opinio juris

Opinio juris sive necessitatis is the psychological element of customary international law. A rule of custom requires two things: general and consistent state practice, and acceptance of that practice as law (opinio juris). Without the second, a practice is only usage or courtesy (comity).

The ICJ in the North Sea Continental Shelf cases held that states must feel they are conforming to a legal obligation; mere frequency of action is not enough. Evidence of opinio juris comes from official statements, legal opinions, national legislation and judgments, votes on UN General Assembly resolutions, and treaties.

Example

Because states adopted the equidistance method without any sense of legal obligation, the ICJ found no opinio juris and no binding custom.

In Indian law

• Article 38(1)(b), Statute of the International Court of Justice
• North Sea Continental Shelf Cases (ICJ, 1969)

See also

customary international law · custom · treaty · International Court of Justice

Read more in the study notes

• Origin and development of human rights (Human Rights Law and Practice)
• Sources of law: legislation, precedent and custom (Legal Methods)
• Sources of international law (Public International Law)
• The General Assembly and the Security Council (Public International Law)