01. public international law

The question

The course has so far examined law principally as the law of a state, the municipal law that governs persons within a territory. A further body of law governs the relations of states with one another and operates beyond the boundaries of any single legal system. This module examines that law in its several forms, and it begins with public international law, the body of law that governs the relations of states and of the other subjects of the international legal order. The question this sub-unit answers is how a body of law can exist and bind where there is no world legislature to enact it, no world court with compulsory authority to apply it, and no world government to enforce it. The answer reveals an order whose structure differs profoundly from that of the municipal law examined so far.

The nature and subjects of public international law

Public international law is the law that governs the relations among the members of the international community, and its primary subjects are states, the territorial sovereign entities that the first unit identified as the makers of municipal law and that here appear as the bearers of international rights and duties. The defining feature of the order is that its primary subjects are also, collectively, its principal lawmakers, since the law binding states is made largely by the states themselves through their agreements and their practice.

This feature connects the order to the analysis of sovereignty in the first unit. A state is sovereign within its territory, subject to no higher authority in its internal affairs, and the international legal order is the law that governs the relations among these sovereign entities, each formally equal to the others. Alongside states, the order recognises further subjects: international organisations, such as the United Nations, created by states and endowed with a measure of international legal personality, and, in defined respects, the individual human being, who bears certain rights and duties directly under international law, a development the sub-unit on human rights examines.

Consider a dispute between two states over the boundary of their territorial waters. The dispute is governed by public international law, which determines the extent of each state's maritime entitlement and the principles by which the boundary is drawn, and it is a dispute between sovereign equals, neither subordinate to the other, to be resolved by the law that the states have made for themselves through treaty and custom. The example shows the distinctive character of the order: a law among equals rather than a law imposed by a superior.

Public international law is therefore the law governing the relations of states and the other subjects of the international community, an order whose primary subjects are also its principal lawmakers, and this character distinguishes it at the outset from the municipal law of a state.

The sources of international law

The question how international law is made is answered by its sources, which were introduced in the unit on sources and are here examined in their proper setting. The authoritative statement of the sources appears in Article 38 of the Statute of the International Court of Justice, which identifies the principal sources the Court applies, and these have become the accepted catalogue of the sources of international law.

The principal sources are three, and they recall the analysis of the earlier unit. The treaty, the agreement between states, is the foremost source, by which states create binding obligations among themselves, ranging from a bilateral agreement between two states to a multilateral convention that may bind much of the world. Customary international law, examined in the first unit, is the second principal source, constituted by the general and consistent practice of states followed out of a sense of legal obligation, the opinio juris, and it binds states generally, including those that have concluded no treaty on the matter. The general principles of law recognised by civilised nations form the third source, supplying principles common to developed legal systems where treaty and custom are silent. Judicial decisions and the teachings of the most qualified publicists serve as subsidiary means for determining the law.

Suppose a question arises whether a state may expel a foreign diplomat. The answer is found first in the relevant treaty, the convention on diplomatic relations to which most states are party; were there no treaty, it would be found in customary international law, in the general and consistent practice of states concerning diplomats, followed out of a sense of obligation. The sources operate together, the treaty stating the rule for its parties and custom binding generally, and the lawyer identifies the governing source as the first step in the analysis.

The sources of international law are therefore the treaty, custom, and the general principles, the same catalogue introduced earlier in the course, and the international legal order is made through these sources by the states that the order binds.

Sovereign equality and peremptory norms

The structure of the international order rests upon a foundational principle, the sovereign equality of states, the principle that all states are juridically equal, each possessed of the same fundamental rights and subject to the same fundamental duties, regardless of disparities in size or power. The principle follows from the absence of any authority above the states: where there is no superior, the subjects stand as equals, and the law that binds them is the law to which they have, through treaty and practice, consented.

This consensual character has an important consequence and an important limit. The consequence is that a state is ordinarily bound only by the rules it has accepted, whether by treaty or by participation in the practice that generates custom. The limit is the existence of peremptory norms, known by the Latin jus cogens, a small category of fundamental rules from which no derogation is permitted and which bind every state irrespective of its consent, such as the prohibitions of aggression, genocide, and slavery. The existence of such norms qualifies the otherwise consensual structure of the order, marking certain principles as so fundamental that no state may contract out of them, and connecting the international order to the moral foundations examined in the discussion of natural law in the first unit.

Imagine that two states conclude a treaty providing for conduct that amounts to aggression against a third state. The treaty is void irrespective of whether either party objects, because it conflicts with a peremptory norm from which no agreement may derogate; the consent of the parties cannot validate what jus cogens forbids. The example shows the limit of consent in the international order, the point at which a fundamental norm overrides the agreement of states.

Sovereign equality and the consensual structure it implies, qualified by the peremptory norms that bind irrespective of consent, are therefore the foundational principles of the international order, defining both the freedom of states to make their own law and the limits that freedom encounters.

Enforcement in the absence of a world government

The most striking feature of public international law, and the one that most tests its claim to be law, is the manner of its enforcement, for the international order has no world government, no police, and no court with general compulsory jurisdiction over states. This condition returns the course to the question, raised in the first unit, whether law requires a sovereign enforcer, and the international order furnishes the principal test of that question.

International law is enforced, where it is enforced, through means that differ fundamentally from the centralised enforcement of municipal law. A state injured by another's breach may resort to lawful countermeasures, withholding performance of its own obligations to induce compliance; states may act collectively through international organisations, the Security Council of the United Nations possessing authority to impose measures in response to threats to peace; and the practice of states is shaped by the reciprocal interest each has in a system of rules that all observe, since a state that breaches its obligations invites others to do the same. International courts and tribunals decide disputes, but ordinarily only where the states concerned have consented to their jurisdiction. The decentralised character of enforcement means that international law is observed for the most part not through coercion but through the convergent interest of states in a stable order, and its breaches, though they occur, do not deprive it of its legal character any more than the breach of a municipal law deprives that law of its character.

Consider a state that violates a trade obligation owed to another under an international agreement. The injured state cannot call upon a world police force; it may, however, invoke the dispute settlement machinery the agreement provides, and, if a breach is established, may be authorised to suspend equivalent obligations of its own in response, a measured pressure that induces compliance without force. The example shows enforcement operating through authorised countermeasures and institutional process rather than through the centralised coercion of municipal law.

Enforcement in the international order is therefore decentralised, operating through countermeasures, collective action, and the reciprocal interest of states, and the order's reliance on these means rather than on a central enforcer is the feature that most distinguishes it from municipal law while leaving its legal character intact.