Marriage 2.26.41

Certainly, if evil is derived from marriage, marriages can be condemned and cannot be excused. You place their work and fruit under the devil’s authority, because every cause of evil is without good. The person born from marriage is attributed to seed, however, not to crimes. The cause of the seed lies in the constitution of bodies. Whoever misuses those bodies damages the merit of what is good, not its kind. It is therefore perfectly clear that good is not the cause of evil.

If, then, original evil is derived even from marriage, the marital union is the cause of evil, and that through which and from which an evil fruit appeared must itself be evil. As the Lord says in the Gospel: “A tree is known by its fruits” (Matthew 12:33; compare Matthew 7:16–20). Why do you think anyone should listen to you when you say that marriage is good, yet declare that nothing but evil comes from it? Marriage, then, is clearly guilty if original sin is derived from it, and it cannot be defended unless its fruit is shown to be innocent. But marriages are defended and pronounced good; their fruit is therefore shown to be innocent.