BOOK REVIEW / Great philosophical ideas hit the flaw: Bryan Appleyard on Martin Heidegger, a genius who never played the hero game: Martin Heidegger: A Political Life HUGO OTT Tr Alan Blunden HarperCollins pounds 20

THE CASE is simple: Martin Heidegger 'the greatest seeker after truth this century has known', was a Nazi. He was a philosophical titan, the godfather of existentialism and a thinker of cold, driven, ferocious genius. Being and Time is one of the texts by which our age is known, a summit of the Western imagination. And yet . . .

Since 1945, when Heidegger began formulating his own apologia for his political crimes, his version of events has generally been accepted. This version states that, yes, he was taken in by the claims of National Socialism, yes, he did, for a time, regard Hitler as the eruption into history of a force of Being, the bearer of a new Germanic dispensation. But he soon realised his error and, from 1934 to 1945, was more or less in opposition to the regime.

This version allowed his involvement to be regarded as little more than a brush with Nazism, a momentary aberration that could even be excused on the grounds of the intensity of the man's greatness. It was attributable, claimed Hannah Arendt, 'partly to the delusion of genius, partly to desperation'. By such means Heidegger could be retained as an almost complete hero. Those in love with the philosophy could still love the life and the man.

Hugo Ott has been undermining this comfortable version for some years. In spite of a continued restriction of access to some of the Heidegger archive, he has patiently examined the evidence as it stands. The results are damning. Not only do they expose Heidegger's involvement with Nazism as far longer and far nastier than the official version, they also reveal a man of duplicity, arrogance and opportunistic ruthlessness. The result is that the old, cosy compromise is detonated. We have to face the truth that, somewhere deep in the workings of one of the most powerful minds of our age, real genius and real evil were thrust into awful proximity.

This is a matter that requires a cold, disinterested head and Ott is nothing if not cool, and also intellectually disinterested in that he is a historian. There is almost nothing in this book about Heidegger's philosophy; indeed, Ott frequently pronounces himself unqualified whenever he approaches the deep waters of ontology and the metaphysics of logic. He is not even particularly concerned with the philosopher's motives. Ott's sole concern is with the historical truth of Heidegger's Nazism.

For one year from 1933 to 1934 Heidegger was Rector of Freiburg University and all Ott's investigations of the man's politics begin and end with that terrible year. The official version - as propagated by Heidegger himself in his posthumously published apologia Facts and Thoughts - is that he drifted into the rectorship and pulled out immediately he saw the truth of Nazism. The evidence in his favour is that he did resign and, through the ensuing years of the regime, there is evidence that he was mistrusted by the authorities.

But Ott's case is that this is not evidence of his opposition to Nazism, but rather of his own conviction that he alone understood the deep truth of the ideology. He was forced to resign and was subsequently mistrusted because of the little men in the party; only he grasped the historic immensity of the National Socialist moment. From this perspective Heidegger's political posture cannot so easily be glossed over because the philosopher himself perceived the politics as growing directly out of the philosophy. Ott's evidence on this point seems overwhelming. Time and again Heidegger announced, in his characteristically mystical yet precise prose, that Hitler and Nazism were the supreme historical expression of his own conception of Being. His astonishing address on being elevated to the rectorship in 1933 is proof enough of this conviction, but to learn that he had the words of the Horst-Wessel Lied, the song of the Hitler Youth, printed on the back of the programme for the ceremony rather closes the file on Heidegger's attitude at that point.

It was an attitude that dismayed lesser but, at that crucial moment, wiser minds. Herbert Marcuse, a pupil, described his master's Nazism as 'an act of self-abasement on the part of existentialism that is without equal in the whole of intellectual history'. But still there remains open the defence that it was no more than a kind of naive abstraction, a simple ignorance of the human reality behind the great words and grand ideas. Karl Jaspers, another shocked philosopher, went some way to endorsing this view when he said Heidegger was 'like a boy who is dreaming.' But Ott effectively closes this line of defence as well. Even at the most personal level Heidegger appears to have behaved like a good Nazi. He displayed anti-Semitism - in particular against his old mentor Edmund Husserl - of a peculiarly unpleasant kind in that it appears to have been opportunistic.

In this realm of little, personal Nazism the single most damning story concerns the chemist Hermann Staudinger. This was where the new evidence lay that was the initial inspiration for Ott's research. He discovered that Heidegger flagrantly collaborated with the Nazis against an academic colleague who was believed to have pacifist tendencies. The Gestapo and the great philosopher colluded to destroy the career of a fine scientist because, during the First World War, he showed himself to be not entirely convinced of the virtues of militant German nationalism. It is one small, grim episode among millions of others, but it establishes beyond doubt that Heidegger's Nazism, far from being a passing, abstract aberration, was vicious, personal and wholehearted.

Clearly Ott does not like his man and, equally clearly, a more sympathetic writer could have produced a different book on the basis of the same evidence. But even the most craven fan of Heidegger the man could scarcely argue with the fact that he was a full-blooded National Socialist, practically as well as theoretically, and, equally, he could not deny that, as Ott points out, he never fully recanted. His post-war apologetics are all aimed at excusing his behaviour, they do not say that National Socialism is wrong and, indeed, at times he appears to be implying that the Third Reich was merely a botched attempt and that, one day, the Germans would rise again, fired with the spirit of Being.

Perhaps the thinker of great thoughts really was a child, not an innocent boy but a power-worshipping infant, wrong-headed, petulant, shifty and vicious. But this is no consolation for, in that case, what do we mean by 'great thoughts'? Do they have no moral force in the world? What kind of greatness is it that can contemplate the most self-evidently evil conduct of our day and pronounce it good?

This is a formidable, awkward, engrossing book. Its avoidance of philosophy is its great strength in that it enforces a focus on the facts of the case, yet it leaves the reader unsatisfied. For, in the end, though Ott proves that Heidegger thought his philosophy and his Nazism were one, he cannot show that they really were. We need to separate out the two. One way would be to remove the philosophy to some technical, amoral realm where it really does not matter one way or the other. But this would be a dreadful, intellectual cop-out and a betrayal of philosophy. Another way would be to erase Heidegger completely from the canon - an evident absurdity in the face of the mighty, irreducible greatness of Being and Time. No, the real task is to draw, truer, more human values from the thought than this hideously flawed thinker was able to do himself and to accept that genius will seldom, if ever, obligingly play the hero game.