The Quest for Opinio Juris: An Analysis of Customary Law, from Hart’s Social Rules to Expectations and Everything in the Middle

Abstract

The present essay addresses the conceptual structure of customary law, understood as a set of customary rules. More specifically, it deals with the core question of what opinio juris entails as a constituent element of customary law. The work will begin with an analysis of samples of common strategies in contemporary legal theory that deal with opinio juris when analyzing the structure of customary law. Subsequently, following Hart’s notion about what constitutes social rules, and introducing explanatory features from Game Theory applied to social philosophy and some insights from Behavioral Economics, the goal of the present study is to propose a different conceptual path for analyzing and identifying customary law with what could be understood as “opinio juris”, given the conceptual necessity of finding the normative element that lies within the usus, or social practices.