Do you go weak at the knees at the sight of the woman or the man of your dreams? Does your heart beat a little faster when a midnight text flashes on your Blackberry? Have you booked your special night out for that most hallowed romantic evening of the year? If so, what on earth are you thinking of? As a rational reasonable humanist, why are you allowing yourself to be seduced by sentimental cards, over-priced red roses, by the whole crazy irrationality of this thing called love?

After all, as a rationalist you surely recognise that the very notion of love and being in love is essentially a cultural construct. “While some writers define love as a basic human need,” writes Anouchka Grose in her new book No More Silly Love Songs, “there are also those who see it as a product of our culture – something that was invented quite late in human development. Some historians and anthropologists would argue that love as we know it dates back to the Middle Ages, or that each period and society invents its own notion of love.”

We can trace the idea back even further. In Plato’s Symposium, for example, the participants propose a series of conflicting characteristics that we still recognise today: love is presented as an ideal state of human perfection, a weakness, a madness, a physiological condition, an inspiration for heroism or a quest for eternity. Many 21st-century starstruck lovers would identify with Aristophanes’ seductive notion of creatures divided in two, forever seeking their perfect other half.

But no culture has elevated the idea and the ideals of love to such a central position as our own. It’s a conceit embedded deep in the modern psyche. We talk about loving as distinct from being in love, we fall in love, some fall out of it again; we know it to be different from the love we feel for family, friends, for our children. It’s romantic, erotic, passionate. Being in love is a state so commonly assumed to exist, indeed to be coveted and longed for, that we don’t feel the need to define it. In A Lover’s Discourse Roland Barthes conveys the emotions, the experiences, the madnesses of love while at the same time questioning its provenance. To announce “I love you” is, he says, to render the very term meaningless: “I-love-you has no usages. Like a child’s word, it enters into no social constraint; it can be a sublime, solemn, trivial word, it can be an erotic, pornographic word. It is a socially irresponsible word . . . Though spoken billions of times, I-love-you is extra-lexicographical; it is a figure whose definition cannot transcend the heading.”

And since there’s no proof, no real evidence for the existence of love, believing in it is an act of faith – like believing in God. In The God Delusion Richard Dawkins makes this very comparison, questioning whether irrational religion might be “a by-product of the irrationality mechanisms that were originally built into the brain by selection for falling in love? Certainly, religious faith has something of the same character as falling in love and both have many of the attributes of being high on an addictive drug.”

A similar comparison is made by William James in his Varieties of Religious Experience. “Like love, like wrath, like hope, ambition, jealousy, like every other instinctive eagerness and impulse, it adds to life an enchantment which is not rationally or logically deducible from anything else.”

Even the language we use to describe the heightened state of being in love is close to descriptions of the religious experience. We speak of enchantment, of ecstasy, of rapture, of epiphany. Love is heaven, love is divine, it’s paradise. And love, like religion, inspires acts of heroism, of sacrifice, and of the creation of great works.

But this analogy is bound to cause understandable consternation for humanists. You might protest that there’s nothing metaphysical about love, surely? It’s grounded firmly in this life, in relationships, commitment, affection, companionship. It couldn’t be more human.

That’s all very well if you’re talking about how you feel about or relate to someone else. But the notion of love itself is as abstract as that of God. Which may be why we make assumptions about what it is to be in love without analysing quite what we mean. We take for granted that the experience of falling in love is irrational – very often inexplicable.

And our assumption is reinforced by all the literature that attempts to describe it, from fairy tales to romance, from metaphysical poetry to the modern novel. Charming princes will fall in love after one glimpse of their beloved – even if she’s been asleep for a hundred years, or is comatose in a glass box. Love is often described as a thunderbolt, a flash of lightning, an electric shock. Romeo and Juliet fall in love as soon as they set eyes on each other at the ball. And in Midsummer Night’s Dream the relationships between the lovers are irrelevant: what matters is the magic dust sprinkled into their deluded eyes.

Actually, Puck’s interventions do have their modern-day equivalent. Step forward the proponents of neuroscience, who claim that it is possible to identify the area of the brain where love resides, and that moreover our emotions can be explained by chemicals. Show someone a photograph of the person they love and that part of their brain will buzz with activity – though this claim is a bit flimsy. What if it the brain responds to pictures of everyone the subject loves, including children, mothers, aged aunts or a pair of killer shoes?

Ah, but romantic love can be identified through chemicals, reply the neuro-boosters. They tell us that dopamine, norepinephrine and serotonin are generally released in larger doses during the initial phase of attraction, while oxytocin and vasopressin are more important in the formation of lasting relationships. But all that shows is the chemical changes that occur as a result of this heightened emotional state. They’re not the same thing as that state, nor can chemicals, unlike Puck’s magic potion, actually create it. (You won’t get anyone to fall in love with you by injecting them with a few ccs of dopamine.)

Neither are these chemicals a particularly reliable barometer for our emotional state. For those released in the initial stages of love are very similar to those gushing through a new mother. “Human infants are born completely helpless, so have to be looked after for years,” explains Grose. “This means that mothers and, to a lesser extent, fathers have to stay pumped full of love chemicals in order to tolerate the inconvenience. The neurotransmitters released in nursing mothers – and in the babies they are caring for – are the very ones that are released in the experience of sexual love.”

This similarity between the two heightened states would not have surprised Freud, whose insights into the complexities of infantile sexuality led him to conclude that all the different types of love are linked. Early experiences of passionate attachment to parents, rejection and separation will dictate future attitudes to adult relationships.

So Freud regards love as a neurosis, rather like Dawkins, who argues that it is a necessary evolutionary disorder which has developed to ensure the procreation of the species. Both are scornful of any higher claims for the state of being in love. But surely, you might argue, there’s plenty of evidence for its existence. Centuries of art, literature, music – all can be reduced to this one conviction: that love between two people is the most abiding, the most true value. And this has been true since the world began – ever since Adam and Eve.

But hang on – we don’t believe in Bible stories, however much they still have resonances for the human condition. Our automatic reference to such examples just shows how far western thought has been dominated by this hapless belief in love, quite as it has been by the Abrahamic religions. Just because everyone’s fallen for it doesn’t make it true.

Surely, though, you’ll protest, there are fundamental differences between the two states regardless of superficial similarities. For a start, love doesn’t cause wars, cruelty or any of the other acts of evil perpetrated in the name of religion. Except, of course, that’s not really true. Love may not have been responsible for the Holocaust or the Rwandan massacres. But it has occasionally sent men to their mass deaths. Think of the Trojan wars and the role of the much-adored Helen; think of the Spanish Inquisition; think of Antony and Cleopatra acting out their bedroom passion in the battle for dominance of the empire.

Far, far more often, though, love has been an excuse for endless acts of cruelty and betrayal, even murder and certainly wicked revenge. Lovers feel they have a license to act as they wish regardless of the trail of broken hearts and bloodied lives they may leave in their wake. Abraham was prepared to kill his only son to prove his belief in God. Countless husbands and wives, bosses, best friends, teachers, children will feel exonerated in their destruction of the lives of others, because they’re in love.

Even so, you’ll insist, love is still very much a human quality. You don’t get magic or miracles or the promise of a better life hereafter. Wrong again. Love is a kind of magic – remember those magic moments, the magic of being in the arms of a loved one. Think of the miracles of love, how it can transform your day with a single rose or the touch of a certain beloved finger on your cheek.

And like religion, love dangles the great promise of eternal happiness. This is why romantic fiction always ends with a marriage, the arrival in heaven, worldly concerns transcended by a ring and a kiss and a cloud of tulle. Indeed, rather like the seeking after religious affirmation, love is frequently presented as an impossible ideal, just as heaven is impossible to reach on earth and God impossible to know. The greatest love poem of all, Dante’s Divine Comedy, is a paean to this notion – Beatrice is the ideal and perfect beloved, but never to be reached.

And this unreachable ideal is at the heart of the medieval tradition of courtly love, popularised by the troubadours – travelling poets who stayed at court under the patronage of the lord. Their poems dealt with the themes of love and adoration between married women and their husbands’ noble knights. The women were ideals of virtue for whom their besotted lovers must perform heroic tasks in order to please them. The knights in the stories would become manly, decent, morally uplifted during the course of their trials, but would never get near enough even to touch the objects of their worship.

So the association of love with anguish and suffering, with the quest for an ideal but the ultimate rejection, stems from this code. And the European tradition, according to Anouchka Grose, has a much older precursor in the form of the ghazal, a type of Arabic love poem. Here, the love would usually be for a young slave or soldier but, says Grose, the flavour would be the same. “The love had to be illicit, the sense of longing and separation very much lingered over and enjoyed.” And, significantly, “the lover wasn’t any normal mortal with whom you simply wanted to have sex, but an emissary of the divine.”

This notion that true romance must remain unrequited invites an irresistible parallel with religion. There has always been this strong correlation between erotic and heavenly ecstasies, ever since Saint Teresa of Avila shuddered with orgasmic pleasure at her visions of an angel plunging his golden spear into her heart until it penetrated her entrails.

Noting the similarities between the symptoms of religious mania and sexual compulsion, Richard Dawkins quotes the testimony of the philosopher Anthony Kenny, who was ordained as a Roman Catholic priest and recalls the joy he felt at the laying on of hands to celebrate Mass: “It was touching the body of Christ, the closeness of the priest to Jesus, which most enthralled me. I would gaze on the Host after the words of consecration, soft-eyed like a lover looking into the eyes of his beloved.”

But it’s not just that divine revelation can produce powerful sexual feelings. Conversely, sexual passion itself can be so intense that it can be mistaken for metaphysical rather than earthly bliss. In Transcendent Sex, Jenny Wade interviews 92 people who claim some other-worldly experience of sexual intimacy. Many describe the sensation as religious, making them feel at one with God or with the cosmos.

This reverse effect, whereby sexual rapture is transmuted into the divine, informs Christian interpretations of Solomon’s Song of Songs. You wouldn’t think there could be much doubt about the opening line: “Let me kiss him with the kisses of his mouth.” But the willing bride welcoming her lover to bed, by divine sleight of hand, becomes in the Christian canon the Church opening its arms to its spiritual groom, or God.

And thereby the woman conspires in her own subordination. “When she receives the loved man, the woman is inhabited, visited like the Virgin by the Holy Spirit, like the believer by the wafer,” scoffs Simone de Beauvoir in The Second Sex. “This explains the obscene analogy between holy hymns and ribald songs: it is not that mystical love always has a sexual side; but the sexuality of the woman in love takes on a mystical tone. ‘My God, my beloved, my master . . .’, the same words spill from the lips of the kneeling saint and the woman in love lying on the bed; the saint offers her flesh to Christ’s arrows, she holds out her hands to receive the stigmata, she implores the burning of divine Love; the woman in love also offers and waits: darts, stinger and arrows are embodied in the male sex.”

But, you might protest, we’ve come a long way from the time when marriages were a matter of convenience and women simply bought and owned. The development of modern love is surely positive, a recognition of the humanity and the rights of women? But feminism offers a rather harsher interpretation.

In her angry study In the Name of Love, Jill Tweedie argues that modern love, embodied in the wedlocked couple, is a recipe for inequality. “The man has been encouraged to become a tin pot dictator in the marital police state, the woman his doormat. Or, sometimes, vice-versa. What would never be tolerated in other areas of life is licensed in love – abuse, insult, denigration, humiliation, physical violence, violation of privacy, the destruction of friendships, of beliefs, of sex and of the self. To enter the kingdom of love they have had to stoop, to shrink to crawl and thus atrophied in every part, they claim love’s crown.”

And Tweedie has no time for what she regards as a precursor of modern attitudes to romance – those wretched troubadours. “Those belles dames who believed themselves adored, who thought their favours were all men desired, were, as was so often to happen, fooled.” She argues that this false, idealised love was just an excuse for men to go off and do what they wanted: which usually meant fighting in tournaments or adventuring to the crusades. Romantic love, she believes, has always been a false ideal, only thinly disguising just how much women are despised by men. More often than not, it is used as a defence for appalling abuses.

Simone de Beauvoir is equally savage. “Men might be passionate lovers at certain moments of their existence,” she allows, “but there is not one who could be defined as ‘a man in love’; in their most violent passions, they never abandon themselves completely; even if they fall on their knees before their mistresses, they still wish to possess them, annex them; at the heart of their lives, they remain sovereign subjects; the woman they love is merely one value among others; they want to integrate her into their existence, not submerge their entire existence in her. By contrast, love for the woman is a total abdication for the benefit of a master.”

And the result? “The love act requires a woman’s profound alienation; she is awash in the indolence of passivity; eyes closed, anonymous, lost, she feels transported by waves, caught up in torment, buried in the night: night of flesh, of the womb, of the tomb; reduced to nothing, she reaches the Whole, her self effaced.”

But does this wholesale dismissal of love have to be quite so nihilistic? Is there no way for us to love without absurd beliefs or appalling abuse? Anouchka Grose remains ambivalent. Love may be an illusion, she writes, but it’s one that we seem to need – even if our desire for its perfection is unrealistic. “Realism has no place in romance,” she writes. “Romance is precisely a defence against what’s real. Love is the fantasy architecture we build to bridge the gulfs between people. . .”

And the national hysteria mounting over our latest public fairytale romance, that of Prince William and his Kate, does seem to reinforce our collective need for the delusion of love. We should have learned the true fate of overblown romance after that last glorious public wedding. Thirty years ago millions cheered and wept when Charles, admittedly rather awkwardly, plonked that first chaste kiss on Diana’s virgin lips. That affair may have ended in tatters, but we go on believing, against all the evidence, in happy-ever-afters and love lasting for ever.

So as rationalists, are we to abandon our misplaced faith in true love? Not necessarily, counsels Simone de Beauvoir. But it can only flourish if the conditions are right. “The day when it will be possible for the woman to love in her strength and not in her weakness, not to escape from herself but to find herself, not out of resignation but to affirm herself, love will become for her as for man the source of life and not a mortal danger. For the time being, love epitomises in its most moving form the curse that weighs on woman trapped in the feminine universe, the mutilated woman, incapable of being self-sufficient.”

And Jill Tweedie echoes the sentiment: “Love cannot thrive in inequality or extreme poverty. It requires enough leisure for introspection and enough introspection for empathy. It demands that the individual feels a certain control over life because, in too great a storm, we tend to seek any refuge. It thrives on honesty and therefore must do away with great need, since need compromises honesty. It is rational, it knows its own roots, it is moral and controllable because it stems from the head and not the heart. Any resemblance it bears to love as we know it today is mainly accidental.

“That sort of love is still in embryo form, fragile compared to other ties because it derives no strength from ancient needs. Its roots are not in the past but in the future. It is a beginning, a new survival mechanism slowly evolving to create a better world.” So bring out the satin hearts, the cuddly bears, the diamonds, the oysters, the soppy cards and the tear-filled promises. But bear in mind that we’re still building that perfect heaven of sexual equality that will make it all come true.

No More Silly Love Songs by Anouchka Grose is published by Portobello. A new translation of Simone de Beauvoir’s The Second Sex, by Constance Border and Sheila Malovany-Chevallier, is published by Jonathan Cape