Each year the Booker prize provokes passionate argument and the shortlist is pooh-poohed. So why would an academic want to get involved in such a circus? Gillian Beer, chair of judges, explains the attraction

Why do the Booker?" a graduate student asked me with exasperation. Why would an academic want to take part in this public and commercial enterprise? Should I not be concentrating on the writing already achieved and signalled as excellent? Should I involve myself in a competition that brings me some gain, some publicity and a moment in the heat of the book trade? What is the worth of the Booker prize to readers and writers? What does it do?

Let me try to answer by reflecting on my experience this summer. The final decision is still to come. I may be flayed at the prize-giving dinner and served up on Channel 4, which is televising the proceedings. I may drop into proper anonymity like a stone in a well. What matters is the outcome to the writers and their future readers.

It is no good being a Booker judge unless you love fiction. All summer my head has been full of crossed worlds, jostling for occupation. Some of them open brilliantly, then scatter, leaving you with a sense of loss. The hardest thing for a writer turns out to be keeping a novel going through its whole length. "Conclusions are at best negations," wrote George Eliot, and I have become familiar with authors' panic as the conclusion approaches. Over and again I encountered novels that faltered or simply fell into chaos two-thirds of the way through. Things began to happen pell-mell. Rape, child abuse, bereavement, incest, even the Holocaust, cropped up, more like items on a menu than events. Yet those same preoccupations wound deviously through some of the finest works.

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The books start to come in slowly, in early April, and become a landslide by early July. By that stage, even an avid reader can begin to feel that the books are eating you, not you the books. Sometimes you read with gritted teeth, sometimes with reckless enjoyment. On first reading, I always jot down my impressions at the end, rather than making notes as I go along, so that I read with the rhythm of the book. Some books that you quite soon suspect will not eventually make it onto the shortlist still absorb you. One such for me this year was It Begins with Tears by the Jamaican novelist Opal Palmer Adisa, so rich in its immersion of the reader in the experience of a small village and its people. Or Like by Ali Smith, one of whose fictional voices entered that of a seven-year-old girl with extraordinary directness.

"Booker books" are said to be difficult or slight, poetic or scummy, too English or too politically correct, genteel or obscene, scatological or bourgeois. Only Tristram Shandy could manage to be all these at once. Over Booker's 29 years, the prize has gone to writers as various as Anita Brookner and James Kelman, Salman Rushdie and Roddy Doyle, J. M. Coetzee and A. S. Byatt, Kerri Hulme and William Golding, Kingsley Amis and Ben Okri. It has marked shifts of fashion and marketing. And it has so far survived the death of the author, the death of the novel and heralded the return of the repressed, the readers who now buy the shortlisted novels in their thousands. Few shortlists have been greeted with enthusiasm at the time but only a few years later they have resolved into a "golden age" for which journalists sigh in the face of a new "dull" list.

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But is there a form of repression in literary prizes themselves? Of course there is, as there is in any game. The book you write must be published in London. To be entered for the Booker prize a writer must be born or domiciled in Great Britain, the Republic of Ireland, or the present or recent Commonwealth. Effectively, this means the whole English-speaking world except the United States, which broke away longer ago than Fiji (still eligible). That constraint leaves out some of the strongest fiction of the present age: Toni Morrison and Don DeLillo, for example. But it gives space to writers around the world using English in new ways. Perhaps the strongest gain of the Booker prize has been making English speakers everywhere aware of the extraordinary range of fresh literary possibilities released by the language, in Africa, in India, in the Orkneys, in London suburbs, in transits between the Caribbean and Britain. For British readers this changed experience of their language has also begun to change national identity. It has confronted them with the past that has brought about the worldwide prevalence of English, as Fred D'Aguiar's novel about a slave voyage, Feeding the Ghosts, does this year.

For the sake of the judges' eyes and sanity there are further constraints on numbers: each publisher may submit only two novels, together with one novel by a previously short-listed or winning author, even if they have several such authors on their list. In addition, the panel of judges is required to call in not fewer than 12 and not more than 20 further works. The rules were changed from three to two novels apiece a few years ago when an alarming 146 novels were submitted. Even so, we were this year faced with 106 works. Some had no chance whatever, shallow slovenly works that seemed unaware how many skills are needed to write fiction. But a great many were vigorous inventive works, rich on the page, good to read.

This makes the Booker experience wonderfully worthwhile for the five judges but also agonisingly difficult. How to communicate through six novels the reserves of talent around? We as judges have the hard work of interminable novel reading; we lose sleep, friends, entertainment and all the other kinds of reading available. But we are admitted to an extraordinarily intimate understanding of what is troubling and engrossing people now: topics such as stalking, uneven relationships, survivors' tales, generations on, whether the descent be that of slavery or antisemitism or lost indigenous peoples, science and its outcomes, particularly genetic re-tooling. Notable in their investigation of those particular topics were very diversely imagined novels such as Ian McEwan's Enduring Love, Caryl Phillips's The Nature of Blood, Jeanette Winterson's Gut Symmetries and Simon Mawer's Mendel's Dwarf. There were also novels absolutely of the present such as Alan Warner's These Demented Lands. And who could have foreseen that a piano sequence by Janacek,"On an Overgrown Path", would be essential to the meaning of two works, Bernard McLaverty's Grace Notes and Mawer's Mendel's Dwarf? By reading many novels produced in the same year you read more than their sum. Themes emerge that bind across fictions; similar topics produce quite unlike language. A palimpsest of the present is created.

The judges read independently. Each year sees a new set of people. The advantage of a new team each year is that no continuing agenda emerges; people do not get set in their ways and pressure is more difficult. (A French judge remarked to me that he was astonished when serving on the Booker not to be approached by publishers, or even so much as offered a meal.) The disadvantage is that the team is one of neophytes, few of whom know each other already. So a great deal can depend on the dynamics that build up late on in the process. Change any judge and you are likely to change the final list: that is inevitable since the judges have done the reading from scratch rather than received summary advice from outside.

After four months the team comes together for the long shortlisting meeting. Astonishingly, your favourite books are rubbished by other judges who in turn look at you, hurt, while you wave away the masterpiece they have identified. For everyone but the judges the shortlist is the only thing that matters. Sometimes being on the shortlist is represented as failing to win the Booker when, as the judges know only too well, being on the shortlist is in itself an unusual achievement. The compromises entailed in drawing up the shortlist are not just a matter of power play or quarrelling. (As we emerged from the shortlisting meeting we were asked: "Did you quarrel?" It was clear that to give satisfaction we should have.) The compromises are to do with listening to one another, weighting the insights and refusals, like a great seminar with no secondary authorities to which to turn.

Being a judge of the Booker means taking the risk of reading without recourse to critics other than those alongside you. It is a knife-edge form of teaching. The judges offer the concentrated fruits of reading that most of us do not have time to undertake. This is not a prize for lifetime achievement, or for a famous writer's secondbest book, or even for what we expect a novelist may do in the future. It is a prize that opens the field, seeks what is best in what is new this year. It sets first-time authors in the same space as the established and listens to the voices emerging. It provokes passionate argument and I am glad to have had a hand in that provocation. Whether I shall feel satisfied when the decision and the dinner arrive I do not know. But by then the books will be in other readers' heads and hands.

Gillian Beer is King Edward VII professor of English literature, University of Cambridge. The winner of the Booker Prize will be announced on October 14.

BOOKER PRIZE SHORTLIST

Jim Crace, Quarantine, Viking, Pounds 16.99

A tale about Jesus's 40 days and nights in the wilderness. The lives and often brutal loves of the people of Judea contrast with the torment of the Galilean in the desert. (7-2)

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Mick Jackson, The Underground Man, Picador, Pounds 15.99

A network of tunnels has just been completed beneath the Duke's estate but the rarely glimpsed Duke is far from happy. No one understands his sorrow: an elusive memory that no amount of digging through the past can illuminate. (5-1)

Bernard MacLaverty, Grace Notes, Jonathan Cape, Pounds 14.99

Up-and-coming composer Catherine McKenna rejects her Irish Catholic background and alcoholic parents to pursue her music. On a Scottish island she falls in love with a diver but after the birth of their daughter her life changes irrevocably as their relationship collapses. (2-1 favourite)

Tim Parks, Europa, Secker & Warburg, Pounds 9.99

Jerry Marlow is one of a coachload of delegates bound for the European Parliament in Strasbourg. Is he on the trip to support a petition to keep the job he does not really want, or because his ex-mistress is of the party? (6-1)

Arundhati Roy, The God of Small Things Flamingo, Pounds 15.99

Set in a pickle factory in southern India, the book tells the tale of two-egg twins, Rahel and Estha and their struggle to fashion a childhood in the shadow of the wreck that is their family. (9-4)

Madeleine St. John The Essence of the Thing Fourth Estate, Pounds 9.99

Nicola and Jonathan have shared Nicola's Notting Hill flat for several years when Nicola returns, after popping out for cigarettes, to find the predictable and solid Jonathan demanding a separation.(8-1)

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Odds: William Hill and all descriptions from publishers' promotional literature.