Scholion I. On the Law of Nations

According to some, the law of nations is referred to positive law, which is a determination of the law of nature, and thus can be defined: positive law determining the law of nature, introduced by the human race, and indeed through custom. To this belong, for example, the immunity of legates, the commerce of letters and markets with other nations, the prohibition of slavery strictly so called, the prohibition of injuring private goods in war, with the things to be excepted being excepted, etc. It differs from civil law insofar as the latter has been established by individual states and therefore can also be abrogated by individual states, whereas the law of nations has been introduced by the human race and can be abrogated by it alone.

According to others, the law of nations pertains to natural law, from which its precepts are derived as necessary conclusions. Hence, just as natural law, it is immutable. Thus, for example, "the law of nature... neither prescribes nor prohibits the division of stable properties; for it does not absolutely and per se prescribe that this field should belong to Peter rather than Paul, or be common to all. But it is of the law of nature that human beings live peacefully with one another. But human beings cannot live peacefully among themselves unless stable properties have been divided. Therefore stable properties are to be divided."¹

According to some, the distinction from natural law is in this: that natural right belongs to man as an animal, or regards actions which are common to man with brute animals, such as living and procreating; the law of nations belongs to man as such. According to others, the distinction comes from this: that natural law holds absolutely, while the law of nations holds conditionally, that is, once some fact has been posited, for example occupation.

St. Thomas, concerning whose opinion there is dispute, has these words in I-II, q. 95, a. 4: "To the law of nations belong those things which are derived from the law of nature as conclusions from principles, such as just purchases, sales, and other things of this sort, without which human beings cannot live together with one another; this is of the law of nature, because man is naturally a social animal, as is proved in book 1 of the Politics (c. 2, at the beginning). But those things which are derived from the law of nature by way of particular determination belong to civil law, according as each state determines something adapted to itself." And in the same place, ad 1: "It must be said that the law of nations is indeed in some way natural to man, according as he is rational, insofar as it is derived from natural law by way of a conclusion which is not very remote from the principles. Hence human beings easily consented in matters of this sort. Nevertheless it is distinguished from natural law, especially from that which is common to all animals."

Corollary. The law of nations differs from law between nations, or international law, which is constituted by express pacts entered into among the rulers of nations (n. 94).

¹ Zigliara, Ethica, n. 26, III.