The rule pacta sunt servanda is one of the foundations of the international law of treaties. The duty to perform treaties in good faith contributes decisively to the stability of international relations. However, there are situations where the continuing strict obligation to comply with a treaty appears inequitable or impossible to comply with.
The disappearance of an object which is indispensable for the execution of the treaty prevents the compliance with the treaty obligations. Likewise, a fundamental change of circumstances may make it unacceptable for one party to continue to be bound by the treaty. On the other hand, softening the principle of pacta sunt servanda too much might entail legal insecurity.
Hence, there is an inherent tension between the principle of pacta sunt servanda and the necessary dynamic of the law, which is bound to remain open to subsequent changes. A systematic presentation of the limits of pacta sunt servanda in cases of changed circumstances is thus indicated. Recent jurisprudence of international tribunals, such as the arbitral decisions in the Rainbow Warrior case (1990) and in LAFICO v Burundi (1991), the judgement of the International Court of Justice in the Gabcíkovo-Nagymoros case (1997), as well as the Racke-decision of the European Court of Justice (1998) shows the timeliness of the inquiry.
This project investigates those mechanisms of the international law of treaties and of the law of state responsibility, which regulate reactions to subsequent changes in the absence of applicable treaty provisions. The notion of
"subsequent changes of circumstances" is broadly understood and not limited to the classical case of rebus sic stantibus, as embodied in Article 62 of the Vienna Convention of the Law of Treaties (VCLT); obsolescence and supervening impossibility of performance (Art 61 VCLT) are examined in addition. Furthermore instances of the law of state responsibility, force majeure and necessity (Art 23, 25 ILC Articles on State Responsibility) which are circumstances precluding the wrongfulness of non compliance with treaty obligations, are analysed.
Open questions regarding the application of the different mechanisms, the procedures for their assertion and their legal consequences as well as their relevance for the rule of pacta sunt servanda are addressed. The question is raised, furthermore, whether the mechanisms are sufficient to alleviate the tension between the pacta sunt servanda rule and changing circumstances. Are there other means to adapt a treaty to subsequent changes? Might the late formulation of reservations as proposed by Special Rapporteur Pellet or the principle of approximate application as relied upon by Slovakia in the Gabcíkovo-Nagymoros case be viable options?
Finally, there are indications that the rule pacta sunt servanda needs to be applied differently to different categories of treaties. An indication for this assumption is to be found in Art 62 (2.a) VCLT, which exempts treaties
establishing a boundary from the application of Art 62 VCLT. On the other hand, politically highly sensitive treaties (treaties of alliance, treaties establishing military bases) are considered of being subject to denunciation.
Given the inconsistent state practice, it may not be possible to formulate a general theory of the relevance of pacta sunt servanda to different categories of treaties. However, the examination should at least lead to the isolation of its cardinal elements.
