The favor contractus principle has a double impact on the legal regime of reservations:
- In order to facilitate both the entry into force of a convention and
a wide participation to it, the Vienna Convention establishes
practically no obstacles to the declaration of reservations,
although this is done at the price of the integrity of the treaties.
Furthermore, silence amounts to agreement (Article 20 (5))
so that in the reality of treaty relations, in particular with regard
to universal treaties, the entry into force of a reservation can be
almost automatically assumed.
- However, a return to treaty integrity is made even easier, since a
reservation can be withdrawn at any time even without the
consent of those States which had previously accepted
(Article 22 (2)). In that case, the favor contractus principle
supersedes the free consent rule.
In accordance with the free consent principle the issue of the permissibility of reservations does not arise when a treaty straightforwardly prohibits them.
The issue is of minor importance when a treaty accepts only specific reservations; in that case one has to question whether a specific reservation is still covered by the authorization expressed in the treaty.
The matter gets complicated when one has to decide whether a reservation is compatible with object and purpose of the treaty in question (see Article 19 (c)).
Since the Advisory Opinion of the International Court of Justice of
it is this compatibility with object and purpose of the treaty which constitutes the touchstone of its admissibility.
Despite its vague content - but in default of a better alternative - the "incompatibility with the object and purpose of the treaty"-formula
has been included into the Vienna Convention not in its Article 19(c) but also in its Articles 18, 20 (2), 31 (1) and 33 (5). According to this formula the States decide for themselves whether the reservation declared by another State Party is to be considered compatible with the object and purpose of a given treaty or not.
If a State Party comes to the conclusion that the reservation made by another State is not permissible, then it can raise an objection by the end of a period of twelve months after it was notified of the reservation (Artikel 20 (5)). The objection's effect is that the provisions to which the reservation relates do not apply to the extent of the reservation as between the State which has made the reservation and the one which has raised an objection.
However, if the State which raises the objection wants to exclude the entry into force of the whole treaty between itself and the reserving State, it has to do do it explicitly (Article 21 (3)). It is only in that case that there is a difference between the legal effects following from the acceptance of a reservation and those which are the consequences of objecting to it. Paradoxically, the legal consequences are otherwise the same.
Eventually, disputes concerning the admissibility of reservations can only be solved through a dispute settlement mechanism. Such a procedure has to be foreseen either in the concerned treaty or in an agreement otherwise entered into by the States Parties.
A very controversial issue in this regard is whether a reservation incompatible with the aim and purpose of a treaty is to be considered as lack of agreement or whether it is only the reservation itself which has to be considered null and void.
This is a particularly thorny issue in case of reservations made to human rights treaties.
This question can even lead to ideological confrontations when a State makes a reservation which declares the priority of islamic law (Sharî'a) over the provisions of such treaties.
In general, the procedure to be followed in case of reservations is characterized by the fact that for reasons of legal security the various unilateral declarations, i.e.
- the reservations themselves, the objections to them
as well as
- the withdrawal of reservations and objections
must be formulated in writing (Article 23 (1) and (4)).
If a reservation is formulated when signing the treaty without expressing at the same time the consent of the State to be bound by it, the reservation must be formally confirmed when the State expresses its consent to this effect (Article 23 (2)).
In multilateral treaty practice, it is the task of the various depositaries to receive the reservations, the objections and the withdrawals and to inform the other States Parties about these communications (Article 77 (1)(c) and (e)).
