As a young boy, I was fascinated by romantic tragedies such as Gustave Flaubert’s Madame Bovary (1856) and Amos Oz’s My Michael (1968). These novels served as cautionary tales, warning what could happen if passion withered and true love died. Take the undoing of Emma Bovary, who tries to relieve the banality of her life through a series of adulterous affairs. Ultimately rejected by her lovers and deep in debt, Emma swallows arsenic and kills herself. Like her, Hannah Gonen (the wife of Michael) is full of passion and dreams, but stunted by her marriage to a pragmatic, unimaginative man. As time goes on, her marriage devolves into sadness and depression, and her dreams – along with her sanity – are squashed.

Emma and Hannah appear to be victims of a myth, a dangerous romantic ideology still enshrined in our rituals and songs: love can overcome all obstacles (there is no mountain high enough); love is forever (till death us do part). This seductive romantic ideology assumes the uniqueness of the beloved along with a kind of fusion. Soul mates are meant only for each other; the lovers form a single entity; each of the partners is irreplaceable in all the world. (Millions of people go by, but they all disappear from view – because I only have eyes for you.) Ideal love is total, uncompromising, and unconditional. No matter what happens outside the circle of the relationship, true love endures.

Romantic ideology still has its allure, but the idea that passion can last a lifetime has lost credence in modern times. One argument against enduring intensity comes from thinking rooted in the work of the great 17th-century Dutch philosopher Baruch Spinoza: emotions occur when we perceive a significant change in our situation. Change cannot last forever. Ergo, passionate love must fade.

In line with that, many studies have consistently shown that sexual desire and intense romantic love decrease drastically over time. The findings show that the frequency of sexual activity with one’s partner declines steadily, occurring half as often after one year of marriage compared with the first month, and falling off more gradually thereafter, especially after the child-rearing years. This decline has been found in cohabiting, heterosexual couples and in gay and lesbian couples. Accordingly, many scholars have claimed that enduring intense love is uncommon, almost always evolving into companionate love which, as time goes by, is low in attraction and sexual desire. Love is a trade-off, the prevailing wisdom goes: we can either soar briefly to the highest heights or we can have contentment for many years. It is fruitless to despair like Emma and Hannah, because no one can have both.

Or can they? New research suggests that common wisdom might be wrong, and that a significant percentage of long-term couples remain deeply in love. In 2012, the psychologist Daniel O’Leary and his team at Stony Brook University in New York asked study participants this basic question: ‘How in love are you with your partner?’ Their national survey of 274 individuals married for more than a decade found that some 40 per cent said ‘very intensely in love’ (scoring seven on a seven-point scale). O’Leary’s team did a similar study of New Yorkers and found that 29 per cent of 322 long-married individuals gave the same answer. In another national study in 2011, the dating site Match.com found that 18 per cent of 5,200 individuals in the US reported feelings of romantic love lasting a decade or more.

Research in neuroscience identifies the possible mechanism behind these results. In a study published in 2012, Stony Brook psychologist Bianca Acevedo and colleagues reported on 10 women and seven men married an average of 21 years and claiming to be intensely in love. The researchers showed participants facial images of their partners while scanning their brains with fMRI. The scans revealed significant activation in key reward centres of the brain – much like the patterns found in people experiencing new love, but vastly different from those in companionate relationships.

it is painfully hard to fulfil the romantic ideal while staying inside our culture’s boundaries and social norms; only dead fish swim with the stream

I must admit that these findings puzzled me. Are we actually victims of romantic ideology? Should we cease striving for true love or hold out until a soul mate appears? In our modern times, these questions do not have an easy answer. After all, it is painfully hard to fulfil the romantic ideal while staying inside our culture’s boundaries and social norms; only dead fish swim with the stream.

Nevertheless, I still sided with Emma and Hannah – I wanted to believe in romantic ideology, and embraced its central assumption that genuine romantic love can last for many years. Although this might be regarded as a cliché of a kitsch culture, it is in fact a radical idea running counter to many psychological studies and commonly held beliefs.

To make my case, I would have to reconcile the Stony Brook studies with Spinoza’s notion and mine – that emotion requires change. I thought I might do so by distinguishing between superficial romantic experiences on the one hand and profound love on the other – that is, between relationships where sexual attraction is paramount and those fuelled by shared experience and personal flourishing. Both forms of love are passionate, I reasoned, but only one of them can survive.

Ibegan my thought experiment by comparing acute emotions such as anger to sentiments such as grief. A sentiment does not merely consist of having a given acute emotion again and again – it also shapes our attitudes and behaviour in a permanent way. A flash of anger might last a few minutes or more, but our grief over the loss of a loved one resonates constantly, colouring our moods, our demeanour, and the way we relate to time and space. Likewise, in the realm of love we can distinguish between two phenomena: romantic intensity and romantic profundity. Romantic intensity expresses the momentary value of acute emotions. Romantic profundity embodies frequent acute occurrences of intense love over long periods of time along with life experience that resonates in all dimensions, helping the individuals flourish and thrive.

But romantic profundity is not merely about duration, it is also about complexity. An analogy can be found in music. In 1987, William Gaver and George Mandler, psychologists from the University of California, San Diego, found that the frequency of listening to a certain kind of music increases the preference for it – up to a point. Too much familiarity is prone to produce boredom, especially if the composition is simple. The more complex the music, the less likely it is for boredom to set in.

As with music, so it is with love. The complexity of the beloved is an important factor in determining whether love will be more or less profound as time goes on: a simple psychological object is liked less with exposure, while a complex object is liked more. A complex psychological personality is more likely to generate profound romantic love in a partner, while even the most intense sexual desire can die away. Sexual desire is boosted by change and novelty and diluted by familiarity. Romantic profundity increases with familiarity if the other person, and the relationship itself, is multifaceted and complex.

It was the novelist Ursula K Le Guin who wrote in The Lathe of Heaven (1971): ‘Love doesn’t just sit there, like a stone; it has to be made, like bread, remade all the time, made new.’ Indeed, it is in sharing what is important in our life that love becomes profound. Joint substantial activities have lasting impact on our lives and can also shape our personality. Superficial activities affect only the surface of our lives – they are more immediate in impact and limited in scope.

The difference between romantic profundity and romantic intensity draws context from Aristotle’s distinction between eudaimonic well-being (realising one’s potential) and hedonic well-being (immersion in fleeting pleasure). In 2004, Carol Ryff, a psychologist at the University of Wisconsin-Madison, collated multiple studies connecting eudaimonic well-being with biomarkers for cardiovascular, neuroendocrine and immune health, along with resistance to and recovery from disease. She found that, in the lab, eudaimonic well-being has been associated with lower levels of salivary cortisol, a sign that stress is at bay; lower levels of the proinflammatory cytokines, which can underlie autoimmune disease; and longer periods of REM sleep, associated with deep rest and dreams. Those achieving eudaimonic well-being had lower levels of biomarkers associated with Alzheimer’s disease, osteoporosis and arthritis as well.

Superficial activities, such as casual sex, gossiping, and watching television, might be enjoyable even though they do not contribute much to our long-term flourishing

As an engine of eudaimonic well-being, the benefits of profound love run deep. Aristotle’s notion of human flourishing is not a temporary state of superficial pleasure; it refers to fulfilment of our talents and capacities over the arc of life. Superficial activities, such as casual sex, gossiping, and watching television, might be enjoyable even though they do not contribute much to our long-term flourishing, and can even be harmful in excess. On the other hand, profound love and happiness require optimal functioning, tapping essential capacities and intrinsic activities in a systematic manner over a sustained period of time. This is the difference between a fleeting pleasure and a lasting treasure. As long as the partners are flourishing and passion stays at least moderately intense, profound love can endure. Romantic profundity counteracts the loss of intensity that would otherwise occur with time.

Yet profound love, too, can die. The lovers might change, circumstances might alter the landscape, and chemical attraction might dissipate too much to keep passion alive.

To grasp the calculus of risk, let’s go back to some basic love math, which centres around two variables. The first variable or ‘evaluative pattern’ is sexual attraction. The second is ‘praiseworthiness’ – the positive appraisal of personal characteristics ranging from a sense of humour to honesty and creativity, traits we admire in our friends. Romantic love demands sexual attraction on the one hand and friendship on the other. These requirements form the bottom line. Without them, there is no romance at all.

An attractive woman might want to be loved not merely for her beauty but also for her actions and personal traits. A less attractive woman might wish the reverse: that her beloved values her external appearance as much as he does her kindness or wisdom. She would be offended if her partner said: ‘You are rather ugly and I am not sexually attracted to you, but your brilliant brain compensates for everything.’ In W B Yeats’s poem ‘For Anne Gregory’ (1933), a woman wants to be loved not for the yellow colour of her hair, but for herself alone. An old man tells her: ‘only God, my dear,/Could love you for yourself alone/And not your yellow hair.’

The two evaluative patterns involved in romantic love are not independent: a positive appraisal of your partner’s characteristics is greatly influenced by his or her attractiveness. In her book Survival of the Prettiest (1999), Nancy Etcoff, a cognitive scientist at Harvard Medical School, clearly shows that attractiveness significantly influences ratings of intelligence, sociality, and morality. This is the ‘attractiveness halo’, in which a person perceived as beautiful is assumed to have other good qualities as well. Thus, attractive people are more successful in job interviews and get higher salaries. The opposite phenomenon occurs when praiseworthy qualities such as wisdom and social status render the lover more attractive in a partner’s eyes. Thus, the rich, famous or powerful evoke more intense sexual desire.

Over time, of course, a lover’s score on each scale can change. Attraction has more weight in the short term while praiseworthiness is more important later on. At any point in a relationship, failure to score high enough on either scale leads to dissatisfaction – and to what I call the feeling of ‘romantic compromise’.

Even when love has been profound, the sense of too much compromise can entice us to pursue something new. In the US TV series The Good Wife (2009-), the protagonist Alicia Florrick is asked how she makes love outlast passion. ‘I think it’s not just about the heart,’ she says. ‘Sometimes the heart needs steering.’ The lucky group of couples who are the most profoundly in love have never, or at least hardly ever, needed to steer their hearts; they have been free to follow their loving hearts, because they have taken them straight to the relationships they want to sustain anyway. But the rest of us maintain our relationships through compromise. We give up a romantic value, such as romantic freedom and intense passionate love, in exchange for a nonromantic value, such as living comfortably without financial concerns. Nevertheless, the more the combined score of attraction and praiseworthiness decreases, the greater the compromise, and the more we yearn for the road not taken – the one with romantic freedom or a different romantic partner.

the greater the compromise, the more we yearn for the road not taken – the one with romantic freedom or a different romantic partner

Romantic compromise poses two major hurdles to enduring love. The first is accepting a negative aspect in one’s partner, such as not being sufficiently attractive or wise; this is part and parcel of every kind of compromise and it is often easy to live with since everyone has some flaws and there is not much we can do about it. The second hurdle – forgoing the chance to find a better partner – is often harder to resist because it appears more within our control. In light of the growing number of alluring options in modern society (in the words of Mae West: ‘So many men, so little time’), the problem of romantic compromise, and hence of our inability to be satisfied with our own lot, has increased to the point where it is the major obstacle to achieving or sustaining profound love at all.

Indeed, in 2012, the psychologist Justin Lavner and colleagues at the University of California, Los Angeles studied women reporting ‘cold feet’ – indicative of compromise – prior to a wedding. The doubters went on to divorce 2.5 times more frequently than women without premarital doubts, and had less satisfied marital trajectories if they did remain married. Such doubts should not always prevent us from getting married because absolute certainty is unrealistic. However, we should take into account their nature and extent: at the beginning of a relationship, doubts revolve around romantic intensity, attractiveness and sexual desire. Over the years, the focus of compromise shifts to those qualities such as kindness and wisdom that help us thrive. Doubts in the latter category are of greater concern, because partners who can’t help each other flourish are tempted by outsiders to fit the bill.

In the geography of love, the landscape is always rugged. After every take-off, turbulence throttles down. Even when lovers don’t compromise, and even when they flourish, their romance can be shattered by the most florid and insidious expectation of romantic ideology: the utterly false notion that lovers must fuse into one. Part of the concept comes from Plato, who pictured love as the process of seeking our missing half. Yet this Siamese-twin model of love implies a loss of personal freedom and a loss of self – the two essentials necessary for profound love to thrive.

love is not about each partner having the other as his or her object; love is about what happens between the partners. It is dialogical

In her forthcoming book Zwischen Ich und Du (‘Between Me and You’), Angelika Krebs, a philosopher at the University of Basel, follows the ideas in Martin Buber’s I and Thou (1923) to argue persuasively that love is not about each partner having the other as his or her object; love is about what happens between the partners. It is dialogical. Lovers share what is important for flourishing in their emotional and practical lives.

The affinity between such lovers creates a functional harmony in which personal identities do not just thrive but evolve. Lovers might develop similar preferences for music or theatre, or even begin to wear similar clothes. Such lovers often testify that they frequently have similar thoughts or that they understand each other even before words are spoken. But even here, identities are not fused – they are shared. Profound romantic satisfaction is not about possession but about flourishing; the other person is not an extension of you, but a partner for a dynamic fulfilling way of life.

One literary work that lights the way is Leo Tolstoy’s Anna Karenina (1877). Anna is so tormented by her unhappy love for Vronsky that she throws herself under a train. But the contrasting characters Levin and Kitty manage to flourish and thrive in their love. Levin, unique for his ability to feel deeply and openly, believes there is ‘only one creature in the world who could concentrate for him all the brightness and meaning of life. It was she. It was Kitty.’ Still, the story of their love is not straightforward: Kitty first rejects Levin while awaiting another lover. After Kitty and Levin finally get together, they squabble. The message is clear: even when romantic ideology wins the day, in fiction as in life, it is always on the verge of losing. Winning requires people who are honest and compassionate, yet so totally themselves that they would not ever want to dominate the other. Their complex love is profound and open; their shared life and passion lead to the flourishing of both.

Despite so much cynicism in recent years, romantic love can soar on the wings of profundity. For love to be profound, the partners’ personal characteristics do not have to be the best in town – they just need to be in harmony. When the fit is there, passion can be fanned by profundity instead of intensity so that the romance endures.