Herr Hitler before the hate set in

The Viennese satirist Karl Kraus once famously described his native city as a "laboratory for apocalypses". It was in Vienna that Georg Ritter von Schönerer expounded his extreme nationalist and racist policies. It was also the city where the populist mayor Karl Lueger capitalised on hatred of Jews and other outsiders to maintain a vice-like grip on the municipal politics of the capital. And, of course, it was Vienna where Adolf Hitler spent his formative years. It was there that he famously imbibed the anti-Semitism that he put into such murderous practice in Germany after 1933. We know because Hitler told us so in Mein Kampf , the radical manifesto-cum-autobiography he penned while incarcerated in Landsberg prison after the abortive Munich beer hall putsch of 1923.

If this was the conventional view of Hitler's political and intellectual formation, it will now have to be completely revised in the light of Brigitte Hamann's brilliant new portrait of the dictator as a young man. Hitler's Vienna is the first truly comprehensive study of his youth that not only draws on all the available evidence, but also situates Hitler within his urban social, cultural and intellectual milieu. Part of the strength of the book lies in the new documentation Hamann has unearthed, in particular concerning the eyewitness Rudolf Häusler, and various residence records, but she has also rearranged and recontextualised what was already known but improperly understood. Inevitably - and this is fully acknowledged by Hamann - there is still quite a lot of educated guess-work.

Hamann corrects numerous misconceptions about Hitler's early years. He was not, as some have claimed, of partly Jewish descent; he never lived at most of the addresses attributed him by enterprising Viennese tour guides; and he was never - as he himself later claimed - a building worker. Above all, the book provides a persuasive and empathetic picture of what life must have been like for the struggling artist. Odd to relate, some of the passages are even poignant, such as the vignette of Hitler and his friend Kubiszek queueing hatless and coatless in the freezing cold for a cheap opera ticket in order to save money on the cloakroom; or of the two indigents racing home to their hostel from the opera early to save the small fee for late entry after 10pm: "Kubiszek then had to play the concluding part of the opera, which they had missed, on his piano."

The conception of the book is biographical and chronological, but its structure is thematic. By turns Hamann takes us through the subtle gradations of poverty down which young Hitler descended the social scale after his arrival from provincial Linz. She introduces us to the "social problem", the growth of social democracy, the charismatic Lueger, the controversy surrounding massive Czech immigration and the antics of a parliament riven with confessional, ethnic and linguistic strife. This unhappy experience of representative bodies, as he later expanded in Mein Kampf , put Hitler off democracy for good, especially when contrasted with the lure of Lueger's populist demagogy, which was perhaps the single greatest political influence on young Hitler.

Intellectually, Hamann locates Hitler's later preoccupations with breeding and "purity" within the fetid Viennese subculture of quacks, phrenologists and racial cranks, personified by Jörg Lans von Liebenfels, Guido von List, Hans Horbiger and others.

She stresses that Hitler's Weltanschauung seems to have been an eclectic "grab-bag" that should not be traced back to one particular author; she suggests that his familiarity with the ideas of better-known thinkers such as Darwin, Nietzsche, Schopenhauer and even Houston Stewart Chamberlain, was via the pages of radical Viennese newspapers rather than through direct engagement with their works.

To this extent, Hitler was being truthful when he later said that "Vienna was and remained for me the hardest, though most thorough school of my life ... In it I obtained the foundations for a philosophy in general and a political view in particular which later I only needed to supplement in detail, but which never left me."

But the greatest and most sensational aspect of Hitler's Vienna is its detailed and utterly compelling discussion of Hitler's relationship with Jews before the first world war. Given all that we know about the intellectual climate of prewar Vienna, and the protestations of Mein Kampf ,the received wisdom that Hitler made the transition from the "traditional" anti-Semitism of his Linz years to the radical racial hatred of later years in Vienna, was not implausible. But we now know it to be entirely unsubstantiated by evidence. Hamann disposes of the tenacious myth that Hitler held his Jewish family doctor responsible for the painful death of his mother; in fact, Hitler remained on good terms with Dr Bloch and even intervened to facilitate his emigration in 1938. Hitler was not refused entry to the Academy of Art by Jewish professors, nor was this his perception. Perhaps most stunning of all, however, is Hamann's description of Hitler's numerous Jewish friends and business associates during his Vienna days, at least one of whom later appealed to him directly after the Anschluss, just as the good Dr Bloch had done. We will no longer be able to think of Hitler in Vienna without thinking of his Jewish friend, Josef Neumann, who sold his paintings, the Galician Jew Jakob Altenberg and the Hungarian Jew Samuel Morgenstern, both of them dealers who paid him a decent price, or of the Jahodas, the cultivated upper-middle-class Jewish couple whose company Hitler enjoyed on a few occasions.

Of course, amicable relations with individual Jews are not, and never have been, incompatible with visceral racial anti-Semitism in the abstract.Perhaps even more significant, therefore, is the admittedly slender evidence that Hamann advances for Hitler's relevant intellectual positions.For example, he counter-intuitively sides with the "crooked-nosed Mahlerians", and the "Hebrews" in the bitter Viennese struggle over the interpretation of Wagner. He also remained a firm admirer of the politician Karl Hermann Wolf, who differed from his mentor Schonerer not least in his marginally more favourable attitude to the Jews. Above all, Hamann stresses that there is only one isolated implausible eyewitness reference to Hitler's anti-Semitism in Vienna.

In short, the Hitler who left for Munich in 1913 probably shared the conventional prejudices of his time and place, but he was almost certainly not yet the radical racial annihilatory anti-Semite he later became. Rather, the decisive moment in the formation of Hitler's anti-Semitism must have been, as Hamann suggests - or rather surmises - the shock of defeat in 1918. It was only then that he decided to become a politician.

Brendan Simms is fellow in international relations, University of Cambridge.