Validity of Treaties, and Jus Cogens

In one line

A treaty is presumed valid, may be impeached only on the grounds the Convention states, and the grounds run from defects that merely make consent voidable to coercion and conflict with a peremptory norm, which make the treaty void.

The presumption, and the closed list: article 42

Article 42(1). The validity of a treaty, or of the consent of a State to be bound, may be impeached only through the application of the present Convention.

Article 42(2). Termination, denunciation, withdrawal or suspension may take place only as a result of the application of the provisions of the treaty or of the Convention.

That is the article that makes the rest of Part V an exhaustive code rather than examples. A State that wishes to escape a treaty must point to a ground in the treaty itself or in the Convention.

Article 43, the residue. Invalidity, termination, denunciation, withdrawal or suspension shall not in any way impair the duty of any State to fulfil any obligation embodied in the treaty to which it would be subject under international law independently of the treaty. So killing the treaty does not kill the customary rule inside it, which is the mirror image of article 38 in [Rights and Duties of the Parties, and Third States].

Separability and loss of the right: articles 44 and 45

Article 44(1) and (2). A right to denounce, withdraw or suspend, and a ground for invalidating, terminating, withdrawing or suspending, may be exercised or invoked only with respect to the whole treaty, unless the treaty otherwise provides or the parties agree, and except as articles 44(3) to (5) and article 60 provide.

Article 44(3), when clauses may be severed. Where the ground relates solely to particular clauses, it may be invoked as to those clauses only where (a) they are separable in their application, (b) it appears from the treaty or is otherwise established that acceptance of those clauses was not an essential basis of the consent of the other party or parties to be bound as a whole, and (c) continued performance of the remainder would not be unjust. All three conditions must be satisfied.

Article 44(4). In cases of fraud and corruption, the injured State may choose: the whole treaty, or, subject to paragraph 3, the particular clauses.

Article 44(5), the rule to memorise. In cases falling under articles 51, 52 and 53, that is coercion of a representative, coercion of a State, and conflict with a peremptory norm, no separation of the provisions is permitted. The treaty falls entirely.

Article 45, loss of the right. A State may no longer invoke a ground under articles 46 to 50 or articles 60 and 62 if, after becoming aware of the facts, it has expressly agreed that the treaty is valid or remains in force, or must by reason of its conduct be considered as having acquiesced.