Martin Heidegger (Undated photograph)

Martin Heidegger (1889 - 1976) was a 20th Century German philosopher. He was one of the most original and important philosophers of the 20th Century, but also one of the most controversial. His best known book, "Being and Time", although notoriously difficult, is generally considered to be one of the most important philosophical works of the 20th Century.

His outspoken early support for the Nazi regime in Germany has to some extent obscured his significance, but his work has exercised a deep influence on philosophy, theology and the humanities, and was key to the development of Phenomenology, Existentialism, Deconstructionism, Post-Modernism, and Continental Philosophy in general.

Heidegger (pronounced HIE-de-ger) was born on 26 September 1889 in Messkirch in rural southern Germany, to a poor Catholic family. He was the son of the sexton of the village church, and was raised a Roman Catholic. In 1903, he went to the high school in Konstanz, where the church supported him by a scholarship, and then moved to the Jesuit seminary at Freiburg in 1906. His early introduction to philosophy came with his reading of "On the Manifold Meaning of Being according to Aristotle" by the philosopher and psychologist Franz Brentano (1838 - 1917).

In 1909, after completing high school, he became a Jesuit novice, but was discharged within a month for reasons of health. From 1909 to 1911, he started to study theology at the University of Freiburg, but then broke off his training for the priesthood and switched to studying philosophy, mathematics, and natural sciences. He completed his doctoral thesis on psychologism in 1914, before joining the German army briefly at the start of World War I, (he was released after two months, again due to health reasons). While working as an unsalaried associate professor at the University of Freiburg, teaching mostly courses in Aristotelianism and Scholastic philosophy, he earned his habilitation with a thesis on the medieval philosopher John Duns Scotus in 1916.

In 1916, he came to know personally the Phenomenologist Edmund Husserl who had joined the Freiburg faculty, and in 1917 he married Elfrie de Petri, a Protestant student of his (their first son Jörg would be born in 1919). In 1918, he was again called up for active military duty, and served as a weatherman on the western front during the last three months of the war.

After the War, in 1918, he broke definitively with Catholicism, and returned to Freiburg as a (salaried) senior assistant to Husserl until 1923. He did not approve of Husserl's later developments, however, and soon began to radically reinterpret his Phenomenology. In 1923, he was elected to an extraordinary professorship in Philosophy at the University of Marburg, during which time he had extramarital affairs with two of his students at Marburg, Hannah Arendt (1906 - 1975) and Elisabeth Blochmann (1892 - 1972), both philosophers in their own right, and both Jewish.

In 1927, he published "Sein und Zeit" ("Being and Time"), his first publication since 1916, which soon became recognized as a truly epoch-making work of 20th Century philosophy. It earned him a full professorship at Marburg and, soon after, on Husserl's retirement from teaching in 1928, the chair of philosophy at Freiburg University (which he accepted, in spite of a counter-offer by Marburg). He remained at Freiburg for most of the rest of his life, declining offers from other universities, including one from the prestigious University of Berlin. Among his students at Freiburg were Herbert Marcuse (1898 - 1979), Ernst Nolte (1923 - ) and Emmanuel Levinas (1906 - 1995).

With Adolph Hitler's rise to power in 1933, Heidegger (who had previously shown little interest in politics) joined the Nazi party, and was elected Rector of the University of Freiburg (his inaugural address, the "Rektoratsrede", has become notorious). During this period, he not only cooperated with the educational policies of the National Socialist government, but also offered it his enthusiastic public support. He resigned his position in 1934, although he remained a member of the academic faculty. He retained his party membership until the end of World War II, despite some covert criticism of Nazi ideology and even a period of time under the surveillance of the Gestapo.

During the 1930s and 1940s (sometimes referred to as "the turn"), his writings became less systematic and often more obscure, and he developed a preoccupation with the question of language, a fascination with poetry, a concern with modern technology, as well as a new-found respect for the early Pre-Socratic Greek philosophers. He himself always denied any turn, arguing that it was simply a matter of going yet more deeply into the same matters.

After the War, he was dismissed from his chair of philosophy because of alleged Nazi sympathies, and forbidden from teaching in Germany from 1845 to 1951 by the French Occupation Authority. When the ban was lifted, he became Professor emeritus at Freiburg and taught regularly until 1958, and then by invitation until 1967.

During the last three decades of his life, he continued to write and publish, although there was little significant change in his philosophy. He divided his time between his home in Freiburg, his second study in Messkirch, and his isolated mountain hut at Todtnauberg on the edge of the Black Forest, which he considered the best environment in which to engage in philosophical thought.

Heidegger died on 26 May 1976, and was buried in the Messkirch cemetery.

Heidegger's writings are notoriously difficult and idiosyncratic, indulging in extended word play, employing his own spelling, vocabulary and syntax, and inventing new words for complex concepts.

"Sein und Zeit" ("Being and Time"), published in 1927, was his first significant academic work, and is considered by most to be his most important and influential work. Heidegger's main concern was always ontology or the study of being and in this book he asked the question "what is 'being'?" His answer was to distinguish what it is for beings to be beings ("Sein") from the existence of entities in general ("Seindes"), and concentrating on the being for whom a description of experience might actually matter, the being for whom "being" is a question, the being engaged in the world (“Dasein").

However, for Heidegger, genuine philosophy can not avoid confronting questions of language and meaning, and he maintained that the description of Dasein could only be carried out in terminology inherited from the history and tradition of Western philosophy itself. Thus he saw "Being and Time" as just a first step, to be followed by the “destruction” of the history of philosophy (a retracing of philosophy's footsteps, and a transformation of its language and meaning). He never completed this second step.

Although often considered a founder of Existentialism, (mainly because his discussion of ontology is rooted in an analysis of the mode of existence of individual human beings), Heidegger vehemently rejected the association, just as he came to reject Husserl’s Phenomenology. However, his works such as "Being and Time" and "What is Metaphysics?" were certainly a big influence on Jean-Paul Sartre (and especially on his "Being and Nothingness").

After the World War II, and Heidegger's so-called "turn", he wrote of the commencement of the history of Western philosophy, the Pre-Socratic period of Parmenides, Heraclitus, and Anaximander, as a brief period of authentic openness to being. This was followed, according to Heidegger, by a long period, beginning with Plato, increasingly dominated by the forgetting or abandonment of this initial openness, occurring in different ways throughout Western history.

Heidegger's important later works include "Vom Wesen der Wahrheit" ("On the Essence of Truth", 1930), "Der Ursprung des Kunstwerkes" ("The Origin of the Work of Art", 1935), "Bauen Wohnen Denken" ("Building Dwelling Thinking", 1951), "Einführung in die Metaphysik" ("An Introduction to Metaphysics", 1953), "Die Frage nach der Technik" ("The Question Concerning Technology", 1954), "Was heisst Denken?" ("What Is Called Thinking?", 1954), "Was ist das - die Philosophie?" ("What Is Philosophy?", 1956), "Unterwegs zur Sprache" ("On the Way to Language", 1959) and "The End of Philosophy" (1964).