I. To the Question

8. Here one must see first what is required for strict commutative justice in the contract of matrimony (and this on the part of the contracting parties), and what is added, beyond this, for complete justice in such a contract (and this on the part of the superior). Second, one must see what, in the event, suffices for justice as to the matter that is being asked about, and how it may become sufficient and completely just.

A. What is Required on the Side of the Contracting Parties for Strict Commutative Justice in the Matrimonial Contract

9. About the first I say that in every exchange justice requires, as concerns the exchangers and the things exchanged, equality of value in the things exchanged, as far as possible, for the end for which the exchange is done.

10. Now this exchange in the contract of matrimony is done for two reasons: one the procreation of offspring, the other as a remedy for avoiding fornication.

11. As to the first, the body of a man is of greater value than that of a woman, because the same man can at the same time fertilize more women than the same woman could conceive from men. As concerns this end, therefore, bigamy seems, by strict justice, to be licit, so that a man may exchange his body with the bodies of as many women as he can fertilize, in the way it is possible for a man to fertilize them. Hence it is not against nature in other animals that one male have several females. And yet in the state of innocence, when matrimony was and would have been precisely for this office, bigamy did not exist and would not have existed. For there would have been no necessity for a man to have exchanged his body with several women for procreating several offspring, because there would have been sufficient procreation through the simple exchange of one man with one woman, since neither the man nor the woman would then have been sterile.

12. As concerns the second end [n.10], which is only for the state of fallen nature, namely for avoiding fornication, the body of the man and the woman are of equal value.

13. And so, by strict justice in the state of fallen nature, when considering this contract as it is for both ends, the exchange of one body with one body is required.

14. I add that the completion of justice in this exchange comes only from the authority of the superior who institutes or approves such or such exchange; because although there are things that belong to the inferiors as to owners, yet such or such exchange of them is determined to be just by the legislator, and much more so in the issue at hand, about the mutual exchange of bodies, in relation to the legislator who is God. But he has by rule established, both for the state of innocence and the state of fallen nature, that this exchange of bodies must be done by one with one. In this, therefore, is justice complete.

B. What, in the Event, Suffices for this Justice and How it May Become Sufficient and Completely Just

15. About the second article [n.8] I say that ‘dispensation’ is a declaration of right or a revocation of right; for God was able either to declare his law about this exchange or in some case to revoke it - and reasonably in this case when a greater good came from its revocation than from its observation.

16. But now, when there was necessity for multiplying the human race either simply or for the divine cult, because, to be sure, there were few worshippers of God, it was necessary that the worshippers of God procreate as much as they could, because in the succession of them alone did faith and the divine cult abide. So for that time did God reasonably make dispensation so that one man might exchange his body with several bodies of women, for the greater multiplication of worshippers of God, which multiplication without this would not happen. And thus did he in fact make dispensation, as is presumed about Abraham and certain others of the fathers.

17. But as to how justice will be preserved here, considering the contract on the side of the contracting parties, is made clear as follows: because when something is ordered to two ends, a principal one and a less principal one, it is reasonable to use it in the way in which it has more value for the more principal end, although something thereby be taken away from the less principal end. An example: food is of value for pleasure, which is less principal, and for nutrition, which is more principal; food, according to right reason, is to be used in the way in which it is of value for nutrition, although in this it be of less value for pleasure.

18. But this matrimonial contract is for rendering the carnal debt (so that fornication may be avoided) as for the less principal end, and for the good of offspring as for the more principal end. Therefore, according to right reason, the contracting parties should so exchange that the exchange is of more value for procreation, though it be of less value for rendering the debt. But in this way is exchange made of the body of one man for several bodies of women - and just as this is absolutely to be done, so in case of necessity should it necessarily be done, namely when the principal end is most necessary; and then the less principal end is to be neglected as it were.

19. And from this is plain how there is justice on the side of the parties, because each party should, according to right reason, want to dismiss something of its right in exchanging and receiving relative to the less principal end so as to receive the equivalent relative to the more principal end, which each should more desire, although from someone would something need to be exchanged that it would be a detriment for them to remit. And at times is it in some case necessary, when to be sure one is bound to such remission; and it is licit and necessary to carry it out, when this is ordained by a superior; the fact is plain because Sara in Genesis 16.1-4 as it were compelled Abraham to go in to Hagar her handmaid, so that at least thus would he have from the handmaid the son he could not have from her.

20. If you object that this would in modern times be bigamy and illicit, I reply that although it be illicit by reason of the fact it is not now dispensed by the legislator (indeed that part of the law of nature, “they were two in one flesh” was brought back by Christ, Matthew 19.5-6 [d.31 n.29]), however, speaking of justice on the side of the contracting parties and of the contract, it is not licit now, because the principal end is not necessary now, for the reason that many of the faithful devote themselves to generation, whose children are ordained to the cult of God and are religiously educated; and so without such contract is the faith multiplied. Therefore, when the necessity to take something away from the second end by necessity of the first end ceases, the contract must be kept, so that justice there in relation to both ends may be kept; but this is above all that one man have one wife.

21. But if in some event, by war or disaster or disease, a multitude of men were to fall and a multitude of women were to remain, bigamy could now be licit, considering precisely the justice on the part of the exchangers and the exchangings; and also ought women, on their own part, to want to make exchange thus with men, more with fewer, as to the second end, but equal with equal as to the first end, and then ought a woman to want this according to right reason, so that the good of offspring may come about by the commingling of her man with another woman; nor would there be a lack there save only of the completion of justice, which is by divine approval, and approval would perhaps then be given and be specially revealed to the Church.