Introduction to International Law Sources

As Starke notes, “The material sources of international law may be defined as the actual materials from which an international lawyer determines the rule applicable to a given situation.” The term “source” refers to methods or procedures by which international law is created. We can distinguish between formal sources and material sources. G. Fitzmaurice describes them as direct and indirect sources, or proximate and remote sources.

Material sources represent the “origins” of law, while formal sources consist of acts or facts that give law its binding character. The essence of the distinction lies in the difference between what inspires law’s content and what grants that content its obligatory force. Formal sources include legal procedures that create binding rules. Material sources provide evidence of rules that, once proven, become legally binding.

The sources of international law fall into five categories:

1. International conventions
2. International customs
3. General principles of law recognized by civilized nations
4. Decisions of judicial or arbitral tribunals and juristic works
5. Decisions or determinations of the organs of international institutions

The third source, “General Principles of Law Recognized by Civilized Nations,” first appeared in Article 38 of the statute of the Permanent Court of International Justice. This statute also retained it in the International Court of Justice, which lists these sources:

1. International conventions
2. International customs
3. General principles of law recognized by civilized nations
4. Judicial decisions and the teachings of highly qualified publicists as subsidiary means for determining rules of law.

While Article 38 does not mention decisions of international institutions, this has become a recognized source.

International Conventions

International treaties serve as a vital source of international law today. They provide states with a deliberate method to create binding international obligations. Article 38 of the International Court of Justice lists international conventions, whether general or particular, as the first source.

According to Article 2 of the Vienna Convention on the Law of Treaties, 1969, “A treaty is an agreement whereby two or more States establish or seek to establish relationships between them governed by international law.” However, this definition is somewhat narrow. Professor Schwarzenberger asserts, “Treaties are agreements between subjects of international law creating a binding obligation in international law.”

Despite its narrow definition, the Vienna Convention acknowledges this fact. Article 3 clarifies that the convention does not affect the legal force of agreements not covered by it, including those between states and other subjects of international law.

International treaties can be classified into two types:

Law-Making Treaties

Law-making treaties create rules of international law directly. Their development accelerated in the mid-19th century due to changing circumstances. Customary laws, once the dominant source of international law, proved inadequate, prompting states to establish treaties to adapt their relations.

Law-making treaties divide into two categories:

1. Treaties enunciating rules of universal international law (e.g., the United Nations Charter).
2. International treaties establishing general principles, such as the 1958 Geneva Conventions on the Law of the Sea and the Vienna Convention on the Law of Treaties, 1969.

These treaties function similarly to domestic legislation, allowing international law to evolve with changing times. They can only express universal principles if supported by key states, as treaties lacking backing from major powers may not effectively establish general rules.

Treaty Contracts

In contrast, treaty contracts involve agreements between two or more states, binding only the parties involved. While they do not create universal law, they can contribute to customary law’s development when similar rules appear across multiple treaties. A treaty can later gain recognition from additional states as they establish similar agreements. Additionally, treaties can provide evidence of rules that have evolved into law through independent development.

International Customs

International customs remain a significant source of international law. They represent the oldest source of international law and continue to hold importance today. Customary rules develop over extended historical periods.

Article 38(b) of the Statute of the International Court of Justice identifies international custom “as evidence of a general practice accepted as law.” To understand “custom,” we must distinguish it from “usage.” The two terms often overlap, but usage refers to habits states repeat without full legal recognition. Starke explains, “Usage represents the twilight stage of custom; custom begins where usage ends.”

Custom becomes recognized when states consistently act in a particular manner in similar situations.

Key Elements of Custom

The key elements of an international custom include:

1. Long Duration: While long duration is vital for municipal law, international law emphasizes general acceptance as law over the duration of practice.
2. Uniformity and Consistency: Customs must reflect a constant and uniform usage by states.
3. Generality of Practice: Although universality isn’t required, the practice should be generally observed by numerous states.
4. Opinio Juris et Necessitatis: International custom reflects a general practice accepted as law.

Leading Cases on Custom

In West Rand Central Gold Mining Company Ltd. v. R., the court established that a valid international custom requires satisfactory evidence of general consent among states.

In Military and Para-Military Activities in and Against Nicaragua, the World Court noted that a state’s appeal to exceptions within a recognized rule confirms rather than weakens that rule.

General Principles of Law Recognized by Civilized Nations

Paragraph (c) of Article 38 identifies general principles of law recognized by civilized nations as the third source of international law. This source has gained importance in recent years, signifying a key development in international law.

General principles include only those widely recognized by leading legal systems. As Professor Schwenzer notes, they comprise legal principles common to many civilized nations. Principles like “good faith,” “negligence,” and “res judicata” exemplify this source. A general principle may arise from national legal systems and gain international application, highlighting justice and fairness.

Important Cases Involving General Principles

In R. v. Keyn, the court affirmed that international law is based on principles of justice and equality, showcasing the importance of general principles recognized by civilized nations.

In United States v. Schooner, the court emphasized that international law should align with principles accepted by civilized states.

Judicial and Arbitral Decisions

The International Court of Justice serves as the primary tribunal for international law. Although its decisions do not create binding general rules, they provide crucial guidance. Article 59 specifies that ICJ decisions bind only the parties involved in a specific case.

Juristic Opinion

The writings of highly qualified jurists also aid in developing international law. Their opinions serve as subsidiary means for determining rules.

Resolutions of International Institutions

While Article 38 does not explicitly mention the decisions of international organizations, their role has become increasingly significant. Resolutions from entities like the United Nations can influence customary law and state behavior.

Conclusion

Understanding the sources of international law is essential for navigating global governance complexities. These sources—including treaties, customs, general principles, judicial decisions, and the influence of international institutions—form the framework for international relations and uphold the rule of law.

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