Abstract
The use of the terms “traditional” and “modern” to describe alternative interpretations of customary international law is recent. Nevertheless, the viewpoints attached to them and the debates they have engendered have existed for at least the past forty years. The emergence of these two alternative interpretations of customary international law has generated much debate within the field. Both “traditional” and “modern” custom have very different interpretations of the role state practice and opinio juris play in the formation of customary international law. This has resulted in confusion over what the precise meanings of these two components of customary international law actually are. Could part of the explanation for the emergence of these two radically different takes lie in the idea that both state practice and opinio juris are increasingly proving inadequate in explaining the process of international norm formation? The growth of international criminal tribunals has resulted in a degree of institutionalized and hierarchical norms that have had no historical precedent in the international system. Although these international criminal tribunals were designed as self-contained legal regimes, their jurisprudence has, nevertheless, begun to be elevated into norms of customary international law. Couple this phenomenon with the increasing rise and influence of transnational actors within the international system, and a complex picture of actors and institutions emerges where the old formula of state practice and opinio juris no longer describes the reality of the situation. This article proposes that, to understand the new realities of the international system, one must turn to socio-legal studies and to the new groundbreaking work within that field on norm formation, implementation, and interaction.