Annotation LXXIX

”For this cause a man shall leave father and mother, and shall cleave to his wife.” — Matthew 19:5

On the marriage-unions lawful by the law of nature.

Thomas Cajetan, in the commentaries on Matthew, seems to hold that all marriage-unions between [persons] joined by blood and affinity are lawful, except between mother and son, [and] father and daughter. For thus he left [it] written on this passage: “God instituted not only marriage, but instituted persons apt for marriage — by exempting from marriage [only] father and mother; [for] it is against the divine and natural law that a man be joined in marriage with [his] father or mother. And therefore it is said that a man shall leave [for the sake of] marriage — a daughter [her] father, and a son [his] mother — and shall cleave not to [any] woman, but to a wife; not to any [wife] whatever, but to his own. By this signifying that all other persons are apt to be spouses. For from the fact that he excluded only father and mother, he signified the rest — namely brothers and sisters, nephews and nieces — [to be] free to be husbands and wives.” Ambrose [Catharinus], bishop of Compsa, explaining these [things], in the fifth book of [his] Annotations, attacks Cajetan with a prolix disputation, because by these words he openly denied that unions between [blood-]related persons are unlawful by natural and divine law, except that which is between father and daughter, [and] mother and son. Which opinion the same bishop detests as unchaste. Cajetan wrote copiously on this matter in the commentaries on the Secunda Secundae of St. Thomas, question 154, article 9, where the curious reader will be able to read what impelled him to this assertion.