In the decentralized international legal system, lacking formal institutions of law – making the question of identifying the sources of international law is complicated.
A pragmatic response to the question has been found in the provisions of Article 38 of the statute of the international court of justice, which provides that the court is to 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- Judicial decisions and the teaching of the most highly qualified publicists of the various nations, as subsidiary means for the determination of the rules of law”.
It is clear that Article 38 does not provide a complete list of the sources of international law. It is rather a direction to the court as to the various materials it should consider when deciding disputes submitted to it.
Moreover, apart from the single reference to “Subsidiary means” in (d), there is no indication in Article 38 of the priority or hierarchy of the sources of international law. Because it was intended that the court should consider each “source” simultaneously, given that international law must be regarded as an integrated system of legal rules and not merely an amalgam of various unrelated principles. So, initially, existing relevant treaty provisions between the parties to the dispute must be applied. In the event of no prevailing provision, a custom, which is accepted as legally binding, should be applied.
If neither a treaty provision nor a custom can be identified the “general principles of law” may be invoked; while finally, under Article 38 judicial decisions and writing may be utilized as subsidiary means of determining the rules of international law.
Each category of law cited in Article 38 will now be examined.