When Graham Swift won the Booker Prize for his novel Last Orders a bizarre row erupted. A newspaper pointed out that Swift's novel transposed the structure of William Faulkner's classic American novel As I Lay Dying to contemporary south east England. The controversy dramatized the huge difference between the Booker and the Turner, between Britain's literary and visual cultures. A Booker Prize judge admitted to having never read As I Lay Dying. Odder still was the assumption that Swift's echoes of Faulkner were a guilty secret. Success in the literary world rests on notions of authorship and originality that have long since passed away in art.
Accusing a Turner Prize winner of plagiarism would be pathetic. The Turner is given to artists who work with found materials, who quote the history of art, who mock the myth of authorship. It's chosen by judges who understand and respect the tradition of the new. And yet, it resurrects the oldest way of distinguishing good and bad; the oldest emblem of judgement.

The rise of the Turner to a prominent place in British culture has paralleled the decline of the Booker. The literary prize has not coped at all well with the rapid cultural changes of the 1990s. It insists on a liberal, responsible definition of what a Good Book is, when the fictions that shake up the culture are nothing of the sort. The Turner Prize could not be more different. It's aggressively modern, daring like an IKEA advert to tell the public what's good for them, yet at the same time titillating them with the danger of the new. It's a delicious combination of the Tate's formal architecture and the works' formless adventure; a museum vitrine containing sea monsters.

And yet the strangest aspect of the Prize is never discussed. For a long time the Turner was "controversial". With conservative critics questioning the very basis of the Prize, there was naturally a knee-jerk defense of Whiteread and Hirst, insisting on their intrinsic worth as prizewinners. And yet the real, unstated excitement of the Turner is that it raises unsettling questions about what makes one work of art better than another. Why was Damien Hirst judged better than Mona Hatoum? Douglas Gordon better than Gary Hume? What makes Gillian Wearing better than Cornelia Parker? The Turner allies itself with a tradition of twentieth century art that has systematically debunked all notions of artistic value, originality and authorship; and yet at the end of a century's Dadaism and Situationism, after Duchamp, after Lawrence Weiner, after Beuys, the Turner Prize is... a prize. A prize for the best artist.

It's like a city wrecked by war and revolution where the crippled survivors, dragging themselves out of the rubble, hold a competition for the best bomb shelter. This year, for the first time since Hirst, there's a real sense that one artist is, in some hard to express yet profound way, superior to all the rest. Chris Ofili is more than the favourite. Like James Cameron at this year's Oscars, he's King of the World. If he doesn't get the Turner Prize, questions will be asked in the House; the heavens will rain fire on Millbank. Which brings us back to that question: what makes one artist better than another? It's the question we are forced to ask as we stroll through the exhibition, and yet it's a question contemporary art rejects. The last modern movement that based itself on the unmistakable talent of the artist's hand was Abstract Expressionism. Since then, that word "talent" has been flushed down Sarah Lucas's lavatory. We all get the joke when Jake and Dinos Chapman are awarded Bs at Art O Level . The exam tests skills that have nothing to do with contemporary art. Art isn't about conforming to a rule. It's about establishing a new imaginative space.

So why have a prize for it? And not just any old prize. The Turner is such a compelling event that other art prizes are springing up in emulation. There's the Paul Hamlyn Prize, which awards salaries to six promising young artists to get on with their work; and in New York the Hugo Boss Prize, the Guggenheim's answer to the Turner, which went this year to Douglas Gordon. These contests have none of the Turner's glamour precisely because they refuse the responsibility of judgement. The Paul Hamlyn prize spreads out its largesse with fuzzy liberalism. The Hugo Boss prize gives the impression of a choice made by an art world computer. The Turner alone insists on discriminating between art that is interesting and art that is The Best.

In Chris Ofili's painting The Adoration of Captain Shit And The Legend Of The Black Stars, white hands clutch at the pants of a black superhero who ignores their need. The painting is boastful and self-mocking. Ofili is the art world's Captain Shit, famous for the elephant dung his canvases rest on long before people noticed what a good painter he is. Ofili has no complacency about painting as an art, about the sufficiency of draughtsmanship and colour; his paintings are ideas. They establish a space that is not painting in any sense we recognize, yet is not anything else, either.

The Adoration of Captain Shit is really two paintings. The pop image of Captain Shit, the public face of Ofili's art, is superimposed over the legendary Black Stars; faces concealed, made secret, by the stars painted over them. These heroes are hidden from our gaze; they exist in a dimension beyond the image. At night the space around them glows fluorescent green, and Captain Shit disappears.

The body of the Captain is filled with globes of paint that make him thickly, richly present. But he has no substance; he's a facade. The secret world is the real world. Ofili's painting is deeply satisfying. The fascination of the Turner Prize is that it calls upon us to search for this kind of aesthetic satisfaction, while negating all the qualities that have been held in the past to give it. Kant's judgement of taste has gone mad. There is, however, an unwritten code of judgement at work in the Turner Prize. When any consensus over aesthetic quality has gone, art becomes a political phenomenon. As Walter Benjamin wrote in The Work of Art in an Age of Mechanical Reproduction, the forces of reaction aestheticise everything; they insist on the aura of the work of art. The radical response is to politicize art.The Turner Prize is a consummately political event. It presents itself as somewhere between a gambling den and a cathedral, speculative and holy, but what it really does is to create a new kind of public space. This is a space where people come to contemplate art, to enjoy a kind of secular piety; and yet the Turner insists on turning that contemplation back on the world, as politics. All recent Turner winners, from Rachel Whiteread to Gillian Wearing, have been fascinated by the public meaning of camera.

Every year the Prize goes to the artist who makes the biggest public impact. It defines good art as public art, whether in the grand manner of Whiteread's House or Hirst's desire to be part of pop culture. Douglas Gordon makes monumental videos; Gillian Wearing shows us our lives. What all these artists share, and what the Turner Prize with its atmosphere of a great event brings out in their work, is a desire to communicate with the broadest possible public.The Chris Ofili known for his elephant dung and his pop iconography is absolutely in this tradition. His art has the instant appeal of comic book art or Hogarth's prints. It has the hilarious addition of a substance that does not belong in the gallery's pristine space. But this is a front. The joke of Captain Shit and The Legend of The Black Stars is that the white hands clutch at a facade, a man who is all image, without seeming aware of the world behind him; the world of the Black Stars, something less resolved, less understandable than the surface image.

Ofili's joke works against the Turner Prize. The art world want a piece of him, they can't get enough of him. But they don't see the underlying mystery; they don't see the sublime region beyond his Hogarthian self-image as a blustering social being. And they don't realize what they're missing. Ofili has depicted the gap between what can be represented in contemporary British art, and what is more difficult to acknowledge; the gap between art as public sign, and as private work. The secret Ofili is almost embarrassed to share is that he knows how to create beauty.

Jonathan Jones