Introduction
The international legal system is distinct from domestic legal systems primarily because it lacks a central legislative body with the authority to create binding law for all states. Consequently, the question of where international law comes from—its sources—is of fundamental importance. The traditional and most authoritative starting point for identifying these sources is Article 38(1) of the Statute of the International Court of Justice (ICJ). This provision, while not exhaustive, provides a framework for understanding the origins of the rules that govern relations between states. This essay will outline and explain the principal sources of international law as identified in Article 38(1), namely international conventions, international custom, and general principles of law, as well as the subsidiary means for the determination of rules of law.
International Conventions (Treaties)
Article 38(1)(a) of the ICJ Statute lists "international conventions, whether general or particular, establishing rules expressly recognized by the contesting states" as the first formal source of law. These conventions, more commonly known as treaties, are formal written agreements between two or more states. They are the most direct and explicit method of creating legal obligations. Treaties function in a similar way to contracts in domestic law, as they establish rights and duties for the parties that have consented to be bound by them, a principle known as pacta sunt servanda (agreements must be kept).
Treaties can be bilateral (between two states) or multilateral (between three or more states). While many treaties are contractual in nature, dealing with specific issues between a limited number of states, others are 'law-making' treaties. These are multilateral conventions with a large number of state parties that are intended to establish norms of general application, such as the Vienna Convention on the Law of Treaties (1969) itself, which governs the creation and operation of treaties.
International Custom
The second source listed in Article 38(1)(b) is "international custom, as evidence of a general practice accepted as law". Customary international law (CIL) is unwritten law that evolves from the established practices of states. For a rule of CIL to be established, two elements must be proven. The first is an objective element: widespread and consistent state practice. This refers to the actual behaviour of states, including their official statements, legislative acts, and actions on the international stage.
The second is a subjective element known as opinio juris sive necessitatis (an opinion of law or necessity). This means that states must engage in the practice not out of habit or convenience, but because they believe they are under a legal obligation to do so. The ICJ confirmed the necessity of both elements in the North Sea Continental Shelf Cases (Federal Republic of Germany v Denmark; Federal Republic of Germany v Netherlands) [1969] ICJ Rep 3. The Court found that even a significant amount of state practice was not sufficient on its own to create a customary rule without evidence that states acted out of a sense of legal duty.
General Principles of Law
Article 38(1)(c) refers to "the general principles of law recognized by civilized nations". This source is generally understood to comprise principles that are common to the major domestic legal systems of the world. Their primary function is to provide a solution where treaties or custom do not provide an answer, thereby preventing the ICJ from being unable to decide a case due to a gap in the law (a situation known as non liquet). Examples of such principles include the concept of good faith, the principle of res judicata (a matter already judged cannot be re-litigated), and the right to a fair hearing. These principles are not 'created' at the international level but are rather 'borrowed' from domestic law to support the international legal framework (Shaw, 2017).
Subsidiary Means
Finally, Article 38(1)(d) identifies "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". It is important to note that these are not formal sources of law themselves, but rather means for interpreting and clarifying the content of the law derived from the first three sources. Judicial decisions, including judgments of the ICJ and other international tribunals, are not binding precedents in the common law sense (as per Article 59 of the ICJ Statute), but they are highly persuasive and are often used to provide authoritative interpretations of the law. Similarly, the writings of respected international law scholars can help to identify and explain legal rules, particularly where state practice is unclear.
Conclusion
In summary, the sources of international law are formally enumerated in Article 38(1) of the ICJ Statute. Treaties and customary international law are the most significant sources, creating binding obligations through the express consent or established practice of states. General principles of law serve to fill gaps, while judicial decisions and academic writings act as subsidiary means for determining legal rules. Although Article 38 provides the essential framework, it is a product of its time and there is ongoing debate about its completeness, with some arguing for the inclusion of other sources such as the resolutions of international organisations. Nevertheless, a clear understanding of the sources listed in Article 38 remains the cornerstone of studying and applying international law.
References
- North Sea Continental Shelf Cases (Federal Republic of Germany v Denmark; Federal Republic of Germany v Netherlands) [1969] ICJ Rep 3.
- Shaw, M. (2017) International Law. 8th edn. Cambridge: Cambridge University Press.
- Statute of the International Court of Justice (1945).
- Vienna Convention on the Law of Treaties (1969).
