For Oxford political theorist and former Thatcherite John Gray the central point is that there is no central point. David Walker reports on a self-confessed 'contrarian'.

Philosophy is back. So Sunday papers say. At dinner parties they are talking concepts, values, isms. The culture has opened an unwonted space for ideas. Look at the lionising of Amitai Etzioni. He is American, and there is a certain element of intellectual voyeurism in the way fashions get imported across the Atlantic, but the domestic thirst for at least a medium-sized Idea is apparent.

You can diagnose the condition in several ways. It is a demand for something to replace the individualism that has been the guiding public philosophy for the past 15 years. It is a hankering after some concept or theory to lay over the heaving mass of change, social and economic, beneath our feet. One result is boom times for the - admittedly few - British thinkers about politics and society who are "out", available as media-friendly, lucid commentators.

These are certainly happy days for the Oxford political theorist John Gray. A new monograph on Isaiah Berlin has just been published and a book of essays (Enlightenment's Wake) is due from Routledge in the autumn. He has been in demand, as a home-grown critic of the Americans. What that entails is a perch on The Late Show and punditry on Newsnight. That is par for the intellectual course. But a fortnightly column in The Guardian and now chat with Melvyn on Start the Week; for a British intellectual that starts to look like celebrity indeed.

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We must not take this too far. Few of Gray's media interviewers are likely to read his book on Berlin, the dense argument that requires some familiarity with old timbres in difficult books. Berlin/Gray's heroes include Johann Gottfried von Herder and the even less well-known Johann Georg Hamann. Herder's Abhandlung uber den Ursprung der Sprache is likely to be unfamiliar, even in the producer's gallery at The Late Show.

Little do the presenters know, for Gray - from a media point of view - turns out not to be a runner for the Big Ideas stakes. For his central point is that there is no central point, no Big Idea, nor any possibility of one: indeed, all Big Ideas are pretty much as good as one another, and there is no way of playing one off against another. Values, versions of The Good are, in Gray's terms, incommensurable - the question is how to continue living and talking to one another through the pain that insight brings. Liberty, equality, fraternity, freedom, justice; individual rights, group identity: the "subversive" argument of Berlin/Gray is that they may for ever be in conflict.

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We inhabit, in short, an ineffably pluralist world - the task of philosophy is to realise the enormity of that while assuaging the agony of actually making choices among values.

The subtext of the Berlin book could be "against certainty", for it is a sustained argument (clearly Gray's but praying Berlin in aid at every turn) that no values are eternal, no version of humanity's potential secure "in some objective heaven". The civilised woman or man (the phrase comes from Joseph Schumpeter) realises the relative validity of their convictions, yet stands for them unflinchingly. Gray quotes Berlin approvingly: "To demand more than this is perhaps a deep and incurable metaphysical need; but to allow it to determine one's practice is a symptom of an equally deep and more dangerous moral and political immaturity."

Despite the radicalism - or irresponsibility - of a conclusion that could so easily lead to an everlasting scepticism or an autistic relativism, Gray is enjoying his theorist's life. His abandonment of Thatcherism has been successfully accomplished and he is now respectfully listened to on the left for his strong views on the limits of free market liberalism. Liberals of another stripe (liberalism comes in many flavours, or should that be flavors?) have welcomed his inveighing against the authoritarian potential of "communitarianism". Yet those same liberals may find his rehabilitation of nationalism a bit difficult to swallow.

John Gray is, he says, a "contrarian". Just as his former heroine never saw an institution but she wanted to hit it with her handbag, you get the impression with Gray that he is never happier than when having a go at the conventional wisdom, even a wisdom he used to hold. Usually that is some version of the liberal position.

Liberalism, to him, is less a position than an attitude, an almost smug belief that there is a bedrock, that all the world's a calm, rational place where Rawlsian calculations can be made or Dworkinian legality applies.

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It is not that Gray's world is darker. It is more diverse, less orderly. It is an arena of debate and dispute between the Enlightenment (natural optimists) and the pessimistic Romantics, including such Counter-Enlightenment thinkers as Joseph de Maistre, de Tocqueville and the German particularists, notably Herder. He aligns himself with an older tradition of political theorising in Britain ornamented with such names as T. H. Green and, primus inter pares, John Stuart Mill, simultaneously a liberal conservative and a liberal socialist. Like them, he says, the political theorists need to be in daily engagement not with politics - at least as they unfold in antiquated national legislative institutions - but with trends and tendencies, what he (under German influence perhaps) calls History.

Thus his conversation is studded with the brass buttons of contemporary anxiety: globalisation, the politics of identity, fundamentalism, environmentalism. And History has little space for Liberalism, at least of the American rights kind. It is as if he wants to keep saying to them, it is a hard, unfathomable, unAmerican world out there.

There are those - among his Oxford colleagues, for example - who regard him as something of a chameleon, blue in the 1980s, pink in the 1990s. How could he have been contributing to the Salisbury Review and the right-wing think-tanks then and be so soft on Blair now? Intellectual apostasy comes easy. A body of work that moved from major studies of J. S. Mill to Friedrich Hayek to Isaiah Berlin might be called eclectic - except to its author. To pigeonhole Gray we would need to say he is a political theorist with lines open to the philosophers. How would you classify Berlin himself, he asks - as a philosopher manque whose principal works are rich readings of other writers?

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Gray is a fellow of Jesus College, Oxford, and shows every sign of being content to remain there. Son of a working-class home, grammar-school educated, his Geordie accent still distinct, Gray looks like a prime candidate for the transatlantic embrace. And so it has been. He has visited extensively at American institutions, but turned down permanent offers. He found offputting a certain doctrinaire character in American intellectual life. Besides he would miss British conversation - he mentions one over long years with Raymond Plant that convinced him, the expositor of Hayek, there was such a thing as social justice after all.

So what, ultimately, is Gray's own position? The book on Berlin, reviewers have observed, is a work of ventriloquism: he has made the ancient sage speak for him, and some have doubted whether the resulting accents were Berlin's at all. Gray says he is a pluralist, someone who rejoices in the inherent diversity of values and paths towards the good, and is tempted to say that what is more human is the capacity to choose, even to choose the bad . . . a kind of existentialism. But he strongly resists the suggestion he is a relativist who believes any one position is as good as another. He sees one of his tasks now to argue strongly against that old maxim de gustibus non est disputandum. He plans a book on pluralism, that is to say the ways in which holders of incompatible views - fundamentalists and liberals, say - can recognise each other and so talk.

Pluralists, to encapsulate his position, must never be solipsists.

Behind that lies - he argues this strongly - a sense that there is, after all, a "common moral horizon" for humanity. There is a single anthropology. We all, Christian, non-believer, Muslim, abhor certain affronts to human dignity (such as torture). How close does the position come to the kind of liberal fundamentalism espoused, say, by an Ernest Gellner? How close does it come to the doctrine of universal rights the Americans hold?

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Gray, at 46, is still young. There is a lot more to be said. There is a lot more of the contrary in him. The exquisite agony of choosing the right or the left, the liberal or the nationalist, the free or the equal is not going to prevent his writing, or his appearing on the BBC. John Gray's Isaiah Berlin is published at Pounds 18.00 by HarperCollins.