviet Union with Skinner. They took lessons in Russian and in 1935 Wittgenstein traveled to Leningrad and Moscow in an attempt to secure employment. He was offered teaching positions but preferred manual work and returned three weeks later.

From 1936 to 1937 Wittgenstein lived again in Norway and worked on the Philosophical Investigations. In 1938 he traveled to Ireland to visit Maurice Drury, a friend who was training as a doctor, and considered such training himself, with the intention of abandoning philosophy for psychiatry. The visit to Ireland was at the same time a response to the invitation of the then Irish Prime Minister, Eamon de Valera, himself a mathematics teacher. De Valera hoped that Wittgenstein's presence would contribute to an academy for advanced mathematics.

While he was in Ireland, Germany annexed Austria in the Anschluss; the Viennese Wittgenstein was now a citizen of the enlarged Germany and a Jew under its racial laws. He found this intolerable and started to investigate the possibilities of acquiring British or Irish citizenship with the help of Keynes, but this put his siblings Hermine, Helene and Paul, all still living in Austria, in considerable danger.

After G. E. Moore's resignation in 1939 Wittgenstein, who was by then considered a philosophical genius, was appointed to the chair in Philosophy at Cambridge. He acquired British citizenship soon afterwards, and in July 1939 he traveled to Vienna to assist Gretl and his other sisters.

By this time Wittgenstein's view on the foundations of mathematics had changed considerably. Earlier he had thought that logic could provide a solid foundation, and he had even considered updating Russell and Whitehead's Principia Mathematica. Now he denied that there were any mathematical facts to be discovered and he denied that mathematical statements were "true" in any real sense: they simply expressed the conventional established meanings of certain symbols. He also denied that a contradiction should count as a fatal flaw of a mathematical system. He gave a series of lectures on the foundations of mathematics discussing this and other topics, documented in a book.The book contains lectures by Wittgenstein as well as discussions between Wittgenstein and several attending students including young Alan Turing.

During World War II he left Cambridge and volunteered as a hospital porter in Guy's Hospital in London and as a laboratory assistant in Newcastle upon Tyne's Royal Victoria Infirmary. After the war, Wittgenstein returned to teach at Cambridge, but he found teaching an increasing burden: he had never liked the intellectual atmosphere at Cambridge, and in fact encouraged several of his students, including Skinner, to find work outside of academic philosophy.

Wittgenstein resigned his position at Cambridge in 1947 to concentrate on his writing. He was succeeded as professor by his friend Georg Henrik von Wright. He stayed at Kilpatrick House guesthouse in East Wicklow in 1947 and 1948. Much of his later work was done on the west coast of Ireland in the rural isolation he preferred. By 1949, when he was diagnosed as having prostate cancer, he had written most of the material that would be published after his death as Philosophical Investigations, which arguably contains his most important work.

He spent the last two years of his life working in Vienna, the United States, Oxford, and Cambridge. He worked continuously on new material, inspired by the conversations that he had had with his friend and former student Norman Malcolm during a long vacation at the Malcolms' house in the United States. Wittgenstein began to work on another series of remarks inspired by his conversations, which he continued to work on until two days before his death, and which were published posthumously as On Certainty.

Wittgenstein died from prostate cancer at the home of Dr. Bevan, his doctor, in Cambridge in 1951. His last words were: "Tell them I've had a wonderful life".

Selected works:

• Logisch-Philosophische Abhandlung, Annalen der Naturphilosophie, 14 (1921)
• Tractatus Logico-Philosophicus, 1922
• Philosophical Investigations, 1953
• Remarks on the Foundations of Mathematics, 1956
• The Blue and Brown Books, 1958
• Philosophical Remarks, 1975
• Remarks on Colour, 1977
• Philosophical Grammar, 1978
• Remarks on the Philosophy of Psychology, 1980
• On Certainty
• Culture and Value
• Zettel

Bibliography about Ludwig Wittgenstein:

• How To Read Wittgenstein, by Monk, Ray, 2005
• Wittgenstein Flies a Kite: A Story of Models of Wings and Models of the World, by Sterrett, Susan G., 2005
• Wittgenstein and Psychology: A Practical Guide, by Harré, Rom; Tissaw, Michael A., 2005
• Wittgenstein: A Very Short Introduction, by Grayling, A. C., 2001
• A Wittgenstein Dictionary, by Glock, Hans-Johann, 1996
• Wittgenstein: An Introduction, by Schulte, Joachim; trans. William H. Brenner and John F. Holley, 1992
• Pulling Up the Ladder: The Metaphysical Roots of Wittgenstein's Tractatus Logico-Philosophicus, by Brockhaus, Richard R., 1990
• Ludwig Wittgenstein: The Duty of Genius, by Monk, Ray, 1990
• Young Ludwig: Wittgenstein's Life, 1889–1921, by McGuiness, Brian,1988 
• Insight and Illusion: Themes in the Philosophy of Wittgenstein, by Hacker, P. M. S., 1986
• Wittgenstein, by Bartley, William Warren, 1985
• Ludwig Wittgenstein: A Memoir, by Malcolm, Norman, 1958