The other week the New York Times ran a fawningly long profile of a "big thinking" ultra-conservative Catholic intellectual. It stressed his powerful Oxford credentials, his Big University Post (at a non-Catholic institution–take that elite liberal institutions!), his influence over Catholic leadership, his ties to Bush, Glenn Beck's admiriation of him, and, most importantly for our purposes, his frequent use of the word "reason" in place of an actual argument. So powerful his intellect, you see, that Cardinal Rigali of Philadelphia, aped his words in a recent speech.
Even marriage between a man and a woman, Rigali continued, was grounded not just in religion and tradition but in logic. “The true great goods of marriage — the unitive and the procreative goods — are inextricably bound together such that the complementarity of husband and wife is of the very essence of marital communion,” the cardinal continued, ascending into philosophical abstractions surely lost on most in the room. “Sexual relations outside the marital bond are contrary not only to the will of God but to the good of man. Indeed, they are contrary to the will of God precisely because they are against the good of man.”
Now I may not be a logician of this fellow's calibre, but I'm trying to think of which principle of logic grounds the union of a man and a woman in life-long monogamous non-divorcing holy Catholic and procreative matrimony. I'm going to guess that it must be one of those Latin principles, an abstraction, in other words, few could understand. Maybe it's ex falso quodlibet sequitur.
I think, however, it's more likely the principle of petitio principii–begging the question.
*edited for sense later in the day.