Thomas Aquinas, Summa Theologiae

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 ." Therefore lust is forbidden.

Further, it is numbered among the works of the flesh: Gal. 5:19 .

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 ): "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.

Articulus 3

Argumentum 1

Ad tertium sic proceditur. Videtur quod luxuria quae est circa actus venereos, non possit esse aliquod peccatum. Per actum enim venereum semen emittitur, quod est superfluum alimenti, ut patet per philosophum, in libro de generat. Animal..

Sed in emissione aliarum superfluitatum non attenditur aliquod peccatum. Ergo neque circa actus venereos potest esse aliquod peccatum.

Argumentum 2

Praeterea, quilibet potest licite uti ut libet, eo quod suum est.

Sed in actu venereo homo non utitur nisi eo quod suum est, nisi forte in adulterio vel raptu. Ergo in usu venereo non potest esse peccatum. Et ita luxuria non erit peccatum.

Argumentum 3

Praeterea, omne peccatum habet vitium oppositum. Sed luxuriae nullum vitium videtur esse oppositum.

Ergo luxuria non est peccatum.

Sed Contra 1

Sed contra est quod causa est potior effectu. Sed vinum prohibetur propter luxuriam, secundum illud apostoli, Ephes. V, nolite inebriari vino, in quo est luxuria.

Ergo luxuria est prohibita.

Sed Contra 2

Praeterea, Galat. V, enumeratur inter opera carnis.

Corpus

Respondeo dicendum quod quanto aliquid est magis necessarium, tanto magis oportet ut circa illud rationis ordo servetur.

Unde per consequens magis est vitiosum si ordo rationis praetermittatur. Usus autem venereorum, sicut dictum est, est valde necessarius ad bonum commune, quod est conservatio humani generis. Et ideo circa hoc maxime attendi debet rationis ordo. Et per consequens, si quid circa hoc fiat praeter id quod ordo rationis habet, vitiosum erit. Hoc autem pertinet ad rationem luxuriae, ut ordinem et modum rationis excedat circa venerea.

Et ideo absque dubio luxuria est peccatum.

Ad 1

Ad primum ergo dicendum quod, sicut philosophus, in eodem libro, dicit, semen est superfluum quo indigetur, dicitur enim superfluum ex eo quod residuum est operationis virtutis nutritivae, tamen indigetur eo ad opus virtutis generativae.

Sed aliae superfluitates humani corporis sunt quibus non indigetur. Et ideo non refert qualitercumque emittantur, salva decentia convictus humani. Sed non est simile in seminis emissione, quae taliter debet fieri ut conveniat fini ad quem eo indigetur.

Ad 2

Ad secundum dicendum quod, sicut apostolus dicit, I ad Cor. VI, contra luxuriam loquens, empti estis pretio magno.

Glorificate ergo et portate deum in corpore vestro.

Ex eo ergo quod aliquis inordinate suo corpore utitur per luxuriam, iniuriam facit domino, qui est principalis dominus corporis nostri.

Unde et Augustinus dicit, in libro de decem chordis, dominus, qui gubernat servos suos ad utilitatem illorum, non suam, hoc praecepit, ne per illicitas voluptates corruat templum eius, quod esse coepisti.

Ad 3

Ad tertium dicendum quod oppositum luxuriae non contingit in multis, eo quod homines magis sint proni ad delectationes. Et tamen oppositum vitium continetur sub insensibilitate. Et accidit hoc vitium in eo qui in tantum detestatur mulierum usum quod etiam uxori debitum non reddit.