Chapter 124 — That matrimony should be the union of one man with one woman

It is also to be observed, that it seems like all animals that are used to copulate have a natural instinct to resist another’s intercourse with their consort: hence animals fight on account of intercourse. And there is one common reason for this as regards all animals, because every animal desires to indulge at will in the pleasure of intercourse, even as in the pleasure of eating. This freedom ceases if many males have access to one female, or vice versa, just as an animal is deprived of the free enjoyment of its food if another animal usurps the food it desires to consume. Hence animals fight both for food and for intercourse. But with regard to men there is a special reason, because, as already stated, (Ch. 123.) man naturally desires to be assured of his offspring, and this assurance would be altogether nullified in the case of promiscuous intercourse. Therefore, the union of one man with one woman comes from a natural instinct.

A difference, however, is to be noted here. For as regards one woman not being united to several men, both the foregoing arguments avail. But as regards one man not being joined to several women, the second argument is of no use, since the certainty of having offspring is not removed if one man be joined to several women. The first argument, however, avails against this: for just as freedom of access to the woman is denied if she have another man, so too the same freedom is denied the woman if the man have several women. Hence, as certainty of having offspring is the chief good sought from marriage, no human law or custom has permitted polyandry. This was considered to be wrong even among the ancient Romans, of whom Maximus Valerius (Maximus Valerius, Facta et Dicta Memorabilia bk. 2, ch. 1.) relates that they deemed that not even on account of sterility should the marriage bond be severed.

Again. In every animal species where the father has a certain care for his offspring, the one male has but one female (as may be seen in birds, where both unite in feeding their young); for one male would not suffice to rear the progeny of several females. On the other hand, where the male animal has not the care of the offspring, we indifferently find the union of one male with several females, or of one female with several males: such is the case with dogs, hens, and so forth. Since, then, of all animals the male of the human species is preeminent in the care of his offspring, it is clearly natural to man that one man should have one wife, and vice versa.

Besides. Equality is a condition of friendship. Hence if a woman may not have several husbands (because this removes the certainty of offspring), if it were lawful for a man to have several wives, the friendship of a wife for her husband would not be freely bestowed but servile, as it were. And this argument is confirmed by experience, since where men have several wives, the wives are treated as servants.

Further. In perfect friendship it is impossible to be friends with many, according to the Philosopher. (Nicomachean Ethics 8.6.) Hence if the wife has but one husband, while the husband has several wives, the friendship will not be equal on either side: consequently, it will be not a freely bestowed friendship, but a servile one, as it were.

Moreover. As we have already stated, (Ch. 123.) matrimony among men should be so ordered as to be consistent with good morals. Now it is contrary to good morals that one man have several wives, for this leads to discord in the family, as shown by experience. Therefore, it is not right for one man to have several wives.

Hence it is said: They shall be two in one flesh (Gen 2:24).

Hereby polygamy stands condemned, as also the opinion of Plato, (Plato, Civitas, v; Timaeus.) who said that wives should be possessed in common, which opinion was adopted by Nicolas (one of the seven deacons) in the New Law. (Augustine, On Heresies, ch. 5.)