Custom

Custom is often understood as being typical of “primitive” systems of law with no strong differentiation between political and legal spheres and no clear distinctions among the processes through which law is made, interpreted, and applied. Custom is of great importance to international law, with its horizontal structure: the subjects of law are also its authors and, more often than not, are also responsible for interpreting and applying legal rules and imposing legal consequences. The voluntarist approach in international law, which explains law’s validity by reference to the consent of states to be bound by rules, produces an account of international law’s validity which can provide an explanation for the sources of validity of all international legal rules. This approach has been subject to sustained criticism from many quarters, however, for leaving little room for the operation of democratic principles, for its heavy reliance on legal fictions (this is particularly true of custom), and for placing international law at the mercy of state self-interest, among other reasons. At the domestic level, it is much more difficult to understand the validity of custom in the same way as that of other legal rules—notably legislation and judge-made law—for the simple reason that the latter are organized in a formal manner, by means of a constitution, and are rooted in the political authority of the state. The authority that stands behind custom is much more difficult to identify. In colonial and post-colonial settings, the distinction between custom and state-based law is clear enough, and clearly recognized: customary rules are often understood to belong to an entirely different legal system which coexists with a system imposed by the colonial power. Outside the colonial context, custom retains its distinctiveness from sources such as legislation and jurisprudence, but without the further distinction provided by the very different societies and cultures from which the two bodies of law proceed. Here, custom’s distinctiveness lies in its being a different type of source: the procedures and activities which give rise to customary rules bear little resemblance to those that produce legislative provisions or judicial decisions. Custom could easily be conceptualized as belonging to a different normative system altogether, though one that intersects and interacts with state-based law and is generally considered to be part of the legal landscape. In international law, such a sharp distinction between custom and other sources is not made: custom is simply one type of law. Certain customary rules constitute cornerstones of the international legal system, notably its rules of recognition—that is, the secondary rules according to which legal rules are brought into existence. The other two sources of law, treaties and general principles, are understood to be legal sources by virtue of customary rules. In order to be able to treat custom as law, one would assume that we need plausible answers to two interrelated questions: first, how is it that custom is law, and second, what is it that makes custom law. The first question goes to the authority that stands behind custom and permits it to be law, giving it validity as law. The second goes to the making of distinctions between law and other normative systems. Customary law, as law, is not merely practice or usage; nor is it morality, but how do we know the difference? What is the secret ingredient that makes custom law? As stated, one would assume a need for answers to these questions, but satisfying, generally applicable, and generally accepted answers to these questions are elusive. I will begin with the second question, which is more straightforward as it focuses our attention on practical distinctions that …