Summa contra Gentiles3.122 Chapter CXXII. How, according to the divine law, simple fornication is a sin I and that matrimony is natural

Hence it is clear how futile is the reasoning of those who say that simple fornication is no sin. For they say: Take, for instance, a woman who is not bound by the marriage tie, 1 Ch. cxv. 2 Ibid. 3 Ibid.

or under any authority, paternal or otherwise. If with her consent, a man have intercourse with her, he does her no wrong: since she pleases herself, and has the disposal of her own body. He does not wrong a third party: because, in the supposition, she is under no one’s authority. Therefore there is no sin.

Nor, seemingly, is it enough to reply that he does a wrong to God.—Because we do not wrong God unless we wrong our own good as stated above. But this would not seem to be contrary to man’s good. Consequently no wrong, seemingly, is done to God thereby.

Likewise, it would not seem to meet the case if one reply that the man wrongs his neighbour by scandalizing him.—For one may be scandalized at something that is not a sin in itself, so that it becomes a sin accidentally. But the point at issue is whether simple fornication be a sin, not accidentally, but in itself.

Accordingly we must seek the solution from what has been said above. For it has been stated that God cares for everything in respect of what is good for it. Now, it is good foir everything that it obtain its end: and its evil is that it turn from its end. This applies to the parts as well as to the whole: so that man’s every part, even as his every act, should attain to its due end. Now, though the seed be superfluous for the preservation of the individual, it is necessary for the propagation of the species. Other superfluities such as excretions, urine, sweat and the like are not necessary for anything, and so it is only their discharge that is good for man. Seed, however, has another end in view, since it is emitted for the purpose of generation, which is the object of coition. Moreover generation would be in vain, if due nourishment were not to follow: because the offspring would not survive if deprived of its due nourishment. Hence the emission of seed should be ordered in such wise, that befitting generation, and rearing of the offspring may follow.

It is therefore clearly contrary to man’s good that the seed be emitted in such a way that generation cannot ensue:

and if this be done deliberately it must needs be a sin.—I mean, if it be done in a way that is directly opposed to generation, such as every emission of seed without the natural union of male and female: hence sins of this kind are said to be against nature. If, however, it be accidental that generation cannot ensue, it is not on this account contrary to nature, or sinful: for instance if the woman be sterile.

In like manner it must be contrary to man’s good, if, though seed be emitted so that generation can ensue, the proper upbringing of the offspring is hindered. For it must be observed that in those animals in which the female alone suffices for the rearing of the offspring,—dogs for instance—the male and female do not remain together after coition. On the other hand, in all cases in which the female does not suffice to rear the offspring, the male and female remain together after coition, as long as may be necessary for the rearing and development of the young. We have an instance of this in certain birds, whose young are unable to seek food as soon as they are hatched. For since the bird does not feed its young on milk,—which is ready at hand through being prepared by nature, as in the case of quadrupeds—and needs to go in search of food for them, and besides this fosters them by incubation; the female alone would not suffice for all this. Wherefore divine providence has given the male of such animals the natural instinct to remain with the female for the rearing of the offspring.—Now it is clear that in the human species the female is far from sufficing alone for the rearing of the children, since the needs of human life require many things that one person alone cannot provide. It is therefore in keeping with human nature that the man remain with the woman after coition, and not leave her at once, indulging in promiscuous intercourse, as those do who have the habit of fornication.

Nor is this argument weakened because some woman has sufficient means to rear her offspring by herself. Because natural rectitude in human acts depends, not on what is accidentally in one individual but on that which is proper to the whole species. Again, we must observe that, in the human species, the offspring needs not only nourishment for its body, as with other animals, but also instruction for its soul. For other animals have their natural forethought which enables them to provide for themselves: whereas man lives by reason, which can attain to forethought only after long experience: so that children need to be instructed by their parents who are experienced.

Moreover children are not capable of this instruction as soon as they are bom, but only after a long time, and especially when they reach the age of discretion. Besides, this instruction requires a long time. And even then, on account of the assaults of the passions whereby the judgement of prudence is perverted, they need not only instruction but correction. Now a woman is insufficient for these things, in fact there is more need for a man for such things, for his reason is more perfect for instruction, and his arm is stronger for punishment. Consequently a short space of time such as suffices for birds is not sufficient for the education of the offspring in the human species, and a great part of life is required for the purpose. So that, as in all animals it behoves the male to remain with the female as long as the father is needed by the offspring, it is natural in the human race that the man should have not a short-lived but a lasting fellowship with a definite woman: and this fellowship is called matrimony. Therefore matrimony is natural to man: and the intercourse of fornication, which is apart from matrimony, is contrary to man’s good. For this reason it must needs be a sin.

Moreover, the emission of seed without the requisite intention of procreation and education, must not be thought a slight sin, for that it is a small sin, or none at all, to use some part of one’s body for some other purpose than that for which nature intended it: for instance if one walk on one’s hands, or use one’s feet to do what the hands should do. Because by suchlike actions man’s good is not prejudiced very much; whereas the inordinate discharge of semen is perversive of a natural good, which is the preservation of the species. Wherefore, after the sin of murder, in. u whereby human nature is deprived of actual existence, this kind of sin, whereby the generation of human nature is hindered, holds, seemingly, the second place.

The foregoing conclusions are confirmed by divine authority. That the discharge of semen in such wise that no offspring can ensue, is unlawful, is clear from the words of Levit. xviii. 22, 23: Thou shalt not lie with mankind as with womankind... thou shalt not copulate with any beast; and of 1 Cor. vi. 10: Nor the effeminate, nor Hers with mankind... shall possess the kingdom of God.

Again, that fornication and all intercourse with other than one’s own wife, is unlawful, is evident from the words of Deut. xxiii. 17: There shall be no whore among the daughters of Israel, nor whoremonger among the sons of Israel: and of Job iv. 13: Take heed to keep thyself... from all fornication, and beside thy wife never endure to know a crime: and of 1 Cor. vi. 18: Fly fornication.

Hereby we exclude the error of those who denied that there was a greater sin in the emission of seed than in the discharge of other superfluities: and of those who said that fornication is no sin.