Thomas Aquinas

“ Therefore it cannot be the result of compulsory consent.
I answer that, The marriage bond is everlasting. Hence whatever is inconsistent with its perpetuity invalidates marriage. Now the fear which compels a constant man deprives the contract of its perpetuity, since its complete rescission can be demanded. Wherefore this compulsion by fear which influences a constant man, invalidates marriage, but not the other compulsion. Now a constant man is reckoned a virtuous man who, according to the Philosopher (Ethic. iii, 4) , is a measure in all human actions. ”

“ Some say that the Pope cannot command a man to accept a bishopric, because consent should be free. But if this be granted there would be an end of ecclesiastical order, for unless a man can be compelled to accept the government of a church, the Church could not be preserved, since sometimes those who are qualified for the purpose are unwilling to accept unless they be compelled. Therefore we must reply that the two cases are not parallel; for there is no bodily service in a spiritual marriage as there is in the bodily marriage ”

“ Further, "Of all fearsome things death is the limit," according to the Philosopher (Ethic. iii, 6) , as though it were the most perfect of all things that inspire fear. But the constant man is not compelled by death, since the brave face even mortal dangers. Therefore no fear influences a constant man. ”

“ Nor does he sin if he does otherwise, because there is no appearance of evil in not fulfilling a promise that one has made unwillingly.
Art. 4 - Whether compulsory consent makes a marriage as regards the party who uses compulsion? Objection 1: It would seem that compulsory consent makes a marriage, at least as regards the party who uses compulsion. For matrimony is a sign of a spiritual union. But spiritual union which is by charity may be with one who has not charity. Therefore marriage is possible with one who wills it not. ”

“ Yet certain bodily injuries are less grievous than certain others; and chief among them are those which relate to the person, such as death, blows, the stain resulting from rape, and slavery. Wherefore the like compel a constant man to suffer other bodily injuries. ”

“ I answer that, Since in marriage there is a kind of perpetual service, as it were, a father cannot by his command compel his son to marry, since the latter is of free condition: but he may induce him for a reasonable cause ”

“ Now the constant differs from the inconstant man in two respects. First, in respect of the quality of the danger feared, because the constant man follows right reason, whereby he knows whether to omit this rather than that, and whether to do this rather than that. ”

“ Further, no one should promise, especially with an oath, for one whom he cannot compel to keep the promise. Now parents promise future marriages for their children, and even confirm their promise by oath. ”