Pundits proffer a number of reasons why the notion of adultery jangles in our collective psyche. Unfortunately, but predictably enough, they state the obvious and explain nothing. Maybe it has something to do with the notion that America has the soul of Increase Mather in the body of Henry Miller. Maybe it has something to do with our growing fixation on all things prurient. And maybe, as in the recent cases of Gen. Joseph Ralston and Lt. Kelly Flinn, it even has something to do with our outrage at institutional hypocrisy. But the real reason why the Seventh Commandment has plopped into our lap like a hot potato is far simpler -- and therefore far from obvious: Why should we be expected to respond intelligibly to the notion of adultery, when marriage -- as idea, institution and reality -- no longer has any intelligible meaning or binding purpose?

Once upon a time, after a long and painful evolution, Western religious traditions settled upon three terms necessary for any man and woman to enter into a covenant of marriage. The procreation and nurture of children, the socialization of sexual desire and mutual selfsacrifice. Where any one of these terms was willfully set aside, no marriage existed. It was this delineation of marriage that came to determine common law and civic mores.

What made adultery adultery was obvious. Sexual intercourse with someone other than your spouse contradicted the covenant of marriage. Plain and simple. Yet, since the Enlightenment, we have been busily dismantling this artifice plank by plank. First, the notion of contract became synonymous with the notion of covenant. Marriage became a quid pro quo affair. I will meet your needs, if you meet my needs. The German philosopher Immanuel Kant, not usually known for Teutonic bluntness, could describe marriage as a contract for the reciprocal deployment of genitalia. If you think this unduly pessimistic, consider that over the last hundred years, divorce litigation has shifted from the moral obligation to protect the injured and vulnerable to wrangles over property and custodial rights.

The next plank to go was the procreation and nurture of children. From crude abortifacients to pharmaceutical craft, from sheep's gut to latex, from Trojan warriors to sheathed Sheiks and now to Lifestyle contortionists, the implacable march of birth control has made children an optional commodity. Now, with wombs to rent and zygotes to freeze, children have become fungible as well as optional. There's no longer any reason to assume that marriage should entail the bearing and nurture of children -- or that a single individual cannot design (and continually redesign) his or her family to the specifications of taste or whim. You may believe that for a child to flourish he or she ought to have, if possible, a father or mother; but -- in words that are now the arbiter in all modern debates -- that's only your opinion.

We've taken a little longer to wrench the final plank away, but modernity has finally corroded all constructions that socialize human sexuality. In the tart words of Malcolm Muggeridge, if birth control is permissable and children no longer an interruption, than any orifice will do. Sex -- S&M or missionary position, it really doesn't matter -- has become "safe." This is surely the most Orwellian euphemism ever minted. Consequently, when self-fulfillment takes priority over self-sacrifice, it's difficult to see any reason why sex should be shaped by the emotional needs of one's partner except in so far as those needs hinder or enhance Great Sex.

When asked what her same-sex union meant, one gay woman opined, "I have a right to my lover's body, and she has a right to mine." Ralph Cramden or O.J. Simpson couldn't have said it better.

Even more importantly, where sex is divorced from long-term consequences, the notion of monogamy ceases to be self-evident. Where we used to speak of one-night stands, an acquaintance of mine now talks, quite seriously, about his commitment to serial monogamy. As the song goes, if you can't be with the one you love, you might as well love the one you're with.

It is paradoxical indeed, but perhaps not coincidental, that gays and transgendered persons push to expand the definition of marriage at the very time when the definition of marriage has ceased to possess any cultural coherence.

To ask whether Kelly Flinn or Joseph Ralston should be punished for adultery is to ask a nonquestion -- unless, like the military, you're foolish enough to believe that words possess determinable meanings. Flinn and Ralston merely engaged in discrete acts of genital deployment, to which the military establishment chose to call indiscreet attention. We are right to dismiss such charges as antiquated nonsense. For if we take the charge of adultery seriously, we risk giving credence to the idea that marriage has a definitive meaning. And such a risk we as a culture just cannot afford to take. We have come too far and labored too long in the task of social demolition to turn back now.

The Rev. David Lewis Stokes Jr., an occasional contributor, is rector of St. Stephen's (Episcopal) Church in Providence, and teaches courses in Western Civilization and Old Testament at Providence College.