b) Pacta tertiis nec nocent nec prosunt
A treaty binds the parties and only the parties; it does not create obligations for a third State without its consent (Article 34), since sovereignty implies that there is no agreement without free consent. "Third State" means a State which not a party to a given treaty (Article 2 (1)(h)).
The acceptance of an obligation by a third State must be expressed both expressly and in writing (Article 35), in order to avoid doubts as to the extent of the obligation which had been previously defined by others.
A consent which as been expressed in such a way can be qualfied as quasi-contractual. Hence, it is only logical that the obligation can only be revoked or modified with the consent of all parties to the treaty as well as of the third State, unless it is established that they had otherwise agreed (Article 37(1)).
Although a third State cannot be granted a right without its approval, its assent is nevertheless presumed (Article 36(1)). A third State which exercising such a right is under an obligation to comply with the conditions for its exercise provided for in the treaty or established in conformity with the treaty (Article 36(2)). The rights granted to a third State can be revoked by the States Parties unless it is established that the right was intended not to be revocable or subject to modification without the consent of the third State. In such a case, the burden of proof lies with the third party benefiting from the right or rights.
The principle according to which a treaty cannot create rights or obligations for a third party without its consent is expressed in Latin by the phrase "pacta tertiis nec nocent nec prosunt". This rule also applies when two or more parties of a multilateral convention conclude an agreement to modify the convention only in relation to each other, since they hereby exclude third States from their agreement in spite of the fact that the latter are parties to the original treaty (see Article 41).
