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Part II International Responsibility—Development and Relation with Other Laws, Ch.11 The Law of Responsibility and the Law of Treaties

Joe Verhoeven

From: The Law of International Responsibility

Edited By: James Crawford, Alain Pellet, Simon Olleson, Kate Parlett

From: Oxford Public International Law (http://opil.ouplaw.com). (c) Oxford University Press, 2023. All Rights Reserved. Subscriber: null; date: 28 March 2023

Reparations — Responsibility of states — Circumstances precluding wrongfulness — Wrongful acts — Treaties, conclusion — Vienna Convention on the Law of Treaties — Treaties, interpretation — Countermeasures — Peremptory norms / ius cogens

(p. 105) Chapter 11  The Law of Responsibility and the Law of Treaties

As the Tribunal in Rainbow Warrior pointed out, ‘in the international law field there is no distinction between contractual and tortious responsibility’.1 In his fifth report on State responsibility, Ago explained the absence of such a distinction in ‘the legal order of the international community’ by the non-existence of an ‘instrument like legislation, which is at the same time voluntary and authoritative’.2 Twenty-five years later, Ago’s view appears to have been endorsed by the ILC in the final text of the Articles on State Responsibility. In the report of the ILC, it is indeed pointed out that the absence of any reference to such a distinction in the draft is a consequence of article 12, which states:

There is a breach of an international obligation by a State when an act of that State is not in conformity with what is required of it by that obligation, regardless of its origin or character.3

The Commentary to article 12 notes that the articles ‘apply to all international obligations of States, whatever their origin’.4

This affirmation is ambiguous. In the domestic laws where it is applied the distinction does not deny the rule according to which all breaches of an obligation engage the responsibility of the actor, rather only implies that the legal regime may be different depending (p. 106) on whether a contract is at issue. And in the ones where it does not exist, its absence can either be explained by the fact that the responsibility that results from the breach of a contractual obligation is subject to the general (droit commun) law or because of a lack of a general duty of care, which makes it necessary to resort to particular torts. It is true that international law now does not differentiate the legal regime of responsibility according to the (general) customary or treaty character of the breached violation. This is however not because this duality of regimes has been regarded as ill-timed. It is simply that there has been hardly any opportunity—or none has been seized—to make a statement of the established distinction between contractual responsibility and quasi-delictual responsibility. The situation would have been different had those issues been discussed in the Articles on State Responsibility adopted by the ILC. They were not. At the very most, the 1996 Draft Articles adopted on first reading subjected the reparation resulting from a crime (under former article 195) to rules partly applicable to other wrongful acts,6 introducing a distinction between criminal and delictual responsibility, if not between contractual and delictual responsibility. But the distinction was removed on second reading, which makes no mention of an international ‘crime’. Consequently, the rules applicable to responsibility are identical in respect of both categories. Of course, it cannot be excluded that a different approach will be taken in the future, even if the mutual relationship existing between a treaty rule and a customary rule should still remain different from the one existing in domestic law between a statute and a contract. Any doubt concerning their binding force reserved, the provisions of the Articles are not such that they categorically exclude that a distinction be made as far as reparation is concerned on the basis of the contractual or statutory character of the breached obligation.

If international law presents some specific characteristics in this respect, it is simply that it ignores the distinction made under domestic law between civil as opposed to criminal liability. Such a distinction was made in the famous article 19 of the first reading draft, referring to international delicts as distinguished from international crimes. Its exact scope remained largely uncertain, but it need not now be clarified. The ‘crime’ indeed was abandoned on second reading, as a result of a proposal of the new Special Rapporteur, James Crawford. There still remains a reference to ‘serious breaches of obligations under peremptory norms of general international law’, whose demarcation from ‘crimes’ remains unclear. But in any case the ‘particular consequences’ of such ‘serious breaches’, as specified in article 41 of the final Articles, are unable to give any consistency to a concept of ‘criminal’ responsibility in international law. Consequently there is no need to enter into the diffi culties traditionally related to that category under domestic law, including the identity of criminal as opposed to civil fault and the duality of the procedure and related problems (electa una via etc) for obtaining reparation.

These remarks do not imply that the responsibility envisaged by the ILC is of a civil character, equivalent to that category usually found in domestic legal system. Clearly, the ILC draft is concerned with reparation for the injury caused by an ‘internationally wrongful act’. But it deals also with countermeasures which might be taken against the State responsible for that act, which also pertains to ‘responsibility’ notwithstanding the contrary conclusion apparently suggested by the restrictive wording of article 28. Punishing a State which does (p. 107) not comply with its obligations is not the point; it is only to obtain their fulfilment in a system which does not entail any type of forced execution. It comes close to a sanction, even though it does not require any criminal responsibility. The relationship between the law of treaties and the law of responsibility must be examined with this in mind.

The relationship between the law of treaties and the law of responsibility has not been specifically addressed in any codification projects. Article 73 of the Vienna Convention on the Law of Treaties provides that ‘shall not prejudge any question that may arise in regard to a treaty … from the international responsibility of a State’,7 while article 56 ARSIWA makes clear, according to its Commentary, ‘that the present articles are not concerned with any legal effects of a breach of an international obligation which … stem from the law of treaties’ or other legal fields.8 It is therefore necessary to refer to international practice or possibly to the respective logic of articles 56 and 73 to examine the relationship between the law of treaties and the law of responsibility.

It is common to emphasize that ARSIWA refer to secondary obligations, ie those that result from breach of a primary norm. The distinction between primary and secondary rules for the purposes of ARSIWA does not shed any light on the relationship between the law of responsibility and the law of treaties. Neither is it clear that a violation of a treaty will necessarily entail breach of a primary obligation; that violation indeed calls into question the rule conferring a binding force to a pactum between States, as expressed in article 26 of the Vienna Convention, much more than the treaty whose provisions are breached. Sure, article 26 is without any practical purpose as long as promises are not exchanged, but it is still the first to be breached when those promises are not fulfilled. This ought to be prevent one from giving too much importance to approximate categorizations.

The law of treaties and wrongfulness

There is a wrongful act when a State (or any other subject of international law) fails to respect its obligation. This entails the responsibility of a State.9 The law of responsibility determines the content of that responsibility, that is to say, the consequences of the breach of the obligation. The law of treaties is not normally concerned with the content of a State’s responsibility; in principle it is limited to the question of ‘the existence, content and duration of the obligations’.10 As the International Court confirmed in the Gabcíkovo-Nagymaros Project case:

Nor does the Court need to dwell upon the question of the relationship between the law of treaties and the law of State responsibility, to which the Parties devoted lengthy arguments, as those two branches of international law obviously have a scope that is distinct. A determination of whether a convention is or is not in force, and whether it has or has not been properly suspended or denounced, is to be made pursuant to the law of treaties. On the other hand, an evaluation of the extent to which the suspension or denunciation of a convention, seen as incompatible with the law of treaties, involves the responsibility of the State which proceeded to it, is to be made under the law of state responsibility.11

(p. 108) While this conclusion may be justified (and it may be relevant beyond issues of denunciation or suspension), it does not preclude certain consequences of wrongful acts being drawn from the law of treaties, principally the invalidation or termination of certain engagements.

Four articles of the Vienna Convention12 refer expressly to wrongful conduct, as they are concerned with nullity: these are articles 49 (fraud), 50 (corruption), 51, and 52 (coercion). The purpose of these provisions is to determine the circumstances under which consent can be invalidated, without prejudging the consequences in terms of the responsibility which may arise from those same circumstances. Neither do the provisions the Vienna Convention relating to the consequences of violations of obligations for the maintaining into force of a treaty prejudge their consequences in terms of responsibility. Article 60, which incorporates the exceptio non adimpleti contractus, implies that the treaty sought to be suspended or terminated has been violated by a State party. Such is not the case as far as articles 61 and 62, which deal with impossibility of execution and fundamental change of circumstances, are concerned since they do not necessarily imply the existence of a fault. Those articles simply provide for that a State is prevented from terminating the treaty when such an impossibility or such a change is the result of a violation by that State of its obligations.

In principle there is no intersection between this area of the law of treaties and the law of responsibility, subject to two reservations. The first concerns the circumstances precluding wrongfulness in articles 20–25 ARSIWA. From the moment the wrongfulness of an act is precluded as it results from the Vienna Convention, the ‘violation’ of the treaty referred to in its articles 60, 61, and 62 should not be taken as established. Any other conclusion would be incoherent. The second reservation relates to the confl ict between article 61 of the Vienna Convention (impossibility of performance) and article 23 ARSIWA relating to force majeure, which embraces, but is not restricted to, impossibility of performance. It necessarily results from this that force majeure may operate where there is no impossibility of performance. But the contrary is not true. The impossibility to perform necessarily constitutes force majeure, at least when it does not result from a breach by the State invoking it of its obligations. Such a radical dissociation between those rules logically results in accepting that any suspension or termination of a treaty must be excluded as long as there is no impossibility of performance, even when the contracting State not complying with its obligations cannot be reproached for acting wrongfully if it establishes force majeure. This is not contradictory in itself. There is a certain logic in maintaining a treaty law link while excusing the provisional non-fulfilment of obligations contained in that treaty. Nevertheless it seems reasonable to consider that the impossibility of performance that justifies the termination of the treaty under article 61 of the Vienna Convention is fulfilled when force majeure under article 23 is definitive, even if it is true that this leads to a particularly flexible interpretation of the notion of ‘object indispensable for the execution of the treaty’. And it goes without saying that if the temporary impossibility of execution of the treaty suspends its application, then the temporary lack of respect for its dispositions should not be regarded as wrongful in the sense of ARSIWA. But it would have been more coherent to specify in the Vienna Convention that temporary force majeure may also authorize the suspension of the treaty, instead of excusing its violation on the basis of article 23 ARSIWA.

(p. 109) The law of treaties and reparation

It is mainly the violation of the provisions of a treaty which raises the issue of reparation, when it has turned out to be harmful for another State. It can nevertheless not be excluded that this question can arise from the simple fact that the treaty is concluded as long as the existence of damage is established.

(a)  Reparation and violation of a treaty

The distinction between contractual responsibility and quasi-delictual responsibility rests in domestic law on the separate conditions governing the reparation in case of breach of a contract. Although it is not necessary to examine the domestic regimes in detail, nevertheless, it is interesting to consider their essential characteristics. In countries which apply the Napoleonic code for instance, articles 1381–1383 govern quasi-delictual responsibility, and articles 1384ff contractual responsibility. The case law has since attenuated the differences existing between those regimes, while possibly introducing other distinctions. There is no need to enter into the details of those domestic regimes, as such irrelevant for international law. It nevertheless is interesting to keep in mind their essential characteristics, so as to verify whether such a distinction is compatible or not with international rules. Globally, it rests, at least in Napoleonic traditions, on rules that substantively regulate responsibility—limitation of reparation to foreseeable damage in the case of a breach of contract; absence of solidarity between debtors in delictual or quasi-delictual matters; exclusion of adjustment of responsibility (exemption clauses, etc) in non-contractual matters)—and on dispositions which determine their implementation (mise en oeuvre) such as formal notice, jurisdictional competence, prescription, etc. Clearly, the solutions are not necessarily identical in each domestic system; still these kind of issues always are the ones on which two relatively different regimes of responsibility are based.

It has never been contested in international law that the violation of a treaty obliges the State concerned to repair its harmful consequences, no matter whether this violation results from the breach of the provisions agreed on by the parties or of the rules governing their suspension or termination in whole or in part. The provisions of ARSIWA are fully applicable in this respect, for instance to decide on the attribution of a wrongful act to the State, on the circumstances precluding wrongfulness which are without prejudice to the question of compensation for any material loss according to article 27 ARSIWA, or on the forms of reparation. However they do not definitively settle any of those issues. Solidarity between debtors is apparently the only exception in this respect. While no reference was made in the Arangio-Ruiz report, this solidarity was clearly dismissed at the initiative of the new Special Rapporteur on second reading. True, the terms of article 47 remain partly unclear; nevertheless, the ILC Commentary is unambiguous in this regard. But subject to this article, the other issues are left unanswered. No conclusion whatsoever could be drawn from such a silence; the fact simply is that no answer is given in the text. It is only relevant to note that in the absence of any mechanism of compulsory settlement of disputes it would in any case be difficult to give any very useful ‘procedural’ content to the distinction between contractual and quasi-delictual responsibility, even if evolutions are possible—and desirable—as was actually suggested in the propositions made by the Rapporteur Arangio-Ruiz. That said, ARSIWA does not incorporate a distinction between contractual and quasi-delictual responsibility, and consequently any separation (p. 110) of the consequences between the two. This is not to suggest that such a distinction does not have a place in public international law; it is rather merely that the rules of public international law may be too elementary to usefully support a distinction.

(b)  Reparation and conclusion of the treaty

It is possible that the mere existence of a treaty can constitute a violation of international law, for instance where it conflicts with peremptory norms of international law (jus cogens) or is incompatible with an agreement previously concluded by all or some State parties. In these circumstances, it can be difficult to apply the usual rules of responsibility and reparation. Still, as a matter of principle, responsibility and reparation if an injury occurred are beyond dispute.

It is also possible that the decision of a State to conclude a treaty may have been taken subsequent to the wrongful act of another State; it matters little if the State which committed the wrongful act is a party or not. In such a case, there must also be reparation for the injury caused by the wrongful act from the moment when the causal link is established. Every wrongful act indeed gives rise to an obligation to make reparation for any injury. The only difficulty is that according to articles 49–52 of the Vienna Convention, the victim State might invoke the wrongful conduct as invalidating its consent to be bound by the treaty when it is constitutive of fraud, corruption, or coercion; in consequence the treaty will disappear, at least if it is bilateral. Clearly, the two perspectives are different, and do not normally intersect.13 So while the law of responsibility imposes an obligation to make reparation for injury resulting from a breach of an obligation, the law of treaties determines the existence of that obligation. Nullity results from the non-fulfilment of conditions on which the existence of a valid agreement depends; it is wholly separate from the question of fault. Nullity may therefore be invoked even where there is no fault, in cases of error or incompetence. Where the conclusion of a treaty is wrongful, the law of treaties does not prejudge the consequences. If there is an interference, it results only from the fact that the nullity may possibly suppress the injury by invalidating the consent of the injured State. But this illustrates a purely factual consequence (effet de fait) of the invalidity, as such totally unrelated with the relationship possibly existing between the law on treaties and the law on responsibility. Does this mean that the victim State is free to choose between nullity and reparation? Logically, the answer must be no. In addition to the injured State’s obligation not to contribute to the injury,14 where nullity can be invoked, if it is not invoked this must constitute consent, which is a circumstance precluding wrongfulness; but nullity cannot be ruled out where it cannot be cured (coercion). Needless to say, the obligation to afford reparation nevertheless subsists as long as the injury did not disappear by the mere fact of the nullification of the consent or of the waiver of nullity.15

Law of treaties and countermeasures

In accordance with the ILC Articles, countermeasures authorize a State to not perform its obligations, in order to induce another State to comply with its obligations.16 They constitute a kind of reprisal, which as such are far from being praiseworthy but must still be accepted in a system which contains no centralized sanctions.

(p. 111) It goes without saying that the obligations which are not performed in the name of countermeasures may arise from treaties. In other words, obligations imposed by treaties can be derogated from by virtue of a countermeasure, just as the countermeasure can be taken to obtain respect for treaty obligations. The conditions on which the lawfulness of countermeasures depends and which are set out in ARSIWA will not be discussed here.17 However, it is necessary to consider the potential relationship between the law on treaties and countermeasures as they exist under the law of responsibility.

(a)  The principle

In principle, a derogation to any treaty can be taken by a countermeasure in order to induce another State to fulfil its obligations, including its obligations under that treaty. However, the derogation must be provisional: article 49(2) states that ‘[c]ountermeasures are limited to the non-performance for the time being’ of obligations, even if the severity of this provision is somewhat alleviated by article 49(3) stating that that ‘the resumption of performance of the obligations in question’ will only take place ‘as far as possible’. It is further understood that all other general conditions (injured State, proportionality etc) must be respected.

There is nothing in the Vienna Convention on the Law of Treaties which challenges that conclusion. Excluding treaties from the scope of the Articles would indeed have resulted in greatly weakening the effectiveness of countermeasures.

(b)  The exceptions

As always, there is no principle without exceptions.

(i)  Obligations arising from peremptory norms of general international law (jus cogens)

According to ARSIWA article 50(1), a countermeasure can never undermine a rule of jus cogens. This is readily understandable. How could a unilateral derogation from something that does not allow for treaty derogations be explained? These are the ‘intransgressible principles of international customary law’, to use the words of the International Court.18

The exception does not concern treaties since they should not constitute general international law. It is only true that treaties, especially multilateral, may be declaratory of a general rule of international law. If that general rule has a peremptory character, countermeasures cannot be taken which would derogate from those. It follows that obligations of treaty provisions which do not have a peremptory character can always be derogated from.

(ii)  Diplomatic or consular inviolability and the settlement of disputes

According to ARSIWA article 50(2):

A State taking countermeasures is not relieved from fulfilling its obligations

(a)  under any dispute settlement procedure applicable between it and the responsible State [addressee of the countermeasure]

(b)  to respect the inviolability of diplomatic or consular agents, premises, archives and documents.

(p. 112) The exception is clear. In practice, it has little consequence for multilateral instruments concerning diplomatic and consular relations (principally the Vienna Conventions of 1961 and 1963), since the rules formulated in those treaties have largely acquired customary value. Nevertheless, the exception retains its relevance for bilateral treaties which establish any such inviolability.

On the other hand, the importance of the exception does not extend to the settlement of disputes. There is in effect no procedure that is imposed on States as a matter of custom; international law contents itself by prescribing a peaceful settlement. The ‘procedure applicable’ between the State taking the countermeasures and the addressee necessarily implies that an agreement has been concluded between the two, from which article 50(2) prohibits any derogation.

(iii)  A contrary convention

It cannot be excluded that States will make an agreement not to use the law on countermeasures in their mutual relations to derogate from certain treaties, or even renounce in a more general manner recourse to countermeasures. This is for example implicit in the constitutive treaty of various international organizations or other associations, notably the European Union.

The exception finds its full meaning when a treaty mechanism of sanctions is complementing the rejection or limitation of countermeasures. It is not explicitly confirmed by the draft articles. Nevertheless, it is difficult to see that anything puts this exception into doubt.

(iv)  Article 60 of the Vienna Convention on the Law of Treaties

Article 60 of the Vienna Convention governs the consequences of ‘material breach’ of a treaty by a State party for the maintaining into force of that treaty. When the treaty is bilateral, the other party can invoke the breach as a ground for terminating or suspending its operation; in principle the same logic is applicable when the treaty is multilateral, although article 60 attempts to retain in force as much of the treaty as possible between some contracting states, an objective which explains the provisions of article 60(2).

A particular reading of the Vienna Convention led some authors, previous to the completion of the ILC Articles, to maintain that article 60 constitutes the only lawful basis for the suspension or termination of a treaty when its obligations are breached by a State party.19 In other words, it may not in such a case be derogated from on the basis of the general rules on countermeasures. Why? That remains unclear. Apparently, some internal logic of article 60 would impose such a conclusion.

Whatever the merits of such an analysis, two points seem beyond dispute. First, the termination of the treaty can only be decided on the basis of article 60, article 49(3) being reserved. Countermeasures indeed can only justify a temporary non-fulfilment by a State of its obligations; in other words, they only authorize the suspension of a treaty obligation.20 Second, a suspension can only ever be decided on the basis of the law on responsibility when the breached obligation which justifies the recourse to countermeasures is not imposed by the treaty the application of which is suspended.

(p. 113) Consequently, only two questions remain as between article 60 and the ARSIWA provisions on countermeasures. First, does the law of countermeasures authorize the suspension of a treaty by one of the contracting States, when the breach of its obligations by one of the other State parties is not material in the sense of article 60(1) and 60(3)? Second, when the breach is material, is the State party able to invoke either article 60 or the law of countermeasures in order to suspend application of the treaty in question? One might say that this question has no practical importance, but the procedural requirements of the Vienna Convention are more restrictive than those in ARSIWA.21 These questions do not appear to have a clear answer, although they have been mentioned several times in the ILC. There would be a certain logic in prioritizing the law on treaties in this area. This appears to be confirmed by the spirit of the ICJ judgment in Gabcíkovo-Nagymaros Project. In a context where general rules are lacking, which is increasing the importance of treaty agreements, it would be perfectly understandable that the suspension of a treaty was not permitted on the basis of the law of countermeasures in the situation envisaged by article 60, particularly where other countermeasures are usually available. It is easy to see that it makes no difference whether the breach of the obligations is of a material character. But this conclusion finds no express support in the Vienna Convention or ARSIWA—even if these instruments do not explicitly regulate this issue—or in the prevailing doctrine—whose commentaries are far from being exempt from all ambiguity—or in the case law—especially since no international arbitrator or judge has ever expressed anything on the issue. And it seems contradicted by the elation with which States apparently breach their obligations in order to protest against breaches by other States.

Further reading

  • D Bowett, ‘Treaties and State Responsibility’ in Le droit international au service de la paix, de la justice et du développement. Mélanges Michel Virally (Paris, Pedone, 1991), 137
  • P Dupuy, ‘Droit des traités, codification et responsabilité internationale’ (1997) 43 AFDI 7
  • M Martin Lopez, ‘La terminación y la suspensión de los tratados internacionales a título de contramedida’ (1999) Anuario de derecho internacional 529
  • P Reuter, Introduction au droit des traits (3rd edn, Paris, PUF, 1995)
  • L-A Sicilianos, ‘The Relationship Between Reprisals and Denunciation or Suspension of a Treaty’ (1993) 4 EJIL 341
  • Ph Weckel, ‘Convergence du droit des traités et du droit de la responsabilité internationale’ (1998) 102 RGDIP 647
  • P Weil, ‘Droit des traités et droit de la responsabilité’, in R Rama Montaldo (ed), Liber amicorum en hommage au Pr. Eduardo Jimenez de Aréchaga. Le droit international dans un monde en mutation (Montevideo, 1994),
  • reproduced in P Weil, Ecrits de droit international (Paris, PUF, 2000)
  • A Yahi, ‘La violation d’un traité: l’articulation du droit des traités et du droit de la responsabilité internationale’ (1993) 26 RBDI 437(p. 114)


Rainbow Warrior (France/New Zealand), 30 April 1990, 20 RIAA 215, 251 (para 75).

R Ago, Fifth Report on State Responsibility, ILC Yearbook 1976, Vol II(1), 3, 12 (para 30).

Art 12, ARSIWA.

Commentary to art 12, para 3.

See J Crawford, Chapter 29.

See art 52, ARSIWA and G Arangio-Ruiz, Seventh Report on State Responsibility, ILC Yearbook 1995, Vol II(1), 3, 6 (para 18).

1155 UNTS 311.

Commentary to art 56, para 3.

Art 1, ARSIWA.

10  ‘[L]’existence, le contenu et la durée des obligations’ conventionnelles: P Weil, ‘Droit des traités et droit de la responsabilité’, in R Rama Montaldo (ed), Liber amicorum en hommage au Pr. Eduardo Jimenez de Aréchaga. Le droit international dans un monde en mutation (Montevideo, 1994), reproduced in P Weil, Ecrits de droit international (Paris, PUF, 2000), 195.

11  Gabcíkovo-Nagymaros Project (Hungary/Slovakia), ICJ Reports 1997, p 7, 38 (para 47).

12  1155 UNTS 331.

13  On the interpretation of art 52 see J Verhoeven, Droit international public (Louvain-la-Neuve, Larcier, 2000), 400.

14  Art 39, ARSIWA.

15  Art 20, ARSIWA.

16  Art 49, ARSIWA.

17  See below, Chapters 79–86.

18  Legality of the Threat or Use of Nuclear Weapons, ICJ Reports 1996, p 226, 257 (para 79).

19  See especially D Bowett, ‘Treaties and State responsibility’, in Le droit international au service de la paix, de la justice et du développement. Mélanges Michel Virally (Paris, Pedone, 1991) 137.

20  See B Simma, ‘Reflection on Article 60 of the Vienna Convention on the Law of Treaties and Its Background in General International Law’ (1970) 20 Zeitschrift für öffentliches Recht 14.

21  Arts 65–68, Vienna Convention on the Law of Treaties, 23 May 1969, 1155 UNTS 331.