When Michael Jackson dangled his small child out of a hotel window, did his fans desert him? Of course not, says Terry Eagleton, and therein lies the nature of celebrity

Celebrities go a long way back. It's just that in the Middle Ages they were known as saints. Then, as now, ordinary people felt the need for charismatic, larger-than-life characters whom they could venerate, imitate, throw a halo around, fashion a cult out of. David Beckham will no doubt prove less durable than St Benedict, and hasn't yet had a religious order founded in his name; but both men serve as role models, paradigms, figures who are at once intimate and awe-inspiring. This, indeed, is the secret of superstardom - that the celeb is just like us yet utterly out of reach, commonplace and transcendent at the same time. Freud called it the ego ideal, and in the 1960s it was signified by rock stars with names that craftily blended the homely with the exotic: Billy Fury, Marty Wild, Tommy Steele.

Otherworldliness is still with us, though today such people are known as the rich rather than the saintly. And since it is notoriously hard to combine the two, the wheel may be said to have come full circle. Celebs are expected to kick over the traces, since part of what we admire about them is their transgressiveness. Once it was monarchs who were above the law; nowadays it is movie stars. Celebrities are natural anarchists, but they combine the megalomania of being a law unto themselves with the glamour and prestige of the Establishment, thus gratifying our conformist instincts along with our dissident ones. They also allow us to indulge our vindictive impulses: if they fall from grace too theatrically, we can enjoy the Oedipal delights of savaging them like a parent who has let us down.

Their relationship to their fans is thus more like that of a lion tamer to his faithful but secretly resentful beasts than one of a prophet to his disciples. One false move too many and their charisma can be bitten off at a single snap.

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Not that celebrities easily come unstuck. This is because coming unstuck is part of their celebrity, rather as being an alcoholic was part of being an early 20th-century American writer. The supposedly glamorous lives we find so engrossing may consist largely of vomiting into hotel sinks and dangling babies out of windows, but since the hotels in question are five star, even the sordidness seems exotic. This is one reason why "celebrity academic"

sounds every bit as much a contradiction in terms as "Texan haute cuisine", since academics can certainly be sordid, but are rarely exotically so.

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Besides, celebrities are symbolic figures rather than real ones, and their symbolic status can survive a good many real-life blemishes. Would Michael Jackson's fans desert him even if he had been caught red-handed in his alleged offences on Fox TV? Some of them would, no doubt; but for others it would hardly matter, since the Jacko they adore is a fantasy figure, and thus by definition incapable of being tainted by reality. It would be like imagining the Pope paring his corns. What is at stake is a signifier, not a substance. The Pope could appear in St Peter's Square wearing a red nose and frilly knickerbockers, and the adoring crowd of nuns and monks would simply smile indulgently at the Holy Father's sense of humour. Celebrity is as immune to the slap of the real as is ideology.

Saints used to be revered because they smacked of eternity in their unfathomable virtue, and celebs have an aura of infinity as well. And it is the infinity of wealth and power they exude that we find so fascinating, just as the 18th century was entranced by that inexhaustible power that it called the sublime. The sublime beggars the imagination, whether it be the raging ocean, the idea of Reason or Madonna's bank account. There is an erotic enticement in the idea of being able to do anything you like, just as there is fantasmal fulfilment in the idea of resources that can never be spent. Celebrities are the postmodern version of the horn of plenty, the Land of Cockayne, the fairy-tale purse that can never be empty. In a world running out of both oil and elbow room, this vision has its allure.

The cult of celebrity is surely, among other things, a reaction to what the sociologist Max Weber termed the "disenchantment" of modernity. Once charisma yields to bureaucracy, the siege of Troy to chemical warfare, and Cardinal Richelieu to Peter Mandelson, it is impossible to feel that the world is quite as magical as it was in the days of spying Jesuits, heroic warriors and merry monarchs. How can there be a truly epic literature, Marx once inquired, in the era of steam engines and cotton looms? Or, one might add, of call centres and fast-food joints? The trouble with middle-class society is that it is drably unheroic, dedicated as it is to the distinctly prosaic business of preserving social order and augmenting its profits. The magic, then, has to be artificially manufactured - smuggled in as a kind of agreeable extra, rather like morality. And it is here that celebrity has its uses. Just as reality becomes increasingly virtual in a postmodern age, so fulfilment becomes increasingly vicarious. Celebrities, like servants in the view of some 19th-century aesthetes, are there to do your living for you. If you can't own a private jet yourself, an alter ego known as Mick Jagger can do it for you. It is rather like the old Eastern European joke about the difference between the Soviet Union and the slightly more liberal regime of Yugoslavia: whereas in the Soviet Union only the politicians drove cars, in Yugoslavia the people themselves drove cars through their elected representatives.

None of this would have come as a surprise to Freud, for whom what we amusingly call reality is shot through with fantasy from end to end. For him, the so-called real world is just a kind of Soho of the psyche, a low-grade place of projection and displacement. Freud knew all about the business of collective libidinal investment in some fantasised power-figure, a process that in his own time took the form of Fascism. What might have come as news to him is the emergence of what one might call the meta-celebrity, meaning those who are best known simply for being famous.

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Celebrity at its most imposing, ironically, is an empty signifier, one that names nothing but itself. To be celebrated for something in particular would seem only to diminish one's glory.

This has always been true of royalty, just as it was true in the past of the odd figure such as Beau Brummel. Today, however, from Sir David Frost to Posh Spice, Jordan to the Duke of Edinburgh, fame is not the accolade of the gifted but a status all of its own, one that can provide a substitute for being gifted. A celebrity artist these days usually means one who is a celebrity rather than an artist. Sir David was once described as a man who "rose without trace", meaning that the more legendary he became, the harder it was to say what he was legendary for.

In one sense, this is the logical culmination of the whole concept of celebrity. For even celebs who are renowned for what they do are fundamentally adored for what they are. Celebrity is a twisted form of love, since both involve a fascination with the very being of the other person. This is one reason the stars of soap operas often achieve celebrity status, since soap operas exploit our insatiable curiosity about individual people (a curiosity to which no detail is irrelevant), rather than being about especially talented or remarkable people. We do not listen to The Archers for dramatic twists of plot or epic events.

Like the Man in the Crowd in Poe's short story of that name, celebrities die when they are deserted. They are fictions who live only in the public eye, apparitions who (like objects in the philosopher Bishop Berkeley's view) are there only as long as we perceive them. The public figure once belonged to what Jurgen Habermas has called the public sphere and played a vital role in the formation of public opinion. Nowadays, the public sphere has mostly given way to public relations, of which the celebrity is the creature. It would be a mistake, however, to think that this manufactured magic is merely window-dressing. On the contrary, it may be vital to the kind of society we live in. We need only think of sport, with its iconic heroes, epic battles, fabular legends, tribal conflicts and loyalties. If the popular energies channelled into these harmless pursuits were freed for other ends, our rulers would do right to tremble at the thought of what might ensue.

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Terry Eagleton is professor of cultural theory and John Rylands Fellow at Manchester University. His latest book is Holy Terror , published by Oxford University Press, ?12.99.