John Davies talks to Bernard Williams, the philosopher who once advised governments and married a minister and who has just retired from Oxford.

At first, there is a problem about interviewing Bernard Williams. He has just retired from his fellowship of Corpus Christi, Oxford (and from being White's professor of moral philosophy), and has given up his college room, out of which a large number of books have to be moved into his north Oxford home. The day appointed for our meeting turns out to be the day when the books will be delivered, and I am advised to steer clear of the ensuing chaos.

When we do finally meet, however, we sit in a front room that contains few evidences of a life devoted to philosophy. Excluding the bound copy of a PhD thesis that Williams is reading "as a favour" for another university, the contents of the bookshelves - novels, the new biography of Robert Runcie, art books and opera CDs - give the impression, rather, of a family of culture buffs.

It is an accurate picture. Williams's second wife, Patricia, is the National Gallery's director of publishing, and he himself spent nearly 20 years on the board of English National Opera. Reading D. H. Lawrence when young, he says, contributed to his becoming interested in ethics and theories of the self. And when he gets around to talking about his own ideas, Williams offers an analogy with the artists of impressionism.

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"Impressionism was called the painting of modern life," he explains. "It didn't look as if it was made out of the old salon material, it looked like something people were actually doing ... I would like there to be moral philosophy that was a bit like Seurat. Something that was directly related to everyday life, but that also made it look rather strange and new because it was rather monumental and had a very strong structure."

In his philosophical writing, Williams has often taken his examples from the arts - Anna Karenina, Brunnhilde in Wagner's Die Walkure, the life of Gauguin - in his championing of individual experience against large, all-encompassing philosophical theories. Indeed, it is almost as if he feels that philosophy has not got as much to say about human behaviour as has art.

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"I think moral philosophy is an almost impossible subject," he declares at one point. "On the one hand highly theoretical moral philosophy is abstract and falsified. Its theories tend to be artificial academic constructs, very little to do with how people live their lives. On the other hand, if you try to write something with the kind of immediacy or concreteness or untidiness or imaginative echoes of those ideas by which people really do live their lives I you're in the realm of imaginative fiction."

In dictionaries of philosophy Williams seems to be most often cited for his critiques of other philosophers' works rather than for anything positive. A colleague such as Martin Hollis, of the University of East Angli,a will say that he has "a good claim to be the leading British philosopher of his day", but will go on to describe Williams's Ethics and the Limits of Philosophy, perhaps his most important work, as "ferociously destructive", with only a "few fragments" of constructiveness here and there. "He is very clever, and has a lovely eye for the central questions. If only he had the central answers."

To the accusation of negativity Williams has an answer. "I don't see (Ethics and the Limits of Philosophy) as negative, I see it hopefully as liberating. It seems to me people get themselves in situations in which they feel they have no right to have certain kinds of moral thoughts because they don't fit in with with some very impoverished theoretical picture of what constitutes moral thought. Roughly, if it isn't about obligation or consequences, it doesn't count. That's not the way most people think most of the time about most things."

Ross Harrison, a reader in philosophy at Cambridge and a Williams admirer, puts it another way: "If by destructive you mean he has made people think again, then perhaps his overall effect has been constructive."

But there are other aspects to Williams's philosophical output. He has been keen to distance himself from what he describes as "a marked indifference to history" in post-war Oxford philosophy of recent decades, such as that of J. L. Austin and his disciples.

Williams might also have written a book on Nietzsche: "I remember spending a summer reading him in Italy, and writing a lot of notes. But I came to the conclusion that I didn't know how to write a book about Nietzsche."

As a contemporary philosopher, Williams has probably had a higher profile outside academia than most of his colleagues. This is partly for non philosophical reasons, as the (first) husband of the then Labour minister Shirley Williams; they married in 1955 and divorced in 1974. But there have been other public roles; he has been a broadcaster since the 1950s, first on the old Third Programme and then on BBC television's Brains Trust, a discussion programme that went out live on Sunday afternoons.

He was called on by Labour in the late 1970s, when "Harold Wilson had an enormous disposition to create royal commissions all over the place'', sitting on the royal commission on gambling and then chairing a Home Office committee on obscenity and film censorship. Neither of these had any effect on legislation, a fact ruefully acknowledged in a lecture Williams later gave entitled, self-explanatorily, "The Pathway to the Pigeonhole''.

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The recommendations of the gambling commission, he says, were "almost entirely'' ignored "when as far as I could see it was simply in the interests of the government to take them up. One of them was a proposal for a national lottery which has now been carried through but in a less cautious manner than we recommended. So the government could have been raising money for good causes for the past 20 years."

As for the committee on obscenity, its recommendations also fell on stony ground. The committee recommended banning material that created "a recognisable presumption that a crime was committed in the work of its creation ("which got rid of snuff movies and child pornography") Williams explains. It also proposed a new offence of "public offensiveness" so that "everything else to which people objected... would be confined to sex shops and the like and not be publicly displayed". The committee reported in 1979, the year of Margaret Thatcher's first election victory; having been appointed by a Labour home secretary (Merlyn Rees), its proposals were not taken on board by his Conservative successor.

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At the relatively young age of 49 Williams became provost of King's College, Cambridge. His earlier academic career, having begun with a degree in Greats at Oxford and a fellowship of All Souls, had proceeded via New College and two London colleges and the Knightbridge professorship at Cambridge. As provost he was, according to one King's fellow, "a very sharp operator who kept people on their toes''. Williams himself says he "quite enjoyed'' administration.

But by the late 1980s Williams was looking around for "another real job'' to take on after King's. Already a visiting professor at Berkeley; he decided to accept its offer of a professorship, and emigrate, provoking cries that Britain was losing one of its leading philosophers to the brain drain.

Now he says he "made a very naive mistake. It's one thing to be a visitor (in California), or be by oneself. It's another thing to try and set up an entire family life there". Not that his wife was unhappy. "In some ways she liked it very much. In such a situation the trouble is, if I can put it in a nutshell, the kids are rather at sea.'' (They have two sons, now aged 20 and 17.) "They don't know what the expectations are or how to match up to them, and you can't help them because you're as much a stranger as they are."

All the same, Williams says, his sons "showed a lot of resilience and courage. We could have stayed there. But Oxford rang and offered me a job'' (the White's professorship, formerly held by Williams's undergraduate tutor, R. M. Hare) and the consequence was that the emigrants returned in 1990, after just two years abroad.

"It all had its rather absurd aspects,'' he reflects. "I left with a certain amount of political fanfare, a lot of fuss that wasn't of my making. When I decided to go to America, certain people associated with representative bodies to the universities said 'Look, this is a matter for public interest because of the way the universities are being treated by the government'. So I was suddenly caught up in that, and thought to be a conspicuous feature of the brain drain. But I did say it was a personal decision not a political one. Of course when I came back it all looked rather ridiculous, enough to be a little embarrassing."

Having returned to teaching philosophy at Oxford after an interval of some 30 years, did Williams notice much change? The discipline in general, he thinks, "has got various virtues it didn't have when I was young. It's less amateurish".

"The subject's better organised and broader. It's got a more professional approach to history but it isn't quite as much fun as when I was young. That particular period was rather irresponsible. In the 1950s we travelled frightfully light. You really did have the feeling that you could make some of it up."

He confesses to ambivalent feelings about the research assessment exercise. "I think it's mightily smartened people up from simply giving the same courses and doing nothing in a few cases. It's a stimulus to work. Another underestimated advantage of it is that it's actually altered the pecking order because of the enterprise shown by some universities. The old hierarchy has been broken up by places like St Andrews and Warwick who have made quite a mark, which I think is altogether to the good.

"On the other hand, it has a terrible publish-or-perish aspect. Simply too much is written . . . And the awful fact about philosophy is that, unless it's moderately good, it's probably no use to anybody."

Williams also feels there is too much "scientism'' in the subject now, particularly in the philosophy of mind. "As I get older I become more aware of the connections between philosophy and what in an old fashioned phrase I'd call a humanistic education. It seems to me that what makes philosophy interesting is its relations not just to some of the sciences, but also to history and literature and criticism."

Perhaps appropriately, his next book will be one of political philosophy. After some years outside the Labour party, he is once more a member. But he is also thinking of collecting together all his writings on opera. These range from essays for ENO and Covent Garden programme books to "a most surprising commission" the 7,000-word entry on opera in the Grove Dictionary of Opera.

"No expert would write such a piece, because that's what the whole dictionary's about,'' Williams explains. "So (the editor) Stanley Sadie had the idea of getting this rank amateur to write about what opera is and what it can do."

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