Blame Bill Clinton: Ever since the former president confounded Congress — and the nation — with his semantically driven definition of sex, the nature of the act has become increasingly vague. In 2005, the federal government released a study that found more than 50 percent of American teenagers had engaged in oral sex; furthermore, they considered oral sex a less-significant substitution for intercourse. And as the generation enters adulthood, this attitude toward sex is affecting its relationships. A recent study conducted by the University of Northern Iowa and Pennsylvania State University finds that undergraduates in relationships hold their significant others to a stricter definition of sex than they hold themselves. Participants were asked if their own involvement in several different sexual behaviors would count as sex; they were then asked if those same behaviors would be considered sex if their boyfriend or girlfriend were to engage in them outside of the relationship. The results point to a definite double standard. "Participants answering for themselves were less likely to indicate a behavior was having sex for all behaviors except penile-anal and penile-vaginal intercourse," researchers Gary Gute, Elaine M. Eshbaugh and Jacquelyn Wiersma write in the October 2008 issue of the Journal of Sex Research. In addition, "men were also more likely than women to indicate most behaviors were having sex." Why are people fudging the facts? Ilene Donin, a New York City therapist who was not involved in the study, says this murkiness allows women to maintain a perceived preservation of purity, one that has extended beyond the twenty-something set. "I have been told by women in their thirties and forties that they will 'do everything but' have intercourse," she says. "That, to them, is far more intimate and more of a commitment." Men, on the other hand, might have more hard-wired reasons for their willingness to view any indiscretion as cheating. "Men believe that when women have sex it is not just a pleasure-seeking behavior but an emotional experience, so it is very threatening," Donin says. "And I believe that on some very basic level, men still see women as their property." All of this makes the future of relationships seem pretty dismal — which, according to The New York Times, isn't a problem, as relationships are becoming a thing of the past, anyway. "Hooking up is a casual sexual encounter with no expectation of future emotional commitment. Think of it as a one-night stand with someone you know," writes Charles M. Blow in a Dec. 13 article. "Under [this] new model, you hook up a few times and, if you really like the person, you might consider going on a date." Just don't hook up behind your boyfriend's back. That's cheating. Maybe.

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Sally Law has written about health and sexuality for the Cleveland Clinic, and has appeared regularly as a guest host on Sirius Radio. Her column, The Science of Sex, appears weekly on LiveScience.