Saint Alphonsus Ligouri, proclaimed Doctor of the Church in 1871, was the founder of the Redemptorists and one of the church’s greatest moral theologians (he is known as the “patron of moral theologians”). Professor Smith summarizes his views on the issue in question in the following italicized quote:

For instance, in the 1912 edition of Theologia Moralis, Editio Nova by St. Alphonsus Liguori (written in 1748), we read this question: “Whether a man sins mortally by beginning intercourse in the posterior receptacle (the anus), so as to consummate it afterwards in the appropriate receptacle (the vagina)?” The answer given to that question is: “[Various theologians] deny it is a mortal sin as long as there is no danger of pollution [ejaculation outside of the vagina] because all other touches (as they say), even if sexual, are not gravely illicit among spouses. But it is more generally and truly affirmed [to be a mortal sin] by [various theologians], because coitus itself of this kind (even if without insemination) is true sodomy, although not consummated, just as copulation in the natural vessel of another woman is true fornication, even if insemination does not take place.”[1] Liguori supports the view of those who argue that anal penetration as foreplay is a mortal sin.(emphasis added) (http://www.catholiceducation.org/articles/sexuality/se0211.htm)

In his Encyclica Studiorum Ducem, Pope Pius XI presents St. Thomas Aquinas as the church’s preeminent theologian. In paragraph 20 of the encyclical the Pope states: “He also composed a substantial moral theology, capable of directing all human acts in accordance with the supernatural last end of man. And as he is, as We have said, the perfect theologian, so he gives infallible rules and precepts of life….” (see http://www.papalencyclicals.net/Pius11/P11STUDI.HTM). Father Brian Harrison, in the quote which follows, shows how Aquinas saw this sin of sodomitic foreplay as a serious moral violation. Because he explains the matter so well, I quote at length from his article at http://amaiceducation.blogspot.com/2012/04/marital-foreplay-father-david-watt.html

“For one thing, arguments from silence can cut both ways: the silence might also be due to the fact that earlier Catholic bishops and theologians took for granted the sinfulness of such actions, considering them so obviously impure that it was hardly necessary to spell this out in writing. Furthermore, the silence was not total over the centuries. St. Thomas Aquinas, in discussing “the sin against nature” (under which heading he understands the whole ensemble of deviant acts listed near the beginning of my previous paragraph), has a couple of terse remarks that could really only refer to impure and unnatural forms of foreplay. In ST IIa IIae, Q. 154, art. 11, at the end of the corpus, he speaks of a man and woman “not observing the natural manner of copulation, either as to undue means, or as to other monstrous and bestial methods of copulation” (my emphasis). Since these “monstrous and bestial methods”, being clearly the worst of the “either/or” alternatives he has in mind, would have to include consummated (orgasm-attaining) acts of oral and anal sex, what could the previous alternative be (“undue means”) other than unconsummated acts of the same sort? The very end of the next article (Q. 154, art. 12, ad 4) is similar, but clearer. Here Thomas again brands as an unnatural sin the behavior of a man and woman who “do not observe the right manner of copulation”. But he adds that such a sin “is more grievous if the abuse regards the receptacle (vas) than if it affects the manner of copulation in respect of other circumstances”. Now, classical theologians used the word vas to mean the place wherein the semen is deposited in ejaculation. The only “fitting receptacle” was of course the wife’s vagina. Any place else was called an “unfitting receptacle” (vas indebitum). So in saying this kind of sin is more grievous when it involves “abuse regarding the receptacle”, Aquinas clearly means it is more grievous when ejaculation occurs, i.e., when the wife’s mouth or anal cavity in fact becomes a receptacle for the semen. But that in turn can only mean that the less grievous form of this sin – that form which Aquinas has in mind when he mentions “other circumstances” involved in the “manner of copulation” – must be sins in which similar oral or anal contact takes place, but without reaching the point of orgasm on the part of either the male or the female.

And how grave are such sins? These same articles of the Summa make it clear that St. Thomas sees unnatural male-female acts as being the least grievous form of the “sin against nature” except for masturbation. But, like all orthodox Catholic moralists, he considers even unconsummated masturbation to be per se mortally sinful (“grave matter”, in theological language). So does the Catechism of the Catholic Church, which says that masturbation, defined simply as deliberately seeking isolated sexual pleasure from one’s own organs (i.e., with or without reaching orgasm) is “gravely disordered” (no. 2352). So it is clear that Aquinas, even though he does not spell this out, would logically consider even unconsummated oral and anal sex between husband and wife to be mortally sinful, thus creating a need for sincere sacramental confession prior to approaching Holy Communion.)”

From the discussion above, we see that two great moral theologians (probably the two greatest) and Doctors of the Church (not to mention Saints), Saint Alphonsus Ligouri and Saint Thomas Aquinas, view sodomitic foreplay in marriage as a serious violation of the moral law. Vatican II emphasized the virtue of conjugal chastity. The Council stated:

“The sexual characteristics of man and the human faculty of reproduction wonderfully exceed the dispositions of lower forms of life. Hence the acts themselves which are proper to conjugal love and which are exercised in accord with genuine human dignity must be honored with great reverence. Hence when there is question of harmonizing conjugal love with the responsible transmission of life, the moral aspects of any procedure does not depend solely on sincere intentions or on an evaluation of motives, but must be determined by objective standards. These, based on the nature of the human person and his acts, preserve the full sense of mutual self-giving and human procreation in the context of true love. Such a goal cannot be achieved unless the virtue of conjugal chastity is sincerely practiced. Relying on these principles, sons of the Church may not undertake methods of birth control which are found blameworthy by the teaching authority of the Church in its unfolding of the divine law.(14)

All should be persuaded that human life and the task of transmitting it are not realities bound up with this world alone. Hence they cannot be measured or perceived only in terms of it, but always have a bearing on the eternal destiny of men” (emphasis added by underlining) (Gaudium et Spes, n. 51).

Thomas L. Mulcahy, J.D., M.A.