Dominicus Prummer on Unnatural Acts

Up through the early twentieth century, the sexual acts of manual / oral stimulation were consistently considered gravely immoral by Catholics, as well as all other Christians. They were rarely mentioned out of concern for decency. Still, an early witness can be found in the Paenitentiale Theodori (c. AD 700), which regards them as fornication, which then meant any act fit for a brothel (fornix). Later medieval penitentials and summas classified them as unnatural vice, which was the worst offense against chastity. St. Thomas mentions it only obliquely, as "other monstrous and bestial manners of copulation." (cf. ST. II, Q. 154, A. 11)

A definitive guide to moral theology used by priests in the early twentieth century was the Manuale theologiae moralis secundum principia S. Thomae Aquinatis in usum Scholarum by Dominicus Prummer. You can still buy reprints of a condensed English translation titled "Handbook of Moral Theology". In Sec 863, Prummer confirms that manual stimulation is a sin even conjugally.

Modern Catholics (even so-called "traditionalists") have tried to dodge this by making such acts permissible as long as they do not result in pollution. On its face, that would seem congruent with the traditional moral theology described by Prummer: "Not only the conjugal act itself but also touches and looks and all other acts are lawful between the married, provided that there is no proximate danger of pollution and the sole intention is not mere sexual pleasure." (859, 1) Also: "b) anything that is done for mere sexual pleasure is a slight sin, provided it is not directly contrary to the offspring or to conjugal fidelity; c) whatever is useful for or necessary for the perfect fulfillment of the conjugal act and the fostering of marital love is not sinful." (862,3)

Yet here Prummer clearly has in mind ordinary kisses and caresses. It can hardly legitimize unnatural vice, condemned elsewhere as intrinsically sinful, and in no way necessary to the conjugal act. Catholics who try to legitimize oral or manual stimulation of the genitals have simply been desensitized by our degenerate culture into thinking this is just another form of affectionate contact, ignoring its perverse, unnatural quality.

Some may appeal to the so-called "unitive" purpose of marriage, or canon law's bonum coniugum, "good of the spouses," as justifying non-procreative libidinous acts, but this would be to interpret "good" in a hedonistic sense. The pre-Vatican II analog to bonum coniugum was "conjugal fidelity," which more clearly indicates a spiritual good. Further, the modern Catechism says that the unitive and procreative values of marriage cannot be separated. (CCC 2363) Lastly, as anyone who hasn't been desensitized should perceive, the evil of unnatural vice is not limited to its lack of procreation, but extends to its perverse and demeaning aspects.

Another approach is to claim that earlier moral theology was unfairly "androcentric" as it did not have due regard for the differences of women. Supposedly, these formerly forbidden acts are necessary for equitable satisfaction. Ironically, this "feminist" emphasis on physical "climax" reduces female sexuality to male sexuality, i.e., a sharply defined moment of physiological gratification. Women who take this path end up having the same hedonistic attitude toward sexuality as promiscuous males. Those who place less emphasis on this, by contrast, tend to have a more balanced view, finding satisfaction primarily in the emotional aspects of the marital act, without constantly seeking the next neurochemical high.

Beyond their objective sinfulness, the traditionally forbidden carnal acts are highly inadvisable, since they lead to a cycle of raised hedonic expectations. Then the marital act becomes reduced to using each other for pleasure, notwithstanding poetic talk of a deeper personal connection (humans are exquisitely resourceful at creating false rationales for their actions, especially addictive behaviors).

More important than finding the precise boundary between what is lawful and unlawful, one should have a basic Christian attitude toward sexuality as something you use for a good purpose, not a pleasure that controls you like a drug. Taking the path of ars erotica makes the pleasure an end in itself, in which case you will likely seek ever more subtle refinements and escalations, as plainer acts become less satisfying. This is pretty much the path the world has chosen, as shown by our ever-escalating pornographic culture.

For further reading: see the writings of St. Alphonsus Liguori (cf. Sermons for All the Sundays in the Year) and the essay, “Alphonus Liguori's Moral Theology of Marriage: Refreshing Realism, Continued Relevance," which summarizes some of his teachings on matrimony, discussed more fully in the third volume of his Theologia Moralis.