- •I. Sources of international law as applied by the International Court of Justice
- •What is the force of a treaty for a State which has signed it but has not ratified it yet?
- •Can a third State be bound by a provision of a treaty?
- •What is the relationship between a treaty and jus cogens norms?
- •Jus cogens
- •Erga omnes
- •Principles of interpretation of a treaty. How can travaux preparatoires be relevant to the treaty interpretation?
- •What is customary international law? What are the elements of customary international law?
- •International customary law
- •How does a rule become customary international law?
- •Two criterias
- •Silke Sahl What is Customary International Law?
- •Evidence of Customary International Law
- •§ 103 Evidence of International Law
- •What is opinio juris? How can it be proven?
- •What is State practice? Where can it be found?
- •1) Both physical and verbal acts of States constitute practice that contributes to the creation of customary int. Law.
- •2) The practice of the executive, legislative and judicial organs of a State can contribute to the formation of customary international law.
- •2) State practice concerned must be both extensive and representative.
- •3) The time necessary to form a rule of customary international law through the adoption of virtually uniform, extensive and representative practice.
- •Can a provision of a treaty become customary international law? If so, what is required for a norm of a treaty to become customary?
Silke Sahl What is Customary International Law?
"Customary international law results from a general and consistent practice of states followed by them from a sense of legal obligation."[1]
This definition was published in §102 (2) of the Restatement of the Law, Third, Foreign Relations Law of the United States, published by the American Law Institute in 1987. The Restatement's reporters' notes for this section state that "No definition of customary law has received universal agreement, but the essence of Subsection (2) has wide acceptance" and goes on to explain various difficulties in defining custom."[2]
When is state practice considered to be customary international law? The Restatement calls for two-pronged approach to determining custom requiring both a general and consistent practice and a sense of legal obligation (opinion juris sive necessitates). J.L. Brierly describes it as follows: "Custom in its legal sense means something more than mere habit or usage; it is a usage felt by those who follow it to be an obligatory one. There must be present a feeling that, if the usage is departed from, some form of sanction probably, or at any rate ought to, fall on the transgressor."[3] Obviously, terms such as "a feeling that", "will probably" and "ought" are difficult to prove. As Mark Janis puts it in his book, An Introduction to International Law, "The determination of customary international law is more an art than a scientific method."[4] This is a complex and fascinating area of law that is addressed by the many excellent books and articles on customary international law. This guide focuses on finding the resources that provide evidence of international custom.
Evidence of Customary International Law
The Restatement describes the evidence of international law in §103. Of particular interest to the researcher of custom is §103(2)(d) which describes the evidence of pronouncements of states:
§ 103 Evidence of International Law
(1) Whether a rule has become international law is determined by evidence appropriate to the particular source from which that rule is alleged to derive (§ 102).
(2) In determining whether a rule has become international law, substantial weight is accorded to
(a) judgments and opinions of international judicial and arbitral tribunals;
(b) judgments and opinions of national judicial tribunals;
(c) the writings of scholars;
(d) pronouncements by states that undertake to state a rule of international law, when such pronouncements are not seriously challenged by other states.[10]
The Restatement comments state "Thus, for customary law the "best evidence" is the proof of state practice, ordinarily by reference to official documents and other indications of governmental action."[11] InPrinciples of Public International Law, Ian Brownlie lists the following sources as evidence of custom: "The material sources of custom are very numerous and include the following: diplomatic correspondence, policy statements, press releases, the opinions of official legal advisers, official manuals on legal questions, e.g. manuals of military law, executive decisions and practices, orders to naval forces etc., comments by governments on drafts produced by the International Law Commission, state legislation, international and national judicial decisions, recitals in treaties and other international instruments, a pattern of treaties in the same form, the practice of international organs, and resolutions relating to legal questions in the United Nations General Assembly."[12]