Thomas Aquinas

“ The reason why consent to marriage after taking the vow of virginity is sinful, is because that consent gives a power to do what is unlawful: even so would a man sin if he gave another man the power to receive that which he has in deposit, and not only by actually delivering it to him. ”

“ The essential cause of marriage is the end to which it is by its very nature ordained, and this is always good, namely the begetting of children and the avoiding of fornication. But the accidental final cause thereof is that which the contracting parties intend as the result of marriage. And since that which is intended as the result of marriage is consequent upon marriage, and since that which comes first is not altered by what comes after, but conversely; marriage does not become good or evil by reason of that cause, but the contracting parties to whom this cause is the essential end. ”

“ Hence it is evident that they said well who asserted that to consent to marriage is to consent to carnal intercourse implicitly and not explicitly. For carnal intercourse is not to be understood, except as an effect is implicitly contained in its cause, for the power to have carnal intercourse, which power is the object of the consent, is the cause of carnal intercourse, just as the power to use one's own property is the cause of the use. ”