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Max Planck Encyclopedia of Public International Law [MPEPIL]

Pacta Sunt Servanda

Anthony Aust

From: Oxford Public International Law (http://opil.ouplaw.com). (c) Oxford University Press, 2015. All Rights Reserved.date: 22 July 2019

General principles of international law — Vienna Convention on the Law of Treaties — Treaties, conclusion — Treaties, entry into force — Good faith — Treaties, invalidity, termination, suspension, withdrawal — Pacta sunt servanda — Object & purpose (treaty interpretation and)

Published under the auspices of the Max Planck Foundation for International Peace and the Rule of Law under the direction of Rüdiger Wolfrum.

A.  Introduction

The pacta sunt servanda rule embodies an elementary and universally agreed principle fundamental to all legal systems (General Principles of Law). Although its good faith (bona fide) element runs through many aspects of international law—and the legal effect of certain unilateral statements rests on good faith—it is of prime importance for the stability of treaty relations (treaties). The oft-quoted Latin phrase means no more than that agreements which are legally binding must be performed. The third preamble to the Vienna Convention on the Law of Treaties (1969) (‘VCLT’) notes that ‘the principles of free consent and of good faith and the pacta sunt servanda rule are universally recognised’. The rule is stated in the one sentence of Art. 26, entitled pacta sunt servanda: ‘Every treaty in force is binding upon the parties to it and must be performed in good faith’.

In its final report and set of draft articles with commentary on draft Art. 23 VCLT (later Art. 26 VCLT), in para. 1 the International Law Commission (ILC) saw the phrase as representing ‘the fundamental principle of the law of treaties’. The International Court of Justice (ICJ) held that the principle of good faith is a legal principle which forms an integral part of the pacta sunt servanda rule (Case concerning the Gabčíkovo-Nagymaros Project [Hungary v Slovakia], paras 114, 142; Gabčíkovo-Nagymaros Case [Hungary v Slovakia]). It goes almost without saying that the pacta sunt servanda rule applies only to instruments that qualify as treaties. The VCLT of course applies to many other stages in the treaty-making progress.

A simple illustration of the application of the good faith principle is the provision in Art. 23 (1) of the United Nations Charter that the ‘Republic of China’ and the ‘Union of Soviet Socialist Republics’ shall be permanent members of the Security Council (United Nations [UN]; United Nations, Security Council). Although the names of both States have since changed, it would not only have been politically inept, but legally an act of bad faith, for any Member of the UN to propose that the Charter be first amended before either State could take its seat. In other words, like domestic law today, international law looks more to the substance than the form.

B.  Scope of Application

The pacta sunt servanda rule is qualified so as to apply only to a treaty which is ‘in force’ (Treaties, Conclusion and Entry into Force). A State which has signed a treaty subject to ratification, or expressed consent to be bound by a treaty, but the treaty has not yet entered into force, has only a limited obligation under Art. 18 VCLT not to defeat the object and purpose of the treaty prior to its entry into force (Treaties, Object and Purpose). Art. 18 VCLT requires a State:

to refrain from acts which would defeat the object and purpose of a treaty’ when:

(a)  it has signed the treaty…subject to ratification, until it shall have made its intention clear not to become a party to the treaty; or

(b)  it has expressed its consent to be bound by the treaty, pending the entry into force of the treaty and provided that such entry into force is not unduly delayed.

Occasionally, it is argued that a State which has not yet even ratified a treaty must, in accordance with Art. 18 VCLT and the pacta sunt servanda rule, nevertheless comply with it, or at least do nothing inconsistent with its provisions. This is clearly wrong, since the act of ratification would then have little or no purpose, the obligation to perform the treaty being then not dependent on ratification and entry into force.

The requirement in Art. 18 para. (a) VCLT is much easier to apply, and we now have a high-profile example. The United States (‘US’) did not like the Rome Statute of the International Criminal Court (ICC), which the previous Administration had signed. Signature, being a physical act, only its legal effect can be nullified; a treaty cannot therefore be ‘unsigned’. Even the most careful use of erasing fluid would not be effective legally. Since under the rule in Art. 18 VCLT the legal effect of simple signature by the US was that it had an obligation to refrain from acts which would defeat the object and purpose of the treaty until it had made clear its intention not to ratify it, the US needed to send a diplomatic note to the depositary saying that it did not intend to become a party (see also Démarche, Diplomatic). This it did on 6 May 2002. The legal effect is similar to the withdrawal of an instrument of ratification before entry into force (see also Treaties, Conclusion and Entry into Force).

Under Art. 18 para. (b) VCLT, once a State has expressed its consent to be bound (eg has ratified), the obligation to refrain from acts which would defeat the object and purpose of the treaty continues pending its entry into force, provided that event is ‘not unduly delayed’. There is uncertainty both as to the extent of the obligation and the proviso. What is certain is that only by examining the treaty in question in the light of all the circumstances can one determine whether the provision might apply (see also Interpretation in International Law). There is virtually no practice but, given the manner in which it is worded, the discussions in the ILC, and the views of writers, it is possible to formulate the following propositions.

A State is not required to comply in any general sense with a treaty or its object and purpose before it enters into force for that State. The obligation is only to ‘refrain’ (a relatively weak term) from acts which would ‘defeat’ (a strong term) the object and purpose of the treaty. The State must therefore not do anything which would prevent it being able fully to comply with the treaty once it has entered into force. It follows that it does not have to abstain from all acts which will be prohibited after entry into force. But the State must not do an act which would (not merely might) invalidate the basic purpose of the treaty. Thus, if the treaty obligations are premised on the status quo at the time of signature, doing something before entry into force which alters the status quo in a way which would prevent the State from performing its obligations under the treaty would be a breach of the article. The test is objective, and it is not necessary to prove bad faith. In the following examples, there would probably be a breach of the obligation:

  1. a)  The treaty provides for the return of objects, which are then destroyed by the possessor State before entry into force.

  2. b)  The treaty provides for territory to be ceded. Before entry into force the ceding State transfers part of the territory to a third State.

  3. c)  A number of States sign the treaty, each undertaking to reduce their existing armed forces by one-third. Entry into force has not been unduly delayed. After ratifying the treaty, a State then announces that it has embarked on a long-term programme to double its forces. The position would be different if the State had signed subject to ratification: its announcement would then amount in effect to an expression of its intention not to become a party.

The pacta sunt servanda rule does not apply to an invalid treaty (Treaties, Validity). But this is by no means easy to apply, there being a natural presumption that every treaty is valid (Art. 42 VCLT), which is not at all easy to rebut.

10  Similarly, the pacta sunt servanda rule does not apply if a treaty is terminated or suspended (Treaties, Suspension: Treaties, Termination).

11  The VCLT does not provide a rule regarding the effects of armed conflicts on treaties (Armed Conflict, Effect on Treaties). A study by the ILC shows that the outbreak of an armed conflict does not ipso facto terminate or suspend the operation of treaties (UN Doc A/CN.4/570). The ILC has now embarked on a study of the effect of an armed conflict on treaties.

C.  Legal Consequences of the Rule

12  It goes without saying that if a party to a treaty does not perform it, the party will, to the extent of the non-performance, be in breach of its international obligations to the other party or parties. This would raise issues of State responsibility for the breach. A breach which is ‘material’ also entitles another party to invoke the breach as a ground for termination of the treaty or suspending its operation in whole or in part (Art. 60 VCLT).

13  The pacta sunt servanda rule in Art. 26 VCLT is immediately followed in Art. 27 VCLT by its corollary: a party may not invoke the provisions of its internal law as justification for its failure to perform a treaty, which would include supranational law such as that of the European Union (see also European Community and Union Law and International Law, International Law and Domestic [Municipal] Law). Thus, if a new law, or modification to an existing law, is needed (the law may already be in place) in order to carry out the obligations imposed by a treaty, a negotiating State should ensure that this is done at least by the time the treaty enters into force for that party. If this is not done, not only will the State risk being in breach of its treaty obligations, but it will be liable in international law to another party if this results in that party or its nationals suffering harm. Although it may be tempting, a State cannot plead that it is waiting for its parliament to legislate. Even if the treaty does not enter into force for the State at the time it consents to be bound, the date of entry into force may come earlier than expected. It is therefore desirable that any necessary legislation is in place before the State gives its consent, though the actual coming into force of the legislation can certainly be postponed until the entry into force of the treaty for that State.

14  It goes without saying, that even when a treaty does not require full implementation in domestic law, a party must ensure that it will be able to comply with those obligations which do not need legal implementation. This is particularly so with certain provisions of treaties on disarmament.

15  A State cannot plead a change of government to excuse failure to implement a treaty, since the treaty is entered into on behalf of the State, not the regime then in power (see also Regime Change). So, international law requires the new government of the State to perform the treaty, unless it can lawfully terminate or withdraw from it. It is not easy for a party to plead the invalidity of the treaty on the ground that its consent to be bound was expressed in violation of its internal law (Art. 46 VCLT).

16  A State must also ensure that its new treaty obligations do not conflict with its other treaty obligations (Treaties, Conflicts between; see also Treaties, Conflict Clauses).