Rights and Duties of the Parties, and Third States

In one line

Every treaty in force binds the parties and must be performed in good faith, internal law is no excuse, and a treaty creates neither obligations nor rights for a non-party without its consent.

Pacta sunt servanda: article 26

Every treaty in force is binding upon the parties to it and must be performed by them in good faith.

That is the whole of article 26, and it is the foundation of the entire law of treaties. Every rule that follows is either an application of it or a carefully limited exception to it.

Three elements. The treaty must be in force, which sends the reader back to article 24. It binds the parties, which sends the reader to article 34. And performance must be in good faith, which means more than literal compliance: a party may not perform in a manner that deprives the other of the benefit of the bargain, nor exercise a right for a purpose other than that for which it was conferred.

Internal law is no excuse: article 27

A party may not invoke the provisions of its internal law as justification for its failure to perform a treaty. This rule is without prejudice to article 46.

Why the rule must exist. If a State could excuse breach by pointing to its own law, every treaty obligation would be defeasible at the will of the obligated State's legislature, and pacta sunt servanda would mean nothing.

How far it goes. It covers the whole of internal law: constitution, statute, subordinate legislation, and the decisions of the State's own courts. It does not require the State to change its internal law, but the State answers internationally for the consequences of leaving it as it is.

The saving. Article 46, dealt with in [Validity of Treaties, and Jus Cogens], concerns something different: not an excuse for non-performance but a plea that consent was invalid because it was given in manifest violation of a rule of internal law of fundamental importance regarding competence to conclude treaties. That plea is narrow, and article 27 makes clear it is the only way internal law bears on the matter.

India. The same principle explains the position in [International Law in Indian Courts]. India's monist or dualist position matters to what an Indian court will apply; it does not affect India's answerability under article 27 for a failure to perform.

Non-retroactivity: article 28

Unless a different intention appears from the treaty or is otherwise established, its provisions do not bind a party in relation to any act or fact which took place or any situation which ceased to exist before the date of the entry into force of the treaty with respect to that party.