Sex, lies and videotape

The "great artists" on show in an adults-only exhibition at the Barbican have more excuses than porn

At first glance, it seems to show a tender moment: an older man pulls back the cover to admire the body of a sleeping, naked woman. Oblivious to his presence, she lies with her arms above her head as the man's shadow falls across her hips, turning her pubic area into a dark triangle. Closer inspection reveals a hint of horns amid the man's unkempt hair, and a classically educated viewer would know, from the title of the etching, what happens next. Rembrandt's Jupiter and Antiope (1659), one of only four or five works by the Dutch master with explicitly sexual content, shows the prelude to a rape. According to legend, the god Zeus (the Romans' Jupiter) was so entranced by the beauty of Antiope, a Theban princess, that he disguised himself as a satyr and "took her by force", in the euphemistic language of classical studies. Anti ope's trajectory was downhill all the way from then on, involving an unwanted pregnancy and enslavement by her family, and demonstrating the apparently limitless capacity of ancient myth-makers (rather like modern-day rape juries) to punish the victim.

Rembrandt's etching is one of the most stellar works on display in an exhibition at the Barbican Art Gallery in London. "Seduced: Art and Sex From Antiquity to Now" spans a huge range of artists and art forms, including classical European sculpture, Roman wall paintings, Japanese prints, Chinese watercolours, Indian manuscripts, the exuberant paintings of Fragonard and Boucher, and the sadomasochistic photographs of Robert Mapplethorpe. There is an inevitable gender imbalance in the early material, but the later work includes that of female artists such as Louise Bourgeois, Marlene Dumas, Tracey Emin and the photographer Nan Goldin. One of the most striking contemporary works is k r buxey's Requiem, a video of a woman enjoying cunnilingus; unlike Andy Warhol, whose better-known 1963 film Blowjob she acknowledges and subverts, buxey places herself in front of the camera and her facial expressions are reminiscent of the religious ecstasies of medieval female saints. (This will come as no surprise to anyone who has noticed the intensely sexual nature of accounts of the visions of Saint Catherine of Siena.)

One of the quirkier items in the exhibition is a giant plaster cast of a bronze fig leaf, created for Michelangelo's David in 1857 to spare the blushes of Queen Victoria. From the close of antiquity, when Christian repugnance for the human body became the dominant sensibility in western culture, certain works by the world's greatest artists were censored or hidden away on the grounds of supposed obscenity. Some of the material on show at the Barbican was once concealed from general view in special rooms or cabinets, available only to those deemed immune from "corruption". Such prudery seems comical today, but the close connection between puritanism and its apparent opposite, libertinism, is not always acknowledged. Like puritans, libertines recognise the subversive power of sex, but they deal with it in a different way; it is no accident that the Marquis de Sade, who has a place in "Seduced" in the shape of some positively gymnastic illustrations from his works, was educated by Jesuits.

The presence of so many explicitly sexual images in a single exhibition raises fascinating questions about the whole business of sexual representation, the obvious one being whether there is a sensible and sustainable distinction between pornography and art. The show's distinguished curators, Marina Wallace, Martin Kemp and Joanne Bernstein, deal with it briskly: "The pornographic image has one job to do: to arouse for the purpose of eventual climax. It may do its job with artistry, but it does not aspire to the reach and interpretative openness of art. Porn ography aims to eliminate distracting variables, such as complexity of character."

Actually, this is a minefield, and the exit from it does not beckon quite so easily. It is convenient to dismiss pornography - not a nice word, with its Greek root porneia referring to acts of prostitution - as essentially commercial in nature. Yet even the greatest art usually involves at least one commercial transaction, between artist and patron; it is simply more obvious in pornography, with its frank objective of exciting the reader or viewer, than an exchange in which a Bourbon king commissions a recognised artist to paint a nude portrait of his young mistress.

It is true that the commercial pornography industry makes vast profits - greater than those of the world's biggest technology companies combined, as the curators of the exhibition point out - but that is something of a blind alley. What is really offensive is that most of the material it creates is violent, degrading and illegal, especially the huge numbers of images involving children. Several famous people have gone to jail in recent years for downloading such images and it is reasonable to suspect that some of the adults involved are sex slaves - young women forced to take part in explicit videos and DVDs by sex traffickers.

In other words, the issue is not money, but power and its abuse. Interestingly, the curators of "Seduced" seem to have edged towards this more useful distinction without understanding that it renders redundant their attempt at creating separate categories of pornography and art. "We have excluded exploitative images that are savagely aggressive or degrading," they say. "Consent is an important watchword. The title, 'Seduced', indicates mutual and consenting action and reaction." Sexual images which are aggressive and abusive are unacceptable, according to these criteria, confirming the proposition that the problem is not that an image might aim to arouse, but rather how that arousal is achieved. Many of the feminist critiques of pornography were so heavily influenced by the nastiness of some contemporary material that - mistakenly, in my view - they tipped over into outright rejection of sexual imagery. It has always seemed to me far more sensible to identify what is offensive about particular images or books than to set up spurious categories of "erotica" on the one hand and "pornography" on the other.

Looked at through this lens, some work by indisputably great artists becomes much less innocent. The theme of seduction, no matter how beautifully drawn or painted, is often a cover for a rape fantasy, which is the category into which Rembrandt's Jupiter and Antiope falls. So do other pictures in the exhibition such as Fragonard's The Beautiful Servant, where the unequal power relation between the protagonists is explicitly admitted in the subtitle, Pointless Resistance. François Boucher's Leda and the Swan (circa 1740) shows a naked woman about to be penetrated by a swan - its elongated neck and raised wings resemble a huge penis and testicles - in another rape-myth from the ancient world. Picasso's 1903 painting of himself being fellated, known as La Douleur, reinforces the notion of the man's sexual dominance even though neither of the protagonists appears to be getting much pleasure from it.

The absence of the male nude - by which I mean men as explicitly sexual objects - from "great" western art is the big giveaway in this respect. (The work of 18th-century Turkish illustrators such as Shaykh Muhammad Ibn Mustafa al-Misri and the Japanese woodblock prints known as shunga, intended to give pleasure to women as well as men, suggest that non-Christian cultures were less repressed.) Men can appear partly naked if they are about to go into action, like Rembrandt's Jupiter, but straight men don't want to look at erect penises. For centuries, most western erotic works assumed a heterosexual male audience, and the expectation that sexual images should be about male dominance has proved surprisingly resilient. Mapplethorpe's male photographic studies from the 1970s and 1980s caused a furore because they challenged taboos about race and sadomasochism, but what is most subversive about them is that they show men having things done to them that are more usually done to women in pornography.

Some women have reacted to this long history of objectification by restaging the images with themselves as authors, as k r buxey does in her most unsettling work, replicating scenes from commercial pornography in which several men surround a woman and ejaculate in her face. Bringing these issues of exploitation and dominance to the forefront has had at least one negative effect, producing still images and videos that are widely accepted as art rather than pornography, but in which the sex is ugly and disturbing. It has also - and this is ultimately a good thing - exposed the way in which female arousal and pleasure still have to fight for space.

Tracey Emin's insistence on revealing her own sexual history in her work has been met with sneers and derision, mistaken for boasting when it is a brave act of self-exposure. Ilona Staller's deliberately decorative images of herself having sex, posed in the studio where she made pornographic films and shot by the same photographer, appear under the name of her former husband Jeff Koons, who silkscreened them in oils on to canvas and turned them into "art". They call to mind Roman wall paintings by unknown artists that show women and men enjoying sex with a tenderness distinctly lacking in the productions of some "great" artists.

The Old Masters have always been allowed more excuses (and had more champions) than today's porno graphers, but they share many of the same patriarchal assumptions. Decades of feminist criticism have shown that each and every image of the human body expresses ideas about power and gender. I can admire the tech nical perfection of a Rembrandt or a Picasso, but if it denies the possibility of female arousal and orgasm, I am not seduced.

"Seduced: Art and Sex From Antiquity to Now" is at the Barbican Art Gallery, London EC2, until 27 January 2008. Details: www.barbican.org.uk