Chapter 122 — How simple fornication is a sin according to the divine law, 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, or under any authority, paternal or otherwise. If a man have intercourse with her with her consent, 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. (Ch. 121.) But this would not seem to be contrary to man’s good. Consequently, no wrong seems to be done to God thereby.

Likewise, it would not seem to meet the case if one reply that the man wrongs his neighbor 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 (Ch. 112. seqq.) that God cares for everything in respect of what is good for it. Now, it is good for 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 intercourse. 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 a way that suitable generation and education 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: if this be done deliberately it must 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 intercourse. 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 intercourse 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, as in the case of quadrupeds, is ready at hand through being prepared by nature—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. Therefore, 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 intercourse, and not leave her at once, indifferent as to what happens, as do fornicators.

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, but man lives by reason, which can attain to forethought only after long experience. Thus children need to be instructed by their parents, who are experienced. Moreover, children are not capable of this instruction as soon as they are born, 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 judgment of prudence is perverted, (Nicomachean Ethics 6.5.) 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. Thus as in all animals the male must 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: 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 be a sin.

Moreover, the emission of seed without the requisite intention of procreation and education must not be thought a slight sin because 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. For by such actions man’s good is not prejudiced very much; but the inordinate discharge of semen is perversive of a natural good, which is the preservation of the species. Therefore, after the sin of murder, whereby human nature is deprived of actual existence, this kind of sin, whereby the generation of human nature is hindered, seems to hold the second place.

The foregoing conclusions are confirmed by divine authority. That the discharge of semen in such a way that no offspring can ensue is unlawful is clear from the words of Lev 18:22–23: You shall not lie with a male as with a woman, and: You shall not lie with any beast; and of 1 Cor 6:9–10: Neither the effeminate nor sodomites . . . 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 Deuternomy 23:17: There shall be no prostitute of the daughters of Israel; neither shall there be a whoremonger of the sons of Israel. And: Take heed to keep yourself from all fornication, and beside your wife never endure to know a crime (Tob 4:13). And: Fly fornication (1 Cor 6:18).

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.