As the conversation continues, however, I realize that the denizens of the Round Table might have enjoyed this little lunch after all, because soon some of us get a little bitchy.

To begin, I'm married, Waite is married, Gallagher is married. But while we're all married, according to these two women marriage is under attack. Something compelled them to set the marriage record straight. Being married makes you healthier and wealthier, and you have better sex than single people, they say.

"After I finished your chapter on sex," I tell the women, "my first thought was I wanted to run out and have an affair."

Both writers laugh. "Why is that?" Waite asks, smiling.

I pause. I don't want to start on an antagonistic note. The chapter on sex is puritanical and, worse, unrealistic. These two women insist that the only good sex in your life will be had in matrimony. Forget that two-week affair you had right after college when you hitchhiked to Paris. That was just youthful folly, counting for nothing. As for your present married life, say it's midnight, the baby is howling and your 3-year-old has the mumps. According to something called the "National Sex Survey" -- the only source for the two women's arguments -- the thing that's foremost on your mind at that moment is fornicating with your spouse.

"The National Sex Survey," I say. "What is this?"

"You remember the Time magazine cover story from about two or three years ago?" Gallagher asks.

"Also called the 'Chicago Sex Survey,'" Waite adds.

"Also called officially the 'National Health and Social Life Survey,'" Gallagher says. "It was done on about 3,000 adults ages 18 to 59 in 1994."

"It is the gold standard," Waite adds.

No one asked me any questions in 1994. I think surveys are science fiction. But all I say is, "So we can believe it?" Both women insist that we can. "So according to the survey, what do kids do for one's sex life?" I ask.

Gallagher looks at her coauthor. "Did we look at that?"

"Well, you can tell ...," Waite starts to say, but stops when the waitress comes up. She says, "I'll have the fruit plate with the mango sorbet, and can I have some more iced tea, please?"

"I'll have the poached salmon," Gallagher says.

I just order coffee.

The waitress splits, and Waite continues talking: "What basically happens to frequency of sex is, it tends to fall with duration of the relationship. It's also true that the frequency of sex falls if you have kids, especially if they're young, because they're up in the night and you're exhausted -- those sorts of things."

"Your book doesn't go into that," I say.

"It has nothing to do with marriage," Gallagher pipes up. "I was a single mother for 10 years. You're pretty conscious about trying to make a decent living and take care of your kids. This is not time for gabbing about."

Waite catches my eye. I realize she is trying to be charming. "Basically the argument is: If you know you're committed to your partner, you pledge to be sexually faithful. The survey asked, 'Do you expect this relationship to be sexually exclusive?' Something like 97 percent of married people say, 'Yes.' Then you know that your sex life with this other person is for a long time, so you know that if you're going to get sexual satisfaction, your best bet is to give sexual satisfaction, to figure out what your partner wants and likes and learn how to do it. People have an incentive -- this is economist talk -- to develop relationship-specific skills because they know this is the only game in town."

Private Life Romance, relationships, and the personal side of Table Talk