Ius Gentium: Natural Law or Positive Law?

by dgboland © 2000

Aristotle divides law into natural law and positive law. Natural law is determined by our understanding of what we are, or our human nature. Positive law is determined simply by the will of the lawmaker. Under natural law something is forbidden because it is wrong, being unsuitable to our human nature, properly understood. Under positive law something is wrong because it is forbidden. The two kinds of law are clearly quite opposite. Aristotle might say they are contraries.

Natural law, however, is more fundamental. Positive law cannot change or abrogate natural law. Positive law is concerned with human activities or behaviour that natural law has not ruled on. Positive law, as St. Thomas says, can only add to natural law; it cannot subtract from it. Thus, another way of looking at the division of law into natural law and positive law is to say that postive law is law that is additional to natural law.

In the light of this division of law, how are we to characterise that order of laws that is called the ius gentium? According to St. Thomas, ius gentium is something added to natural law. This would seem to place it squarely within positive law. Yet, St. Thomas makes it quite clear that something is forbidden under ius gentium because it is contrary to reason, i.e. because it is wrong, not wrong simply because it is forbidden. In that regard, then, ius gentium resembles natural law rather than positive law.

The resolution of the problem here lies, as is often the case, in a distinction to be made. St. Thomas retains the strict sense of natural law of what we immediately understand about ourselves in the light of our human nature, but makes a distinction within positive law. He points out that there are two ways in which something may be added to what we intuitively, as it were, know should be done. Thus he says: " something may be derived from the natural law in two ways: first, as a conclusion from premises, secondly, by way of determination of certain generalities. The first way is like to that whereby, in sciences, demonstrated conclusions are drawn from the principles. The second mode is like to that whereby, in the arts, general forms are particularised as to details; thus the craftsman needs to determine the general shape of a house to some particular shape." [I-II, 95, a. 2. c]

Positive law, then, taken in the broad sense of what is posited by reason and will over and above what we know naturally, as it were, includes both ius gentium and positive law in the strict sense - what is determined by the "art" (political prudence) or even mere will of the civil government. It is only in this narrower area of positive law that something can be wrong simply because it is forbidden. Ius gentium is distinct from natural law, taken in the strict sense of the absolutely first or self-evident principles of morality. But when natural law is taken in a broader sense of what is intrinsically suitable to human nature fully considered (what is within ethico-political science), ius gentium rather belongs to natural law than to positive law. For "the law of nations is indeed in some way natural to man, in so far as he is a reasonable being, because it is derived from the natural law by way of a conclusion that is not very remote from its premises." [I-II, 95, a. 4. ad 1]

Both natural law and ius gentium, therefore, have the force of law beyond national and political boundaries. There are many important social institutions, indeed, that St. Thomas identifies as pertaining to ius gentium. Perhaps the two most important are marriage and property. Hence, the folly of those who would attempt to deny the special bond of the marriage contract, because it is something natural to human nature. "What God has joined together, let no man put asunder" is the scriptural admonition regarding the natural obligation taken on in the marriage-covenant. The civil law (positive law) simply has no authority to dissolve it. Similarly, those who attack the institution of property in land and goods mistake badly the basic requirements of our rational nature. It seems also that St. Thomas included in ius gentium the institution of free trade, provided it is fair trade. For he places "just sales and purchases" amongst the conclusions to be derived from natural law.

The ius gentium is clearly an area of law that deserves much closer study. It is unfortunate that it tends to be overlooked because of an uncritical and simplistic interpretation of the division of law into natural and positive. It is even more unfortunate that its precepts then tend to be relegated to the status of the merely conventional.

dgboland ©2000


Don Boland is a lecturer at the Centre for Thomistic Studies, in Sydney, Australia.

This article posted December 2000. It was published in Universitas, No. 8 (2000).
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