Jürgen Habermas was born in 1929 near Düsseldorf and belonged to the generation that grew up in the ruins of Nazism; he entered Frankfurt in 1956 as Adorno's assistant. His 1962 habilitation Strukturwandel der Öffentlichkeit (The Structural Transformation of the Public Sphere) was already programmatic: it told how the space of equal intersubjective debate born in the London coffee houses and Paris salons of the eighteenth century — the bourgeois public sphere — was later turned by advertising and mass media into an apparatus for 'manufacturing consent.' That single argument set him apart from the dark picture drawn by the first generation of the Frankfurt School (Adorno, Horkheimer, Marcuse) in their 1947 Dialectic of Enlightenment; instead of accepting that the Enlightenment had been lost, Habermas was already looking for the conditions under which it might be regained.

The Theorie des kommunikativen Handelns, published in 1981, grounds that programme over two thick volumes. Its starting point is Max Weber's diagnosis of modernity: modernisation turned the world into an order ruled by an 'instrumental reason' calculating means and ends, with science, law, and art falling apart into separate expert spheres. For Adorno and Horkheimer reason could take no other form; Habermas argues that there is a second form of reason as well — communicative reason. Drawing on the speech-act theory of Austin and Searle, he shows that whenever I sincerely make a claim to you, language itself embeds three validity claims (truth, normative rightness, sincerity) into our conversation. The fact that these claims can be redeemed only in an 'ideal speech situation' that is equal, free of coercion, and decided solely by the force of the better argument is what makes modernity possible at all.

The book's second great distinction is between lifeworld (Lebenswelt) and system. The lifeworld is the fabric of our shared meanings, everyday language, and the transmission of culture and family; the system is the means-end coordination steered by money (the market) and power (state bureaucracy). For Habermas the crisis of late modernity is 'the colonisation of the lifeworld': system categories (efficiency, customer satisfaction, performance review) seep into education, health care, and family life and displace communicative order. The first generation of the Frankfurt School delivered a similar diagnosis under the name of 'the culture industry,' but Habermas's way out is different: the answer to colonisation is a robust public sphere, the rule of law, and rights-based democracy.

Habermas is still alive at ninety-six. His later Faktizität und Geltung (Between Facts and Norms, 1992) develops a theory of constitutional citizenship and deliberative democracy, and through the 1990s he conducted a long dialogue with Rawls about political liberalism. Against Foucault's analytics of power, Derrida's deconstruction, and Lyotard's thesis of 'the end of grand narratives' he keeps mounting an indefatigable defence of the Enlightenment — 'modernity is an unfinished project' is his phrase. His twenty-first-century interventions on the European public sphere, the relation between religious and secular reason after 9/11, and the condition of truth in the digital age all draw on the same framework. The first generation of Frankfurt was modernity's judge; Habermas is its stubborn repairman.