What is Church Teaching on Oral Stimulation and Oral Sex within marriage?
Pope Pius XII taught that it is gravely immoral for the husband, nor the wife do perform any sexual act to climax, outside of the natural marital act. The wife may not perform oral sex (fellatio) on her husband to climax. The husband may not perform oral sex on his wife to climax. In both cases, the couple sin gravely.
"By the force of this law of nature, the human person does not possess the right and power to the full exercise of the sexual faculty, directly intended, except when he performs the conjugal act according to the norms defined and imposed by nature itself. Outside of this natural act, it is not even given within the matrimonial right itself to enjoy this sexual faculty fully. These are the limits to the particular right of which we are speaking, and they circumscribe its use according to nature....."
It is often claimed, especially online, that the wife can climax before or after natural marital relations, as a result of oral, anal, or manual sex (or "stimulation"). But that claim is a grave error. First, the Church has never taught such a thing. No proponent of that claim ever quotes or cites a magisterial document saying anything like that. Second, as you can see from the quote above, the Church has taught the exact opposite. Neither the husband nor the wife can climax outside of the natural marital act.
Third, everyone agrees that oral sex on either spouse is a grave sin, done in isolation from the marital sexual act. So it would make no sense to say that a gravely immoral act becomes moral when done a certain number of minutes or hours before natural marital relations, and immoral for a longer length of time. In Catholic moral theology, when an act is a grave sin on its own, it never becomes moral by being done about the same time as another good act.
St. Alphonsus Liguori specifically condemned the idea that an unnatural sexual act becomes moral when done about the same time as natural marital relations. See the article: Saint Alphonsus Liguori on Marital Chastity. Saints Jerome, Augustine, and Aquinas agree, as do a number of well-respected present-day priests and theologians. See the book: The Catholic Marriage for a full explanation.
What if the husband or wife uses oral, anal, or manual stimulation, without climax, as a type of foreplay before natural marital relations? Are these types of sexual acts permissible when climax only occurs during the natural marital act? No, they are not permissible. The consummated form of oral, anal, and manual sex are each unnatural and intrinsically evil. When these same acts are done as stimulation, without climax, they do not change into a moral type of act.
For the teaching of the Church requires that each and every sexual act be marital, unitive, and procreative. But oral, anal, and manual sex are neither unitive, nor procreative. And the absence of climax does not make the acts unitive or procreative. Moreover, the basic principles of ethics taught by the Church require that each deliberate knowing choice of the human person be judged on its own merits. It is never the case that one act is judged by the merits of another act, occurring about the same time. Therefore, unnatural sexual acts do not become unitive and procreative by being done about the same time as natural marital relations.
There are a number of other Church teachings which also pertain to the limits of sex within marriage. For a full discussion, see the other online articles here, Catechism.cc, as well as these books: The Catholic Marriage Bed and Roman Catholic Marital Sexual Ethics. The Catholic Marriage Bed, in particular, addresses some of the recent popular, but erroneous ideas about this topic. Here is the chapter list:
The Catholic Marriage Bed
Unnatural Acts in Marriage:
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