opinio juris

law

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July 1, 2026

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Opinio juris sive necessitatis is a Latin phrase meaning "opinion that an act is necessary by rule of law". It is a fundamental element in the formation of customary international law. For a practice to become binding international custom, it must not only be a consistent and uniform usage by states (the material fact) but also be accepted by states as a legal obligation. This acceptance, or opinio juris, signifies that states believe the practice is required by law, not merely followed out of habit or convenience. Without this legal conviction, a widespread practice remains mere usage and does not create binding international law.1

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law of war
Law by custom
…and in the belief (called opinio juris: “opinion of the law”) that that practice is in conformity with international law. Much of this customary international law has found its way into the various conventions described above. Therefore, it may properly be argued that, although a particular state is not a…
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…and in the belief (called opinio juris: “opinion of the law”) that that practice is in conformity with international law. Much of this customary international law has found its way into the various conventions described above. Therefore, it may properly be argued that, although a particular state is not a…
Read More