3 Custom

Definition: international custom — Article 38(1)(b)'s "general practice accepted as law" — is unwritten law formed by the conduct of states: the classic two-element doctrine:1. Objective element — state practice: general, consistent, and reasonably continuous conduct (diplomatic acts, legislation, treaties, votes, naval and military practice, pleadings; duration matters less than density — the "instant custom" debate for the continental shelf and space law);2. Subjective element — opinio juris sive necessitatis: the conviction that the practice is followed as legal obligation, not habit, comity or convenience — the dividing line between lacoutume and la courtoisie (the Paquete Habana's line; the North Sea Continental Shelf cases' requirement that opinio juris be shown, not presumed).Refinements (the exam's higher marks):• Persistent objector rule: a state that has consistently objected from a custom's formation is not bound (the doctrine's limits: it cannot defeat jus cogens or erga omnes norms);• Regional and special custom: custom among a region or group (the Asylum case's failed regional-custom proof — the burden of showing the practice's consistency);• Jus cogens: peremptory norms (the prohibition of aggression, genocide, slavery, torture; self- determination) — accepting no derogation, voiding conflicting treaties, and overriding consent (VCT Articles 53/64; the ICJ in Nicaragua and elsewhere assuming the concept's existence);• Codification's effect: a codifying convention declares custom (binding non-parties as custom); a crystallizing convention fixes developing…