Reply to Objection 3: This argument would hold, were there no other and more efficacious remedies for the disease of concupiscence; which is false.
Reply to Objection 4: Persons are said to be unlawful subjects for marriage through being contrary to the law whereby marriage is established. Now marriage as fulfilling an office of nature is established by the natural law; as a sacrament, by the Divine law; as fulfilling an office of society, by the civil law. Consequently a person may be rendered an unlawful subject of marriage by any of the aforesaid laws. Nor does the comparison with the other sacraments hold, for they are sacraments only. And since the natural law is particularized in various ways according to the various states of mankind, and since positive law, too, varies according to the various conditions of men, the Master (Sent. iv, D, 34) asserts that at various times various persons have been unlawful subjects of marriage.
Reply to Objection 5: The law may forbid a thing either altogether, or in part and in certain cases. Hence between that which is altogether according to the law and that which is altogether against the law (which are opposed by contrariety and not according to affirmation and negation), that which is somewhat according to the law and somewhat against the law is a middle term. For this reason certain persons hold a middle place between those who are simply lawful subjects and those who are simply unlawful.
Reply to Objection 6: Those impediments which do not annul a marriage already contracted sometimes hinder a marriage from being contracted, by rendering it not invalid but unlawful. And if it be contracted it is a true marriage although the contracting parties sin; just as by consecrating after breaking one's fast one would sin by disobeying the Church's ordinance, and yet it would be a valid sacrament because it is not essential to the sacrament that the consecrator be fasting.
Reply to Objection 7: When we say that the aforesaid impediments annul marriage already contracted, we do not mean that they dissolve a marriage contracted in due form, but that they dissolve a marriage contracted "de facto" and not "de jure." Wherefore if an impediment supervene after a marriage has been contracted in due form, it cannot dissolve the marriage.
Reply to Objection 8: The impediments that hinder a good accidentally are infinite in number, like all accidental causes. But the causes which of their own nature corrupt a certain good are directed to that effect, and determinate, even as are the causes which produce that good; for the causes by which a thing is destroyed and those by which it is made are either contrary to one another, or the same but taken in a contrary way.
Reply to Objection 9: The conditions of particular persons taken individually are infinite in number, but taken in general, they may be reduced to a certain number; as instanced in medicine and all operative arts, which consider the conditions of particular persons in whom acts are.