A. On Notion, Degrees, and Lines of Affinity

7. Here the idea of affinity can be set down as this: a certain tie [bond] between person and person contracted from carnal union with a person consanguineous with a second. For it is always the case that, because a person carnally united is consanguineous with someone, then she, with whom he is carnally united, is made affinal with that someone and conversely. And there is as it were an exposition of the word ‘affinal’, that it is an ‘accession to the confines of’; for he who is joined carnally with someone of a certain consanguinity accedes, by this, to the confines of that consanguinity, and therefore he has a tie of access to everyone of that consanguinity.

8. To this tie degrees and lines can be assigned (as before in the case of consanguinity [n.d.40 nn.9-13]), and for all these there is one brief rule: by whatever degree of consanguinity someone is distant from someone else, by that whole degree of affinity is she, who is carnally known by the former, distant from the same person. I do not say ‘wife’, because this is not required; for not only [by carnal union] with a wife but with a concubine or prostitute is affinity with those consanguineous with that very man contracted (indeed [contracted] in incest [too]).

9. Nor is it sufficient for affinity properly speaking that she be wife, but carnal mingling is required, as is said in Gratian, Decretum, p.2 cause 35 q.10 ch.1, “Of fraternity,” where it is said about spouses that “if they have been one flesh, it cannot be that someone is closely related to one of them without this pertaining to the other of them;” wherein is understood that affinity is not contracted save by means of carnal mingling.

10. However, by extending affinity, it is said that it is contracted not only with a wife known carnally but also with a wife not known, where (supply) there is a matrimony but not a consummated one and, what is more, with her with whom betrothals precisely are contracted.

11. And here is to be noted that this tie, contracted with someone because of her union with someone consanguineous (and this either through matrimonial union or consent of betrothals), is commonly called the justice of public honorableness.

12. And this affinity is closeness of relationship arising from betrothals, getting its strength from institution of the Church, because of public honorableness. And about this impediment there is a rule that no one consanguineous with a husband can marry or have his wife, nor can someone consanguineous with his wife have him as husband.