This international principle is embodied in preambular para. 3 of the Vienna Convention. First of all, it is the corollary of the prohibition of the threat and use of force contained in the Charter of the United Nations (Article 2 (4)) which legitimates such behaviour only in specific circumstances. The severance or absence of diplomatic (or consular) relations between two or more States does not prevent the conclusion of treaties between those States (Article 74).
According to the principle of free consent, international agreements
are binding upon the parties and solely upon themselves. These parties cannot create either obligations or rights for third States without their consent (rule of pacta tertiis nec nocent nec prosunt - Article 34). The only explicit exception to this rule appears in Article 22 (1) which is an expression of the favor contractus principle and concerns the withdrawal of reservations.
Another important principle which can be deducted from the free
consent rule is expressed by the latin phrase lex posterior derogat legi
priori. According to this rule, a later treaty prevails over an earlier one when two treaties exist which relate to the same subject-matter (Article 30 para. 3). This principle will be dealt with in the context of treaty amendments.
It is understood that by giving its consent, a State binds itself in respect of its entire territory and not retroactively, unless a different
intention is established (Articles 28 and 29).
