As Habermas says in his Introduction, this is a collection of essays which does not constitute ‘a systematic whole’ (7). Nevertheless, the essays do have a unifying thread – a common concern with a problem which is both one of practical politics and one for modern philosophy. Modern society, both at the national and the global levels, conceives of itself as liberal and essentially secular, the heir to the Enlightenment. But the implications of that inheritance are unclear. On the one hand, Enlightenment thought is anti-metaphysical and opposed to settling issues by reference to alleged authorities. This leads to a view of the desirable society as one which is pluralist, in the sense that it does not require of its members any particular worldview or conception of the good, and values tolerance of different perspectives, including those of different religious traditions.

The thought of the Enlightenment, however, also leads to quite a different view: this is what Habermas calls ‘hard naturalism’. This is itself a kind of metaphysics, in the sense that it gives the ‘objectivating’ view of the empirical physical sciences a special status, as revealing the fundamental nature of reality, including human reality: human beings are just one kind of object in the material world, and their behaviour is governed by the same mechanistic laws as those of other material objects. For the hard naturalist any kind of religious claim is no more worthy of serious consideration than a belief that the earth is flat or that the future can be predicted on the basis of the patterns of tea leaves at the bottom of a cup. ‘Hard’ naturalism goes with a conception of secularism according to which it involves opposition to all forms of religious orthodoxy: a truly secular society, on this conception, would allow no room for any contribution by religious traditions to public discourse.

In Western Europe, we have indeed experienced a radical secularization in this sense: as Habermas says, this was earlier believed to be the model for all human societies as they ‘modernized’. Technological and economic modernization were thought to be inevitably accompanied by the growth of this kind of secularism. The problem with which Habermas's essays are concerned arises because, to the surprise of those who thought in this way, the rest of the world (including arguably the most technically and economically ‘modern’ country of all, the U.S.A.) has on the contrary experienced a resurgence of religious orthodoxy and of religiously-based values. Even Europe itself cannot entirely escape the consequences of this development, both because of internal revivals of religious belief and because of its importation of religiously-based cultures from other parts of the world. From a political point of view, the problem this creates is that of accommodating religious perspectives within the pluralism of a liberal society without destroying the ‘civic solidarity’ required for the effective functioning of democracy, in which issues are resolved by rational debate between equals rather than by authority derived from tradition.

A solution to this problem is possible, Habermas argues, only if both kinds of tradition – those based on Enlightenment naturalism and those based on religion – can be persuaded to reflect on the limits of their respective points of view (102). On the religious side, this is a task for theology; but on the side of naturalism, philosophy, because of its non-sectarian character, can play a major role. Philosophy needs to reflect on ‘the cognitive presuppositions that must be fulfilled if civic solidarity is to function effectively’ (6).

In the essays in Part I, he explores from this point of view his own ‘intersubjectivist’ programme in the philosophy of mind. He rejects the Cartesian view of the ‘subject’ as a detached observer of an entirely separate ‘objective’ world, and with it the concept of Reason as a faculty which gives us insight into eternal truths. His own early experience of the difficulties of communication resulting from his cleft palate, as he explains in the first essay, had given him the sense of human beings as ‘animals that, by virtue of being embedded from the outset in public networks of social relationships, first develop the competences that make them into persons’ (13). And his later study of philosophy, including Peirce, Frege, Wittgenstein and Davidson, and other philosophers in the pragmatist and analytic traditions, led him to a ‘detranscendentalized’ conception of reason as ‘the formal-pragmatic presuppositions of communicative action’ (25). Putting it perhaps too simply, what is ‘rational’ is what human beings discover through dialogue with each other in which each participant has equal status and in which participants treat each other with mutual respect. ‘As fallible, situated beings, we have no way of ascertaining truth other than through discourses that are both rational and open-ended’ (44). ‘Objective’, on this conception, means what ‘is “given” to us as “the same for everyone”’(31).

This can be seen as one way of interpreting the legacy of the Enlightenment, a continuation of some aspects, for instance, of Kant's rejection of the idea that reason is a source of transcendent metaphysical truth rather than a means of organizing our human experience of the world. (Habermas discusses his relation to Kant in several places in these essays). But it is opposed to another interpretation, according to which to be rational requires the adoption of ‘hard naturalism’ which, as already mentioned, rejects out of hand ‘the possibility that contributions formulated in religious language could have a rational content’ (5). Hard naturalism is itself a form of metaphysics, and genuine post-Enlightenment modernity, as Habermas sees it, requires us to live in a ‘post-metaphysical’ world. Habermas advocates instead a ‘soft’ naturalism, according to which ‘those states of affairs are “real” that can be represented in true statements. But reality is not exhausted by the totality of scientific statements that count as true according to current empirical scientific standards’ (153). In other words, scientific accounts of the world are not the only sources of rationality or truth. In the essays in Part III, Habermas makes a number of valuable points on this basis about recent attempts to base deterministic accounts of human thought and action on the findings of the neurosciences.

One consequence of this for social theory is that a truly modern society is one which is genuinely pluralist. The social solidarity which is necessary for the survival of democracy can be secured only if the representatives of different worldviews – non-religious and religious (including many different varieties of religious belief) can participate in the general debate on equal terms and with mutual respect. This will be a ‘post-secular’, as well as a ‘post-metaphysical’ society, in the sense that no one conception of what is true or what is good, not even those of secular ‘rationalism’, will be dominant (the parallels with Rawls's account of liberalism are recognized by Habermas). But in another sense, it will be a ‘secular’ society, in that religious views will have no more authority than any other.

This involves concessions by both the non-religious and the religious. To respect all views equally requires the non-religious to be willing to learn from religious traditions of thought about, above all, moral issues. It is only, Habermas contends, because we already know from these traditions what it means to have moral duties that we can have the intention to construct a post-traditional morality (see 88). Philosophy, as Habermas puts it (110), has assimilated networks of moral concepts from Christianity in particular: it may also have developed them in new directions, but it has not exhausted their original force, and it can deepen its reflections on, for instance, respect for persons by listening to religious contributions to the general dialogue. Believers too, however, if they are to participate in a democratic society, have to make concessions, which in their case are greater. They have to argue for their point of view in terms which can be accepted equally by both non-believers and those who follow other faiths. They have to distinguish between being a member of their own faith community and being a citizen of the wider society. Above all, they have, as citizens, to renounce the claim to universal validity which is part of what Habermas calls the believer's ‘ethical self-understanding’. This is a greater sacrifice for believers than any made by secular consciousness, particularly when it comes to moral and legal issues. Habermas cites, among other examples, the difficulties which devout Catholics experience in the face of the legalization of abortion. And, apart from the moral sphere, fitting into modern society involves adaptation of their doctrines and forms of life to fit the norms of that society. But this, in Habermas's view, is the price which has to be paid ‘in order to assert themselves within the differentiated structures of modernity’ (305).

This seems to me to be questionable. If religious believers are genuinely to be treated with respect in a ‘post-secular’ society – if their contributions to the general debate are really to be valued equally – then the distinctive nature of their perspective must surely be valued, as Habermas himself implies in some passages referred to above. And the distinctive character of their perspective is precisely that it does not conform to the ‘soft naturalist’ norms of modern society: it is not just a particular ‘way of seeing things’ which has some meaning for oneself, as other ways may have for other people. As Habermas himself acknowledges, for the religious believer other ways of life are not just different, but mistaken. For members of non-Western cultures living in Western societies, there is the further difficulty, accepted by Habermas, that they must find their own path to modernization from within their own culture, rather than by adopting Western norms. There seems to be something here which Habermas has not fully worked through. One may also doubt whether the threat to social harmony comes from those believers who are prepared to accept a distinction between demanding a right to respect for their beliefs and being willing to abide by the laws agreed by the majority. Is it not rather from those fundamentalists, of all faiths, who utterly reject any such accommodation? Telling the latter that adaptation to the norms of rational dialogue is the price to be paid for being given a hearing in a modern democracy is hardly likely to persuade them. In this sense, nothing which Habermas has to say in these essays can be said to provide a realistic solution to the problem of creating a stable modern social order in which religious belief can have its proper part.

The difficulty with a collection of essays of this kind is that, written as they are for a diversity of occasions, they inevitably cover much more ground than can be summarized in a review of this length. What has been said above is an attempt to isolate the thread which Habermas sees as running through them all, but even these common ideas are expressed in somewhat different ways in different places, and there is much of the discussion which is only marginally related, if that, to these common ideas. Whatever reservations one may have about the central themes, however, there is rich material for reflection in these essays for those interested in a variety of topics, ranging from philosophy of mind, questions of determinism and free will, the history of modern philosophy, and problems of truth and meaning to the nature of democracy and the possibilities of a new world order. Habermas manages to integrate his discussion of these diverse problems in a way which is regrettably not common in English-speaking philosophy, and for this reason above all this is a book which is well worth reading.