About this topic
The sources of international law explain where a binding international rule gets its authority. The topic centres on Article 38 of the Statute of the International Court of Justice (ICJ), which lists treaties, custom, general principles of law, judicial decisions and the writings of scholars, and also gives the Court a special power to decide ex aequo et bono.
Two coastal countries, Aravia and Belmora, come before the fifteen judges of the World Court. Belmora says Aravian fishing boats must stay out of its bay, because a regional fishing treaty forbids them. Aravia replies that it never ratified that treaty, and that its fishermen have used the bay for two hundred years. Both then ask the Court whether, if the rules are unclear, it can simply decide what is fair.
The problem raises three questions, which the law of sources answers (see the last part of these notes):
- Can a state be bound by a treaty it never accepted?
- Can a long practice become law?
- Can a judge decide by fairness alone?
Meaning of a source of international law
Inside a country, law comes from above: Parliament passes a statute and everyone is bound. The international community has no world Parliament and no world government. International law therefore grows mostly from below, from the conduct and consent of states.
| Point | Domestic (national) law | International law |
|---|---|---|
| Law-maker | Parliament | No world Parliament or world government |
| Direction of law-making | From above: a statute binds everyone | From below: from the conduct and consent of states |
A source of international law answers one question: from where does a binding international rule get its authority?
Article 38 of the Statute of the ICJ
The best-known list of the sources of international law is in Article 38 of the Statute of the International Court of Justice.
The ICJ: fact file
- The ICJ is the principal judicial organ of the United Nations.
- Its Statute forms an integral part of the United Nations Charter, signed at San Francisco on 26 June 1945.
- The Court first sat in April 1946, at the Peace Palace in The Hague, in the Netherlands.
- It has 15 judges, each elected for 9 years.
- It replaced the Permanent Court of International Justice of the League of Nations era.
Text of Article 38
Article 38(1):
"The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply:
(a) international conventions, whether general or particular, establishing rules expressly recognized by the contesting states;
(b) international custom, as evidence of a general practice accepted as law;
(c) the general principles of law recognized by civilized nations;
(d) subject to the provisions of Article 59, judicial decisions and the teachings of the most highly qualified publicists of the various nations, as subsidiary means for the determination of rules of law."
Article 38(2):
"This provision shall not prejudice the power of the Court to decide a case ex aequo et bono, if the parties agree thereto."
Memory aid: "three, two, one"
| Number | What it covers | Provision | Role |
|---|---|---|---|
| Three | Treaties, custom and general principles of law | Article 38(1)(a), (b) and (c) | Sources that make law |
| Two | Judicial decisions and scholarly writings | Article 38(1)(d) | Tools that only help find law |
| One | Power to decide ex aequo et bono | Article 38(2) | Special power to step outside strict law, only with the parties' agreement |
International custom (Article 38(1)(b))
Custom is the oldest source. Long before states signed treaties on the sea or on diplomats, they were following customs on those subjects.
People keep crossing the grass of a field until a clear track appears. The footprints alone prove only a habit. The track becomes a right of way only when people use it as something they are entitled to use. Custom works the same way: it needs the footprints (state practice) and a sense of right (opinio juris).
Two elements of custom
- State practice (the "footprints": what states do and say).
- Opinio juris (the mental element, the "sense of right": the belief that the practice is legally required).
Strictly, Article 38(1)(b) is worded the other way round. The practice is the evidence, and custom is what it proves.
State practice
State practice means what states do and say, including:
- their laws;
- official statements;
- diplomatic correspondence; and
- court decisions.
The practice need not be followed by every state without exception. The ICJ settled this in the North Sea Continental Shelf cases.
North Sea Continental Shelf cases (decided on 20 February 1969): the Federal Republic of Germany, Denmark and the Netherlands had to divide the seabed off their coasts. Article 6 of the Geneva Convention on the Continental Shelf, 1958 used the equidistance principle (a line at equal distance from the coasts), unless the states agreed otherwise or special circumstances justified another line. Germany's coast curves inwards, so this method squeezed its share. Germany had signed but never ratified the Convention, so Denmark and the Netherlands argued that equidistance had become custom.
Held: the Court disagreed. It required that "State practice, including that of States whose interests are specially affected, should have been both extensive and virtually uniform in the sense of the provision invoked". It added: "Not only must the acts concerned amount to a settled practice, but they must also be such, or be carried out in such a way, as to be evidence of a belief that this practice is rendered obligatory by the existence of a rule of law requiring it." States using equidistance had not shown that they felt legally bound to use it, so Germany was not bound.
Principle: custom needs both a settled practice that is extensive and virtually uniform (including the practice of specially affected states) and opinio juris. The Court also told the parties to divide the shelf by agreement in accordance with equitable principles.
The test for state practice is extensive and virtually uniform, not perfect and universal. The practice of states whose interests are specially affected must be included.
Opinio juris: usage and custom
The mental element separates law from politeness.
A 21-gun salute for a visiting head of state is courtesy, not legal duty. If it stopped, no one could allege a breach.
| Usage | Custom |
|---|---|
| A regular practice without any sense of legal duty | A practice followed because states believe the law requires it |
| Not binding; stopping it is no breach | Binding as law |
| Example: a 21-gun salute for a visiting head of state | A usage becomes custom only when opinio juris is added |
A usage becomes a custom only when states follow it because they believe the law requires it.
Local (bilateral) custom
Custom need not be worldwide. It can exist between just two states. The leading case involves India.
Right of Passage over Indian Territory case, Portugal v. India (judgment on 12 April 1960): Portugal held two enclaves, Dadra and Nagar Haveli, surrounded by Indian territory, and reached them from its coastal district of Daman. In 1954, after the enclaves were taken over by groups favouring union with India, India refused passage.
Held: the ICJ accepted that a local custom can arise between only two states through long practice. Portugal had a right of passage for private persons, civil officials and goods in general. But passage of armed forces, armed police, and arms and ammunition had always needed permission, so no right existed there. Given the tension of 1954, India had not acted contrary to its obligations.
Principle: practice creates a right only so far as it was accepted as law.
| Category of passage | Past practice | Result |
|---|---|---|
| Private persons, civil officials and goods in general | Exercised as of right | Right of passage existed |
| Armed forces, armed police, arms and ammunition | Always needed permission | No right of passage |
International conventions or treaties (Article 38(1)(a))
If custom is law written in conduct, a treaty is law written in ink.
Definition of a treaty
The Vienna Convention on the Law of Treaties was done at Vienna on 23 May 1969 and came into force on 27 January 1980. Article 2(1)(a) provides:
"'treaty' means an international agreement concluded between States in written form and governed by international law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation;"
Elements of the definition:
- an international agreement;
- concluded between States;
- in written form;
- governed by international law;
- in a single instrument or in two or more related instruments;
- whatever its particular designation.
The label does not matter. The United Nations Charter, the International Covenant on Civil and Political Rights, the Paris Agreement on climate change, and a protocol amending an earlier treaty are all treaties in law.
General and particular conventions
| General convention | Particular convention |
|---|---|
| Open to the whole international community | Binds only a few states |
| Example: the Geneva Conventions of 1949 | Example: the Indus Waters Treaty of 1960 between India and Pakistan |
Whom does a treaty bind?
The answer lies in the words "expressly recognized by the contesting states" in Article 38(1)(a). Article 34 of the Vienna Convention provides:
"A treaty does not create either obligations or rights for a third State without its consent."
A treaty binds only the states that consent to it. But, as the North Sea Continental Shelf cases show, a treaty rule can later grow into custom, and then it binds even non-parties, as custom.
Agreements involving international organisations
The Vienna definition speaks only of States, but this does not shut out international organisations. Article 3 of the Vienna Convention provides:
"The fact that the present Convention does not apply to international agreements concluded between States and other subjects of international law or between such other subjects of international law, or to international agreements not in written form, shall not affect:
(a) the legal force of such agreements;
(b) the application to them of any of the rules set forth in the present Convention to which they would be subject under international law independently of the Convention;
(c) the application of the Convention to the relations of States as between themselves under international agreements to which other subjects of international law are also parties."
Put simply:
- The Convention governs only written treaties between states, but other agreements (with or between other subjects of international law, or not in written form) keep their full legal force.
- Rules of the Convention that exist independently in international law still reach such agreements.
- Where states and an organisation share one agreement, the Convention still governs relations among the states.
A separate Vienna Convention for treaties involving international organisations was adopted in 1986.
General principles of law (Article 38(1)(c))
Where there is no treaty and no custom, the Court may not say there is no law and refuse to decide. Such a refusal is called non liquet, meaning the law is not clear, and Article 38(1)(c) prevents it.
General principles work like a spare tyre. When treaties and custom run flat, the Court uses principles shared by the world's legal systems.
The purpose of general principles of law is to avoid a non liquet. The phrase "civilized nations" is now regarded as outdated, and is read as covering all nations.
Four general principles
- Good faith (pacta sunt servanda): agreements must be kept. Article 26 of the Vienna Convention provides: "Every treaty in force is binding upon the parties to it and must be performed by them in good faith."
- Res judicata: a dispute finally decided between the same parties cannot be reopened.
- Estoppel: a state cannot deny a position it has officially accepted and never objected to.
- Reparation: every breach of an obligation brings a duty to make reparation, that is, to repair the harm.
If a state officially accepts a border map for forty years and never objects, it cannot deny the map once oil is found nearby. This is estoppel.
Versions of these principles appear in Indian, English, French and many other legal systems, which is exactly what makes them general.
Subsidiary means for determining law (Article 38(1)(d))
Judicial decisions and the teachings of publicists are like two magnifying glasses. They do not write the law, but they help the judge read it. That is why Article 38(1)(d) calls them subsidiary means for the determination of rules of law.
Judicial decisions
Judicial decisions are subject to Article 59 of the Statute:
"The decision of the Court has no binding force except between the parties and in respect of that particular case."
If the Court decides a fishing dispute between State X and State Y, that judgment does not bind two other states that later bring a similar dispute.
- The ICJ does not follow binding precedent, which common lawyers call stare decisis.
- Yet the Court regularly cites its earlier judgments and rarely departs from them, because consistency gives the law credibility.
- Judicial decisions also include arbitral awards and national court judgments.
- National judgments can also be evidence of custom. When courts in many countries refuse to hear claims against a foreign state for its sovereign acts, their judgments become proof of state practice and opinio juris.
Under Article 59, an ICJ decision binds only the parties and only in respect of that case. There is no stare decisis at the ICJ, though in practice the Court follows its earlier decisions for consistency.
Teachings of the most highly qualified publicists
This means the writings of leading international law scholars. The classic example is Hugo Grotius, whose On the Law of War and Peace appeared in 1625.
Scholarly writings explain the law, but a scholar's opinion cannot by itself create a binding rule.
Decision ex aequo et bono (Article 38(2))
Ex aequo et bono means "according to what is right and good". Under this power the Court may decide on fairness alone, even setting aside legal rules.
- It can be used only if the parties agree.
- It is not an automatic fifth step when the other sources fail.
- In practice, states have almost never given the Court this power.
| Ex aequo et bono | Equity inside the law |
|---|---|
| Decision on fairness alone, even setting aside legal rules | A legal rule that itself requires fairness |
| Needs the agreement of the parties (Article 38(2)) | Applied as part of the law |
| Almost never conferred on the Court in practice | Example: in the North Sea Continental Shelf cases, the Court told the parties to divide the shelf by agreement in accordance with equitable principles |
Do not confuse ex aequo et bono with equity inside the law. The direction in the North Sea Continental Shelf cases to apply equitable principles was a legal rule requiring fairness, not a decision ex aequo et bono.
Is there a hierarchy among the sources?
A favourite examination question is whether the sources in Article 38 form a ladder.
- Article 38 sets no formal ranking among treaties, custom and general principles.
- Article 38(1)(d) (judicial decisions and writings) is expressly subsidiary.
- In practice, the Court usually looks first at the treaty between the parties, because the specific rule they chose normally prevails over a general one.
Exam answer: no formal hierarchy among treaties, custom and general principles; judicial decisions and writings are expressly subsidiary; in practice the specific treaty between the parties is usually examined first because the specific rule normally prevails over the general one.
Sources beyond Article 38
Article 38 is not a complete catalogue.
| Material | Legal effect |
|---|---|
| General Assembly resolutions | Generally only recommendations, although they can show what states believe the law to be |
| Soft law | Influential but non-binding material of this kind |
| Security Council decisions | Stronger footing: binding on members under Article 25 of the UN Charter |
Article 25 of the Charter provides: "The Members of the United Nations agree to accept and carry out the decisions of the Security Council in accordance with the present Charter."
Applying the sources: the Aravia and Belmora problem
- Treaty never ratified: Aravia is not bound by the treaty it never ratified, unless the same rule has independently become custom.
- Long practice: two hundred years of fishing can create a right even between two states, but only if Belmora accepted it as a right, not merely tolerated it as a favour.
- Fairness alone: the judges cannot decide by fairness alone unless both countries agree.
Quick revision
- Three sources make law: treaties, custom and general principles of law (Article 38(1)(a) to (c)).
- Two tools help find law: judicial decisions and the teachings of the most highly qualified publicists (Article 38(1)(d)), as subsidiary means.
- One power, used only with the consent of the parties, lets fairness replace law: decision ex aequo et bono (Article 38(2)).
- A state is not bound by a treaty it never ratified, unless the same rule has independently become custom.
- Long practice can create a right even between two states, but only if it was accepted as a right, not merely tolerated as a favour.
- The Court cannot decide by fairness alone unless both parties agree.
