Legal Definitions - Sources of international law

The term Sources of international law refers to the various origins and forms where rules, principles, and obligations governing relations between states, international organizations, and sometimes individuals, can be found. These sources provide the basis for international legal decisions and actions.

A widely accepted framework for understanding these sources is outlined in Article 38 of the Statute of the International Court of Justice (ICJ). The ICJ is the principal judicial organ of the United Nations, tasked with settling legal disputes between states and giving advisory opinions on international legal issues. Article 38 identifies the following primary and subsidiary sources:

• International Treaties (Conventions): These are formal written agreements between two or more states, or between states and international organizations, that create legally binding rules for the parties involved. They can be general, applying to many states, or particular, applying only to a few.
• Customary International Law: This arises from the consistent and widespread practice of states, followed out of a sense of legal obligation (known as opinio juris). It reflects practices that states generally accept as law, even without a formal written treaty.
• General Principles of Law: These are fundamental legal concepts and principles common to the major legal systems of the world, such as the principle of good faith, the prohibition against unjust enrichment, or the idea that agreements must be kept (pacta sunt servanda).
• Judicial Decisions and Scholarly Writings (Subsidiary Sources): While not primary sources themselves, decisions from international and national courts, as well as the writings of highly respected legal scholars, serve as important tools for interpreting and clarifying the rules derived from treaties, custom, and general principles. They help determine what the law is, rather than create new law.

Examples:

1. International Treaty: The Montreal Protocol

The Montreal Protocol on Substances that Deplete the Ozone Layer is an international treaty signed by nearly every country in the world. It commits signatory states to phase out the production and consumption of ozone-depleting substances like CFCs. When a country like Brazil reports its compliance or faces scrutiny for its chemical production, the legal obligations and standards it must adhere to are directly found within the provisions of this treaty. The Montreal Protocol thus serves as a clear example of an international convention establishing binding rules as a primary source of international law.

2. Customary International Law: Diplomatic Immunity

The concept of diplomatic immunity, which protects diplomats from prosecution under the laws of the host country, largely originated as customary international law. For centuries, states consistently granted immunity to foreign envoys out of a shared understanding that such protection was necessary for effective international relations. While later codified in treaties like the Vienna Convention on Diplomatic Relations, its foundational status as a customary practice, accepted as law by nations, demonstrates how consistent state behavior, driven by a sense of legal obligation, forms a vital source of international law.

3. General Principles and Subsidiary Sources: Environmental Damage Dispute

Imagine an international tribunal is asked to resolve a dispute between two neighboring countries where one country's industrial pollution is causing significant environmental harm across the border in the other country. If no specific treaty or clear customary law directly addresses this exact cross-border pollution scenario, the tribunal might refer to the general principle of "no harm" – the fundamental legal idea, common across many national legal systems, that one should not use one's property to harm another's. To further interpret and apply this general principle, the tribunal might consult previous rulings from other international environmental cases (judicial decisions) or analyze detailed commentaries from leading environmental law experts (scholarly writings). These subsidiary sources would help the tribunal determine the precise international legal obligations stemming from the general principle to resolve the dispute.