Sources of International Law
For the purposes of this Guide, International law is the set of agreements, treaties, norms, rules and standards which relate to relations between nations and are binding on them. Article 38 of the Statute of the International Court of Justice (ICJ), the primary judicial body within the United Nations system, defines the general sources of International Law. These include:
- International Conventions[1] recognized between States: The treaties that States have ratified are binding upon them. Mere signing of the treaty does not make its provisions binding on the State, but expresses an intention to observe the provisions of the treaty domestically. The provisions of a treaty become binding upon a state once it has ratified the treaty. Examples of such international conventions include the United Nations human rights conventions.
- Customary Law derived from the general accepted practice of States: Customary Law is not codified into a singular body of law like a treaty rather they are a set of rules which are binding on states due two factors: 1) These rules are widespread and consistently followed by States and 2) these rules are followed because States believe them to be legally binding. The first factor is easy to understand, however, the second factor, also known as ‘opinio juris’ or an ‘opinion of law’, requires further elaboration. Not all widespread and consistent actions done by States are customary law, the reason for this is that they lack the required opinio juris, i.e. these actions are not undertaken out of a legal obligation that the State feels. Opinio juris can, therefore, be defined as the subjective sense of a State that the action it takes, it does so because it is under a legal obligation to act in this manner.Well established principles of customary law can later be codified into treaties. An example of this is the Vienna Convention on Diplomatic Relations of 1961. Diplomatic relations have existed for thousands of years between States, Empires, and Kingdoms as have special rules that States have observed in relation to diplomats. Clearly, therefore, the Vienna Convention did not establish the rules, in fact, these diplomatic rules developed out of widespread and consistent State practice undertaken due to a sense of legal obligation to the other State i.e. customary law. Thus, we can see that the customary law on diplomatic relations was well established much before the Vienna Convention was drafted and the Convention merely codified the custom that already existed. With this reasoning, we can understand that States that have not ratified by the Vienna Convention would still be bound by the customary law on diplomatic relations. Furthermore, if the Vienna Convention was to cease to operate for some reason, States would nonetheless still be bound by the customary law that existed on the issue. Customary law binds all States except those that can demonstrate that they have persistently objected to the custom from before it was established – a difficult task in most cases.
- General principles of law recognized by nations existing in their domestic legal systems.
- Judicial decisions and Scholarly writings of the highest qualified publicists: These two are considered as a subsidiary for determining the rules of international law. Judicial decisions and scholarly writings are non-binding laws however judicial decisions remain more influential for the ICJ and the national courts.
Other non-binding sources of international law also exist which include United Nations General Assembly (UNGA) resolutions, the position of States within the United Nations System, and International Law studies produced by the International Law Commission for the UNGA.
[1] The term convention, covenant, treaty, agreement, etc. can be used interchangeably. Any document, regardless of its name, which expresses the will of the State parties to be legally bound by it will fulfil this definition.
