Saint Jerome, Doctor and Father of the Church
Illicit sexual acts within marriage are equivalent to fornication and adultery, as Saint Jerome taught:
“And it makes no difference how honorable may be the cause of a man’s insanity. Hence Xystus in his Sentences tells us that ‘He who too ardently loves his own wife is an adulterer.’ It is disgraceful to love another man’s wife at all, or one’s own too much. A wise man ought to love his wife with judgment, not with passion. Let a man govern his voluptuous impulses, and not rush headlong into intercourse. There is nothing blacker than to love a wife as if she were an adulteress.” (St. Jerome, Against Jovinianus, Bk 1, n. 49)
Notice that St. Jerome states that “it makes no difference how honorable may be the cause of a man’s insanity.” In other words, the intention which motivates a man to sin is irrelevant to the morality of the act. If a sexual act is a sin, it does not matter how honorable the man’s intentions are, it is still a serious moral disorder, comparable, as a figure of speech, to the serious mental disorder of insanity.
St. Jerome plainly taught that there are sexual sins within marriage. The idea that “nothing is shameful” as long as the marital act occurs at some point in time is plainly rejected by St. Jerome. It is contrary to wisdom and good judgment for a man to have sexual relations with his wife in an inordinate manner. Though St. Jerome does not, like modern-day moral theologians, give explicit descriptions of various sexual acts, it is clear that he rejects the idea that the mere deposit of the right bodily fluid in the right location justifies all other acts.
More on marital chastity in my book: The Catholic Marriage Bed
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