There are many varieties of literary biographer. For example, the biographer who, like the dog-owner and his pooch, morphs into what they're writing about. One recalls that eerie photograph on the dustjacket of Michael Holroyd's life of GBS where the images of Shavian biographer and Shavian biographee looked like dead certs for Private Eye's “Could they be related?” column.

Then there's the biographer who goes into his subject like an intrepid explorer and is never seen for 20 years, such as Norman Sherry and Graham Greene.

There's the “authorised” biographer. The hero-worshipper who, as the phrase goes, “Boswellises” his subject, servile toad that he is (I've been accused of that).

The opposite kind of biographer “Carpenterises” his subject. The late (and personally loveable) Humphrey Carpenter used to get unfettered access from the literary estate and (as with his life of Dennis Potter) the next thing the subject's nearest and dearest would see was a tell-all piece (in this paper quite often) chronicling “My rumpy-pumpy nights with ten-pound hookers”, or whatever.

There are the academic biographers, who bury their subject like radioactive waste at Chernobyl under tons of scholarly concrete. Pick up any biography by Frederick Karl (snatch and press is recommended, they're very heavy) and feel your eyelids droop. It's what hell must be like: eternity, and only biographies by American professors to read.

There's the “don't get mad get even” biographer: Kathleen Tynan on errant spouse Kenneth, for instance (“Can you imagine my surprise, dear reader, when I discovered, under the bed, his tin box full of the most appalling wanky-spanky stuff?”). There's the butcher boy biography: Roger Lewis, for example, on poor hatcheted Anthony Burgess. There's the biographer who gets into a Mystic-Meg relationship with his subject - Peter Ackroyd, notably.

Blackwash, whitewash, blood-red, dull mortar-board grey: take your pick.

Current discussion on the art of “life-writing” has focused on two issues. First is how far, as with delectably naked Amanda Foreman standing behind a stack of her Georgiana, Duchess of Devonshire, it's OK to sex biography up. It's more a movie thing, of course. Do Sylvia, The Edge of Love, or Becoming Jane get us closer to the “real” Plath, Dylan Thomas or Jane? Stupid question (but fun to watch: sex usually is).

The other currently burning question is how many skeletons the biographer should bring out of the closet. That issue has been sharpened by Patrick French's biography of V.S.Naipaul, which offers a portrait with so many warts that one can barely see the Nobel prize-winner's face.

How, one cannot but wonder (as French manifestly wonders), could such an imperfect human being create such perfect art? Another, even more pressing source of wonderment is why the author “authorised” this young scholar - very gifted, but with no track record in Naipaul studies - giving him entirely help-yourself, unhindered access.

Why, for example, allow the opening of his dead former wife's private diaries to the world, containing as they do evidence of extraordinary spousal suffering (diaries, incidentally, that Naipaul himself has never wanted to read). Why give “frank” - ie, self-damning - interviews involving such things as whoring, snobbery and (why mince words) racism? The answer lies in that word “authorised”. It doesn't mean, as it does in other biographies, “licensed”. Naipaul was, one suspects, “authoring” his own life story. The resulting image produced by French was less important to the novelist (scorning as he evidently does most of the human race) than the fact that he, V. S. Naipaul, was creating the image.

Most subjects of biography are like so many pieces of meat on the anatomist's slab. Not Naipaul.

Much as one admires it, and relentlessly readable as the book is, Patrick French's biography makes one uneasy because, deep down, we don't like admired authors to be besmirched. Even if they go along with the besmirching. It's the fart that one can never thereafter get out of one's nostrils - something that, in French's case, will now hover forever over one's enjoyment of, say, A House for Mr Biswas.

There are innumerable other examples. I shall never again reread The French Lieutenant's Woman with quite the untrammelled pleasure that novel used to give me because of the unpleasant nature of its author revealed by Eileen Warburton.

Andrew Motion's life of Philip Larkin is masterly. But many don't like it (and ungenerously include the biographer in their dislike) for the pall it casts over previously much loved verse. How can one admire, as one once did, The Less Deceived when the echo thrown back is the ditty the poet dashed off for a likeminded racist pal: “Prison for strikers, Bring back the cat, Kick out the niggers, How about that?” Motion's biography did not get the prizes it deserved. To adapt Michael Heseltine's epigram: the hand that wields the biographical dagger rarely wins the Whitbread.

So it is with Patrick French. One's grateful for him giving us The World is What It is, but part of one wants the biography unwritten. It hurts us too much. But did it hurt V. S. Naipaul? One very much doubts it. As Paul Theroux observed, in his wounded-disciple's memoir, “Sir Vidia” loves to cast dark shadows: even on himself.

John Sutherland is an author, academic and former chair of the Booker Prize judges. Patrick French is speaking today on his Naipaul biography at the Times Cheltenham Literature Festival

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