Is modern art the cutting edge of creativity or ugly, sensation-seeking and aethetically challenged? Donald Kuspit and Norman Rosenthal cross pallet knives in the last in The Times Higher 's series of Controversial Thesis debates

Was it a sign from above - the judgement of eternity? On May 24, a London fire destroyed dozens of works of art, many of them from the collection of Charles Saatchi, the supporter of the Young British Artist movement. It was Saatchi who put up the money for Damien Hirst's best known work, a dead shark floating in a tank of formaldehyde. It's an unwitting symbol of the Young British Artist himself: an ugly, nasty sensation-seeking avant-garde beast. Hirst's vicious creature looks alive, but, after all, it's clearly dead - a stuffed animal in a museum zoo. Or is it a Hollywood movie?

Like the monster in Steven Spielberg's Jaws, Hirst's shark is a shallow simulation. Initially shocking, it quickly becomes boring, once one realises that it's all an act. In Hirst's work, avant-garde portentousness has become pretentiousness: avant-garde sound and fury signifying nothing but everyday entertainment. More literally than the illusion in Jaws, Hirst's shark is show business, but less horrifying, for we don't see the beast in action but passively afloat in death.

The depths both beasts signify is a farce: they are not bizarre creatures that unexpectedly arise from the mysterious unconscious but predictable media creatures. The so-called shock of the new has become the shlock of the new. The surprise of the new, as the poet Charles Baudelaire called it, has become the spectacle of the neo. This is what we see in Hirst's shark: a Dadaist gesture reproduced on a spectacular scale. It is decadent avant-garde art - avant-garde art that is more populist quantity than enigmatic quality. It is avant-garde art that hides its exhaustion - its lack of insightful innovation - behind its exhibitionism.

ÖйúAƬ

US art critic Clement Greenberg thought avant-garde art had clarified and purified the aesthetics of traditional art rather than overthrown it, as is usually thought. At the same time, the avant-garde spawned the Duchampian cancer of anti-art - Greenberg called it "Novelty Art" - that eventually destroyed art from within. For him, Duchamp's ironical destructiveness was a deliberate attack on aesthetic experience. It is a fragile experience, which is why the attack was successful. Anti-art - or, as Allan Kaprow, the inventor of happenings, astutely called it, post-art, meaning art in which the boundary between art and life is blurred to the extent that it becomes unclear what art is - has become the dominant mode of art-making.

Hirst's huge shark symbolises the triumph of post-art - but also, ironically, its sterility and triviality, for the shark is dead and embalmed and, thus, far from dangerous. It gets its credibility only from its association with Hollywood monsters, that is, its exciting entertainment value. But even that value is rather short-lived: while Spielberg's shark haunts the public domain, Hirst's shark is a trophy in a display case.

ÖйúAƬ

In 1963, the constructivist sculptor David Rabinowitch observed that "art has ceased to exist" because it has become "literal". In 1968, the Italian Arte Povera group - like Kaprow, concerned to submerge art in everydayness - declared: "It is useless to predict the end of art. Art was done with 50 years ago." So why, if art is dead, does Hirst keep beating a dead Dadaist horse?

The more urgent question is why did art die? I suggest the answer was given by another dead-end avant-garde artist, the American abstract painter Barnett Newman. "The impulse of modern art was the desire to destroy beauty," he wrote. Newman thought that it did so in order to express "first principles" and "important truths", but these important truths turned out to be ideological, as the American poet and philosopher William Gass argues. For Gass, to advocate "other values" than the art value of beauty - "fighting for the rights of women, defending the faith, exposing capitalism, supporting your sexual preferences or speaking for your race" - may be a way "to disguise your failure as an artist". "Neither the world's truth nor a god's goodness will win (the artist) beauty's prize." For Gass, "in a world which does not provide beauty for its own sake", the task of art is to do so. For Hegel, Old Master art was "able to beautify every possible subject-matter by engaging our contemplation and our feelings".

There are contemporary artists who have a similar ambition - what I call New Old Master artists, among them the British painters Lucian Freud and Jenny Saville. The beauty of their art also transcends the emotional ugliness and tragic reality of life in the act of mediating it.

Donald Kuspit is professor of art history and philosophy at the State University of New York at Stony Brook and author of The End of Art published by Cambridge University Press. He joins Norman Rosenthal in the Controversial Thesis debate at the National Portrait Gallery, June 17, 7pm.

ÖйúAƬ