Modern Treaty Law and Practice

This suggestion that all states are bound by a (multilateral) treaty once it has entered into force is a common misconception, even among diplomats, and The Times. When a treaty has entered into force, it binds only those states that have consented to be bound by it. A treaty is therefore not like national legislation which, once in force, applies to all to whom it is directed. A treaty is much closer to a contract. But if the treaty reflects (or, rather, comes to reflect) the rules of customary international law a non-party can be bound by those rules, though only as customary international law: it is not a party to the treaty. (For the position of third states, see Chapter 14.)

Each of the states for which a treaty is in force is a ‘party’ (Article 2(1)(g)). Thereafter it should never be referred to by the – uninformative and misleading – term ‘signatory’. But it must also be remembered that when a state expresses its consent to be bound, it does not necessarily mean that the treaty will enter into force for it then: it will depend on whether the treaty is already in force for the states that have already consented to be bound or whether further consents are needed to bring it into force. A state's consent may, of course, have the effect of bringing the treaty into force if it is the last one needed to do that.