The Lines Begin to Blur? Opinio Juris and the Moralisation of Customary International Law

Abstract

According to Article 38(1) of the Statute of the ICJ, customary international law is traditionally composed of two elements, state practice and opinio juris sive necessitatis (“opinio juris”): the practice and the belief that the practice is required by law. The notion of customary international law, however, has been changing and both practice and opinio juris have assumed novel and broader forms. It has been attested that opinio juris has broadened the impetus “to follow the norm out of a sense of legal or moral obligation”. For instance, international tribunals have found “existing customary international law” when actual practice has been absent, but morally compelling reasons have led the court to rule on the illegality of certain atrocities. Hence, the internal inconsistencies in the understanding of opinio juris within the doctrine are centered on morality. This article explores, with references to selected case-law, whether we are in the realm of a new, more inclusive concept of customary international law - in the wake of a new source of international law not explicitly listed in the Article 38(1) of the Statute of the International Court of Justice - or simply uncovering moral norms disguised as custom.

Keywords: international law, legal theory, customary international law, theory of sources of law, inclusive legal positivism