International lawLesson 1 of 3 in the course Sources of international law

Customary International Law: Formation, Scope, and Special Norms

5 flashcards · 5 quiz questions · 5 match pairs · 4 fill-in sentences · English

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Summary

Customary international law develops from established international practices that states follow as law. Unlike treaties, it is often unwritten. This lesson introduces the two elements used to identify custom and the kinds of evidence that can help establish it.

Customary international law consists of legal obligations arising from established or usual international practices. Along with treaties and general principles of law, custom is regarded as a primary source of international law, including by the International Court of Justice (ICJ).

All flashcards

Customary international law
International law formed from sufficiently general state practice accepted as law.
Opinio juris
The belief that a state practice is legally required or permitted.
Persistent objector doctrine
A state that clearly and consistently objects while ordinary custom forms may avoid being bound by it.
Jus cogens
A peremptory norm from which no derogation is permitted.
Erga omnes obligation
An obligation owed to the international community as a whole.

Quiz questions

  1. What two elements are used to identify customary international law?Answer: State practice and opinio juris.
  2. What must a state generally do to invoke the persistent objector doctrine for an emerging ordinary customary rule?Answer: Object clearly and consistently while the rule is forming.
  3. When may a state that has not ratified a treaty still be bound by a rule also found in that treaty?Answer: When the rule independently qualifies as customary international law.
  4. What is the effect of a treaty that conflicts with a jus cogens norm?Answer: It cannot make conduct conflicting with that norm lawful.
  5. Which group consists of forms of evidence identified by the International Law Commission in 1950?Answer: Treaties, national legislation, diplomatic correspondence, and international-organization practice.

Based on the Wikipedia article Customary international law, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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