The German philosopher Jürgen Habermas has long been recognized as the most persistent and influential defender of an Enlightenment rationality that has been attacked both by postmodernism, which derides formal reason’s claims of internal coherence and neutrality, and by various fundamentalisms, which subordinate reason to religious imperatives that sweep everything before them, often not stopping at violence.

In his earlier work, Habermas believed, as many did, that the ambition of religion to provide a foundation of social cohesion and normative guidance could now, in the Modern Age, be fulfilled by the full development of human rational capacities harnessed to a “discourse ethics” that admitted into the conversation only propositions vying for the status of “better reasons,” with “better” being determined by a free and open process rather than by presupposed ideological or religious commitments: “…the authority of the holy,” he once declared, “is gradually replaced by the authority of an achieved consensus.”

In recent years, however, Habermas’s stance toward religion has changed. First, he now believes that religion is not going away and that it will continue to play a large and indispensable part in many societies and social movements. And second, he believes that in a post-secular age — an age that recognizes the inability of the secular to go it alone — some form of interaction with religion is 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.”

The question of course is what does Habermas mean by “introduce”? How exactly is the cooperation between secular reason and faith to be managed? Habermas attempted to answer that question in the course of a dialogue with four Jesuit academics who met with him in Munich in 2007. The proceedings have now been published in Ciaran Cronin’s English translation (they appeared in German in 2008) under the title “An Awareness of What is Missing: Faith and Reason in a Post-secular Age.”

Habermas begins his initial contribution to the conversation by recalling the funeral of a friend who in life “rejected any profession of faith,” and yet indicated before his death that he wanted his memorial service to take place at St. Peter’s Church in Zurich. Habermas decides that his friend “had sensed the awkwardness of non-religious burial practices and, by his choice of place, publicly declared that the enlightened modern age has failed to find a suitable replacement for a religious way of coping with the final rite de passage.” The point can be sharpened: in the context of full-bodied secularism, there would seem to be nothing to pass on to, and therefore no reason for anything like a funeral.

To be sure, one could regard funerals for faith-less persons as a vestige of values no longer vital or as a concession to the feelings and desires of family members, but Habermas chooses to take it seriously “as a paradoxical event which tells us something about secular reason.” What it tells us, he goes on to say, is that secular reason is missing something and without it threatens to “spin out of control.”

What secular reason is missing is self-awareness. It is “unenlightened about itself” in the sense that it has within itself no mechanism for questioning the products and conclusions of its formal, procedural entailments and experiments. “Postmetaphysical thinking,” Habermas contends, “cannot cope on its own with the defeatism concerning reason which we encounter today both in the postmodern radicalization of the ‘dialectic of the Enlightenment’ and in the naturalism founded on a naïve faith in science.”

Postmodernism announces (loudly and often) that a supposedly neutral, objective rationality is always a construct informed by interests it neither acknowledges nor knows nor can know. Meanwhile science goes its merry way endlessly inventing and proliferating technological marvels without having the slightest idea of why. The “naive faith” Habermas criticizes is not a faith in what science can do — it can do anything — but a faith in science’s ability to provide reasons, aside from the reason of its own keeping on going, for doing it and for declining to do it in a particular direction because to do so would be wrong.

The counterpart of science in the political world is the modern Liberal state, which, Habermas reminds us, maintains “a neutrality . . . towards world views,” that is, toward comprehensive visions (like religious visions) of what life means, where it is going and what we should be doing to help it get there. The problem is that a political structure that welcomes all worldviews into the marketplace of ideas, but holds itself aloof from any and all of them, will have no basis for judging the outcomes its procedures yield. Worldviews bring with them substantive long-term goals that serve as a check against local desires. Worldviews furnish those who live within them with reasons that are more than merely prudential or strategic for acting in one way rather than another.

The Liberal state, resting on a base of procedural rationality, delivers no such goals or reasons and thus suffers, Habermas says, from a “motivational weakness”; it cannot inspire its citizens to virtuous (as opposed to self-interested) acts because it has lost “its grip on the images, preserved by religion, of the moral whole” and is unable to formulate “collectively binding ideals.”

The liberal citizen is taught that he is the possessor of rights and that the state exists to protect those rights, chief among which is his right to choose. The content of what he chooses — the direction in which he points his life — is a matter of indifference to the state which guarantees his right to go there just as it guarantees the corresponding rights of his neighbors (“different strokes for different folks”). Enlightenment rational morality, Habermas concludes, “is aimed at the insight of individuals, and does not foster any impulse toward solidarity, that is, toward morally guided collective action.”

The consequences of this “motivational weakness” can be seen all around us in the massive injustices nations and tribes inflict on one another. In the face of these injustices, a reason “decoupled from worldviews” does not, Habermas laments, have “sufficient strength to awaken, and to keep awake, in the minds of secular subjects, an awareness of the violations of solidarity throughout the world, an awareness of what is missing, of what cries out to heaven.”

So what will supply the strength that is missing? The answer is more than implied by the reference to heaven. Religion will supply it. But Habermas does not want to embrace religion wholesale for he does not want to give up the “cognitive achievements of modernity” — which include tolerance, equality, individual freedom, freedom of thought, cosmopolitanism and scientific advancement — and risk surrendering to the fundamentalisms that, he says, willfully “cut themselves off” from everything that is good about the Enlightenment project. And so he proposes something less than a merger and more like an agreement between trading partners: “…the religious side must accept the authority of ‘natural’ reason as the fallible results of the institutionalized sciences and the basic principles of universalistic egalitarianism in law and morality. Conversely, secular reason may not set itself up as the judge concerning truths of faith, even though in the end it can accept as reasonable only what it can translate into its own, in principle universally accessible, discourses.”

As Norbert Brieskorn, one of Habermas’s interlocutors, points out, in Habermas’s bargain “reason addresses demands to the religious communities” but “there is no mention of demands from the opposite direction.” Religion must give up the spheres of law, government, morality and knowledge; reason is asked only to be nice and not dismiss religion as irrational, retrograde and irrelevant. The “truths of faith” can be heard but only those portions of them that have secular counterparts can be admitted into the realm of public discourse. (It seems like a case of “separate but not equal.”) Religion gets to be respected; reason gets to borrow the motivational resources it lacks on its own, resources it can then use to put a brake on its out-of-control spinning.

The result, as Michael Reder, another of Habermas’s interlocutors, observes, is a religion that has been “instrumentalized,” made into something useful for a secular reason that still has no use for its teleological and eschatological underpinnings. Religions, explains Reder, are brought in only “to help to prevent or overcome social disruptions.” Once they have performed this service they go back in their box and don’t trouble us with uncomfortable cosmic demands. At best (and at most), according to Habermas, “the encounter with theology,” like an encounter at a cocktail party, “can remind a self-forgetful secular reason of its origins” in the same “revolutions in worldviews” that gave us monotheism. (One God and one reason stem from the same historical source.)

But Habermas gives us no reason (if you will pardon the word) to believe that such a reminder would be heeded and lead to reason’s being furnished with the motivation-for-solidarity it lacks. Why would secular reason, asked only to acknowledge a genealogical kinship with a form of thought it still compartmentalizes and condescends to, pay serious attention to what that form of thought has to offer? By Habermas’s own account the two great worldviews still remain far apart. Religions resist becoming happy participants in a companionable pluralism and insist on the rightness, for everyone, of their doctrines. Liberal rationality is committed to pluralism and cannot affirm the absolute rightness of anything except its own (empty) proceduralism.

The borrowings and one-way concessions Habermas urges seem insufficient to effect a true and fruitful rapprochment. Nothing he proposes would remove the deficiency he acknowledges when he says that the “humanist self-confidence of a philosophical reason which thinks that it is capable of determining what is true and false” has been “shaken” by “the catastrophes of the twentieth century.” The edifice is not going to be propped up and made strong by something so weak as a reminder, and it is not clear at the end of a volume chock-full of rigorous and impassioned deliberations that secular reason can be saved. There is still something missing.