In 1953, the 24-year-old Jürgen Habermas wrote a newspaper article publicly challenging Germany’s greatest living philosopher to explain himself. What had Martin Heidegger meant in his 1935 book Introduction to Metaphysics when he referred to the “inner truth and greatness” of national socialism? How could Heidegger have allowed the republication of these lectures without any revisions or commentary, particularly as he had claimed his membership of the Nazi party before the war had been an aberration?

This was a key moment in Habermas’s intellectual and moral development. Born in 1929, he had been one of the “anti-aircraft generation” of postwar intellectuals, along with novelist Günter Grass and sociologists Ralf Dahrendorf and Niklas Luhmann, all of whom had, as teenagers, helped to defend Hitler. At 15, Habermas was, like most of his contemporaries, a member of the Hitler Youth. Too young to fight and too old to be exempted from any war service, he manned anti-aircraft defences against the allies’ advance. He later described his father, director of the local seminary, and during the war a Wehrmacht major, as a “passive sympathiser” with the Nazis and admitted that he as a youth shared that mindset.

But he was shaken out of his complacency by the Nuremberg trials and documentaries about Nazi concentration camps. His horrified reaction to what he called his fellow Germans’ “collectively realised inhumanity” constituted what he described as “that first rupture, which still gapes”.

Heidegger didn’t deign to reply to Habermas. That silence may explain why the latter became disenchanted with the philosopher’s intellectual system, and instead joined a bunch of neo-Marxist German Jewish intellectuals we know as the Frankfurt school. Max Horkheimer and Theodor Adorno were the leading lights of the Institute for Social Research, philosophising in the rubble of post-Holocaust Germany after their wartime exile in the US. It was their self-imposed task to interrupt what Horkheimer called postwar West Germany’s “ghost sonata”, its conspiracy of silence about the Holocaust.

Young guns … members of the Hitler Youth. Photograph: Hugo Jaeger/Time Life Pictures/Getty Images

In 1955, Habermas became Adorno’s assistant. He learned from his boss a new moral duty that would shape the rest of his intellectual life. “Hitler,” Adorno wrote, “imposes a new categorical imperative on human beings in their condition of unfreedom: to arrange their thought and action so that Auschwitz would not repeat itself.”

But for the first generation of the Frankfurt school there was a problem in upholding that duty. Under advanced industrial capitalism, humans were pinned beneath the shadow of that intimidating German compound noun Verblendungszusammenhang, or “total system of delusion”. In other words, it was thought, we are bewitched by our consumer durables, made frivolous by the culture industry, thwarted from using democracy to change an irksome system because it is corrupted by money.

Habermas demurred. In a 1979 interview, he said: “I do not share the basic premise of critical theory, the premise that instrumental reason has gained such dominance that there is really no way out of a total system of delusion, in which insight is achieved only in flashes by isolated individuals.” Individuals, he could have added, such as Adorno.

Habermas was one of the Frankfurt School’s few non-Jews. As such, he couldn’t philosophise with the guilt of a Holocaust survivor as Adorno self-consciously did. Instead, over hundreds of thousands of words, he elaborated what amounts to a rebellious response to Adorno’s despairing, elitist philosophy. This culminated in his 1981 magnum opus, The Theory of Communicative Action, which envisaged an “unlimited communication community” wherein participants in an argument learn from others and from themselves and question suppositions typically taken for granted.

Nietzsche called Kant a catastrophic spider, spinning a crazy philosophical web. Habermas has the same arachnoid tendencies, embracing in his web social, moral, legal and political theory, and is similarly prone to burden his writing with architectonic technicalities. For devotees such as this biographer, his web is spun to strengthen humankind from relapsing into barbarism.

Seen in this light, not just his philosophy but Habermas’s incessant interventions in German public life – the time he called out Heidegger in 1953; his Marxism-inflected jeremiads on West Germany’s democratic structures; his attack on student protesters such as Rudi Dutschke as “left fascists” in the late 60s; and in particular his role in the so-called Historikerstreit (historians’ dispute) in the late 80s – are part of the philosophical spider’s stratagem.

Rightwing German historians suggested the Holocaust was not a uniquely evil event. For Habermas, this was a cop-out

The Historikerstreit arose when rightwing German historians suggested the Holocaust was not a uniquely evil event. Ernst Nolte pointed out that the Gulag archipelago was established prior to Auschwitz and inferred from this that Germany “reasonably” turned to nazism in the face of the Bolshevik threat. For Habermas, this was a cop-out: yet another means by which Germans might avoid proper confrontation with their homeland’s shameful history.

All this makes for fascinating reading, though Müller-Doohm – more deferential here than in his better biography of Adorno – clogs the narrative. So many prizes, speeches, op-ed feuds, honorary degrees, festschrifts … For a book about a doyen of critical theory, this one is insufficiently critical of its subject.

Habermas’s fetishising of communication has biographical resonance. He was born with a cleft palate and, despite several operations as a small boy, for the rest of his life has spoken with a nasal intonation. The mockery he suffered then made him sensitive to any form of exclusion and, as he wrote, may have made him recognise something that would be central to his mature philosophy, namely “the medium of linguistic communication without which individual existence would also be impossible”.

Germany’s legacy … chimneys at the former Auschwitz concentration camp in January this year. Photograph: Czarek Sokolowski/AP

His web has been spun in some improbable places. In 2005, this one-time Marxist rebel met a fellow Hitler Youth, Cardinal Joseph Ratzinger, the future Pope Benedict XVI. It was a meeting, incredibly, of the like-minded, as both struggled to work out how multicultural societies could be held together without an overarching conception of the good (a thought that preoccupied not just Habermas but his US counterpart, the philosopher John Rawls). In this binding, Habermas wrote, religion was necessary: “Among the modern societies only those that are able to introduce into the secular domain the essential contents of their religious traditions which point beyond the merely human realm will also be able to rescue the substance of the human.”

He has had some hard thinking to do recently about his dreams for a transnational Europe, following not only the Brexit vote but resentment of Germany’s domination of the EU. He’s also had to put up with his fellow German Wolfgang Streeck arguing that the EU, far from protecting its citizens from the worst the world has to offer, was a deregulation machine exposing them to capitalism gone wild.

Habermas was born with a cleft palate. The mockery he suffered then made him sensitive to any form of exclusion

But Habermas is hardly a complacent defender of the status quo. In an interview with Die Zeit, he argued that German hegemony was threatening the EU’s future: “How must a Spaniard, Portuguese or Greek feel if he has lost his job as a result of the policy of spending cuts decided by the European Council?” Habermas admitted that, for ordinary people, supranationality has meant a loss of political control, though he also argued that the idea of reasserting national control in a globalised marketplace, as the likes of Farage and Le Pen advocate, was delusive. What is his solution? “The only way to get democracy in Europe is through a deepening of European cooperation.”

Now in his 88th year and still tilting at adversaries in print, he remains, for good or ill, something rarely cultivated in Britain: a respected public intellectual, committed to stopping humanity repeating not just the horrors but the evasions of the 20th century. Yet I can’t help savouring a story that undermines Müller-Doohm’s benign interpretation. In 1975, Habermas left his job as co-director of the marvellously named Max Planck Institute for Research into Conditions of Living in a Scientific and Technological World following an acrimonious staff dispute. One close friend, the critic Reinhard Baumgart, accused Habermas of defending himself in the dispute with the “arrogance of the mounted SS against the plebeian rank and file”. Years later, when Habermas and Baumgart bumped into each other on a Munich platform, after exchanging civilities, each retreated to different compartments, into their respective non-communicative silences. Perhaps it’s hard for grudge-holding, sulky humans to realise in this world the ideal speech situations that Habermas has, for more than 60 years, extolled.

Stuart Jeffries’ Grand Hotel Abyss: The Lives of the Frankfurt School is published by Verso. Habermas: A Biography is published by Polity. To order a copy for £25 go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.