Neo-classicism at the Tate: Drama school

Cartoonists have their shorthand symbols, their ways of getting something over quickly and clearly. If the subject is opera, say, then of course they do a fat woman in a horned helmet. Or if it's theatre, they do a man gesticulating in doublet and hose. Wagner, Shakespeare: yes, it makes a kind of sense that these should have become the iconic clichés. But if the subject is art? Well, what they probably do is a neo-classical statue – smooth, white, nude, poised, standing on a plinth. Which is odd, because we don't spend much time in art galleries actually looking at such things.

Neo-classicism was an international, back-to-basics movement, based in Rome. Pompeii and Herculaneum had been rediscovered. Johan Joachim Winckelmann had written his ground-breaking studies of classical art. The neo-classicists wanted to return European art to what they saw as the Greco-Roman mainstream.

In sculpture it meant a purist style – no frills, not much drama, not much sex, just human bodies or human busts, and usually (though not always) a classical subject. It can appear an almost anonymous practice, in which conspicuous personal signatures were avoided. During its heyday, in the late 18th and early 19th centuries, it stood as the highest form of art, and this seems to have survived in collective "cartoon" memory.

Artistically, though, posterity hasn't been impressed. First the statuary was rejected as frigid, academic, antiquarian. Then it was completely ignored. Some old museums still have plantations of the stuff, and visitors today just pass through them, on the way to look at something. But in The Return of the Gods, Tate Britain has found a way to stop us in our tracks.

Its long central hall is filled with marbles. The lighting is dimmed throughout. The individual pieces are picked out in pools of light, throwing their curves into shadowed relief, inviting us to come closer. It's the kind of display normally used for old holy things, and it encourages a quiet and reverent pace. But it's also nearer to how many of the works would have been originally shown in country houses, in intimate shrines, by candlelight.

So meet The Greek Slave by the American Hiram Powers, a respectable looking lady standing demurely in chains – a sensation when it first appeared at the Great Exhibition in 1851. Meet Narcissus, a dreamy youth leaning over, gazing down into an imaginary pool, carved by John Gibson, the foremost British sculptor of his day. Meet, finally, Antonio Canova's The Three Graces. They stand at the end of the gallery, in delicate sisterly embrace, the culmination of your promenade, their swelling buttocks a triumph of lighting effects.

Other works stand out. Thomas Banks' The Fallen Titan is upside-down, mid-tumble, trapped between two carved rocks. John Charles Felix Rossi's The British Athlete is a contemporary subject, a boxer, dukes up, bulldog expression, dressed in tight breeches. And from the Dane Bertel Thorvaldsen, there's Lady Georgiana Russell as a Child, a standing, life-size, nude portrait of a four-year-old girl, covering her modesty with a little bit of drapery.

Now you can't deny that these statues, which want (in a way) to be supremely normal, are actually quite peculiar. Their pure whiteness, for instance, isn't just the colour they happen to be. It's a definite statement. These artists were aware that real ancient sculptures were often painted, though they sometimes had trouble believing it, because it was so much at odds with their high, serene idea of the classical. No, the truly classical statue must be pure white. It marks a human body that's been purified of most of its living functions – pain, strain, desire, emotion.

You see it in their eyes. The eyeballs are as blank as eggs. Other sculptors, even when they refrained from colour, have been known to put the iris and the pupil in, by incising and hollowing out the eyeball. Sometimes they've even put a gleam in the pupil, leaving just a tiny teardrop of stone in the dark carved-out hollow to catch the light. The neo-classicists will have none of this. The reason is, they think of the body as a geometrical solid.

In geometry a cube is a three-dimensional form, it has surfaces, it has edges, it has volume. But if you ask how much a cube weighs, or what it's made of, or what colour it is, or what it feels like to the touch, in geometry there is no answer to these questions.

That's how neo-classical sculpture imagines the human body. It's a solid volume defined by a surface. Its mass, substance, skin texture, hardness, heat, moisture, colour – these matters don't arise. Naturally the eyeballs are blank. Only the body surface is being registered. That's what the marble's for: the exclusive purpose of these statues is to register surface with exquisite sensitivity.

True, in the process, a bit of extra geometry is added. The body is rounded off, smoothed over, its forms and surfaces regularised, its sharp corners softened. When it goes too far, as it does in The Greek Slave, it's as if the figure was wearing a body-stocking. You can easily see these statues as a strange breed of streamlined mannequin, a blatant exercise in bodily perfectionism.

That's the role they often play in contemporary art. The sculptor Marc Quinn has made half a career out of being ironic about neo-classicism. His trick is to play a neoclassical form against a real imperfect body, as in his Trafalgar Square sculpture Alison Lapper Pregnant. Of course, these works aren't really interested in neo-classicism, except as a general token of bad attitudes to the body; and anyway, the artisans who make Quinn's sculptures for him are so incompetent that you'd never guess there was anything going on but the crudest sort of idealisation.

It is very easy to generalise neo-classicism, precisely because it is an art of small differences. It doesn't shout across the room. At a distance the statues can all blend into a bland uniform mass, but they're not just inert templates of perfection. This is a connoisseur's art, designed for close attention, fine judgement, operating on a narrow frequency. The things that distinguish one work from another, that bring a particular statue alive, are little things.

It's mainly in the tension between the ideal mannequin and the stirring signs of bodily life. It's the way the strain of a tendon, the clench of muscle, becomes just visible through the perfected surface. Gibson's Narcissus is the masterpiece of the show, at first sight all smoothness, but on a longer look yielding up these gentle pressure points. Thorvaldsen's little girl is very good too, and perhaps pudgy young bodies are what neoclassicism is best at. Its attempts at bulging muscularity, as in The British Athlete, are awkward affairs. Even though its model is ostensibly the public, religious statuary of the classical world, neo-classicism is essentially a subtle, intimate, domestic art – an object upon which its gentlemanly collectors can exercise their fine feelings. And what kind of commitment they really felt to the polytheistic cultures of the ancient Mediterranean world, what kind of game they thought they were playing with all this classical stuff, is hard to judge.

It always is. European history is continually harking back to the classical past, the classical gods, but it never comes to a crunch. How could it? The classical world itself is and was long gone. But suppose that, along with the inspiring ruins of Pompeii, they'd discovered, living in the south of Italy, some dirty old villagers, who had somehow escaped the attentions of Christianity and still worshipped Jupiter, Mars and Venus with animal sacrifices.

Well, I think that would have been an embarrassment, at least, to the English gents who kept a Temple of Ancient Virtues in their landscaped gardens. They'd have had to discount it somehow, say it was a terrible debasement of its ancient original. Neoclassicism was a game, a serious game perhaps, but it couldn't have survived an encounter with the real thing.

The Return of the Gods, Tate Britain, London SW1 (020-7887 8888) to 1 June