This principle expresses the preference of international treaty law for the maintenance and the conclusion of traties over expiry for reasons of form.
Hence, unless the treaty otherwise provides, a multilateral treaty does not terminate by reason only of he fact that the number of the parties falls below the number necessary for its entry into force (Article 55).
The Vienna Convention also sanctions the prohibition to denounce a treaty or to withdraw from it, if it does not foresee itself these forms of termination. This applies, of course, unless the parties did not wish, be it by tacit understanding, a different solution (see Article 56).
Likewise, in order to uphold the validity of treaties, Article 68 allows parties to revoke at any time before they take effect notifications or instruments designed to lead to invalidity, even this is done only in relationship to one single other party.
In practice, however, the most important expression of the favor contractus principle is contained in the provisions of the Vienna Convention concerning reservations; this website will devote to them a separate chapter. In particular, whereas a reservation has to be accepted implicitely or explicitely by at least one other State Party (Article 20 (2),(4)(c) and (5)), it can be withdrawn at any time without the consent of the State or States which had accepted it in the first place (Article 22 (1)). This is the only explicit exception to the free consent principle.
The favor contractus principle can be found in Article 74, too. This provision clarifies that the severance or absence of diplomatic or consular relations does not prevent concerned States to conclude treaties between themselves.
