A Custom’s Nine Lives: Decolonial Continuities of <i>Opinio Juris</i> in Customary International Law

Abstract “Old” customs stress upon State practice while the “new” on opinio juris. The Right of Passage over Indian Territory case (1960) started a debate from the bench to the bar on the coexistence of general, local, and special customs in the postcolonial law of territory. Although key to, first, the Asian and, then, the African self-determination, the relationship of opinio juris and decolonization remains unexamined. In the Question of the Delimitation of the Continental Shelf between Nicaragua and Colombia case (2023), the International Court of Justice has enriched opinio juris by accepting “considerations other than a sense of legal obligation”. Having lived overland occasionally decoupled from State practices since the Military and Paramilitary Activities in Nicaragua case (1986), the conceptually amphibious opinio juris enters the sea today. Historically, Asian opinio juris (1940s) first normatively fractured colonialism to, subsequently, fertilize the customary law on African decolonization (1950s).