A few days before Christmas, President Bush told Diane Sawyer he would support -- "if necessary" -- a constitutional amendment codifying marriage as the relationship between a man and a woman, and only a man and a woman.

Came The New York Times, a few days after that, with the news of a new poll showing majority public disapproval of gay marriage.

A noisy national argument, precipitated by the courts, is in the works. It is too bad. There is no need today for one more enpurpling, vein-swelling controversy in our national life. But as this particular controversy is headed our way, it behooves us to give some thought to the meaning of marriage: the unchanging meaning of marriage, if you please.

The argument in behalf of such unions is testy and disputatious. It says, flatly, to those who defend traditional marriage, "You're wrong!"

Wrong? inquires the other side. Wrong, how? Wrong, the accusing side comes back, in terms of denying to same-sex couples the comforts of an institution proven nourishing for heterosexuals. What's good for one sexual persuasion is good, supposedly, for another persuasion.

Except that if it is, how come we are just now hearing about it? Is it something we didn't know before or might have known but for our Blind Bigotry?

Well, no, actually. Heterosexual marriage is rigorously logical. So is it exquisitely, exuberantly defensible in theological terms (see the Book of Common Prayer), but the merest mention of theology turns off self-styled foes of "fundamentalism," so let's momentarily shut the church door. Why should society prefer heterosexual marriage to variant kinds?

As it happens, a man and a woman go together in a way -- blush, blush -- that same-sex couples find utterly impossible and always will. There must be a reason, right? Continued...