The remarkable success of Fifty Shades of Grey by E.L. James has taken the literary world by surprise. Its quick and astounding ascent to the top of the New York Times bestseller list invites us to step back a pace and ask what is going on here? Why has this book, ostensibly about the theme of sadomasochism, one even more deeply tabooed than homosexuality, struck such a chord? How does the raising of sadomasochistic themes in 2012 fit into the larger evolution of sexuality and manners?

In James’s novel, we meet Anastasia Steele, a young virgin working in a hardware store, and Christian, a fabulously wealthy young financier, an experienced player who has already had 15 sm relationships. Ana becomes totally captivated by him and is willing to go the whole nine yards for him even though her “subconscious” keeps screaming “No!”

Sadomasochism tends to fill us with unease precisely because it seems such a repudiation of liberal western values. At its very core lies not the infliction of pain but the submission, complete and total, of one individual to another. The submissive, or bottom in the trade, surrenders all autonomy to the dominant figure, or top. The top becomes all-controlling in a way reminiscent of totalitarian dictatorship. How can we possibly reconcile this with western values? How can we explain the striking uptake of Fifty Shades among what is often described as the “mommy set” without assuming that the mommy set has somehow sold out to the North Korean Politburo?

We have to re-jig a couple of assumptions here. One assumption that we as a society have conventionally made for the last thirty years — certainly since 1970s style feminism — is that sex is about power. The early feminist days were full of injunctions about the patriarchy and how male chauvinists used their power to control you in bed in order to control you in every other way as well.

All of a sudden we find an entire generation of fast-track, autonomous young women celebrating not the acquisition of sexual power but its surrender. This is such a striking paradox.

The problem here is that in the 1970s we were switched onto the wrong railway siding. There is such a thing as power relations in sexuality, and we see this played out in rape or in some form of the Stockholm Syndrome, in which the captives come to identify with their oppressors.

But the sexual mainline does not run through power relations, a non-erotic subject. It runs through sensuality. Sex for most people is not about power but about luxuriating in the pleasures of the flesh, about a glass of champagne at ten a.m. Sunday morning and the exquisiteness of calf muscles tightened by high heels or the reach of a muscular male back. Only if we concentrate on sensuality and forget, just for a moment, about power, will we be able to come to terms with Fifty Shades of Grey.

But Fifty Shades of Grey is about a very specific form of sensuality: sadomasochism, which means tying people up and, sometimes, whipping them, or at least administering a few symbolic strokes with a riding crop that redden the skin but do not cause tissue damage. Still, it can be painful. How can this be erotic?

What is erotic here is not the infliction of pain but the exchange of control. This is not everybody’s cup of tea, but for many people the concept of surrendering total control, for a well defined period of time and in the particular context of the bedroom, can be exquisitely sensual. Similarly, assuming control over another person’s erotic experience — it’s you who determines exactly when and how and wearing what outfit she is penetrated — can be a delirious sensual experience. Or determining when and how he is penetrated, ditto. To the glass of champagne on Sunday morning we add a scarf that ties her hands, a pair of handcuffs that fasten his arms behind his back. Does William really accept you as the Mistress with absolute control over him? Let’s test by giving him ten of the best. Does Sally truly acknowledge that you are her Master? Let’s use this new dildo to find out.

So it’s not that William and Sally set out to inflict pain on each other. That is not the point of the exercise. It’s that they set out to experience the sensual dimensions of the exchange of power. We’re back to power, yes, but to avoiding it rather than acquiring it: Most players seek to be bottoms rather than tops. In the sm scene people complain about the shortage of tops.

Fifty Shades of Grey is ostensibly about the sadomasochistic exchange of power but in reality is an incandescent love story revolving around this particular sensual theme, rather than the sensuality of the missionary position or the sensuality of anonymous gay-male sex. Christian Grey is a masterful top, Anastasia Steele, in his thrall, is an unwitting bottom. What brings them together is not their mutual taste for sm – she has none at the beginning, but their overpowering ardour for each other. This is a couple in which sm is conceivable only because they are so totally in love with each other.

So this is a real and powerful human relationship not some pick-up in an sm/leather bar. And that’s why the novel has had such a sensational impact: These are real, flesh-and-blood people, not sexual cartoons, submitting and controlling each other in a way the most trivial expression of which is the exercise of pain and constraint. The most profound expression is deep passion, but it is a kind of lust for a master-slave relationship that until very recently was deeply tabooed in our culture.