It is ironic, at least, that one of the two socially acceptable euphemisms for having sex is "sleeping together." There is probably no activity so antithetical to sleeping, however exhausting and eventually soporific it may be.

Perhaps it is a sign of encroaching middle age, but I now think that a good night's sleep may be a better indication of love and intimacy than even the most passionate evening. Bedtime intimacy can be undone by incompatibility when sleeptime comes along. One cuddles; the other won't. One rolls over; the other complains, or grunts (same thing) or leaves for the safety of the sofa. One wakes up early, ready to go. The other prefers to sleep in, taking full advantage of the already warmed blanket.

Indeed, modern couples who are unintimidated and undaunted by sex fearfully avoid the dangers and humiliations threatened by a night together. One arranges to leave not long after the bewitching -- that is, the sleeping hour. One complains that he or she has to get up very early the next morning -- to go to work, to catch a plane, to catch up on work, to -- it doesn't much matter. It's all an excuse to be left alone. Sleeping together, not sex together, is the testing ground for long-term intimacy. Sleeping together, not sex together, is the most prominent source of misunderstanding and disaster.

Sleeping together, like love itself, says a lot about one's identity, and how one 'fits' -- quite literally -- with another. In my experience, there seem to be two basic types -- although perhaps the more imaginative or more experienced could uncover a half dozen more. There are SNUGGLERS and there are SOLIPSISTS. Snugglers relish the presence of another warm body. There are passive snugglers -- who crave to be held, and active snugglers -- who enjoy holding but resist being held, but most snugglers are both active and passive, or indifferent to the distinction. It is enough for them that the other is present, warm and cuddly. Snugglers can tolerate or adjust to a remarkable amount of rolling, stretching, jerking, groaning, squeezing and even smacking. Even in their sleep, they recognize this as a small price to pay for love, warmth and comfort.

SOLIPSISTS, on the other hand, can stay awake all night because of a fly in the room. The dog on the rug is OK, so long as he doesn't snort, wag or move. The cat who tries to leap on the bed is soon thrown out of the room -- or the house -- and hard.

I confess that I am a solipsist, or at least, I used to be. Solipsists may love sex and, indeed, during the sexual act they may hug and allow themselves to be hugged. But, deep down, they want to be alone. One should never be surprised when a passionate lover who has great trouble sleeping suddenly insists that he (or she) "needs space.'' We have developed all sorts of theories to explain this phrase, but the truth may be that solipsists just want to sleep and wake up alone.

Both snugglers and solipsists will complain rather quickly that their sleeping habits do not betray their real personalities. Solipsists will point out that one might like to sleep alone but nevertheless love intimacy and snuggling. Snugglers will insist that they are in fact quite independent and do not need to hold on or be held onto in order to feel perfectly at home with themselves. I don't believe it. One is never more at home than in sleep, never more oneself, never more free -- as Jean-Jacques Rousseau used to fantasize -- from the artifices, expectations and conventions of society.

In sleep we are free, not free to do much that is productive, perhaps, but free if also compelled to insist on the basics -- not such trivia as food, drink, micturation or love, for these can be provided (up to a point) in dreams - but independence or dependency. These are the basic ingredients of the self -- as Hegel pointed out years ago, as Freudians (in different terms) have argued too. But whatever the multitude of bad arguments about love and sex and regression to childhood, the obvious truth is that if we ever regress it is when we sleep, and sleeping together like sleeping alone is primal. One might well need sex for any number of reasons - because it is socially expected, for encouragement, for the challenge, because it is maximal hedonism, or power, or a way of killing time. But we all need sleep, and how one sleeps is not an expression of that need but rather an insistence on the conditions that foster sleep -- the security of another hugging body, or the isolated safety of sleeping alone.

Two snugglers together is the very portrait of bliss -- the sort of mawkish scene that became a standard scene for nineteenth century academic romantic painting. This is true even of two uncompromisingly active snugglers, whose competition for mutual holding may be as active and as satisfying as their sexual snuggling some hours before. (There may be a temporary problem with two passive snugglers, but they quickly realize that their need to be in an embrace is much more pressing than their preference for being embraced.)

Two solipsists can well survive, but preferably in a king-size bed. (Those twin bedded bedrooms in 1950's movies may not have been prudishness after all; they may have reflected a preponderance of solipsists in the film industry.) There may be nagging doubts at first, for instance, when it is permissible to break away from embrace and set out across the bed on one's own, and there is always the danger that whoever does so first may offend the other -- even though he or she is also a solipsist. Feeling neglected is always the bane of the solipsist -- even if, in a sense, he or she prefers it. Insomniacs are almost always solipsists.

The real tragedy or farce begins when a snuggler and a solipsist come together. It may begin agreeably enough, with a long and pleasant conversation, interests in common and no audible disagreements. The embrace does not betray the secret nor give any evidence of the deep incompatibility between them, and the warm comforts of sex do little to give it away. There is no moment of truth, but rather a slow unraveling of illusion, starting perhaps in the exhaustion that follows, but more likely remaining dormant (so to speak) during an initial and most misleading round of sleep, that fifteen minutes to an hour that is the most sound and satisfying sleep of all. It begins when one -- the snuggler -- reaches around and embraces the other, and is rebuffed, at first gently perhaps but soon with sleepy resentment. Or, it begins when one -- the solipsist -- rolls over and turns away, leaving the snuggler caressing the air and feeling rejected or -- if so inclined -- worrying about being found repulsive.

Needless to say, the one thing leads to another -- but rarely to sleep. The snuggler tries another embrace; the solipsist mutters and pulls away. The snuggler, confused, wonders what has gone wrong. The solipsist -- now beyond the realm of rest and relaxation -- may get up and go to the next room -- "to think'', to drink but really just to be alone and conclude, angrily, that this person is just too possessive to consider. A self-confident snuggler may then go to sleep, having chalked off the relationship as "too weird'' to follow through. A less secure snuggler may well lie awake, plagued with self doubts, hugging the pillow (or both pillows, the other being unused) to sleep. And since we rarely think of sleep as a romantic issue, the idea of an honest confrontation doesn't even arise.

We have all become artfully articulate about sex as an issue, replacing politics (to which our current views of sex are much akin) but we have little practice or even vocabulary to talk about the intimacies of sleep. As a consequence, more couples hit the skids because of sleeplessness than sexual malperformance. One can excuse and talk about clumsiness or lack of coordination; there is no apology appropriate for incompatible sleep.

To make matters all the more complicated, however, one and the same person can be both a solipsist and a snuggler -- at different times, with different partners. This is why sleeping together is so relevant to love. A confirmed solipsist may become a wanton snuggler when he or she is sufficiently in love, and, let me tell you, there is no more magnificent transformation in the world. The many metaphors of lights and fireworks that have been employed to dramatize and poeticize love are nothing compared to the quiet, warm comfort of a converted solipsist. And when two former solipsists find themselves snoring joyfully in each others arms through the night, that is love indeed.

(Earlier versions of this piece appeared in my books About Love (Simon and Schuster, 1988) and Entertaining Ideas (Prometheus Books, 1992).