Note: I've occasionally deleted some or all of the objections.
Objection 2: Further, any excess that makes one forsake the good of reason is sinful, because virtue is corrupted by "excess" and "deficiency" as stated in Ethic. ii, 2. Now in every venereal act there is excess of pleasure, since it so absorbs the mind, that "it is incompatible with the act of understanding," as the Philosopher observes (Ethic. vii, 11); and as Jerome [*Origen, Hom. vi in Num.; Cf. Jerome, Ep. cxxiii ad Ageruch.] states, rendered the hearts of the prophets, for the moment, insensible to the spirit of prophecy. Therefore no venereal act can be without sin.
Objection 3: Further, the cause is more powerful than its effect. Now original sin is transmitted to children by concupiscence, without which no venereal act is possible, as Augustine declares (De Nup. et Concup. i, 24). Therefore no venereal act can be without sin.
On the contrary, Augustine says (De Bono Conjug. xxv): "This is a sufficient answer to heretics, if only they will understand that no sin is committed in that which is against neither nature, nor morals, nor a commandment": and he refers to the act of sexual intercourse between the patriarchs of old and their several wives. Therefore not every venereal act is a sin.
I answer that, A sin, in human acts, is that which is against the order of reason. Now the order of reason consists in its ordering everything to its end in a fitting manner. Wherefore it is no sin if one, by the dictate of reason, makes use of certain things in a fitting manner and order for the end to which they are adapted, provided this end be something truly good. Now just as the preservation of the bodily nature of one individual is a true good, so, too, is the preservation of the nature of the human species a very great good. And just as the use of food is directed to the preservation of life in the individual, so is the use of venereal acts directed to the preservation of the whole human race. Hence Augustine says (De Bono Conjug. xvi): "What food is to a man's well being, such is sexual intercourse to the welfare of the whole human race." Wherefore just as the use of food can be without sin, if it be taken in due manner and order, as required for the welfare of the body, so also the use of venereal acts can be without sin, provided they be performed in due manner and order, in keeping with the end of human procreation.
Reply to Objection 2: As stated above (Question , Article , ad 2; FS, Question , Article ), the mean of virtue depends not on quantity but on conformity with right reason: and consequently the exceeding pleasure attaching to a venereal act directed according to reason, is not opposed to the mean of virtue. Moreover, virtue is not concerned with the amount of pleasure experienced by the external sense, as this depends on the disposition of the body; what matters is how much the interior appetite is affected by that pleasure. Nor does it follow that the act in question is contrary to virtue, from the fact that the free act of reason in considering spiritual things is incompatible with the aforesaid pleasure. For it is not contrary to virtue, if the act of reason be sometimes interrupted for something that is done in accordance with reason, else it would be against virtue for a person to set himself to sleep. That venereal concupiscence and pleasure are not subject to the command and moderation of reason, is due to the punishment of the first sin, inasmuch as the reason, for rebelling against God, deserved that its body should rebel against it, as Augustine says (De Civ. Dei xiii, 13).
Reply to Objection 3: As Augustine says (De Civ. Dei xiii, 13), "the child, shackled with original sin, is born of fleshly concupiscence (which is not imputed as sin to the regenerate) as of a daughter of sin." Hence it does not follow that the act in question is a sin, but that it contains something penal resulting from the first sin.
Objection 4: Further, every mortal sin is contrary to charity. But simple fornication is not contrary to charity, neither as regards the love of God, since it is not a sin directly against. God, nor as regards the love of our neighbor, since thereby no one is injured. Therefore simple fornication is not a mortal sin.
Objection 5: Further, every mortal sin leads to eternal perdition. But simple fornication has not this result: because a gloss of Ambrose [*The quotation is from the Gloss of Peter Lombard, who refers it to St. Ambrose: whereas it is from Hilary the deacon] on 1 Tim. 4:8, "Godliness is profitable to all things," says: "The whole of Christian teaching is summed up in mercy and godliness: if a man conforms to this, even though he gives way to the inconstancy of the flesh, doubtless he will be punished, but he will not perish." Therefore simple fornication is not a mortal sin.
Objection 6: Further, Augustine says (De Bono Conjug. xvi) that "what food is to the well-being of the body, such is sexual intercourse to the welfare of the human race." But inordinate use of food is not always a mortal sin. Therefore neither is all inordinate sexual intercourse; and this would seem to apply especially to simple fornication, which is the least grievous of the aforesaid species.
On the contrary, It is written (Tob. 4:13): "Take heed to keep thyself . . . from all fornication, and beside thy wife never endure to know a crime." Now crime denotes a mortal sin. Therefore fornication and all intercourse with other than one's wife is a mortal sin.
Further, nothing but mortal sin debars a man from God's kingdom. But fornication debars him, as shown by the words of the Apostle (Gal. 5:21), who after mentioning fornication and certain other vices, adds: "They who do such things shall not obtain the kingdom of God." Therefore simple fornication is a mortal sin.
Further, it is written in the Decretals (XXII, qu. i, can. Praedicandum): "They should know that the same penance is to be enjoined for perjury as for adultery, fornication, and wilful murder and other criminal offenses." Therefore simple fornication is a criminal or mortal sin.
I answer that, Without any doubt we must hold simple fornication to be a mortal sin, notwithstanding that a gloss [*St. Augustine, Questions. in Deut., qu. 37] on Dt. 23:17, says: "This is a prohibition against going with whores, whose vileness is venial." For instead of "venial" it should be "venal," since such is the wanton's trade. In order to make this evident, we must take note that every sin committed directly against human life is a mortal sin. Now simple fornication implies an inordinateness that tends to injure the life of the offspring to be born of this union. For we find in all animals where the upbringing of the offspring needs care of both male and female, that these come together not indeterminately, but the male with a certain female, whether one or several; such is the case with all birds: while, on the other hand, among those animals, where the female alone suffices for the offspring's upbringing, the union is indeterminate, as in the case of dogs and like animals. Now it is evident that the upbringing of a human child requires not only the mother's care for his nourishment, but much more the care of his father as guide and guardian, and under whom he progresses in goods both internal and external. Hence human nature rebels against an indeterminate union of the sexes and demands that a man should be united to a determinate woman and should abide with her a long time or even for a whole lifetime. Hence it is that in the human race the male has a natural solicitude for the certainty of offspring, because on him devolves the upbringing of the child: and this certainly would cease if the union of sexes were indeterminate.
This union with a certain definite woman is called matrimony; which for the above reason is said to belong to the natural law. Since, however, the union of the sexes is directed to the common good of the whole human race, and common goods depend on the law for their determination, as stated above (FS, Question , Article ), it follows that this union of man and woman, which is called matrimony, is determined by some law. What this determination is for us will be stated in the Third Part of this work (XP, Question , seqq.), where we shall treat of the sacrament of matrimony. Wherefore, since fornication is an indeterminate union of the sexes, as something incompatible with matrimony, it is opposed to the good of the child's upbringing, and consequently it is a mortal sin.
Nor does it matter if a man having knowledge of a woman by fornication, make sufficient provision for the upbringing of the child: because a matter that comes under the determination of the law is judged according to what happens in general, and not according to what may happen in a particular case.
Reply to Objection 4: Simple fornication is contrary to the love of our neighbor, because it is opposed to the good of the child to be born, as we have shown, since it is an act of generation accomplished in a manner disadvantageous to the future child.
Reply to Objection 5: A person, who, while given to works of piety, yields to the inconstancy of the flesh, is freed from eternal loss, in so far as these works dispose him to receive the grace to repent, and because by such works he makes satisfaction for his past inconstancy; but not so as to be freed by pious works, if he persist in carnal inconstancy impenitent until death.
Reply to Objection 6: One copulation may result in the begetting of a man, wherefore inordinate copulation, which hinders the good of the future child, is a mortal sin as to the very genus of the act, and not only as to the inordinateness of concupiscence. On the other hand, one meal does not hinder the good of a man's whole life, wherefore the act of gluttony is not a mortal sin by reason of its genus. It would, however, be a mortal sin, if a man were knowingly to partake of a food which would alter the whole condition of his life, as was the case with Adam.
Nor is it true that fornication is the least of the sins comprised under lust, for the marriage act that is done out of sensuous pleasure is a lesser sin.
I answer that, Adultery, as its name implies, "is access to another's marriage-bed [ad alienum torum]" [*Cf. Append. Gratian, ad can. Ille autem. xxxii, qu. 1]. By so doing a man is guilty of a twofold offense against chastity and the good of human procreation. First, by accession to a woman who is not joined to him in marriage, which is contrary to the good of the upbringing of his own children. Secondly, by accession to a woman who is united to another in marriage, and thus he hinders the good of another's children. The same applies to the married woman who is corrupted by adultery. Wherefore it is written (Ecclus. 23:32,33): "Every woman . . . that leaveth her husband . . . shall be guilty of sin. For first she hath been unfaithful to the law of the Most High" (since there it is commanded: "Thou shalt not commit adultery"); "and secondly, she hath offended against her husband," by making it uncertain that the children are his: "thirdly, she hath fornicated in adultery, and hath gotten children of another man," which is contrary to the good of her offspring. The first of these, however, is common to all mortal sins, while the two others belong especially to the deformity of adultery. Hence it is manifest that adultery is a determinate species of lust, through having a special deformity in venereal acts.
The following texts are from the Supplement to the Summa. This was completed after St. Thomas's death by one of his students, but is based on Thomas's ideas.
On the contrary, It is by relation that things are related to one another. Now by matrimony certain things are related to one another; for the husband is the wife's husband, and the wife is the husband's wife. Therefore matrimony is a kind of relation, nor is it other than a joining.
Further, the union of two things into one can result only from their being joined. Now such is the effect of matrimony (Gn. 2:24): "They shall be two in one flesh." Therefore matrimony is a kind of joining.
I answer that, A joining denotes a kind of uniting, and so wherever things are united there must be a joining. Now things directed to one purpose are said to be united in their direction thereto, thus many men are united in following one military calling or in pursuing one business, in relation to which they are called fellow-soldiers or business partners. Hence, since by marriage certain persons are directed to one begetting and upbringing of children, and again to one family life, it is clear that in matrimony there is a joining in respect of which we speak of husband and wife; and this joining, through being directed to some one thing, is matrimony; while the joining together of bodies and minds is a result of matrimony.
Objection 1: It would seem that consent is not the efficient cause of matrimony. For the sacraments depend not on the human will but on the Divine institution, as shown above (Sent. iv, D, 2; TP, Question , Article ). But consent belongs to the human will. Therefore it is no more the cause of matrimony than of the other sacraments.
On the contrary, Chrysostom [*Hom. xxxii in the Opus Imperfectum, falsely ascribed to St. John Chrysostom] says: "It is not coition but consent that makes a marriage."
Further, one person does not receive power over that which is at the free disposal of another, without the latter's consent. Now by marriage each of the married parties receives power over the other's body (1 Cor. 7:4), whereas hitherto each had free power over his own body. Therefore consent makes a marriage.
I answer that, In every sacrament there is a spiritual operation by means of a material operation which signifies it; thus in Baptism the inward spiritual cleansing is effected by a bodily cleansing. Wherefore, since in matrimony there is a kind of spiritual joining together, in so far as matrimony is a sacrament, and a certain material joining together, in so far as it is directed to an office of nature and of civil life, it follows that the spiritual joining is the effect of the Divine power by means of the material joining. Therefore seeing that the joinings of material contracts are effected by mutual consent, it follows that the joining together of marriage is effected in the same way.
Reply to Objection 1: The first cause of the sacraments is the Divine power which works in them the welfare of the soul; but the second or instrumental causes are material operations deriving their efficacy from the Divine institution, and thus consent is the cause in matrimony.
Objection 1: It would seem that even in the absence of inward consent a marriage is made by consent expressed in words of the present. For "fraud and deceit should benefit no man," according to the law (cap. Ex Tenore, De Rescrip., cap. Si Vir, De cognat. spir.). Now he who gives consent in words without consenting in heart commits a fraud. Therefore he should not benefit by it, through being released of the bond of marriage.
Objection 2: Further, the mental consent of one person cannot be known to another, except in so far as it is expressed in words. If then the expression of the words is not enough, and inward consent is required in both parties, neither of them will be able to know that he is truly married to the other; and consequently whenever he uses marriage he will commit fornication.
On the contrary, Innocent III says in a Decretal (cap. Tua Nos, De Spons. et matr.) in reference to this case: "Other things cannot complete the marriage bond in the absence of consent."
Further, intention is necessary in all the sacraments. Now he who consents not in his heart has no intention of contracting marriage; and therefore he does not contract a marriage.
I answer that, The outward cleansing stands in the same relation to baptism as the expression of words to this sacrament, as stated above (Article ). Wherefore just as were a person to receive the outward cleansing, with the intention, not of receiving the sacrament, but of acting in jest or deceit, he would not be baptized; so, too, expression of words without inward consent makes no marriage.
Reply to Objection 1: There are two things here, namely the lack of consent---which benefits him in the tribunal of his conscience so that he is not bound by the marriage tie, albeit not in the tribunal of the Church where judgment is pronounced according to the evidence---and the deceit in the words, which does not benefit him, neither in the tribunal of his conscience nor in the tribunal of the Church, since in both he is punished for this.
Reply to Objection 2: If mental consent is lacking in one of the parties, on neither side is there marriage, since marriage consists in a mutual joining together, as stated above (Question , Article ). However one may believe that in all probability there is no fraud unless there be evident signs thereof; because we must presume good of everyone, unless there be proof of the contrary. Consequently the party in whom there is no fraud is excused from sin on account of ignorance.
Objection 1: It would seem that compulsory consent does not invalidate a marriage. For just as consent is necessary for matrimony, so is intention necessary for Baptism. Now one who is compelled by fear to receive Baptism, receives the sacrament. Therefore one who is compelled by fear to consent is bound by his marriage.
Objection 2: Further, according to the Philosopher (Ethic. iii, 1), that which is done on account of mixed violence is more voluntary than involuntary. Now consent cannot be compelled except by mixed violence. Therefore it is not entirely involuntary, and consequently the marriage is valid.
On the contrary, A Decretal says (cap. Cum locum, De sponsal. et matrim.): "Since there is no room for consent where fear or compulsion enters in, it follows that where a person's consent is required, every pretext for compulsion must be set aside." Now mutual contract is necessary in marriage. Therefore, etc.
Further, Matrimony signifies the union of Christ with the Church, which union is according to the liberty of love. Therefore it cannot be the result of compulsory consent.
I answer that, The marriage bond is everlasting. Hence whatever is inconsistent with its perpetuity invalidates marriage. Now the fear which compels a constant man deprives the contract of its perpetuity, since its complete rescission can be demanded. Wherefore this compulsion by fear which influences a constant man, invalidates marriage, but not the other compulsion. Now a constant man is reckoned a virtuous man who, according to the Philosopher (Ethic. iii, 4), is a measure in all human actions.
However, some say that if there be consent although compulsory, the marriage is valid in conscience and in God's sight, but not in the eyes of the Church, who presumes that there was no inward consent on account of the fear. But this is of no account, because the Church should not presume a person to sin until it be proved; and he sinned if he said that he consented whereas he did not consent. Wherefore the Church presumes that he did consent, but judges this compulsory consent to be insufficient for a valid marriage.
Reply to Objection 1: The intention is not the efficient cause of the sacrament in baptism, it is merely the cause that elicits the action of the agent; whereas the consent is the efficient cause in matrimony. Hence the comparison fails.
Reply to Objection 2: Not any kind of voluntariness suffices for marriage: it must be completely voluntary, because it has to be perpetual; and consequently it is invalidated by violence of a mixed nature.
I answer that, No wise man should allow himself to lose a thing except for some compensation in the shape of an equal or better good. Wherefore for a thing that has a loss attached to it to be eligible, it needs to have some good connected with it, which by compensating for that loss makes that thing ordinate and right. Now there is a loss of reason incidental to the union of man and woman, both because the reason is carried away entirely on account of the vehemence of the pleasure, so that it is unable to understand anything at the same time, as the Philosopher says (Ethic. vii, 11); and again because of the tribulation of the flesh which such persons have to suffer from solicitude for temporal things (1 Cor. 7:28). Consequently the choice of this union cannot be made ordinate except by certain compensations whereby that same union is righted. and these are the goods which excuse marriage and make it right.
Objection 1: It would seem that the goods of marriage are insufficiently enumerated by the Master (Sent. iv, D, 31), namely "faith, offspring, and sacrament." For the object of marriage among men is not only the begetting and feeding of children, but also the partnership of a common life, whereby each one contributes his share of work to the common stock, as stated in Ethic. viii, 12. Therefore as the offspring is reckoned a good of matrimony, so also should the communication of works.
I answer that, Matrimony is instituted both as an office of nature and as a sacrament of the Church. As an office of nature it is directed by two things, like every other virtuous act. one of these is required on the part of the agent and is the intention of the due end, and thus the "offspring" is accounted a good of matrimony; the other is required on the part of the act, which is good generically through being about a due matter; and thus we have "faith," whereby a man has intercourse with his wife and with no other woman. Besides this it has a certain goodness as a sacrament, and this is signified by the very word "sacrament."
Reply to Objection 1: Offspring signifies not only the begetting of children, but also their education, to which as its end is directed the entire communion of works that exists between man and wife as united in marriage, since parents naturally "lay up" for their "children" (2 Cor. 12:14); so that the offspring like a principal end includes another, as it were, secondary end.