Cardinal Francis George of Chicago is, arguably, the most intellectually accomplished bishop in the history of the American episcopate. Earlier this year, when the Illinois Legislature began to consider changing state law to “accommodate those of the same sex who wish to ‘marry’ one another” (as the cardinal put it), Professor Dr. George gave the readers of his column in the Chicago archdiocesan newspaper a lesson in metaphysics—and, I suspect, a high-voltage intellectual jolt:

“Sexual relations between a man and a woman are naturally and necessarily different from sexual relations between same-sex partners. This truth is part of the common sense of the human race. It was true before the existence of either...