"Whether a man sins mortally by beginning intercourse in the posterior receptacle (the anus)..."
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. 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." Liguori supports the view of those who argue that anal penetration as foreplay is a mortal sin. (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 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 marital+foreplay. - Comment made to my post on the same subject here.
Talk about an adulterous generation!
From the same source, this good news:
Fortunately (in my opinion), a few contemporary Catholic authors are now explicitly endorsing the teaching that Aquinas expresses in veiled, oblique language in the Summa. For instance, Fr. Thomas G. Morrow has stopped holding his breath waiting for the magisterium to speak on this issue. Instead, he has boldly 'taken the plunge' and published an article expressing what millions of devout and chaste married Catholics have undoubtedly intuited over the centuries without ever talking about it (Cf. "Rethinking Marital Foreplay", Homiletic & Pastoral Review, May 2010, pp. 58-63). According to Fr. Morrow, oral and anal foreplay partially simulate unnatural mortals sins, are therefore acts of lust that treat one's spouse as a pleasure object rather than as a person, and consequently do not measure up to true standards of conjugal love and respect for human dignity. Thus, he concludes, such acts "should be considered illicit, in (or out of) marriage" (p. 63).Bravo! I find these considerations, together with the teaching of St. Thomas and my years of confessional experience, strongly persuasive. The total data available to me up till now ground a more probable opinion against that sort of foreplay, even though I can't prove I'm right by citing a magisterial document condemning it. And as a probabiliorist, I will continue to tell Catholics who ask my opinion that those practices are mortal sins against purity and should definitely not be carried out. - Father David Watt, STL (Gregorian), PhD (Cambridge)