Martin Heidegger

The question Being and Time (1927) asked looks simple: what does it mean to be? We say every day that a book is, that I am, but rarely ask what that "is" itself means. Heidegger quoted Plato's admission of perplexity before this question and argued that, two thousand years on, it was still unanswered and had to be asked again.

He began from the being that asks it, the human being, which he called Dasein ("being there"). Modern philosophy pictured a subject standing apart from the world and then knowing the things outside it; for Heidegger a human being is always already caught up in a web of things, people and meanings. That is what he meant by "being-in-the-world".

The most widely read part of the book is its analysis of everyday life. Most of the time people think and live as "the they" (das Man), the anonymous others, live. Heidegger called this "inauthentic" existence, and with concepts such as being-towards-death (facing one's own death, which nobody can die for us), anxiety and resoluteness he described a way out of that drift. The book appeared as a volume of the phenomenological yearbook edited by his teacher Edmund Husserl and was dedicated to him, but Husserl himself regarded it as a departure from the aims of his phenomenology.

His fame came before the book. Hannah Arendt, who heard him at Marburg, remembered that transcripts of his lectures passed from hand to hand and that his name travelled through Germany "like the rumour of a hidden king". Among those who studied with him at Marburg and Freiburg were Karl Löwith, Hans-Georg Gadamer, Hans Jonas, Günther Anders and Herbert Marcuse. From 1925 he had a secret affair with Arendt, then an eighteen-year-old Jewish student; it became known only after both had died.

His influence spread widely. Through Jean-Paul Sartre it gave rise to French existentialism; Gadamer carried on hermeneutics, the philosophy of understanding and interpretation; Emmanuel Levinas opposed him with an ethics that put the other person before being. Marcuse tried to join Being and Time to Marxism before breaking with him in 1932.

When Hitler became chancellor in January 1933, Heidegger threw himself into what he understood as the National Socialist revolution. He had already voted for the Nazi Party in 1932, and on 21 April he became rector of the University of Freiburg. His predecessor, the Social Democrat Wilhelm von Möllendorff, had resigned the day before, probably under pressure from the regime, and proposed him for the post. On 1 May Heidegger joined the Nazi Party (membership number 3,125,894) and remained a member until the end of the war.

In his rectoral address of 27 May, "The Self-Assertion of the German University", he spoke of "the greatness and glory of this awakening", cast the relation of professors and students as that of "leaders" and "following", and bound the university to the "national community" (Volksgemeinschaft). As rector he took part in Nazi propaganda and in Gleichschaltung, the policy of bringing universities and associations into line with the regime. Jewish colleagues were dismissed during his rectorate, and he denounced two colleagues as insufficiently convinced Nazis. On 11 November in Leipzig he signed the professors' "Declaration of Commitment to Adolf Hitler" and gave a main speech.

He resigned on 27 April 1934. He later said he had stepped down because he could not go along with Nazi university policy; German accounts conclude rather that the policy did not go far enough for him, and that plans such as a central academy to give all future German professors a philosophical schooling found support neither at the university nor in the party. He remained a party member, and in May 1934 became, with Alfred Rosenberg, a founding member of the committee for legal philosophy of the Academy for German Law led by Hans Frank, on which he sat until at least 1936.

His conduct towards his teacher Husserl is a painful chapter. In April 1933 a decree of the state of Baden suspending Jewish officials placed the already retired Husserl on enforced leave; according to English-language accounts it was Heidegger's predecessor, not Heidegger, who notified him. By then Heidegger had broken off direct contact with Husserl. He did not attend Husserl's cremation in 1938, and in 1941, under pressure from his publisher, he removed the dedication to Husserl from Being and Time. He later called his failure to express his gratitude "a human failure".

After the war the university examined his case. Karl Jaspers, whose opinion Heidegger himself had requested, judged him unacceptable on the faculty and proposed suspension from teaching for some years; on 19 January 1946 the senate withdrew his teaching licence. The ban ended with his emeritus status in 1951. Afterwards he largely kept silent about his Nazi past.

The Black Notebooks are the philosophical diaries Heidegger kept in black-bound notebooks from 1931 to 1975. He arranged for them to close his collected works, and the parts covering 1931 to 1941 appeared in three volumes in February and March 2014. In the notebooks of 1938–39, alongside passages criticising Bolshevism and racial theory alike as expressions of "machination" (Machenschaft, his word for the modern drive to turn everything into an object of calculation and control), "Judaism" comes into view for the first time in a problematic way.

Among the published sentences: that "world Judaism" is ungraspable everywhere and spreads its influence without needing military action while "we" are left to sacrifice the best blood of our people; and that Jews, having lived by the principle of race, had no right to complain when it was used against them. In 1939, a year after Husserl's death, he wrote that the occasional increase in the power of Judaism was grounded in Western metaphysics having offered a foothold to an otherwise empty rationality and calculative capacity, and went straight on in parentheses to Husserl's phenomenology. Yet the same notebooks also contain passages critical of biological racism.

Since publication there has been broad agreement among German-language scholars that Heidegger was an antisemite, though most rule out a biological racism. They divide on the next question: how far his Nazi engagement and antisemitism run into the philosophy itself. At one end is Heidegger's own view that his engagement was a mistaken phase without effect on his work; at the other, readings of his whole philosophy as Nazi ideology. In between, the philosopher Donatella Di Cesare reads the 1939 entry as implying that Heidegger considered Husserl philosophically limited by his Jewishness.

In sum: his party membership from 1 May 1933 to 1945, the sentences of the rectoral address, the denunciations of colleagues, his signature on the declaration for Hitler, his work on the Academy for German Law committee and the antisemitic sentences of the Black Notebooks are documented facts. How they connect with the concepts of Being and Time is a matter of interpretation, which is why students and heirs such as Marcuse, Arendt and Levinas reached such different conclusions about him.