There are two tragedies in life, said Shaw. One is not to get your heart's desire. The other is to get it. How right was he? Joan Smith continues our series on emotions
"Hormonal storms," I tell a friend over dinner at the Cafe Flo. It's a euphemism but I'm trying to explain what lies behind my disjointed speech, wild gestures and the rapid changes of subject he has been vainly attempting to follow all evening.

"Hormonal storms?" he repeats, looking at me blankly for a moment. Then comprehension dawns and his mouth stretches into a grin. "Oh," he says, with a knowing look. "You mean lust."

"Of course I don't mean lust," I protest, indignant. 'I'm talking about desire."

He brushes the distinction away, signalling to the waiter to fetch more wine. "Whatever. I like it when you talk dirty."

We are both silent for a moment, me frowning over this reductive response to the glimpse I've just offered into my psyche, and then he adds: "Have you slept with him yet? What sort of car does he drive?" There is a link between the questions, although it isn't immediately obvious. The two things he lusts after - his principal desires in life - are women and German sports cars. My inability to identify car makes beyond general terms like BMW or Peugeot (or sometimes even "blue") drives him to distraction, preventing him from demonstrating his theory that la voiture est l'homme meme. A 5-Series, he wants to know? Power steering? He simply cannot understand how I can go to bed with a man without checking out his wheels - wire- rimmed? - first.

But let's go back to his original assumption. Is he right in suggesting that desire is just a posh synonym for lust? I'm a Classicist so naturally I prefer desire, with its Latin root, to the blunter Germanic alternative. But there's also something unfeminine about lust, even though the eccentric American feminist Mary Daly once tried to reclaim it for women with a book entitled Pure Lust. My thesaurus hasn't caught up either, offering these alternatives for the word "lusty": macho, male, manlike, masculine.

Not that desire, if centuries of propaganda are to be believed, has much to do with women either. The Victorians didn't think women had erotic feelings at all, a notion Coleridge preempted by almost a decade with his lofty pronouncement in 1827 on their supposed sexual anaesthesia: "The man's desire is for the woman," he intoned, "but the woman's desire is rarely other than for the desire of the man." Women, according to this theory, which I think of as the Pathetic Phallacy, just want to be loved. And if that's not on offer, they'll put up with sex instead.

When Marie Stopes published her ground-breaking guide to sex, Married Love, in 1918, she knew she was going into battle against an orthodoxy which would be deeply shocked by what she had to say about female desire. It was not unusual for a girl to go into marriage in a state of "flower- like innocence", she wrote, which rendered her quite unprepared for the fact that married life would bring her into "physical relations with her husband fundamentally different from those with her brother ... There have been not a few brides whom the horror of the first night of marriage ... has driven to suicide or insanity."

The problem Stopes faced was how to tell the truth about women's sexuality as she saw it without outraging many of the people - especially the young husbands to whom Married Love was dedicated - she most wanted to reach. The device she adopted was circumlocution, enthusing about a woman's "wonderful tides, scented and enriched by the myriad experiences of the human race from its ancient days of leisure and flower-wreathed love-making, urging her to transports and to self-expressions, were the man but ready to take the first step in the initiative or to recognise and welcome it in her" - a very long-winded way of saying that women feel desire as much as men, though I'm not sure where the flowers come into it.

In France, similar notions about women's indifference to sex were widespread, refracted, however, through the dark prism of Roman Catholic theology. As late as 1954 the distinguished critic Jean Paulhan was able to write, in an essay on the classic pornographic novel Histoire d'O, that women "have but one requirement, and that is simply a good master". Paulhan, who was secretly the lover of the novel's author, the pseudonymous Pauline Reage, also believed that if individual women did experience desire, its aim was suffering not pleasure. "One must have a whip in hand," he suggested, apparently in all seriousness, "when one goes to visit them."

It's not much of a choice: lie back and think of England, or slip over to France and get lashed. Perhaps I should be grateful to my friend at the Cafe Flo for recognising this as the wishful thinking it undoubtedly is, and admit that what I was feeling, as I sat across from him that evening, was pure, unadulterated lust. On the other hand, the Concise Oxford Dictionary does seem to be on my side in recognising a distinction between lust and desire. "An unsatisfied longing or craving" is how it defines the latter. Lust, by contrast, is altogether more carnal, "a sensuous appetite regarded as sinful".

Here we go again. The "sensuous appetite" bit is fine but why does sin have to come into it? An atheist as far back as I can remember, I've never been able to understand that paralysing Catholic guilt about sex which grips some of my friends and even the occasional lover (bad news, this - worse even, according to my knowledgeable dinner companion, than a man who drives a Mondeo). My personal rules about sex are very simple: if you're going to feel guilty about it afterwards, don't do it. Otherwise, follow your desire. Or do I mean lust?

It's pretty obvious, actually, that the former is much broader in scope than the latter. At various times I've felt an overwhelming desire for each of the following, with more or less the same symptoms of breathless excitement and urgency: a painting by Filippo Lippi in the Metropolitan Museum, New York; a man I've been introduced to only five minutes before; a wild boar steak, char-grilled with rosemary and slivers of garlic; a DKNY dress, miraculously cut and dazzlingly expensive; an Ottoman house on the European shore of the Bosphorus; a slice of chocolate torte from the Blanc Patisserie in Oxford.

Or it may be that I, like everyone else, use both terms rather loosely. When it comes to the man -- and possibly the steak - I could just as well be talking about lust as desire. I'm very conscious, after editing a book on food, that lust and hunger are closely linked, using the same orifices and even borrowing each other's language ('I could eat you up'). Oral sex mimics eating and Madonna devoted an entire song to precisely this conceit on her Erotica CD ("Colonel Sanders said it best, finger-lickin' good"). The celebrated anthropologist, Claude Levi-Strauss, memorably described cannibalism as 'alimentary incest', while the Italian author Italo Calvino included this extraordinary erotic passage in his novel Under the Jaguar Sun:

"Our teeth began to move slowly, with equal rhythm, and our eyes stared into each other's with the intensity of serpents' - serpents concentrated in the ecstasy of swallowing each other in turn, as we were aware, in our turn of being swallowed by the serpent that digests us all, assimilated ceaselessly in the process of ingestion and digestion, in the universal cannibalism that leaves its imprint on every amorous relationship and erases the lines between our bodies and sopa de frijoles, buachinango a la veracruzana, and enchiladas ...."

Don't even ask what's for pudding. Lust and hunger are alike in their intensity, their instant physiological response to a stimulus before there's even been time consciously to register the cause. There's a directness about them both which is uncomplicated by thought; desire is slower, more cerebral, involving the same physical symptoms but with the additions of time and imagination. It's the difference, to go back to the cooking metaphor, between a meal seized in haste when you're starving and a gourmet dinner you've planned days or even weeks ahead. There's nothing wrong with fish and chips but they don't provide the depth of satisfaction that comes from taking your time over a wonderful Italian or Lebanese meal (and we all know that bolting your food almost always leads to indigestion).

In its purely sexual sense, desire is inextricably linked with anticipation and fantasy. It's sitting in a darkened cinema with a lover, your arm brushing his, counting the minutes to the end of the movie; it's thinking ahead to when you get home, to the amber silk lampshade already casting its pale glow on the clean sheets; it's all the little details that go into constructing a seductive mise-en-scene, and wondering breathlessly how the reality will compare with the fantasy.

The problem, though, is that desire is inherently unstable. Umbilically attached to the noun in my dictionary is that sneaky little adjective "unsatisfied"; where lust stands on its own, apparently unaffected by the prospect of satisfaction, the definition of desire in my Concise Oxford insists that it actually depends on not being realised. This makes it synonymous with lack, always tending towards its own extinction; it is desire as paradox, a notion much admired by French theorists of a particularly austere (which is to stay Lacanian) school. According to this theory of gender relations, sex-in-the-head will always triumph over sex-in-the- bed. Presumably it applies to all my other examples too: buy the dress and you'll no longer want it. Eat the cake and you'll throw up. Steal the picture and you'll have lost interest in it before you even get to the airport. George Bernard Shaw's variation, succinctly expressed in Man and Superman is even more depressing: "There are two tragedies in life. One is not to get your heart's desire. The other is to get it."

So are we condemned by desire to an endless cycle of longing and disappointment? The point missed here is that desire demands repetition as well as fulfilment. This is one characteristic that separates it from lust, which requires endless novelty; serial seducers such as Casanova or Don Juan quickly became bored with their conquests and moved on to new challenges. Desire, by contrast, is addictive both of itself and of the desired object - a notion which may lack resonance in cultures obsessed with instant gratification, but which was perfectly understood by Greek and Roman lyric poets such as Sappho and Catullus.

They devoted whole poems to the subject, celebrating the state of desire as languorously as the act of sex itself, to which it was the essential prelude. Sappho's account of the physical and emotional effects of desire, given here in Josephine Balmer's excellent translation, has surely never been bettered:

sight of you, even if for a moment,

then my voice deserts me

and my tongue is struck silent, a delicate fire

suddenly races under my skin,

my eyes see nothing, my ears whistle like the whirling of

a top

and sweat pours down me and a trembling creeps over my

whole body, I am greener than grass ...

Desire, in this account which is more than two-and-a-half millennia old, is enjoyed for itself as well as for what it will almost inevitably lead to. The Victorians, who found Sappho's unbridled eroticism uniquely disturbing, tried to water down the powerful feelings exposed in her poems, claiming they were charming exercises composed for friends or pupils at some mythical girls' seminary on Lesbos. All this proves is that there have been lengthy periods, throughout history, when female desire was truly the love that dare not speak its name.

'Hungry For You: from Cannibalism to Seduction: A Book of Food' by Joan Smith is published by Chatto & Windus in November.