Of course, the irony of an Oxford philosopher losing her mind makes us want to think about the connections between life and art. But more than that was going on in the days following Murdoch's death. Old, pre-Bayley lovers were identified and their pictures printed; Murdoch's domestic arrangements were picked over. Her cheekbones, bicycle-riding and Irish inflections were all set down in detail. Murdoch's life - and her most private life at that - had become the real story.
Last year, almost as much biography was published as general fiction. The genre's growing popularity emerges from the current fascination with the real, or at least a highly mediated version of it, as shown by the popularity of magazines like OK and a rash of television docu-soaps. Blake Morrison's dad and newspaper columns about disappointing husbands all offer the possibility of getting close to another person's life and, in the process, our own. Comparisons can be made, contrasts noted. Measured against these templates the mess of your own divorce, anorexia or alcoholism starts to look positively normal. Reading about other people's lives is the equivalent of coming away from a session of Cafe Rouge girl-talk feeling positively sane and saintly in comparison with your screwy friends.
Once upon a time, novels filled this function too. Victorian fiction created three-dimensional worlds with characters as solid as the furniture on which they sat. People a bit like you or me got themselves into scrapes, had adventures, died or won a fortune. A novel was counted a success if readers discussed the goings-on as if they had really happened. In 1871 the nation worried about how Dorothea Brooke was going to manage as Mrs Casaubon, while two decades earlier many a stolid paterfamilias got teary over the death of Jo the crossing-sweeper in Bleak House.
These days, by contrast, it is hard to get worked up about the fate of anyone who appears in a new novel. Three decades of post-modernism have left us with narrators who refuse to play God, characters who will not be read and plot lines that peter out on the road to nowhere. Modern literary fiction has invested all its considerable cleverness in trying to convince the reader that the world it describes never existed. And the characters, well, the characters never leave the page.
So with novels refusing to provide useful life maps, documentary has been obliged to step into the breach. But just as no one ever met a woman who was quite like Dorothea Brooke, so we don't want to be presented with the dilemmas of people exactly like ourselves. We need them to be the same but different, close enough to be familiar, far enough away to inspire or caution. That's why BBC1's docu-soap Paddington Green, about a dreary corner of central London, has hit the button by having a transsexual star. Lakesiders, which similarly followed everyday shopping-mall folk, featured a girl in her journey from make-up counter to recording studio, a kind of Cinderella with too much slap.
And it's for exactly the same reason that we want our biographies - and our biographers - a little on the exotic side. Product recognition is vital, since publishers are naturally reluctant to pay advances for books about people no one has ever heard of. So the biographical subject needs to have written novels, won battles or painted pictures, while still having feet positively mired in clay. A tacky marriage, a bad habit or two, is just the thing to grab the reader's - and the publisher's - attention.
And, if no one has heard of either subject or biographer, there are ways of annexing other sources of celebrity. Not much was known about Georgiana, Duchess of Devonshire, until HarperCollins published Amanda Foreman's biography last year. But the fact that the 18th- century duchess was born a Spencer, endured a painful marriage and became hooked on a flashy, trashy lifestyle gave her a familiarity that made the most cautious reader feel like investing the decidedly odd sum of pounds 19.99. Likewise Foreman's own picaresque life story - as the daughter of High Noon's screenwriter Carl Foreman, and an early academic failure - handed her publicists plenty to play with. And, as The Guardian pointed out recently, the girl's own good looks hardly harmed. Out of this cluster of extra contexts a commercial blockbuster was forged from what had started life as Foreman's DPhil.
In this gossipy environment, biographers naturally feel under pressure to come up with saucy revelations about their subjects. At times it seems as if there is a kind of psychological striptease going on, with the biographer acting as MC. The recent spate of books on Virginia Woolf, for instance, concentrate on the sexual abuse she suffered at the hands of her half- brothers, the Duckworth boys. Several American studies pretty much read Woolf as a psychiatric case history, and reduce her novels to a set of symptoms. This sudden interest might be understandable if the details of the Duckworths' fumblings had only just come to light. But Woolf herself gave away the information in the early Twenties, during two papers delivered to the Bloomsbury group's Memoir Club, as well as in numerous chats and letters.
It is not the facts that changed over the intervening 70 years, but the context in which they came to be written about. In the late Eighties and Nineties, sexual abuse gained a new resonance in the wake of scandals in Britain and America. Historians of the family had long surmised that girls - and boys - had been "interfered with" for centuries, but it was only in the light of this new hysteria that a recognisable pathology of sexual abuse emerged, which could then be applied retrospectively. Hardly surprising, then, that incidents of child molestation started to pop up not only in biographies of Virginia Woolf - where the proof was strong - but in plenty of other cases where it was not.
And proof will always be the problem when it comes to reconstructing private lives. In the case of those long dead, the evidence will be scattered, though the chances of being landed with a libel suit are slight. And time changes meanings. A series of friendly letters written a century ago may be just that - friendly, not adulterous. It is hard to prove a sexual affair without the evidence of the bedlinen.
Even when all seems clear, a tag of doubt must always remain. When working on my recent biography of George Eliot (Fourth Estate) I looked at a diary written in 1851 by her landlord, John Chapman. Chapman already had a wife and a resident mistress, and it was his habit to note down in his diary whenever he had sex with either of them. One weekend in January the initial "M" (presumably for Marian, Eliot's real Christian name) appears twice on Chapman's pages. I took this to mean that they made love, a shocking revelation for a married man and a single woman in the early Victorian period. The hypothesis builds on what we already know about Chapman's promiscuity and Eliot's vulnerability to any man who wanted her. Contemporary gossip certainly had them down as lovers, and even whispered that there was a child born from the affair. But in the last analysis we can never know exactly what that scribbled "M" signifies in Chapman's diary. He may simply have been making notes about his mother.
Similar problems arise when biographers make judgements about their subjects' most secret habits and desires. Lives from 50 years, let alone two centuries, ago look odd when viewed through the lens of current preoccupations. Sometimes this works in the subject's favour. When Margaret Forster suggested in her 1993 biography of Daphne du Maurier that the novelist had enjoyed an affair with the actor Gertrude Lawrence, it did nothing to harm du Maurier's reputation. In fact, the idea of a little recreational lesbianism only added lustre to du Maurier, who was in danger of being written off as an eccentric Cornish recluse, interested only in boats and dogs.
But in other cases, the changing context can do lasting damage. Andrew Motion's fine biography of Philip Larkin came out in the same year as Forster's book on du Maurier. But the misogamy and racism that Motion reported in his subject's life hardly chimed well with sensibilities in the early Nineties. The book's revelations caused fuss and bother, and Larkin's reputation emerged subtly changed. While nothing could harm his status as a poet - which was hardly Motion's intention anyway - never again could his verse be read with such guiltless ease.
Male biographical subjects suffer most from this habit of viewing past lives through contemporary concerns. This is a feminised age, which values nurturing, co-operation, and invested personal relationships. So any subject who displays a range of pre-Seventies masculine behaviour, including promiscuity, alcoholism or violence, is bound to come off badly.
Female subjects, by contrast, do well in the game of shifting contexts. Even women who lived 150 years ago can be claimed as Bridget Jones prototypes, attractive in a messed-up sort of way. Running after impossible men, getting much too thin and dreaming of stardom, are the kinds of self-loathing behaviours that a Nineties sensibility is happy to spot and celebrate in its Victorian foremothers.
There are signs, though, that biographers may be changing the way they conceive of themselves and their art. The idea of the biographer as the knower and disposer of someone else's secrets has started to seem tawdry. For if we accept that there can never be a final, authorised version of a particular life, then the status of Life Writer (as the academy now has it) must be in some way diminished. Godlike claims of omnipotence, including the promise of secret-spilling, now sound like so much pompous clatter.
A recent spate of books suggests that more thoughtful biographers are facing up to the limitations of their own power. Claire Tomalin, who has written on Katherine Mansfield and Jane Austen as well as on great men's mistresses, has always acknowledged the lacunae in her narrative, the places where she simply "doesn't know" what happened next. Hermione Lee's 1996 Virginia Woolf sets out parallel hypotheses about the same incidents and refuses to adjudicate between them. Geoff Dyer's recent book on DH Lawrence, Out of Sheer Rage, is more concerned with what he doesn't know about his subject than with what he does.
Where once the best biographers rushed to divert the reader's attention from the places where their arguments became patchy, these days they are only too delighted to wear their frailties as a badge of honour. The more gaps there are, they seem to say, the more truthful the rest of my narrative must be. What remains to be seen is whether readers take to this new mood of doubt and uncertainty. For if you're the sort of person who likes - and needs - to believe that there is a place where Real Life happens, then the new generation of "I'm not sure" biographies is likely to leave you feeling very edgy indeed.
The writer's biography `George Eliot: The Last Victorian' is published by Fourth Estate, price pounds 20