International law: nature, definition, origin and basis

1. Definition

The term international law was coined by Jeremy Bentham in 1789. The older name was the law of nations (jus gentium). Three definitions are worth carrying into the exam hall.

• Oppenheim: the law of nations or international law is the name for the body of customary and conventional rules which are considered legally binding by civilised States in their intercourse with each other.
• Starke: that body of law which is composed for its greater part of the principles and rules of conduct which States feel themselves bound to observe, and therefore do commonly observe in their relations with each other, and which includes also the rules of law relating to the functioning of international institutions or organisations, their relations with each other and with States and individuals, and certain rules relating to individuals and non-State entities so far as their rights and duties are the concern of the international community.
• Brierly: the body of rules and principles of action which are binding upon civilised States in their relations with one another.

Oppenheim's older definition confines the law to States. Starke's is the modern one because it takes in international organisations and individuals, which the law now plainly reaches (the UN in the Reparation for Injuries opinion, 1949; individuals in the Nuremberg trials and under human rights treaties). Write Starke's definition and then say why it is to be preferred.

2. Nature: is international law really law?

The objection comes from John Austin. For Austin, law properly so called is a command of a political sovereign, backed by a sanction, addressed to persons in a habit of obedience. International society has no sovereign above States, no legislature, no compulsory court and no police. Austin therefore classed international law as positive morality: rules of opinion, not law. Holland called it the vanishing point of jurisprudence.

The answers to Austin are standard and should be given as points.

• Austin's test is too narrow. It fails to explain customary law even inside a State. Historical and sociological jurists (Savigny, Maine) showed that much law grows out of usage, not command.
• States treat it as law. They do not claim a right to break it; they argue about what it says and justify their conduct in legal terms. Foreign offices employ legal advisers for that reason.
• There are sanctions, though decentralised. Chapter VII of the UN Charter (Articles 39 to 42), self-defence (Article 51), countermeasures, reparation, and the pressure of reciprocity and public opinion.
• There is a court. The International Court of Justice decides disputes on the basis of international law (Statute, Article 38), and under Article 94 of the Charter members undertake to comply with its decisions.
• Courts at home apply it. English and American courts treat custom as part of the law of the land; Indian courts read treaties and custom into domestic law (see the note on the relationship between international and municipal law).
• Codification. Large parts of the law now exist as treaties: the Vienna Convention on the Law of Treaties, 1969, the Vienna Convention on Diplomatic Relations, 1961, and UNCLOS, 1982.

The fair conclusion is that international law is true law but a weak law: weak in enforcement, not in its legal character. The weakness lies in the machinery, not in the obligation.

3. Origin and development

• Ancient period. Rules on envoys, treaties and the conduct of war existed in ancient India (the Arthashastra and the Manusmriti on envoys and war), Greece and Rome. The Roman jus fetiale governed declarations of war and treaties; the jus gentium was law applied to foreigners.
• Medieval period. The Church and the Holy Roman Empire claimed universal authority. Writers such as Vitoria and Suarez discussed just war and the rights of peoples. Gentili wrote on the law of war.
• Hugo Grotius (1583–1645). His De Jure Belli ac Pacis (1625) is the first systematic treatment, and he is called the father of international law. His Mare Liberum (1609) argued for the freedom of the seas against Portuguese claims; Selden replied with Mare Clausum.
• Peace of Westphalia, 1648. It ended the Thirty Years' War and is taken as the start of the modern system of equal, sovereign, territorial States.
• Nineteenth century. The Congress of Vienna (1815) settled rules on the rank of diplomatic agents and international rivers; the Declaration of Paris (1856) on maritime war; the Geneva Convention (1864) on the wounded; the Hague Conferences of 1899 and 1907 on war and arbitration, which created the Permanent Court of Arbitration.
• League of Nations, 1919, the Permanent Court of International Justice (1922) and the International Labour Organisation (1919).
• United Nations, 1945, the ICJ, the prohibition of force in Article 2(4), the International Law Commission (1947) for codification, decolonisation, human rights and the law of the sea.

4. Basis of international law

The question is why States are bound. The theories fall into two camps.

Naturalist theory. International law is part of natural law, binding because it accords with reason and justice. Pufendorf took the extreme view that there is no positive law of nations at all. Criticism: natural law is vague and gives different answers to different people; it does not explain why particular treaty rules bind.

Positivist theory. International law binds because States have consented to it, expressly in treaties or tacitly in custom (Bynkershoek, Vattel in part, Anzilotti). Two variants are examined.

• Auto-limitation theory (Jellinek). The State is sovereign and can be bound only by its own will. International law is a self-imposed limitation on that will. Criticism: what a State imposes on itself it can remove at its pleasure, so the theory explains why law is made, not why it continues to bind. It also cannot explain why a new State is bound by existing custom without having consented.
• Common consent / Vereinbarung (Triepel). The basis is the common will of States, a merged will distinct from the will of each. Criticism: the common will is a fiction, and it still leaves a State free to withdraw.

Pacta sunt servanda (Anzilotti, and Kelsen's basic norm). The binding force rests on the fundamental norm that agreements must be kept. Criticism: it explains treaties well but not custom, unless custom is treated as tacit agreement.

Sociological or consensus view (Duguit, Krabbe and modern writers). Law binds because of social necessity: States cannot live together without rules. Brierly's answer is similar: the ultimate explanation lies outside law, in the fact that man, whether alone or associated in a State, is constrained to believe that order and not chaos governs the world.

Conclusion for the answer. No single theory suffices. Consent explains treaties and much of custom; it fails for new States, for jus cogens (Article 53 of the VCLT), which binds whatever a State consents to, and for obligations erga omnes (Barcelona Traction, ICJ 1970). The modern basis is a mixture of consent, common need and the recognition by the community of States of certain rules as binding on all.

5. Public and private international law

• Subjects. Public international law governs relations between States and other international persons; private international law (conflict of laws) governs private persons in cases with a foreign element.
• Source. Public international law comes from treaties and custom among States; private international law is part of the municipal law of each State, so English and Indian conflict rules can differ.
• Subject-matter. The first deals with sovereignty, territory, the sea, treaties and war; the second with which court has jurisdiction, which law applies and whether a foreign judgment will be recognised (in India, section 13 of the Code of Civil Procedure, 1908).
• Enforcement. Public international law is enforced through State action and international bodies; private international law through the ordinary courts.

How this is examined

January 2026 asked students to examine the theories relating to the nature and basis of international law, with short notes on Hugo Grotius and the auto-limitation theory. June 2025 asked for the origin and development at different stages; August 2024 asked for a definition with the development, and a short note on the basis; February 2025 set the distinction between public and private international law as a short note. For the essay on nature, use the structure Austin, the replies, conclusion (true but weak law). For the basis, give each theory with its criticism and end with the mixed view. For development, a dated list is what the examiner rewards.