---
title: "Sources of International Law and Article 38(1)"
description: "ICJ Statute Article 38(1) lists the sources of international law: treaties, custom, general principles, judicial decisions and publicists, plus overriding jus"
url: "https://modeldiplomat.com/learn/lessons/exam-international-law-sources-of-international-law-treaty-custom-jus-cogens"
---

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Sources of international law (treaty, custom, jus cogens)

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# Sources of international law (treaty, custom, jus cogens)

The formal sources of international law under ICJ Statute Article 38(1): treaties, custom, general principles, judicial decisions and publicists, plus jus cogens.

## The canonical enumeration: Article 38(1) ICJ Statute

The authoritative catalogue of the sources of international law is **Article 38(1) of the Statute of the International Court of Justice (1945)**, which reproduces Article 38 of the Statute of the Permanent Court of International Justice (1920). It directs the Court to apply, in deciding disputes:

- **(a)** international conventions (treaties), whether general or particular, establishing rules expressly recognised by the contesting States;
- **(b)** international custom, as evidence of a general practice accepted as law;
- **(c)** the general principles of law recognised by civilised nations;
- **(d)** subject to Article 59, judicial decisions and the teachings of the most highly qualified publicists, as **subsidiary means** for the determination of rules of law.

A candidate must internalise the hierarchy implicit in this text. Sub-paragraphs (a)-(c) are the **formal (primary) sources** that create binding obligations; sub-paragraph (d) lists **subsidiary means** of identifying the law, not law-creating sources. Article 38(2) separately empowers the Court to decide *ex aequo et bono* (on grounds of equity) only if the parties consent — never invoked in a contentious ICJ judgment to date.

## Treaties: the law of express consent

A treaty is, in the words of **Article 2(1)(a) of the Vienna Convention on the Law of Treaties (VCLT, 1969, in force 1980)**, an international agreement concluded between States in written form and governed by international law. The governing principle is **pacta sunt servanda** (VCLT Article 26): every treaty in force binds the parties and must be performed in good faith. **Article 27** forbids a State from invoking its internal law to justify non-performance.

Treaty-making proceeds through negotiation, adoption, authentication, and expression of consent to be bound — by signature, ratification, acceptance, approval or accession (VCLT Articles 11-15). A signatory that has not yet ratified is nonetheless obliged not to defeat the object and purpose of a treaty (**Article 18**). Reservations are permitted unless prohibited or incompatible with the object and purpose (**Article 19**), the test articulated in the ICJ's *Reservations to the Genocide Convention* advisory opinion (1951).

## Custom: practice plus opinio juris

Customary international law requires two elements, settled in the ICJ's **North Sea Continental Shelf cases (1969)**: (i) a general and consistent **State practice**, and (ii) **opinio juris sive necessitatis** — the belief that the practice is legally obligatory. Practice need not be universal but must be 'extensive and virtually uniform'. A State that consistently objects during the formation of a rule may escape it under the **persistent objector** doctrine, recognised obiter in the *Anglo-Norwegian Fisheries* case (1951). Custom binds all States regardless of consent, distinguishing it sharply from treaty law.

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