Saint Alphonsus Liguori on Marital Chastity

The work titled “Moral Theology” by Saint Alphonsus Liguori contains a few brief passages on marital chastity, that is to say, on which types of sexual acts are permissible in marriage. Of course, all sexual acts are prohibited outside of marriage.

The work in question is ten thick volumes entirely in Latin. There exists no English translation, of which I am aware. The work is a review of opinions by theologians on various moral questions. A question is stated, and then differing answers found among various authors are explained. However, the vast majority of these authors and their cited works are lost in obscurity. The main purpose of the work is to survey opinions of Catholic theologians and authors on various topics in moral theology. So the mere fact that a position is stated in “Moral Theology” does not imply the opinion is sound. Even so, at certain points in the work, Saint Alphonsus Liguori states his own understanding of the topic, rejecting one answer and affirming another.

Book 6, Q. 919

An autem, si vir se retrahat post seminationem, sed ante seminationem mulieris, possit ipsa statim tactibus se excitare, ut seminet?
“Ratio, quia semen mulieris non est necessarium ad generationem; item quia effusio illa mulieris, utpote separata, non fit una caro cum viro.

“Then, if the husband withdraws after climax, but before the climax of the wife, whether it is possible for her to immediately excite herself with touches so as to climax?”

Several cited authors answer “No”, saying that it is not licit for the wife to touch herself in this way. “The reason is that the climax of the wife is not necessary to procreation, and also because the climax of the wife, occurring while separated, is not of one flesh with the husband.”

Saint Alphonsus then cites some authors who answer the question “Yes”, but he rejects their answer saying: “this reason is not persuasive, for if this is permitted to the wife, it ought to be permitted also to the husband.” So Saint Alphonsus agrees with the authors who answered “No”.

From the above text, we can conclude that the Saint rejected the idea of a wife using any technique, whether touches or any other means, to reach climax, after the husband withdraws. For then the two are not one flesh, and so the unitive meaning is absent from the sexual act. In addition, such a sexual act apart from union is also not procreative. The absence of the unitive and procreative meanings is what makes such a sexual act gravely immoral.

Alphonsus does not accept the idea that the wife has a right to obtain sexual pleasure, regardless of the means, as some modern authors imply. Neither does the Saint treat the subsequent act of the wife and the prior act of natural marital relations as if these together constituted “one act”, as other modern authors have claimed.

Moreover, the reasons given by the “No” response, which is the response of the Saint, are completely in accord with the recent teachings of the Magisterium that “each single act”, that is to say, “each and every marital act must of necessity retain its intrinsic relationship to the procreation of human life” and that there is an “inseparable connection, established by God, which man on his own initiative may not break, between the unitive significance and the procreative significance which are both inherent to the marriage act.” [Pope Paul VI, Humanae Vitae, n. 3, 11, 12]

Book 6, Q. 916

In this question, Saint Alphonsus rejects the proposition, so often asserted today, that the married couple may use unnatural sexual acts, as long as the husband completes the act (i.e. climaxes) only in a subsequent act of natural marital relations.

An peccet mortaliter vir inchoando copulam in vase praepostero , ut postea in vase debito eam consummet?

“Whether it is a mortal sin for the husband to begin copulating in a disordered [perverse] orifice, then afterward consummate the act in the proper orifice?”

This is exactly the idea proposed by foolish commentators today. They claim that all manner of unnatural sexual acts (oral, anal, manual “stimulation”) are justified as long as the husband consummates the act by climaxing only in a subsequent act of natural marital relations. And what answer does Saint Alphonsus give to the question?

First, notice that the question asks if this proposal is a mortal sin. As usual, the Saint cites opinions on both sides of the question, first citing some who say “No”, it is not a mortal sin, as long as there is no “danger of pollution” (i.e. danger of the husband climaxing during the unnatural sexual act), and others who say that there is no mortal sin in any sexual acts between the spouses. But the Saint rejects these opinions.

Saint Alphonsus says: “But they [other cited authors] affirm, commonly and correctly,” that it is a mortal sin. So the Saint states that the correct opinion, which was also the common opinion of the theologians of his day, is that such acts are gravely immoral. The reason he gives is quite compelling:

Ratio, quia ipse hujusmodo coitus (etsi absque seminatione) est vera sodomia, quamvis non consummata, sicut ipsa copula in vase naturali mulieris alienae est vera fornication , licet non adsit seminatio.

“The reason is that this manner of his sexual act (even without climax) is truly sodomy, whether or not it is consummated, just as an act of copulation in the natural orifice of another woman is truly fornication, even if there is no climax.”

So Saint Alphonsus Liguori rejected the idea that unnatural sexual acts are moral to use as foreplay, as long as the husband consummates only in a subsequent natural act. And yet this rejected idea continues to be promoted today, mostly by Catholics who hide behind the anonymity of the internet.


Many different excuses are being used today to give approval to the use of unnatural sexual acts within the Sacrament of holy Matrimony. And whether I present the teachings of Saint Augustine and Saint Aquinas (See this article), or of present-day theologians (same article), or the answers given by Saint Alphonsus, I know that some readers will use the flimsiest excuses to dismiss whatever is said, no matter how compelling. But if anyone offers them a way to justify this type of sin, no matter how ridiculous, they adopt it as if it were dogma.

The first principle of ethics is a sincere conscience, which seeks moral truth with severe intellectual honesty. In most discussion on sexual ethics in general and marital ethics in particular, the persons arguing for the approval of illicit acts lack this sincerity. I suppose that many of these promoters of unnatural sexual acts are themselves committing unnatural sexual acts in their marriages. That is why they seek a theological rationalization for their sins, and why they try so hard to convince others to commit the same sins (to make the behavior seem acceptable). And it is true, but very sad to say, that no theological argument carries any weight with them. They do not accept correction for their sins — neither from the Saints, nor from the Magisterium, nor from Sacred Scripture.

Teachers will have the stricter judgment (cf. James 3:1).

If a married couple unfortunately commit these types of gravely immoral acts, they are responsible before God for their private sins. But when Catholics go online to loudly and repeatedly promote the use of gravely immoral sexual acts within marriage, thereby influencing many marriages (not just their own marriage), the harm is multiplied many times over, and so is the culpability. It is a much graver sin to influence many person to sin mortally, than to commit a single mortal sin yourself. If you sin yourself, you might repent and go to Confession. But if you cause others to sin gravely, and you later repent, how will you undo the damage to those souls?

These false teachers who use the internet to convince many Catholics to sin gravely against the Sacrament of Marriage and against their own bodies will be severely punished by God.

Ronald L. Conte Jr.
Roman Catholic theologian and translator of the Catholic Public Domain Version of the Bible.

Please take a look at this list of my books and booklets, and see if any topic interests you.

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6 Responses to Saint Alphonsus Liguori on Marital Chastity

  1. Dad says:

    If you had decided to cheat on your wife and were aware it was sinful and would jeopardize your marriage, would the plan itself be a sin if the other party backed out and the affair never occurred?

    • Ron Conte says:

      Yes, what you are describing is an interior mortal sin. The interior act (in the mind and heart) of deciding to break the marriage vow and commit adultery is itself a grave sin.

  2. Francisco says:

    To Dad, and adding to what Ron said, yes, it is a sin.

    [Matthew]{5:27} You have heard that it was said to the ancients: ‘You shall not commit adultery.’
    {5:28} But I say to you, that anyone who will have looked at a woman, so as to lust after her, has already committed adultery with her in his heart.

    A similar example is that a sniper wants to murder a person, already has the rifle aiming at the person, but comes the police and apprehends him. Even if he didn’t shoot, he already has sinned in his mind and heart.

    Under the three fonts of morality (1)intention, 2)the moral object, and the 3)consequences): the intention is bad. If one of the three is bad, the whole act is immoral.

    • Ron Conte says:

      Actually, the second font is bad in both examples (adultery, murder). It is not the attainment of the moral object that makes the act inherently evil or inherently good. The knowing deliberate choice of any concrete act intrinsically ordered toward an evil object is necessarily objectively a sin, even if the object is not attained.

  3. Matt says:

    I’m glad that Catholics writers are speaking out against this. A few weeks ago I posted a thread, that you responded to, on Catholic Answers Forum sharing that my girlfriend and I were shocked to see the majority of Catholics online supporting extremely immoral, perverse, and ugly acts like oral sex, anal sex, sex toys, etc. within the marriage bed. Anyone who would think that’s acceptable within a sacramental union has no sense of goodness, sanctity or beauty. Most of the people on CAF seemed to have a vested interest in these practices, so will dismiss or misread the Doctors of the Church purposely. I think it’s the pornography-saturated morality of the general culture influencing Catholics, and getting them hooked on perversion.

    On the related topic of pre-marital chastity, in the view of the Doctors is it considered fornication/violation of chastity for an unmarried couple to engage in French kissing and holding one another (accompanied by sexual feelings)? My confessor says it is a mortal sin but I can’t find any moral theologians that discuss this kind of behavior during a courtship period.

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