Customary International Law and Treaties
Customary International Law
Customs develop almost subconsciously within a group and are maintained by the members of that group through social pressures and with the aid of various other, more tangible implements. Customs are not written or codified. While not the best instrument for regulating complex issues in world affairs, custom may meet the contingencies of modern life in particular situations. “Instant customary law” can sometimes prescribe valid rules without undergoing a long period of gestation. Custom mirrors the characteristics of the decentralized international system. It reflects a consensus approach to decision-making, with the ability of the majority to create a new law binding upon all.
Article 38 and the Elements of Custom
Article 38 of the Statute of the International Court of Justice defines custom as “evidence of a general practice accepted as law.” This definition highlights two basic elements in the formation of a custom:
- The material facts: The actual behavior of states.
- The psychological or subjective belief (opinio iuris): The belief that such behavior is “law” (opinio iuris sive necessitatis).
Opinio iuris is the belief by a state that it behaved in a certain way because it was under a legal obligation to do so. French writer François Gény first formulated this idea to differentiate legal custom from mere social usage. Positivists emphasize the importance of this psychological element, asserting that states are only bound by what they have consented to. Other writers have argued that opinio iuris is difficult to prove and therefore not of tremendous consequence.
The Material Fact: State Practice
The actual practice engaged in by states is the initial factor to consider. Several aspects are relevant, including duration, consistency, repetition, and generality.
- Duration: While most countries specify a recognized time-scale for accepting a practice as a customary rule within their municipal systems, international law has no rigid time element. It depends on the circumstances of the case and the nature of the usage. Duration is not the most important component of state practice.
- Continuity and Repetition: The basic rule regarding continuity and repetition was established in the Asylum case (1950).
Opinio Iuris: The Subjective Element
Once a specified usage is established, it’s crucial to consider how the state views its own behavior. The opinio iuris, or belief that a state activity is obligatory, is the factor that transforms usage into custom and makes it part of the rules of international law. A key case illustrating this is the Lotus case.
A significant problem with opinio iuris is that it calls for behavior in accordance with the law. This raises the question: How can new customary rules be created, since that obviously requires action different from, or contrary to, what is currently regarded as law?
The answer lies in treating the matter as a process. States behave in a certain way, believing that such behavior is either already law or is becoming law. Rigid definitions of legality must be modified to assess whether the legitimating stamp of state activity can be provided. States must be aware that when one state takes a course of action, it does so because it regards it as within the confines of international law, and not, for example, as a purely political or moral gesture.
Treaties
Treaties are of obligatory nature, founded upon the customary international law principle that agreements are binding (pacta sunt servanda). Treaties can be divided into two broad categories:
- Law-making treaties: These treaties involve a large number of states elaborating their perception of international law on a given topic or establishing new rules to guide their future international conduct. They are also referred to as normative treaties.
- Treaty contracts: These are not law-making instruments in themselves, as they involve only a small number of states and are limited to a specific topic. However, they may provide evidence of customary rules.