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.
Objection 2. Further, if she who was compelled consents afterwards, it will be a true marriage. But he who compelled her before is not bound by her consent. Therefore he was married to her by virtue of the consent he gave before.
On the contrary, Matrimony is an equiparant relation. Now a relation of that kind is equally in both terms. Therefore if there is an impediment on the part of one, there will be no marriage on the part of the other.
I answer that, Since marriage is a kind of relation, and a relation cannot arise in one of the terms without arising in the other, it follows that whatever is an impediment to matrimony in the one, is an impediment to matrimony in the other; since it is impossible for a man to be the husband of one who is not his wife, or for a woman to be a wife without a husband, just as it is impossible to be a mother without having a child. Hence it is a common saying that "marriage is not lame."
Reply to Objection 1. Although the act of the lover can be directed to one who loves not, there can be no union between them, unless love be mutual. Wherefore the Philosopher says (Ethic. viii, 2) that friendship which consists in a kind of union requires a return of love.
Reply to Objection 2. Marriage does not result from the consent of her who was compelled before, except in so far as the other party's previous consent remains in force; wherefore if he were to withdraw his consent there would be no marriage.
Source: Summa Theologica (New Advent)