Introduction to Sources of International Law:
For there to be international law, it ought to be created, or there ought to be an international law-making system. In domestic law, for instance, common sources of domestic laws are the constitution, the legislature, common law, and customary law, among others. In international law, and per article 38 of the Statute of the International Court of Justice , the following are sources of international law:
1. International conventions, also known as treaties: Article 2 of the Vienna Convention on the Law of Treaties, 1969 defined a treaty as " an international agreement concluded between States in written form and governed by international law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation".
2. International customs or customary international law: Customary international law is characterised in article 38 as “evidence of a general practice accepted as law.” Thus, when states consistently and over a long period act in a particular way, and other states believe the acts to flow from a sense of legal obligation, such acts are likely to be considered customary international law.
3. General principles of law: Principles of law, such as res judicata, fairness and impartiality of judges, Nemo judex in causa sua (no one shall be a judge in their own case), and equality before the law among others are considered sources of international law.
4. 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
These sources are extensively discussed in subsequent notes.