We know every one of these arguments, so it’s sad that we reject them.
1 If one will make a proper consideration, the preceding reasoning will be seen to lead to the conclusion not only that the society of man and woman of the human species, which we call matrimony, should be long lasting, but even that it should endure throughout an entire life.
2 Indeed, possessions are ordered to the preservation of natural life, and since natural life, which cannot be preserved perpetually in the father, is by a sort of succession preserved in the son in its specific likeness, it is naturally fitting for the son to succeed also to the things which belong to the father. So, it is natural that the father’s solicitude for his son should endure until the end of the father’s life. Therefore, if even in the case of birds the solicitude of the father gives rise to the cohabitation of male and female, the natural order demands that father and mother in the human species remain together until the end of life.
Notes A father’s job is never done.
3 It also seems to be against equity if the aforesaid society be dissolved. For the female needs the male, not merely for the sake of generation, as in the case of other animals, but also for the sake of government, since the male is both more perfect in reasoning and stronger in his powers. In fact, a woman is taken into man’s society for the needs of generation; then, with the disappearance of a woman’s fecundity and beauty, she is prevented from association with another man. So, if any man took a woman in the time of her youth, when beauty and fecundity were hers, and then sent her away after she had reached an advanced age, he would damage that woman contrary to natural equity.
Notes So much for trophy wives.
4 Again, it seems obviously inappropriate for a woman to be able to put away her husband, because a wife is naturally subject to her husband as governor, and it is not within the power of a person subject to another to depart from his rule. So, it would be against the natural order if a wife were able to abandon her husband. Therefore, if a husband were permitted to abandon his wife, the society of husband and wife would not be an association of equals, but, instead, a sort of slavery on the part of the wife.
Notes So much for alimony and seeking oneself.
5 Besides, there is in men a certain natural solicitude to know their offspring. This is necessary for this reason: the child requires the father’s direction for a long time. So, whenever there are obstacles to the ascertaining of offspring they are opposed to the natural instinct of the human species. But, if a husband could put away his wife, or a wife her husband, and have sexual relations with another person, certitude as to offspring would be precluded, for the wife would be united first with one man and later with another. So, it is contrary to the natural instinct of the human species for a wife to be separated from her husband. And thus, the union of male and female in the human species must be not only lasting, but also unbroken.
6 Furthermore, the greater that friendship is, the more solid and long-lasting will it be. Now, there seems to be the greatest friendship between husband and wife, for they are united not only in the act of fleshly union, which produces a certain gentle association even among beasts, but also in the partnership of the whole range of domestic activity. Consequently, as an indication of this, man must even “leave his father and mother” for the sake of his wife, as is said in Genesis (2:24). Therefore, it is fitting for matrimony to be completely indissoluble.
7 It should be considered, further, that generation is the only natural act that is ordered to the common good, for eating and the emission of waste matters pertain to the individual good, but generation to the preservation off the species. As a result, since law is established for the common good, those matters which pertain to generation must, above all others, be ordered by laws, both divine and human.
Now, laws that are established should stem from the prompting of nature, if they are human; just as in the demonstrative sciences, also, every human discovery takes its origin from naturally known principles. But, if they are divine laws, they not only develop the prompting of nature but also supplement the deficiency of natural instinct, as things that are divinely revealed surpass the capacity of human reason.
So, since there is a natural prompting within the human species, to the end that the union of man and wife be undivided, and that it be between one man and one woman, it was necessary for this to be ordered by human law. But divine law supplies a supernatural reason, drawn from the symbolism of the inseparable union between Christ and the Church, which is a union of one spouse with another (Eph. 5:24-32). And thus, disorders connected with the act of generation are not only opposed to natural instinct, but are also transgressions of divine and human laws. Hence, a greater sin results from a disorder in this area than in regard to the use of food or other things of that kind.
Notes Thus there can be no such thing as “gay marriage”.
8 Moreover, since it is necessary for all other things to be ordered to what is best in man, the union of man and wife is not only ordered in this way because it is important to the generating of offspring, as it is in the case of other animals, but also because it is in agreement with good behavior, which right reason directs either in reference to the individual man in himself, or in regard to man as a member of a family, or of civil society. In fact, the undivided union of husband and wife is pertinent to good behavior. For thus, when they know that they are indivisibly united, the love of one spouse for the other will be more faithful.
Also, both will be more solicitous in their care for domestic possessions when they keep in mind that they will remain continually in possession of these same things. As a result of this, the sources of disagreements which would have to come up between a man and his wife’s relatives, if he could put away his wife, are removed, and a more solid affection is established among the relatives. Removed, also, are the occasions for adultery which are presented when a man is permitted to send away his wife, or the converse. In fact, by this practice an easier way of arranging marriage with those outside the family circle is provided.
9 Hence it is said in Matthew (5:31) and in 1 Corinthians (7:10): “But I say to you … that the wife depart not from her husband.”
10 By this conclusion, moreover, we oppose the custom of those who put away their wives, though this was permitted the Jews in the old Law, “by reason of the hardness of their hearts” (Mat. 19:8); that is, because they were ready to kill their wives. So, the lesser evil was permitted them in order to prevent a greater evil.