When Anders Breivik launched his murderous attack in Norway in July 2011, he left behind a rambling manifesto which attacked not only what he saw as Europe's Islamicisation but also its undermining by the cultural Marxism of the Frankfurt school. So what is the Frankfurt school? Has its influence has been as deep as Breivik feared and many of the rest of us have hoped?

Many will have heard of the most prominent names from that tradition: Theodor Adorno, Herbert Marcuse and Max Horkheimer, but its reach goes much further, taking in many of the 20th century's most important continental philosophers and socio-political developments.

The Frankfurt school was officially called the Institute for Social Research and was attached to the University of Frankfurt but functioned as an independent group of Marxist intellectuals who sought, under the leadership of Felix Weil, to expand Marxist thought beyond what had become a somewhat dogmatic and reductionist tradition increasingly dominated by both Stalinism and social democracy. Most famously they sought to marry up a combination of Marxist social analysis with Freudian psychoanalytical theories, searching for the roots of what made people tick in modern consumer capitalist society as well as what made people turn to fascism in the 1930s.

The Frankfurt school went back to Marx's early theoretical works from the 1840s and tapped into his more humanist impulses found in the German-French Annals and in his correspondence with Arnold Ruge. It is in these early writings that we find many of Marx's most important writings on the role of religion in history and society. His ideas about the way materialism worked in the world were still being formulated and he had not yet become the economic theoretician he was later known as. It is not that Marx left ideas of religion behind after these early years, but he felt he had dealt with them properly and could move on to more tangible affairs. In a letter to Arnold Ruge in 1842 he wrote:

"Our motto must be: reform of consciousness not through dogmas, but by analysing the mystical consciousness that is unintelligible to itself, whether it manifests itself in a religious or a political form. It will then become evident that the world has long dreamed of possessing something of which it has only to be conscious in order to possess it in reality. It will become evident that it is not a question of drawing a great mental dividing line between past and future, but of realising the thoughts of the past. Lastly, it will become evident that mankind is not beginning a new work, but is consciously carrying into effect its old work."

But the idea that what was required was a reform of consciousness which had become unintelligible to itself is the central working principle of the Frankfurt school. Religious thought, which Marx saw as a part of false consciousness, was to be combated not by a full frontal attack in some sort of Dawkins-like crusade, but by removing the social conditions that created it. Marx was, therefore, not an atheist. Indeed he said of the term atheism that it "reminds one of children, assuring everyone who is ready to listen to them that they are not afraid of the bogey man". But the Frankfurt school did not believe that this reform of consciousness could come about simply by changing the socio-economic base of capitalist society. Religion was, for them, not only the opium of the people, but also a repository of hope that had become unintelligible to itself.

Freud comes into the equation here because these critical theorists thought that his categories of id, superego and ego, which were constantly interacting as the basis of the human psyche, fitted well with the Marxist dialectic of historical struggle and resolution. If societies moved forward historically as the result of class struggle, then individuals were constantly dealing with a struggle between the reality of the world around them and what they thought about that world. Paradoxically, the Frankfurt school saw this as necessary because of the relative success of capitalism rather than its imminent collapse, as the more dogmatic Marxists proclaimed (and indeed continue to proclaim). How was it, they argued, that the great mass of people could be sucked into complicity with their own exploitation? With the emergence of fascism in the 1920s and 30s the question became even more urgent. What led educated people to throw their lot in with the barbarism of fascism? This, for them, was the ultimate in false consciousness. One of the most influential works of the Frankfurt school to deal with this phenomenon was The Authoritarian Personality, a work that purported to be a study of prejudice and that documented the ways in which people, as individuals, were motivated to think and act as they do in a social context, to form in-groups and to exclude others to the point of genocidal extermination.

Paradoxically it is that great enemy of the Frankfurt school, Breivik, who is the perfect example of the authoritarian personality Adorno wrote about: obsessed with the apparent decline of traditional standards, unable to cope with change, trapped in a hatred of all those not deemed part of the in-group and prepared to take action to "defend" tradition against degeneracy. More worryingly, especially set against the rise of groups like Golden Dawn in Greece and widespread trends towards the fear of Islam in mainstream society, Adorno maintained that "personality patterns that have been dismissed as 'pathological' because they were not in keeping with the most common manifest trends or the most dominant ideals within a society, have, on closer investigation, turned out to be but exaggerations of what was almost universal below the surface in that society. What is 'pathological' today may, with changing social conditions, become the dominant trend of tomorrow."