Whether the lust that is about venereal acts can be a sin?
Objection 1: It would seem that lust about venereal acts cannot be a sin. For the venereal act consists in the emission of semen which is the surplus from food, according to the Philosopher (De Gener. Anim. i, 18). But there is no sin attaching to the emission of other superfluities. Therefore neither can there be any sin in venereal acts.
Objection 2: Further, everyone can lawfully make what use he pleases of what is his. But in the venereal act a man uses only what is his own, except perhaps in adultery or rape. Therefore there can be no sin in venereal acts, and consequently lust is no sin.
Objection 3: Further, every sin has an opposite vice. But, seemingly, no vice is opposed to lust. Therefore lust is not a sin.
On the contrary, The cause is more powerful than its effect. Now wine is forbidden on account of lust, according to the saying of the Apostle ( Eph. 5:18 ), "Be not drunk with wine wherein is lust [Douay: 'luxury']." Therefore lust is forbidden.
Further, it is numbered among the works of the flesh: Gal. 5:19 [Douay: 'luxury'].
I answer that, The more necessary a thing is, the more it behooves one to observe the order of reason in its regard; wherefore the more sinful it becomes if the order of reason be forsaken. Now the use of venereal acts, as stated in the foregoing Article, is most necessary for the common good, namely the preservation of the human race. Wherefore there is the greatest necessity for observing the order of reason in this matter: so that if anything be done in this connection against the dictate of reason's ordering, it will be a sin. Now lust consists essentially in exceeding the order and mode of reason in the matter of venereal acts. Wherefore without any doubt lust is a sin.
Reply to Objection 1: As the Philosopher says in the same book (De Gener. Anim. i, 18), "the semen is a surplus that is needed." For it is said to be superfluous, because it is the residue from the action of the nutritive power, yet it is needed for the work of the generative power. But the other superfluities of the human body are such as not to be needed, so that it matters not how they are emitted, provided one observe the decencies of social life. It is different with the emission of semen, which should be accomplished in a manner befitting the end for which it is needed.
Reply to Objection 2: As the Apostle says ( 1 Cor. 6:20 ) in speaking against lust, "You are bought with a great price: glorify and bear God in your body." Wherefore by inordinately using the body through lust a man wrongs God Who is the Supreme Lord of our body. Hence Augustine says (De Decem. Chord. 10 [*Serm. ix (xcvi de Temp.)]): "God Who thus governs His servants for their good, not for His, made this order and commandment, lest unlawful pleasures should destroy His temple which thou hast begun to be."
Reply to Objection 3: The opposite of lust is not found in many, since men are more inclined to pleasure. Yet the contrary vice is comprised under insensibility, and occurs in one who has such a dislike for sexual intercourse as not to pay the marriage debt.
Whether lust is a capital vice?
Objection 1: It seems that lust is not a capital vice. For lust is apparently the same as "uncleanness," according to a gloss on Eph. 5:3 (Cf. 2 Cor. 12:21 ). But uncleanness is a daughter of gluttony, according to Gregory (Moral. xxxi, 45). Therefore lust is not a capital vice.
Objection 2: Further, Isidore says (De Summo Bono ii, 39) that "as pride of mind leads to the depravity of lust, so does humility of mind safeguard the chastity of the flesh." Now it is seemingly contrary to the nature of a capital vice to arise from another vice. Therefore lust is not a capital vice.
Objection 3: Further, lust is caused by despair, according to Eph. 4:19, "Who despairing, have given themselves up to lasciviousness." But despair is not a capital vice; indeed, it is accounted a daughter of sloth, as stated above (Q[35], A[4], ad 2). Much less, therefore, is lust a capital vice.
On the contrary, Gregory (Moral. xxxi, 45) places lust among the capital vices.
I answer that, As stated above (Q[148], A[5]; FS, Q[84], AA[3],4), a capital vice is one that has a very desirable end, so that through desire for that end, a man proceeds to commit many sins, all of which are said to arise from that vice as from a principal vice. Now the end of lust is venereal pleasure, which is very great. Wherefore this pleasure is very desirable as regards the sensitive appetite, both on account of the intensity of the pleasure, and because such like concupiscence is connatural to man. Therefore it is evident that lust is a capital vice.
Reply to Objection 1: As stated above (Q[148], A[6]), according to some, the uncleanness which is reckoned a daughter of gluttony is a certain uncleanness of the body, and thus the objection is not to the point. If, however, it denote the uncleanness of lust, we must reply that it is caused by gluttony materially---in so far as gluttony provides the bodily matter of lust---and not under the aspect of final cause, in which respect chiefly the capital vices are said to be the cause of others.
Reply to Objection 2: As stated above (Q[132], A[4], ad 1), when we were treating of vainglory, pride is accounted the common mother of all sins, so that even the capital vices originate therefrom.
Reply to Objection 3: Certain persons refrain from lustful pleasures chiefly through hope of the glory to come, which hope is removed by despair, so that the latter is a cause of lust, as removing an obstacle thereto, not as its direct cause; whereas this is seemingly necessary for a capital vice.
Whether the daughters of lust are fittingly described?
Objection 1: It would seem that the daughters of lust are unfittingly reckoned to be "blindness of mind, thoughtlessness, inconstancy, rashness, self-love, hatred of God, love of this world and abhorrence or despair of a future world." For mental blindness, thoughtlessness and rashness pertain to imprudence, which is to be found in every sin, even as prudence is in every virtue. Therefore they should not be reckoned especially as daughters of lust.
Objection 2: Further, constancy is reckoned a part of fortitude, as stated above (Q[128], ad 6; Q[137], A[3]). But lust is contrary, not to fortitude but to temperance. Therefore inconstancy is not a daughter of lust.
Objection 3: Further, "Self-love extending to the contempt of God" is the origin of every sin, as Augustine says (De Civ. Dei xiv, 28). Therefore it should not be accounted a daughter of lust.
Objection 4: Further, Isidore [*QQ. in Deut., qu. xvi] mentions four, namely, "obscene," "scurrilous," "wanton" and "foolish talking." There the aforesaid enumeration would seem to be superfluous.
On the contrary, stands the authority of Gregory (Moral. xxxi, 45).