From the Council of London Celebrated by Anselm, A.D. 1102

Canon XXII. Faith given between a man and a woman concerning marriage, secretly and without witnesses, if it shall have been denied by either one, is to be held void.

If the matter concerns the faith of espousals, the invalidation seems reasonable; if concerning the faith of a marriage secretly entered, the decree will have force in the external forum, not in the forum of conscience before God, if the denial of either one is false.

Canon XXIV. Let cognates up to the seventh generation not be coupled, nor, if coupled, remain together.

The same Anselm, in an epistle (Book 3, Epistle 158), whether the nuptials of blood-relatives are forbidden and why, gave this reason for this prohibition. Namely, having posited that our law is charity, which, the more widely it is divided and poured out, so much the richer it remains for the one dividing and is increased, he adds: "Christian religion therefore established that, the limits of consanguinity reaching on every side, according to the decrees of the holy Fathers and canons, up to the sixth degree (cf. what we gave from Peter Damian at A.D. 1065), for preserving charity, let one's own natural affection suffice, which even among barbarians is held impious to violate. But where that fails, there at last, lest it withdraw itself from charity to be bound again, the conjugal bond must be adjoined for prolonging the boundaries of our inheritance, which is charity itself."