Howard Jacobson: When it comes to art and the human condition, keep morality out of it

The larger your imagination the fewer feelings you don't understand

What is it about sex and credulity? Depart – in theatre, film or literature – from the straight and narrow of domestic coupledom and you're accused of fantasising. Acceptance of homosexuality would seem to give the lie to any charge that our society is narrowly sceptical when it comes to the erotic life, but it doesn't. To be gay now is to be petted into innocuousness: amusing the nation outrageously on television but back home just like you and me – holding hands, getting married, adopting children – only without the hetero part.

It's the new Woody Allen film – Vicky Cristina Barcelona – that gives rise to these musings, or at least it's what's being said about it. The good news is that the film is a near return to form. "Near" is a relative concept. We aren't back in Manhattan or Crimes and Misdemeanors territory where every joke dripped in sadness or in blood. But we are a long way from the excruciations of Match Point, Allen's Home Counties tennis embarrassment, which could have been a film about Mars so little was it a film about England.

Exasperating for any artist, I know, to be told he can only do what he can do – which in Woody Allen's case is Manhattan Jewish – but it is usually the case. What you know and have an ear for you know and have an ear for, and what you don't, you don't. It ought not to count against you that you travel badly – the greatest artists conjure an everywhere out of a highly specific somewhere – but it does. To make art is to crave versatility. And in Woody Allen's case there is an added craving. Revenge. Revenge served hot, served cold, served lukewarm. They turned their backs on him so he must turn his back on them. Byron felt the same.

Vicky Cristina Barcelona, anyway, is not set in Manhattan and is not about Jews. But it is about the sexual impulse which I should also have numbered among those subjects Woody Allen knows best. It tells of two American girls at a loose end, emotionally speaking, in Barcelona, and a Spanish painter of impetuously splashy canvases who picks them up. His hope is to sleep with the pair of them simultaneously, but – not to spoil the story – has to content himself with sleeping with them one at a time.

A disappointment which is somehow mitigated when the painter's estranged, deranged and inflamed wife – Penelope Cruz in full endangered species mode – turns up for a piece of the action, that's to say a piece of her husband, a piece of his reputation, and a piece of his new American girlfriend. Woody Allen has always been good on disturbed wives. If that sounds like misogyny, or whatever anything less than prostration before the Goddess Woman is now called, let me add that he is no less good on what in the husband creates the disturbance in the wife. In the case of the Spanish painter a number of unresolved issues around the old Oedipus complex which explain his turning his wife into his mother and his interest in erotic threesomes rather than erotic twosomes, though the principle of the more the merrier might be thought to be explanation enough.

Enter, now, the not-having-any film critic. (Not having any of this malarkey, I mean, not not having any sex.) "It's all fairly daft fantasy," says Derek Malcolm in the Evening Standard, citing, as an example, the unlikeliness of any sophisticated woman falling for a man so obviously predatious. But that's the story of humanity, isn't it? Woman falls for obvious man. Man falls for obvious woman. The Iliad. Anna Karenina. Carmen. The people next door. Even you and I in our salad days, reader, when we were green in judgement – and were we not green in judgement we would not ever populate the planet.

So what's daft? And where's the fantasy? That it's about fantasy – the husband wanting as many pretty women as he can fit into his bed, while still being able to work and still being able to keep his wife, and if he can watch while his wife kisses the pretty women, where's the harm – I would be a fool to deny. But having fantasy as your subject is not the same as fantasising. Make no mistake: Derek Malcolm likes the film. "Don't believe a word of it and you'll be splendidly entertained," he concludes. But what's not to be believed? That married men sometimes inveigle women into being their mistresses? That wives are sometimes deranged into arousal or aroused into derangement by this? That they sometimes exchange saliva with the mistress?

Where has our film critic been all his life?

I encountered a little of this with my most recent novel The Act of Love, which tells of a man's desire to feel the sting of his wife's infidelity. Some enjoyed, some didn't. That's the way of it – you don't get everyone in your bed at the same time in this life, no matter what you tempt them with. But even those who enjoyed it spoke occasionally of a hurdle of credibility to be cleared. Why would a man want to feel the sting of his wife's infidelity? Several male reviewers had to make it plain at the outset that they knew nothing of such a strange and unlikely desire. One or two friends wrote in the same vein. Loved the book but didn't recognise the condition.

Myself, I consider it a duty as a reader to recognise every condition under the sun, a duty as a writer to imagine every condition under the sun, and a duty as a human being to nose into as much as possible. The larger your imagination, the fewer feelings you don't understand. Inspect your heart, I say – you will find all of human life there. And if your heart won't yield, then just look at what's happening in your street. The truth is, no artist can ever hope to encompass the erotic outlandishness of even the most ordinary-seeming men and women. But at least we once took it for granted that it was the duty of art to encompass it if it could.

Now we salt the tail of art with morality. What we don't think should be, we insist cannot be. A prostitute who enjoys her work? Pull the other one. A man who gets off on jealousy? Get out of here. A threesome promising to be a foursome in Barcelona? Come off it.

Ah, reader, it is good that we at least have lived so long and seen what we have seen.