apparently, there are about 237 reasons that got us into this mess

a personal favorite: "i was slumming."

Findings: The Whys of Mating: 237 Reasons and Counting
By JOHN TIERNEY
Published: July 31, 2007

Scholars in antiquity began counting the ways that humans have sex, but they weren’t so diligent in cataloging the reasons humans wanted to get into all those positions. Darwin and his successors offered a few explanations of mating strategies — to find better genes, to gain status and resources — but they neglected to produce a Kama Sutra of sexual motivations.

Perhaps you didn’t lament this omission. Perhaps you thought that the motivations for sex were pretty obvious. Or maybe you never really wanted to know what was going on inside other people’s minds, in which case you should stop reading immediately.

For now, thanks to psychologists at the University of Texas at Austin, we can at last count the whys. After asking nearly 2,000 people why they’d had sex, the researchers have assembled and categorized a total of 237 reasons — everything from “I wanted to feel closer to God” to “I was drunk.” They even found a few people who claimed to have been motivated by the desire to have a child.

The researchers, Cindy M. Meston and David M. Buss, believe their list, published in the August issue of Archives of Sexual Behavior, is the most thorough taxonomy of sexual motivation ever compiled. This seems entirely plausible.

Who knew, for instance, that a headache had any erotic significance except as an excuse for saying no? But some respondents of both sexes explained that they’d had sex “to get rid of a headache.” It’s No. 173 on the list.

Others said they did it to “help me fall asleep,” “make my partner feel powerful,” “burn calories,” “return a favor,” “keep warm,” “hurt an enemy” or “change the topic of conversation.” The lamest may have been, “It seemed like good exercise,” although there is also this: “Someone dared me.”

Dr. Buss has studied mating strategies around the world — he’s the oft-cited author of “The Evolution of Desire” and other books — but even he did not expect to find such varied and Machiavellian reasons for sex. “I was truly astonished,” he said, “by this richness of sexual psychology.”

The researchers collected the data by first asking more than 400 people to list their reasons for having sex, and then asking more than 1,500 others to rate how important each reason was to them. Although it was a fairly homogenous sample of students at the University of Texas, nearly every one of the 237 reasons was rated by at least some people as their most important motive for having sex.

The best news is that both men and women ranked the same reason most often: “I was attracted to the person.”

The rest of the top 10 for each gender were also almost all the same, including “I wanted to express my love for the person,” “I was sexually aroused and wanted the release” and “It’s fun.”

No matter what the reason, men were more likely to cite it than women, with a couple of notable exceptions. Women were more likely to say they had sex because, “I wanted to express my love for the person” and “I realized I was in love.” This jibes with conventional wisdom about women emphasizing the emotional aspects of sex, although it might also reflect the female respondents’ reluctance to admit to less lofty motives.

The results contradicted another stereotype about women: their supposed tendency to use sex to gain status or resources.

“Our findings suggest that men do these things more than women,” Dr. Buss said, alluding to the respondents who said they’d had sex to get things, like a promotion, a raise or a favor. Men were much more likely than women to say they’d had sex to “boost my social status” or because the partner was famous or “usually ‘out of my league.’ ”

Dr. Buss said, “Although I knew that having sex has consequences for reputation, it surprised me that people, notably men, would be motivated to have sex solely for social status and reputation enhancement.”

But then, men were also more likely than women to say they’d had sex because “I was slumming.” Or simply because “the opportunity presented itself,” or “the person demanded that I have sex.”

If nothing else, the results seem to be a robust confirmation of the hypothesis in the old joke: How can a woman get a man to take off his clothes? Ask him.

To make sense of the 237 reasons, Dr. Buss and Dr. Meston created a taxonomy with four general categories:

¶Physical: “The person had beautiful eyes” or “a desirable body,” or “was good kisser” or “too physically attractive to resist.” Or “I wanted to achieve an orgasm.”

¶Goal Attainment: “I wanted to even the score with a cheating partner” or “break up a rival’s relationship” or “make money” or “be popular.” Or “because of a bet.”

¶Emotional: “I wanted to communicate at a deeper level” or “lift my partner’s spirits” or “say ‘Thank you.’ ” Or just because “the person was intelligent.”

¶Insecurity: “I felt like it was my duty” or “I wanted to boost my self-esteem” or “It was the only way my partner would spend time with me.”

Having sex out of a sense of duty, Dr. Buss said, showed up in a separate study as being especially frequent among older women. But both sexes seem to practice a strategy that he calls mate-guarding, as illustrated in one of the reasons given by survey respondents: “I was afraid my partner would have an affair if I didn’t.”

That fear seems especially reasonable after you finish reading Dr. Buss’s paper and realize just how many reasons there are for infidelity. Some critics might complain that the list has some repetitions — it includes “I was curious about sex” as well as “I wanted to see what all the fuss was about” — but I’m more concerned about the reasons yet to be enumerated.

For instance, nowhere among the 237 reasons will you find the one attributed to the actress Joan Crawford: “I need sex for a clear complexion.” (The closest is “I thought it would make me feel healthy.”)Nor will you find anything about gathering rosebuds while ye may (the 17th-century exhortation to young virgins from Robert Herrick). Nor the similar hurry-before-we-die rationale (“The grave’s a fine and private place/ But none I think do there embrace”) from Andrew Marvell in “To His Coy Mistress.”

From even a cursory survey of literature or the modern mass market in sex fantasies, it seems clear that this new taxonomy may not be any more complete than the original periodic table of the elements.

When I mentioned Ms. Crawford’s complexion and the poets’ rationales to Dr. Buss, he promised to consider them and all other candidates for Reason 238.

You can nominate your own reasons at TierneyLab. You can also submit nominations for a brand new taxonomy: reasons for just saying “No way!” Somehow, though, I don’t think this list will be as long.