Classic definitions:
• Oppenheim: international law is "the body of rules which are legally binding on civilised states in their intercourse with each other" — the positivist, states-only definition (and the era's vocabulary).
• Modern definition (the course's working text): international law is the body of legal rules and principles that governs the relations among states and between states and other subjects of international law — international organizations, individuals (in defined roles), and special entities — across war and peace, territory, sea, space, treaties, responsibility and human rights.
• The World Court's statutory frame: Article 38(1) of the ICJ Statute (Unit 2) supplies the functional definition — the law the Court applies: treaties, custom, general principles, and the subsidiary sources.
Nature of international law (the true/false debate to structure answers):
1. Law or morality? John Austin dismissed it as "positive international morality" — rules of conduct set by general opinion, not commands of a sovereign backed by sanction. The answer (Oppenheim's, Starke's and the century's verdict): international law is law because its subjects obey it as law (opinio juris), because its breach attracts sanction (countermeasures, responsibility, Chapter VII enforcement, reputational costs), and because courts and tribunals apply it daily — the weakness of centralized enforcement (no world police) differs in degree, not kind, from weak municipal systems.
2. Law of coordination, not subordination (the structural point): municipal law is vertical (sovereign over subjects); international law is horizontal (equals among equals — par in paremnon habet imperium, an equal has no authority over an equal) — hence its consensual techniques (treaty, custom) and its enforcement's decentralization.
3. Consensual and dynamic: made largely by its subjects (states consent via treaties and persistent custom), and perpetually adapting — to decolonization, technology (sea-bed, space, cyber), and the human-rights revolution.
4. Weaknesses honestly stated: no compulsory general jurisdiction (the ICJ needs consent), enforcement politicized (the veto), and a compliance culture that bends at great-power interests — the realist critique (IR Unit 2) against the legalist faith.
Scope (the subject-map of this course and its sequel): sources and personality (Units 2–3); recognition and succession (Unit 4); nationality, statelessness, refugees (Unit 5); asylum and extradition (Unit 6); state responsibility and treatment of aliens (Unit 7); jurisdiction — territory, persons, sea, air, space (Unit 8); immunities (Unit 9); with Public International Law-II (later semester) covering the law of treaties, the UN system, human rights law, the law of the sea in depth, dispute settlement, international criminal law, and the law of armed conflict.