Nature — four points (structure every answer): Is it true law? (Austin's challenge): John Austin dismissed it as "positive international morality" — not commands of a sovereign backed by sanction. The century's answer: international law is law because its subjects obey it as law (opinio juris); because breach attracts sanction (countermeasures, state responsibility, Chapter VII enforcement, reputational cost); and because courts apply it daily. The weakness of centralized enforcement differs in degree, not kind, from weak municipal systems. Law of coordination, not subordination: municipal law is vertical (sovereign over subjects); international law is horizontal — equals among equals (par in parem non habet imperium) — hence its consensual techniques and decentralized enforcement.
Consensual and dynamic: made largely by its subjects (consent through treaties and custom), perpetually adapting. Weaknesses honestly stated: no compulsory general jurisdiction (the ICJ needs consent), enforcement politicized (the veto), compliance bending at great-power interest. Basis — why do sovereign states feel bound? (the guaranteed theory question): Theory Claim One-line critique Naturalist (Grotius) Binds because it derives from reason/nature Whose reason? unverifiable Positivist (Austin, Anzilotti) Law = the will/consent of states Cannot explain why new states are bound by old custom, or jus cogens Auto-limitation (Jellinek) The state self-restricts its own will What a state limits it can un-limit — obligation collapses into discretion Normative/pure (Kelsen) A hierarchy of norms grounded in the Grundnorm The basic norm is presupposed, not provable Sociological/ necessity States obey because interdependence demands it Explains compliance, not obligation Pacta sunt servanda (VCLT Art. 26) Good faith in promises kept The practical lawyer's answer — the system's members accept that obligations must be honoured