'Let's talk about sex,' is the slogan for the new film about Alfred Kinsey, and in his time that was a pretty heroic thing to do. The man who helped to convince the western world that masturbation is not unnatural and homosexuality not a sin had to struggle against forces of conservatism and intolerance every day of his life; his determination to take them on was what made him something of a hero. But the film also reminds us that his times are not our times.
Because Kinsey lived in an age that could be straightforwardly optimistic about the rewards offered by sexual frankness. He believed that there was no sexual problem that could not be solved by more and more and more information. His mammoth work, resting on interviews with thousands of individuals, epitomised the idea that frank talk is infinitely valuable when it comes to sex. And not just talk - his vast archive of information also contained explicit pictures and film of people having sex and masturbating. Pictures and film that his friends and colleagues were sometimes bullied into providing, for the sake of breaking through the intolerance and prudishness of his era by showing, for instance, whether men squirted or dribbled when they ejaculated.
What Kinsey could not have foreseen is how, once society had changed, the joyful urgency of that movement towards greater explicitness would dissipate. The recent shift in the way that people feel about the pure value of sexual display is not just evidence of a new moral conservatism. In a culture where every kind of sexual behav iour is on view all the time - if not in your newspaper or on your television channel, then a click of a mouse button away - even liberals of the sort who would once have flocked to give their testimony to Kinsey and listen to the testimony of others are tired of feeling like voyeurs.
This is not because we want any return to the old ways of shame and intolerance, but because explicitness has become such a dead end. Every kind of sexual behaviour is so excessively documented and, rather than opening out the possibility of new worlds, that reduces the excitement of discovery. We live in a completely changed world from the 1940s, and now the decision to spend one's life documenting other people's sex histories would not be heroic but utterly banal. For the first time in human history, it is easy for people to watch strangers having sex, to hear strangers talking about sex, to discuss their own sexual behaviour with strangers.
When artists today put their faith in the power of pure explicitness to convey the flavour of desire, they end up with something altogether underwhelming. Nine Songs, which is released this Friday, is the most explicit British film ever to be shown in mainstream cinema. It is Kinsey-esque in its unsmiling celebration of "sex reduced to its physiological functions" (as Liam Neeson puts it in the Kinsey movie).
The director of Nine Songs, Michael Winterbottom, seems to believe that he is making a moral point by allowing us to watch people engaged in real sex on screen. As Winterbottom has said: "Part of the point of making the film was to say, 'What's wrong with showing sex?'"
He laments the coyness of other cinematic treatments of sex. "Cinema has been extremely conservative and prudish," he says. Perhaps Winterbottom has never noticed the growth of the internet and the porn video. The reality is that Nine Songs, with its terribly serious desire to show us everything and turn away from nothing, is not going to usher in an era of more explicit treatment of sexuality in mainstream cinema. Although there is this small genre of film-making - Nine Songs belongs to a category inhabited by a few other films, such as Intimacy, Romance and Baise-Moi - whose unique selling point is showing real sex, it has become a collection of curiosities rather than part of a mainstream movement.
Now that we live in a time where display is so inescapable and everything is out there, artists who really want to get the viewer to taste and feel the power of fictional desire are usually choosing to show very little. Rather than falling into the blandness of a purely physical take on sex - and for all its explicitness Nine Songs is infinitely forgettable and under-characterised - the unexpected truth about the art of this new century is that the cinematic depictions of sexual desire that are most intriguing and memorable are not at all explicit.
Although intimate sex scenes still pop up in mainstream cinema, they are usually there for comic rather than sensual effect: in Sideways, for example, it is the creep's relationship that gets pictured with heaving buttocks and groans, and the hero's one where the camera only goes as far as the bedroom door. In recent years films as different as Closer, Before Sunset, Lost in Translation or Eternal Sunshine of the Spotless Mind have powerfully explored desire through conversation, reminiscence and suggestion rather than thrust and counterthrust. When everything has been said and everything has been shown, being explicit is simply too easy; being sexy is the difficult thing.