I went ahead and translated the entire section On the Sins of Married Persons from the 1866 Compendium Theologiae Moralis, with the footnotes in place. I figured that one footnote by itself wouldn’t be nearly as helpful as seeing it in the full context of the chapter.
So, here it is:
-------------------
Article III — On the Sins of Married Persons
917. Sins may be committed between spouses with regard to the conjugal act, either by excess—that is, by performing acts useless for generation—or by defect, by failing to complete the essential act itself, or by defiling the marriage bed with the crime of onanism. Hence this article is divided into two sections.
§ I. On the Sins of Spouses by Excess.
NOTE. Acts that are apart from intercourse itself but performed on its occasion or under its pretext can be divided into three kinds. (1) Some are harmful to generation, such as sodomy and pollution, and are against nature. (2) Others are useful, such as touches that arouse nature and foster love. (3) Others are neither harmful nor useful and are called beside nature.
918. I. Whatever is necessary for completing the conjugal act, or useful for performing it more easily, quickly, or perfectly, is entirely lawful for spouses. The reason is that whoever has the right to the thing also has the right to the means necessary or useful for it, provided those means are not otherwise prohibited; and for whom the principal thing is lawful, the accessory, as a means ordered to that end, is also lawful.
II. Whatever in the conjugal act harms generation, or of itself brings about pollution outside natural union, is gravely illicit. The reason is that voluntary effusion of seed is lawful only in relation to generation; therefore marriage grants to spouses no right except to that effusion of seed which can of itself serve generation. Otherwise, if men could enjoy the pleasure itself without the consequent burden of nourishing and rearing offspring, the generation of children would easily be neglected, or even deliberately avoided, and thus society itself would tend toward ruin.
III. Whatever indeed does not hinder generation but is of itself less necessary or less useful to the act of generation cannot be imputed as sin except venial; from which, however, such acts are excused by other intrinsic ends, namely, that conjugal affection be preserved and fostered, or at least that concupiscence be quieted (Footnote: Compare what was said above in the note to n. 908, where—from the teaching of Chrysostom and St. Thomas interpreting the Apostle Paul—it was shown that the chief fruit of marriage consists precisely in this: that the ardor of concupiscence be extinguished, and thus a chaste life be led. Concupiscence is extinguished when marriage provides lawful satisfaction to the appetite for pleasure; a chaste life is led when that satisfaction is not sought outside the lawful marriage bed.)—which ends, however, need not be expressly intended, but, as was said above, it suffices that they not be positively excluded.
919. 1°. Among spouses, all honest kisses and touches—even of parts less honest, if done with caution—are without fault when they are given as a sign of conjugal affection or to foster love, even if sometimes by accident an involuntary pollution should follow; for all honest signs of love, even tender ones, are lawful as means to an end for those who by the bond of matrimony ought to become one heart and one flesh. (St. Alphonsus Liguori n. 934 and others commonly.)
2°. Touches and looks that are less modest are likewise in themselves without fault if they are immediately referred to intercourse. Indeed, the same must be held even if they are inherently indecent, provided they are necessary or useful for arousing nature; for then they are a kind of preparation and, as it were, a beginning of the conjugal union. But if acts by which one spouse disposes himself or herself for the conjugal act are such that they easily bring about pollution of themselves, they can be culpable if diligence is lacking to avoid pollution outside intercourse; and this omission of diligence, when such that one might thereby be judged to will pollution, may even be grave fault. If, however, with due diligence employed, pollution follows unintentionally, there is no fault.
(Footnote: The doctrine just stated must be kept in view also regarding the case which the author soon adds—that is, imperfect acts exercised between spouses without intention of intercourse. The author only notes the opinion that does not condemn such acts as gravely sinful. But another opinion, itself quite common (see St. Alphonsus, Lib. 6, n. 931), excuses these acts entirely from fault, even in the one who begins them, if pollution is not intended and there is no danger of consent to it, provided there is some serious reason, e.g., to foster mutual love or to avert the jealousy of the other. And (ibid.) he adds that, probably, even in the one who yields such touches (unless they are such as to appear an initiated pollution), these are licit, even if there be danger of pollution in the other, since the one yielding cooperates in something lawful. This opinion, which St. Alphonsus himself follows (ibid. n. 933), holds even when intercourse is altogether forbidden to the spouses or impossible due to impotence. Regarding the latter, see above note to n. 855. As to the former, the reason for the prohibition must be examined: the rule holds if the ban is for affinity contracted through crime with one’s own wife; otherwise, not, if it be for nullity of marriage. Diana notes similarly (Tom. 2, Tr. 6, Res. 205, n. 2): that if danger of pollution has ceased in both spouses, a husband does not sin mortally if he interrupts begun intercourse before emission to prevent conception, provided it be with the wife’s consent or without her reasonable objection. Indeed, if there is a just cause for preventing emission, e.g., poverty or excessive number of children, and yet they have intercourse to quiet concupiscence, there is no fault if mutual consent is present. Hence even weak spouses who begin intercourse to calm concupiscence and voluntarily do not complete it are not to be condemned even of venial fault; and this may often occur. He then proposes this case: A man begins intercourse with his wife and then, due to danger of illness, withdraws with her consent; pollution sometimes follows. Asked whether such touches are licit, I replied affirmatively: for it is no sin to cooperate in something lawful and honest, even if one foresees pollution, provided there is no danger of consent; because then the pollution is not directly willed nor indirectly willed in its cause, since one is not obliged to omit an otherwise lawful act for fear of pollution, given a just cause. See St. Alphonsus, Vol. 1, note to n. 412, p. 147; Sporer, De Matrimonio n. 500, following Gobat, Theol. Exper. Tr. 10, n. 668–669.)
3°. Spouses do not sin gravely even if, by touches had without intention of intercourse, there arises excitement of the spirits or of the members serving generation, or there follows a slight effusion; although in the unmarried such things would be mortal sins. Reason: with the crimes of voluntary pollution or sodomy excluded, nothing is done against the good of marriage.
(Footnote: The author advances this general principle with deliberate care: that, apart from that disorder which is against nature, scarcely anything can occur between spouses in this matter that can rightly be condemned as a grave sin. Among various authors, one finds some condemning one kind of act as gravely sinful, others condemning another. Yet these are merely particular opinions, not derived from solid and certain principles, but rather from fanciful apprehensions or emotional exaggerations. Some appeal to indecency and turpitude, and, with cries and declamations, they call the acts in question horrendous, abominable, most vile, and so forth — as though the reason for sin or the gravity of guilt were to be sought in the indecency of an act. Yet even the most lawful acts, and indeed those prescribed by nature herself, must, by reason of their natural indecency, be performed in secrecy and darkness. Others appeal to the notion of unbridled lust, as though lust did not show itself most unbridled precisely in that act in which the purpose of marriage is consummated; or as though marriage itself had not been instituted precisely as a remedy for lust; or as though marriage could serve as a remedy for lust in any other way than by allowing that strong desire for pleasure to be satisfied — but only under the condition, as St. Thomas Aquinas notes, that it neither runs beyond the bounds of lawful marriage nor contradicts the natural purpose of generation. In truth, unless one sins against one or the other of these — namely, against the good of fidelity or the good of procreation — no other solid reason appears by which any form of disorder between spouses could certainly be accused as a grave sin. Once this principle is rightly established, it gives the confessor a clear and reliable rule, by which he may protect both the sanctity of the sacrament and the salvation of penitents. The sanctity of the sacrament demands that discussion of these matters occur only under urgent necessity. Hence, the confessor must be entirely averse to prying into such details and should hardly ever ask any question beyond something general, such as whether the penitent’s conscience is troubled by any scruple in this regard — and even that should not be asked without cause. If, however, the penitent raises the matter directly, the confessor must respond. To ensure that such a response is brief, sufficient, and respectful of the sacredness of the sacrament, the rule already stated provides the best possible guidance. The welfare of penitents likewise demands this restraint. For they can easily become troubled by scruples concerning acts which they can scarcely bring themselves to name — and which, in truth, should never be described explicitly by either penitent or confessor. The principle already stated perfectly serves to remove both such scruples and the necessity of naming what modesty forbids to be expressed. Once it is made clear to the penitent that nothing is mortally sinful between spouses unless something is done contrary to the end of marriage or of generation, and that therefore nothing in this regard constitutes matter necessary for confession (though lighter faults may at times occur), all the difficulties mentioned above are effectively resolved. For past actions, once the penitent has confessed in general terms — as is commonly done — to having fallen in some way in this matter, and the confessor, by means of a general question, ascertains that something serious may have been involved, he should immediately refrain from further inquiry. It will suffice for the penitent to confess in general terms, for example: “I have committed a sin against nature,” or, “I have gravely failed in this matter against my conscience.” If necessary, the number of such sins may be asked, and the obligation of confession is thus fully satisfied. For future conduct, the application of this rule prevents penitents from sinning gravely through mere mistaken scrupulosity of conscience, and it also provides an easy means for them to make proper confession if needed. As for venial faults, penitents should be advised in three ways. First, that a spouse is not guilty of even a venial fault if, to avoid offending the other party, he or she passively allows something, not demanding it but merely tolerating it. Second, when that excuse does not apply, and the penitent wishes nonetheless to confess these lighter faults (for confession of venial sins is not obligatory), they should do so in entirely general terms, saying only something such as: “I have been somewhat negligent in the marital duty,” without ever specifying the particular acts involved. The holiness of the sacrament and the danger inherent in such subject matter require that nothing more than what is necessary be expressed. Third, if a penitent should happen to encounter a confessor so imprudent as to ask for further details, the penitent may, and indeed ought, to reply modestly that there is nothing further to be added on that point. Since we are speaking of the necessary caution a confessor must exercise in such matters, it is appropriate to note how he should respond to a woman who is about to be married and is anxious to avoid sin in marital relations. Gobat (Experientia Theologica, Tractate 10, Case 17, nos. 648–649) answers thus: If such a young woman has a living mother, she should be gently advised to speak with her mother about these matters rather than with her confessor (Burghaber adds: or, if not her mother, with another female relative). If she has no mother, or modesty prevents her from asking, the confessor should tell her to obey her husband as her head, even in these matters. If her husband should request something about which she is uncertain, she should gently ask him to refrain; if he insists, claiming that he knows what the laws of marriage permit, she should obey, being assured that she does not offend God when she obeys her superior in a doubtful matter. Later, at the first suitable opportunity, she may ask her confessor privately whether what she consented to was in fact lawful for spouses. Thus, with prudence and restraint, the confessor preserves both the purity of the sacrament and the peace of conscience of the faithful. By holding firmly to the principle that nothing between spouses constitutes a mortal sin of lust except that which gravely violates either fidelity or procreation, he avoids unnecessary questioning, discourages scrupulosity, and upholds both modesty and truth within the sacred forum of confession.)
920. 1°. The wife does not sin gravely—in fact, according to the more common and probable opinion, not even venially—if she excites herself by touch to emission immediately after intercourse in which the husband alone has emitted; (1) because the emission of the wife pertains to the completion of the conjugal act, that spouses may truly be “one flesh”; and just as the wife may prepare herself by touch for intercourse, so also she may complete it; (2) because if women were bound to repress the natural movement following such irritation, they would be continually exposed to great danger of grave sin. (St. Alphonsus n. 919.)
5°. Touch with oneself for venereal pleasure, in the absence of the other spouse, according to the opinion of most authors, cannot be excused from grave sin, even if pollution or its proximate danger be excluded. The reason is that a spouse has no right to use his or her own body in order to satisfy pleasure alone, but only in order to intercourse. (Lacroix n. 339; St. Alphonsus n. 936.) Yet not a few authors cited by St. Alphonsus hold that, pollution being excluded, such fault does not exceed venial sin. St. Alphonsus judges the first opinion more probable and to be recommended.
(Footnote: St. Alphonsus, when he says that this opinion is to be recommended, by no means signifies that confessors should impose on penitents the belief that these acts are mortally sinful; for he sharply rebukes and condemns those who instill consciences with fear of mortal sin when they are not certain of the matter. His meaning is only that penitents should be earnestly deterred from such acts. On this question see Andreas Mendo, Stater. Opin. Diss. 5, Quaest. 19, who presents strong arguments for the contrary view, which are not easily answered.)
6°. Morose delectation (lingering pleasure) over intercourse had or to be had remotely, with pollution excluded, according to the common opinion, is only venial sin. (1) It is some sin, because in this pleasure, not referred to the proximate intercourse, there is found an inordinacy, since the honest end is lacking and the generative faculties are moved in vain, at least inchoatively. (2) It does not exceed venial, because, since intercourse itself is lawful to spouses, it cannot be gravely illicit to delight in it. (Footnote: St. Alphonsus (Lib. 6, n. 937) cites St. Thomas (De Malo, q. 15, a. 2, ad 17): “Pleasures take their moral quality from the acts which cause them; and therefore, just as carnal intercourse is not mortal sin for a married person, but is mortal for an unmarried person, so also there is a similar difference concerning delight and consent in delight. For consent in delight cannot be a graver sin than consent in the act,” as Augustine shows. This argument proves not only that consent in delight (i.e., morose delectation) is not mortal, but even that it is not venial; and this leads directly to the author’s reason: it cannot be gravely illicit to delight in a lawful act, since, as St. Thomas says, “the goodness or badness of delight follows that of the thing in which one delights.”)
§ II. On Onanism in Particular
921. Onanism consists in this: that a man, after beginning intercourse, withdraws before emission and spills the seed outside, in order to prevent generation. Everyone sees that this is to indulge shameful lust without bearing the burdens of marriage. Its name comes from Onan, the second son of the patriarch Judah, who, after his brother Her had died, was obliged by custom to take his brother’s widow Thamar, that he might raise up seed for his brother; but when he went in to his brother’s wife, he spilled his seed upon the ground, lest children be born in his brother’s name. “And therefore the Lord slew him, because he did a detestable thing.” (Genesis 38:9–10.)
§ 922. Points to Be Established
I declare, first: Voluntary onanism is always a mortal sin, as being against nature; therefore, in no case can it ever be lawful for spouses.
The reasons are:
1°. It plainly opposes the primary end of marriage, tends of itself toward the extinction of society, and therefore subverts the natural order.
2°. It was strictly prohibited by the supreme Legislator and Author of nature, as is evident from the text of Genesis just cited.
3°. It is further clear from the forty-ninth proposition condemned by Pope Innocent XI, which reads: “Masturbation is not prohibited by the natural law.”
From this follows: onanism is truly and properly masturbation—that is, pollution outside the lawful use of marriage; therefore, it is gravely sinful.
This is confirmed by various decisions of the Sacred Penitentiary and of the Holy Office, which will be cited below under numbers 927, 928, and 929.
II. I declare, secondly: A husband guilty of onanism can never be excused from grave sin, and therefore can never be absolved unless he sincerely repents of his sin and firmly resolves to avoid it in the future. The reason is clear from what has already been said.
III. I declare, thirdly: The wife can be entirely excused from all sin if, for a serious reason, she renders the marital debt to a husband who practices onanism—provided that she does not interiorly consent to his sin and that she outwardly shows her disapproval by serious admonitions or other clear signs of displeasure.
The reasons are:
1°. She herself is engaging in something lawful, and makes use of her right, of which she cannot be deprived because of her husband’s malice; nor does she cooperate in anything intrinsically evil, since she acts merely passively, and the intrinsically evil act consists only in the husband’s deed, when he departs from the order of nature.
2°. She is not bound by charity to prevent her husband’s sin when doing so would cause her grave inconvenience.
3°. This is evident also from various responses of the Sacred Penitentiary, in which it was declared that such a woman is not to be troubled in conscience. (See the decisions to be cited below under number 931.)
Resolutions
1°. The woman sins gravely who induces her husband to misuse marriage, even indirectly or tacitly—for example, by complaining about the number of children, or about the pains of childbirth or the labor of raising them, or by lamenting that she will die in the next delivery, and so forth. With even greater reason she sins gravely if, against her husband’s will, she withdraws from intercourse once begun before emission has taken place.
2°. Likewise, the woman sins gravely if she interiorly consents to her husband’s detestable action, even if she outwardly shows resistance. For sin must always be hated.
3°. The wife is bound, at least ordinarily, to admonish her onanistic husband of his obligation to act rightly, and, as far as she is able, to turn him away from his perverse habit of acting. Nor is it enough that she admonish him once; while his bad custom continues, she must at times repeat her warnings—unless she is certain that another admonition would in no way be of use. Nevertheless, even then, she is bound to manifest her disapproval in some manner, so that she may not appear willingly to consent to her husband’s sin. This is the common teaching, and such was the reply of the Sacred Penitentiary when consulted on the matter.
4°. It is also the wife’s duty to win over her husband by gentleness, by various signs of affection, by prayers and exhortations, to perform the act rightly, or else to abstain from it altogether. Experience shows that many husbands given to onanism have been brought to amendment of life by their wives in this manner.
What follows are some additional questions on onanism as well as decisions by the Sacred Congregations concerning onanism.
Source
Jean-Pierre Gury (1801–1866); revised and annotated by Antonio Ballerini, S.J. (1805–1881), Compendium Theologiae Moralis, Vol. II (Rome, 1866), p. 808-817.
Available at: https://archive.org/details/compendiumtheol02gury/page/808/mode/2up
-------------------
My Reader's Digest Summary.
From the principles above, it is clear that within marriage, the morality of the conjugal act depends entirely upon its proper ordering toward the twofold good of marriage—fidelity and generation. Whatever directly contradicts the natural order of generation (e.g., onanism; sodomy, i.e., pollution in an undue vessel), or otherwise deliberately frustrates procreation, is intrinsically and gravely sinful.
Whatever violates the good of fidelity—by introducing a third party (even by consent, intention, or imagination), by consenting to acts or thoughts that deny the mutual right, or by refusing that right without just cause—is likewise gravely disordered.
By contrast, all acts that serve as a preparation for the lawful union, even if in themselves less modest or inherently indecent, are permitted when truly directed toward the completion of that union and when care is taken to avoid pollution outside it.
The moderate satisfaction of concupiscence and the fostering of mutual affection, as secondary ends of marriage, excuse lesser imperfections and even elevate conjugal life when governed by charity and modesty. Thus, the rule of conduct for spouses is this: nothing is mortally sinful in the marital act unless it frustrates the end of procreation or violates the good of fidelity; and in all else, prudence, mutual respect, and restraint should preserve both the sanctity of the sacrament and the peace of conscience.
Bottom line: Whatever is done must be ordered to and end in natural intercourse — the one rule.