a. Opinion of Others and the Weighing of It

27. About the second article [n.18]: some say [Thomas Aquinas, Sent. IV d.36 q.1 a.2, arg.2 contra] that a slave can contract matrimony against the will of his master - and this from the preceding article [n.24], because matrimony is of the law of nature and servitude is not, but is rather against the law of nature; and what is of the law of nature is not taken away because of anything that is only of positive law.

28. Another reason is set down [Aquinas, ibid. Richard of Middleton, Sent. IV d.36 princ.4 q.1], that a slave does not so belong to his master that he does not have his own right as concerns natural acts pertaining to preservation of the individual; for it is plain that he can use things necessary for life; therefore, by similarity, as concerns acts pertaining to the preservation of the species. The proof of the consequence is that the preservation of the species, since it is a greater natural good, belongs more to the law of nature.

29. Or in this way: a slave cannot be a brute; hence every man has, as to some acts, his own right, nor can he make himself a slave as to those acts (rather nature would make him so free [as to those acts] that he cannot make himself slave); and of such sort are natural acts that are for the preservation of the individual and also for the preservation of the species, and he cannot obligate himself to any master against these acts; but he can obligate himself so as to be bound to a master as to later acts.

30. These reasons can be solved:

First because an obligation that is not of the law of nature can well impede some liberty that belongs to someone of the law of nature; and so it is here. An example: by the law of nature I owe you nothing, yet if I vow obedience to you I am bound to obey you. Now matrimony is not of the law of nature except secondarily, as was said above [d.26 n.31]; and it seems to be just as much of the law of nature to render to each his own; therefore, from the fact that he has by an obligation made himself to be slave of a master, he is bound to render the master the master’s own, and bound to be held back from that which impedes such rendition, although that other impeding thing would, secondarily according to the law of nature, belong to him when not obligated.

The second reason is not probative, because it is manifest that not everyone who is bound to preserve the individual is bound to multiply the species.

31. And if you say that at any rate it is so licit for him that the fact it is licit for him cannot by man be taken away - this is true in a case of necessity, where the preservation of the species would depend on his act. But because many who are not slaves are intent on generation even in the Christian Law, therefore the act of the slave pertaining to this is not necessary for the preservation of the species, and therefore it is possible by some obligation to preclude him from it. Hence if an obligation to later acts impede prior acts which are not simply necessary for the procreation of offspring, then it does not seem that, because of such non-necessary and prior acts, he must set aside the posterior acts that belong to his master; for the procreation of offspring through him does not seem to be a necessary act simply, because the human race can be multiplied and offspring procreated through others. - There is a confirmation, that before matrimony he is bound to certain acts, as to a, b, c; if he contract matrimony, there will be an obligation to something that is impossible with the b or c; therefore that obligation cannot justly be made, because therein what is another’s is, after the obligation is made, taken away.