§ 2. On Adultery

I. Notion. Adultery is intercourse which injures the fidelity of the marriage bed, whether one's own, or another's, or both at the same time.

Adultery is had even if the other spouse consents. This follows from proposition 50 condemned by Innocent XI: "Intercourse with a married woman, with her husband consenting, is not adultery, and therefore it is enough in confession to say that one has fornicated." The reason, however, is that the said consent does not prevent a sin of injustice from being added to the sin against chastity, as will be more fully explained below.

II. Division. Adultery is distinguished into simple and double, according as one or both are married.

III. Morality. 1. Adultery contains a twofold sin, namely of lust and of injustice (St. Thomas, II-II, q. 154, a. 1, ad 2). It contains a sin of lust because, equally with fornication, it involves the use of venereal things which, as performed by persons not bound by an indissoluble bond, is not perfectly ordered to the education of offspring (n. 33). It contains a sin of injustice because it injures the right either of one's own consort, or of another's consort, or of both. I said or of both, namely if both are married; in that case there are two sins of injustice, because two distinct rights are injured (St. Alphonsus III, 445).

But if one spouse consents to the intercourse of his or her consort with another, there is indeed, as we said above, adultery, and therefore besides lust there is added a sin of another species, and indeed, according to the almost common opinion, of injustice. But it is disputed with respect to whom injustice is committed in this case. Some¹ judge that injustice is not committed against the husband, because no injury is done to one who knows and wills; but it is committed with respect to the conjugal state. But it seems that one should say that action is unjustly taken against the husband himself. For the matter concerns a right of the husband which he cannot renounce except as to his own exercise of it; and therefore that right, notwithstanding the consent, persists. But if the right of the husband persists, it is not seen why injustice is not had with respect to the husband, just as if the consent had not taken place. Add that the conjugal state is not a moral person which enjoys strict rights, so that strict injustice cannot be committed against it (cf. St. Alphonsus, Homo Apostolicus, tr. 9, n. 16).

2. Concerning the relative gravity of adulteries, note: If the adulterating woman is married, the sin is held graver than if the man is, because of graver inconveniences, for example damage to the true heir,² uncertainty of offspring,³ and so forth.⁴ But if both are married, it is still graver, because there are two injustices against each spouse, to be expressed in confession (St. Alphonsus III, 445).

Note 1. The pollution of a married person in some way takes on the nature of adultery, because it injures the right of the consort, who alone has the right to the use of the body of the consort, according to these words of the Apostle: The woman does not have power over her own body, but the man. Likewise also the man does not have power over his own body, but the woman⁵ (n. 104).

Note 2. Intercourse with another's betrothed man or betrothed woman quite probably does not take on the nature of adultery, or quite probably is not opposed to justice, since the arguments of the adversaries prove nothing at all. They argue from the fact that fornication renders the thing promised, that is, the body, notably worse in order to marriage. But first, that which the adversaries suppose is rightly called into doubt, namely that by betrothal there is introduced an obligation of justice to hand over the body such as it was at the time of the promise. If the question is about another promise, this will sometimes be clear from the circumstances; but in the present case the matter seems doubtful. Next, it is by no means clear that the body is rendered notably worse by intercourse in order to marriage (St. Alphonsus VI, 847).⁶

¹ Billuart, De temperantia, dissert. 6, a. 5; Merkelbach, cited work, p. 40.

² Namely, if the woman is married and commits adultery at the time when she conceives, there is danger lest foreign offspring be supposed by the husband and share the inheritance with legitimate children.

³ Namely, it will be doubtful whose offspring it is.

⁴ It is added, namely, that a woman easily becomes sterile from mingling with several men.

⁵ 1 Cor. 7:4.

⁶ Cf. our little work De forma promissionis et celebrationis matrimonii, ed. 5, pp. 10-11.