The world lost one of the great thinkers of our time on March 14: the philosopher-sociologist Jürgen Habermas. His written work spanned nearly 75 years, beginning with newspaper essays he wrote as a freelance journalist in 1952 and winding down in 2025 with short papers, including an essay on faith and hope in the Catholic magazine The Lamp. Within that span of time, he published 60 books, covering topics in social theory and sociology, philosophy, political theory and contemporary politics. His work influenced multiple disciplines—not only philosophy but also political science and law, sociology, communications and theology, among others. 

He also learned from those disciplines, engaging in dialogue with the world’s leading intellects, including the future Pope Benedict XVI, in a 2004 discussion in Bavaria on the role of religion in modern society and democracy. 

While completing my own graduate work in Frankfurt, I spent a year attending Habermas’s lectures and participating in his colloquia and his workshop on legal theory.

Behind Habermas’s prodigious output lay two great passions. The first goes back to his childhood, when he suffered from a harelip that required multiple surgeries. His own challenges of making himself understood impressed on him the importance of language for communication. That passion would later find expression in his work on the role of communicative reason in social cooperation. 

The second passion formed at the end of the Second World War, when Habermas, still in his teens, listened with horror to broadcasts of the Nuremberg trials. As he put it in a short autobiographical essay, he suddenly realized he’d been living in a “pathological and criminal” system. Later, as a politically attuned university student, it became clear to him that neither his professors nor the postwar Adenauer administration in West Germany grasped the depth of Germany’s failure—at once political, intellectual and moral—and its need for radical change. As with other members of his generation, those experiences fed a lifelong vocation, dedicated to developing the philosophical ideas and public arguments supportive of constitutional democracy.  

Habermas wanted nothing less than to reawaken the “unfinished project of enlightenment” that the German philosopher Immanuel Kant had so passionately set forth in the 18th century. To do so, he had to counter the defeatism he saw in modern reason, evident not only in Germany’s slide into authoritarianism but also in the narrow instrumental mindset that dominated Western thought and institutions. To carry out that work, Habermas looked for fresh resources beyond the German tradition, in particular American pragmatism and the democratic constitutional tradition. 

Two lines of inquiry came together in Habermas’s project. One line sought to develop a more capacious, communicative conception of reason that went beyond the technocratic fixation on facts and efficiency. The other line advanced the idea that democratic governance must be open to the public deliberation of citizens. Habermas pursued these projects on two fronts, both as an academic writing scholarly treatises and as a public intellectual intervening in current political discussions.

In his 1962 habilitation (a second dissertation required for a professorship in Germany), Habermas took a major step in his democratic argument. Not translated into English until 1989, The Structural Transformation of the Public Sphere introduced the idea of the “public sphere” by way of social history. In the salons and coffeehouses of 18th-century Europe, Habermas argued, a public space opened in which private citizens could discuss societal issues and influence politics. That work proved very influential, engendering “public sphere theory” as an area of research. 

Three great milestones marked the subsequent development of Habermas’s thought. His two-volume Theory of Communicative Action (1984 and 1987) argued for a wide-ranging communication-based theory of society, synthesizing work across multiple disciplines, including philosophy, linguistics, classical sociology, developmental psychology and cultural anthropology. There, Habermas set forth his expanded conception of communicative reason: Social cooperation ultimately depends on communicative action, the mode of interaction by which people act on the basis of shared views of empirical truth, practical efficacy, moral rightness, authentic self-understanding and so forth. Such agreements are open to challenge and defense on the basis of reasons, which can in turn be tested in rational discourse. 

His analysis of communication and society provided the framework for subsequent work in ethics and legal-political theory, which culminated in his second major milestone, Between Facts and Norms (1996), an extended argument for a deliberative theory of democracy and legitimate law. 

National lawmaking, however, cannot fully address global challenges such as climate change. Similar to Kant, Habermas saw the need for a cosmopolitan constitutional order, albeit one that does not entirely obliterate national sovereignty. He also saw the need to address challenges that religious groups pose for political legitimacy—in particular, groups that oppose modern secular institutions. That endeavor eventually led to the third milestone, his monumental, three-volume Also a History of Philosophy (2023, 2024 and 2025). 

That work tracks the interaction of faith and reason, beginning with the birth of the ancient metaphysical-religious worldviews, then focusing on the Western “discourse” of philosophy and theology that gave birth to modern philosophy, and concluding with the American pragmatist C. S. Peirce. In that history, Habermas argued, one can see a learning process—at once intellectual, social and institutional—to which Christianity made key contributions. Tenets of faith became secular moral principles of human dignity, equality and freedom, used to justify human rights and democratic institutions. 

The panorama of past moral-political progress, Habermas hoped, could encourage efforts to carry the learning process further, toward a just cosmopolitan order capable of meeting global challenges. That project would require ongoing dialogues between people of different faiths as well as between believers and nonbelievers, aimed at reformulating religious insights into cross-culturally acceptable secular arguments for cosmopolitan principles of justice. 

For such dialogues to occur, Habermas argued, non-Western cultures must tap the roots of moral universalism in their own ancient heritages. As he recognized, his historical argument for cosmopolitan hope remains incomplete—he cannot speak for other cultures.

Though not himself a believer, Habermas had a high regard for Catholic theologians, open to harmonizing faith and reason. I think he hoped they in particular could contribute to cosmopolitan dialogue. But effective Christian contributions, he insisted, must issue from our lived faith, expressed in communal Eucharistic practices and worship of a transcendent God. Perhaps he saw Christian hope, energized by faith, as a resource the cosmopolitical project could not do without. 

William Rehg, S.J., is a professor of philosophy at Saint Louis University. He is the author of Insight and Solidarity: The Discourse Ethics of Jürgen Habermas and Cogent Science in Context: The Science Wars, Argumentation Theory, and Habermas.