A. The Scope of Subject-Matter Jurisdiction

It should be uncontroversial that a court or tribunal exercising jurisdiction under a compromissory clause has jurisdiction over claims that an obligation under the relevant treaty has been breached.Footnote ¹² Expressed another way, it should be uncontroversial that a claim by one State that an obligation contained in a treaty has been breached, which is opposed by another State,Footnote ¹³ constitutes a dispute concerning the interpretation or application of the relevant treaty. Indeed, claims of breach are the type of claim most commonly made and ruled on under compromissory clauses. When exercising jurisdiction under compromissory clauses, the ICJ has ruled on breaches of the Vienna Convention on Consular Relations (the VCCR),Footnote ¹⁴ the Vienna Convention on Diplomatic Relations (the VCDR),Footnote ¹⁵ the Convention against Torture,Footnote ¹⁶ and the Genocide Convention,Footnote ¹⁷ among other treaties.Footnote ¹⁸

Until 2015, it was uncontroversial that such claims of breach made by an applicant State, and opposed by a respondent State, constituted disputes concerning the interpretation or application of the relevant treaty. However, in recent years, rather than assessing jurisdiction based on the claims made by an applicant, UNCLOS Annex VII tribunals have adopted a practice of ‘characterising’ disputes. This approach was first used in 2015 by the tribunal in the Chagos proceedings. That tribunal was faced with claims under UNCLOS raising a particularly controversial external issue: sovereignty over territory. The tribunal characterised certain disputes between the parties by assessing where the ‘relative weight’ of the dispute lay: by assessing whether the dispute primarily concerned the interpretation or application of UNCLOS or primarily concerned the external issue (sovereignty over territory).Footnote ¹⁹ A number of subsequent Annex VII tribunals have engaged in similar processes of characterisation.Footnote ²⁰

As argued elsewhere, this practice of characterising disputes when determining whether there is a dispute concerning the interpretation or application of a particular treaty is not supported by authority and is not a principled development in the law.Footnote ²¹ Additionally, the ICJ appears to have rejected such an approach in its 2020 judgments in the ICAO Qatar Appeals. Those proceedings were appeals from decisions of the Council of the International Civil Aviation Organization (ICAO Council), in which the ICAO Council had upheld its jurisdiction to hear certain claims brought by Qatar under the compromissory clauses in two treaties relating to international civil aviation: the Convention on International Civil Aviation (the Chicago Convention) and the International Air Services Transit Agreement (the IASTA).

Before the Court, the four States that Qatar had brought its claims against (the Quartet) argued that the ICAO Council should have characterised the disputes between the parties when determining whether it had jurisdiction.Footnote ²² The Quartet invoked precedents including the award in the Chagos proceedings and argued that the disputes between the parties were properly characterised as concerning external issues: Qatar's non-compliance with obligations relating to terrorism and non-intervention in the internal affairs of other States.Footnote ²³ Contrary to the Quartet's submission, however, the Court did not characterise the disputes between the parties. Rather, in finding that there were disputes concerning the interpretation or application of the two treaties, the Court pointed to the claims made by Qatar, which were claims that the Quartet had breached obligations under the treaties.Footnote ²⁴

More recently, in Alleged Violations of the 1955 Treaty—proceedings brought by Iran against the United States under the compromissory clause in the Treaty of Amity, Economic Relations and Consular Rights between the two States (the 1955 Treaty)—the United States argued that the dispute between the States exclusively concerns a different instrument, the Joint Comprehensive Plan of Action.Footnote ²⁵ In rejecting this argument, and finding that there is a dispute concerning the interpretation or application of the 1955 Treaty, the Court did not characterise the dispute, but rather looked at the claims made by Iran. The Court reasoned as follows: Iran seeks a declaration that the United States is in breach of obligations under the 1955 Treaty; the United States contests that it is in violation of the Treaty; ‘[h]ence there exists an opposition of views which amounts to a dispute relating to the Treaty’.Footnote ²⁶ The Court further stated that, to the extent that the United States’ measures ‘might constitute breaches of certain obligations under the [1955 Treaty], those measures relate to the interpretation or application of that Treaty’.Footnote ²⁷

The key point is that subject-matter jurisdiction—the question of whether there is a dispute concerning the interpretation or application of a treaty—is assessed at the level of the claims made by an applicant. Is there a claim that, for example, an obligation under the relevant treaty has been breached, which is opposed by another State? Assessing jurisdiction at the level of the claims made is consistent with the well-known jurisprudence regarding the meaning of ‘dispute’. As the Permanent Court of International Justice (the PCIJ or Court) stated in the Mavrommatis proceedings—proceedings brought under a compromissory clause—a ‘dispute is a disagreement on a point of law or fact, a conflict of legal views or of interests’.Footnote ²⁸ As the ICJ stated in the South West Africa cases—also brought under a compromissory clause—to establish the existence of a dispute ‘[i]t must be shown that the claim of one party is positively opposed by the other’.Footnote ²⁹ Opposing claims on a particular point of law, such as whether an obligation has or has not been breached, constitute a dispute.Footnote ³⁰

In sum, when exercising jurisdiction pursuant to a compromissory clause, a court or tribunal has subject-matter jurisdiction over claims that obligations under the relevant treaty have been breached, even if those claims raise issues under external rules. This is not to say that the court or tribunal will necessarily be able to determine the external issues raised by the claim. It may not be able to do so. But that is not because the court or tribunal has no jurisdiction over the claim. It is because of two other matters: (i) abuse of process, discussed in Section V; and (ii) applicable law, discussed next.

B. The Distinction between Jurisdiction and Applicable Law

While subject-matter jurisdiction concerns the claims that a court or tribunal can adjudicate, applicable law concerns the law that the court or tribunal can apply in making its adjudication.Footnote ³¹ For example, in the case of a claim that an obligation under a treaty has been breached, the applicable law is the law that the court or tribunal can apply when determining that claim of breach.

In disputes before the ICJ, and disputes under UNCLOS, the applicable law is potentially broad in scope. In the case of disputes under UNCLOS, Article 293(1) of UNCLOS provides that UNCLOS tribunals ‘shall apply this Convention and other rules of international law not incompatible with this Convention’ (emphasis added). In the case of the ICJ, Article 38(1) of the Statute of the Court provides that, in deciding disputes, the Court ‘shall apply’ treaty law, customary international law and general principles of law. Thus, to resolve a dispute over which it has jurisdiction, such as a claim that an obligation under a treaty has been breached, the ICJ and UNCLOS tribunals are not limited to applying the provisions of that particular treaty. They are also able to apply rules within the broad collection of external rules referred to in Articles 38(1) and 293(1), respectively. However, the ICJ and UNCLOS tribunals cannot simply apply any rule referred to in Articles 38(1) and 293(1). They cannot apply any and every external rule that a party may raise in proceedings. There are limits. But before going on to discuss which of the rules in Articles 38(1) and 293(1) the Court or an UNCLOS tribunal can apply in any particular case, and which thus form part of the applicable law for that case, it is necessary to clarify four key points regarding the respective remits of jurisdiction and applicable law.

First, a court or tribunal exercising jurisdiction under a compromissory clause does not have jurisdiction to rule on claims that external rules have been breached. A classic example where a tribunal impermissibly ruled on breaches of external rules is Guyana v Suriname. In those proceedings, the Annex VII tribunal held that, by virtue of the broad applicable law clause in UNCLOS, the tribunal could not only rule on breaches of obligations under UNCLOS, but could also rule on breaches of external rules.Footnote ³² In the dispositif of its award, the tribunal ruled that conduct by Suriname ‘constituted a threat of the use of force in breach of the Convention, the UN Charter, and general international law’.Footnote ³³ It is now widely accepted that courts and tribunals exercising jurisdiction under compromissory clauses do not have jurisdiction to rule on claims that external rules have been breached. This has been recognised by subsequent UNCLOS tribunals,Footnote ³⁴ and also by the ICJ.Footnote ³⁵

Second, notwithstanding the above, in the course of disposing of a claim that is within its jurisdiction under a compromissory clause (such as a claim that an obligation under the relevant treaty has been breached), a court or tribunal may be able to determine whether external rules have been breached. The ICJ stated as much in Croatia v Serbia, proceedings brought under the compromissory clause in the Genocide Convention. There the Court stated that it ‘has no power to rule on alleged breaches of other obligations under international law, not amounting to genocide’.Footnote ³⁶ But the Court continued: ‘That does not prevent the Court from considering, in its reasoning, whether a violation of international humanitarian law or international human rights law has occurred to the extent that this is relevant for the Court's determination of whether or not there has been a breach of an obligation under the Genocide Convention’.Footnote ³⁷ That is, when courts and tribunals are disposing of claims within their jurisdiction under compromissory clauses—in this case, claims that obligations under the Genocide Convention had been breached—they can, at least in some circumstances, determine whether external rules have been breached.

Third, when a court or tribunal is deciding a claim within its jurisdiction under a compromissory clause, whether it can apply a particular external rule—including for the purpose of determining whether the rule has been breached—is a question of applicable law, not of jurisdiction. The question is whether the particular external rule forms part of the applicable law for the claim. The Court sometimes makes statements that could be interpreted as suggesting that whether it can deal with a particular external issue is a question of jurisdiction; for example, in the Certain Iranian Assets proceedings, in which the external issue of State immunities was raised, the Court stated that ‘in so far as Iran's claims concern the alleged violation of rules of international law on sovereign immunities, the Court does not have jurisdiction to consider them’.Footnote ³⁸ But that is not how such statements should be interpreted.

Certain Iranian Assets provides a helpful illustration of this point. The proceedings were brought by Iran against the United States under the compromissory clause in the 1955 Treaty. Iran claimed (among other things) that the United States had breached its obligation under Article IV(2) of the Treaty, which requires the United States to accord Iranian companies ‘the most constant protection and security …, in no case less than that required by international law’, because the United States had breached immunities enjoyed by the relevant companies under customary international law.Footnote ³⁹ To determine whether it had subject-matter jurisdiction over Iran's claims, the Court, as is its usual practice, assessed whether the acts complained of by Iran ‘fall within’ the provisions of the 1955 Treaty.Footnote ⁴⁰ The Court found that the rules of ‘international law’ referred to in Article IV(2) are not rules regarding immunities.Footnote ⁴¹ That is, the Court found that Iran's claim was not well-founded in law: even if the United States had breached immunities enjoyed by the relevant companies, the United States would not have breached its obligation under Article IV(2). The Court consequently did not have jurisdiction over the claim. Footnote ⁴² The question was not whether the Court had jurisdiction over issues of immunities.Footnote ⁴³ The Court clearly does not have jurisdiction over issues of immunities under the 1955 Treaty. The question was whether rules regarding immunities formed part of the law that the Court could apply when deciding Iran's claim under Article IV(2)—whether the rules formed part of the applicable law. They did not, as they are not referred to in Article IV(2).

Fourth, in circumstances where a court or tribunal exercising jurisdiction under a compromissory clause can and does make a determination under an external rule—such as a determination that an external rule has been breached—that determination cannot be included in the dispositif of the judgment or award rendered by the court or tribunal. This is because, in a dispositif, a court or tribunal can only rule on matters within its jurisdiction. As Judge Abraham has explained, ‘each and every part of the operative clause must fall strictly within the scope of the Court's jurisdiction’.Footnote ⁴⁴

In disputes under compromissory clauses regarding whether or not an obligation contained in the relevant treaty has been breached, it is that claim of breach that the court or tribunal has jurisdiction over and that it can rule on in the dispositif.Footnote ⁴⁵ In contrast, determinations made by the court or tribunal under external rules, in the course of disposing of that claim of breach, are not within the court or tribunal's jurisdiction. They are determinations made under rules forming part of the applicable law and cannot be ruled on in the dispositif. The distinction between ruling on a breach of an external rule in a dispositif (which is impermissible) and determining that an external rule has been breached in the course of disposing of a claim (which may be permissible) is highlighted in Croatia v Serbia. As discussed above, the Court was clear that it did not have the ‘power’ to ‘rule’ on breaches of external rules. However, at the same time, the Court stated that in the course of determining whether an obligation under the Genocide Convention had been breached—a matter within the Court's jurisdiction—the Court could consider ‘in its reasoning’ whether external rules had been violated (emphasis added).

A. Secondary Rules of International Law

It should be uncontroversial that courts and tribunals exercising jurisdiction under compromissory clauses can apply secondary rules of international law, such as rules forming part of the law of treaties, the law of State responsibility and the law of diplomatic protection. As the Annex VII tribunal in the Arctic Sunrise proceedings stated, to properly apply provisions of UNCLOS, it may be necessary for an UNCLOS tribunal to ‘resort to foundational or secondary rules of general international law such as the law of treaties or the rules of State responsibility’.Footnote ⁴⁶ Similarly, in the Bosnian Genocide proceedings, the Court stated that, in order to determine whether an obligation under the Genocide Convention had been breached, ‘the Court will have recourse not only to the Convention itself, but also to the rules of general international law on treaty interpretation and on responsibility of States for internationally wrongful acts’.Footnote ⁴⁷

In many proceedings in which external rules are raised, a court or tribunal will be being asked to apply more than just secondary rules of international law, however. The ICAO Qatar Appeals illustrate this. In the underlying proceedings before the ICAO Council, the Quartet contend that the wrongfulness of their actions is precluded because their actions constitute lawful countermeasures.Footnote ⁴⁸ The rule that the wrongfulness of conduct is precluded to the extent that it constitutes a lawful countermeasure is a secondary rule forming part of the law of State responsibility.Footnote ⁴⁹ The ICAO Council could therefore apply that secondary rule when exercising jurisdiction under the compromissory clauses in the Chicago Convention and the IASTA. However, the Quartet's argument that their actions constitute lawful countermeasures is in turn based on an argument that Qatar breached certain obligations found outside of those two treaties, including obligations under the Riyadh Agreements.Footnote ⁵⁰ That is, to determine if the circumstance precluding wrongfulness is made out, the ICAO Council would have to apply those external primary rules as well. When, then, can courts and tribunals exercising jurisdiction under compromissory clauses apply external primary rules?

B. External Rules to Which a Treaty Refers

One situation in which courts and tribunals can apply external primary rules is when the treaty in question makes reference to such rules. A treaty can do this by referring to specific rules of international law or by more generally referring to ‘rules of international law’, and by using a variety of language, such as language referring to ‘obligations’, ‘rights’, ‘agreements’ or ‘principles’ found outside of the treaty in question.Footnote ⁵¹

This situation is most commonly discussed in connection with UNCLOS—a treaty that contains a large number of provisions referring to external rules.Footnote ⁵² It is widely accepted that UNCLOS tribunals can apply external rules referred to in provisions of UNCLOS.Footnote ⁵³ This occurred, for example, in the South China Sea proceedings.Footnote ⁵⁴ There the Philippines argued that China had breached its obligation under Article 94 of UNCLOS to take measures necessary to ensure safety at sea, in conformity with ‘generally accepted international regulations’, because China had taken measures in breach of a particular set of regulations, the International Regulations for Preventing Collisions at Sea (the COLREGS).Footnote ⁵⁵ The tribunal accepted that the COLREGS are ‘generally accepted international regulations’ referred to in Article 94 and stated that, to determine the Philippines’ claim, it ‘must interpret and apply the COLREGS’.Footnote ⁵⁶ The tribunal determined that China had violated the COLREGS and, consequently, that it had breached Article 94.Footnote ⁵⁷

This second situation in which courts and tribunals can apply external rules is relatively limited. While in this situation courts and tribunals can apply external primary rules, they can only apply those primary rules referred to in the relevant treaty. In many cases, treaties refer to few external rules. This is highlighted by recent proceedings before the ICJ in which applicant States have unsuccessfully claimed that particular external rules are referred to in certain treaties. In both Immunities and Criminal Proceedings and Certain Iranian Assets, the Court found that the particular external rules invoked by the applicants were not referred to in the treaties in question. As discussed already, in Certain Iranian Assets, the Court rejected Iran's argument that language in Article IV(2) of the 1955 Treaty referring to ‘international law’ could be interpreted as referring to customary international law rules on immunities.Footnote ⁵⁸ Similarly, in Immunities and Criminal Proceedings, the Court rejected Equatorial Guinea's argument that language in the United Nations Convention against Transnational Organized Crime (the Palermo Convention) referring to ‘the principles of sovereign equality and territorial integrity of States and that of non-intervention in the domestic affairs of other States’ could be interpreted as referring to customary international law rules on immunities.Footnote ⁵⁹

C. External Rules Relevant to Interpreting a Treaty

Beyond the situation discussed in the preceding subsection, courts and tribunals exercising jurisdiction under compromissory clauses can also use external primary rules to interpret the treaty in question. The justification for applying external rules in this situation is the rule reflected in Article 31(3)(c) of the Vienna Convention on the Law of Treaties (the VCLT). As is well known, Article 31 of the VCLT sets out the ‘general rule of interpretation’ for treaties, and Article 31(3)(c) provides that ‘[a]ny relevant rules of international law applicable in the relations between the parties’ ‘shall be taken into account’ in interpreting a treaty.

There are various examples of cases in which courts and tribunals have used external primary rules to interpret the treaty in question. As one example, in the South China Sea arbitration, when interpreting Article 194(5) of UNCLOS, which refers to measures necessary to protect and preserve ‘rare or fragile ecosystems’, the Annex VII tribunal referred to the definition of ‘ecosystem’ in the Convention on Biological Diversity (the CBD). The tribunal stated that, although the word ‘ecosystem’ is not defined in UNCLOS, ‘internationally accepted definitions include that in Article 2 of the CBD, which defines ecosystem to mean “a dynamic complex of plant, animal and micro-organism communities and their non-living environment interacting as a functional unit”’.Footnote ⁶⁰ Applying Article 194(5) as thus interpreted, the tribunal decided that the marine environments in issue were ‘rare or fragile ecosystems’.Footnote ⁶¹

This third situation in which courts and tribunals can apply external rules is also relatively limited. Pursuant to the rule reflected in Article 31(3)(c), courts and tribunals can apply external rules for a specific purpose: to interpret the treaty in question.Footnote ⁶² Article 31(3)(c) provides the interpreter—for present purposes, a court or tribunal—with a basis on which it can use external rules to interpret, or determine the meaning of, a provision in the treaty over which it has jurisdiction. Once the provision's meaning has been determined through interpretation, the court or tribunal can then apply that provision in the treaty over which it has jurisdiction to the facts of the case, as occurred in the example from the South China Sea arbitration discussed above. Article 31(3)(c) provides a court or tribunal with a basis for applying external rules to interpret the treaty over which it has jurisdiction. It does not provide a basis for applying external rules more broadly. In particular, it does not provide a basis for directly applying external rules themselves to the facts of a case.

In some cases where courts and tribunals have invoked Article 31(3)(c) as a basis for applying external rules, they have not used the external rules to interpret the treaty in question or they have directly applied the external rules to the facts of the case. One case which provides an example of this is Oil Platforms. In those proceedings, the ICJ exercised jurisdiction pursuant to the compromissory clause in the 1955 Treaty. The Court considered whether, in response to Iran's claims, the United States had a defence under Article XX(1)(d) of the Treaty, on the basis that the United States’ actions were ‘measures … necessary to protect its essential security interests’.Footnote ⁶³ The Court took the view that this defence could not be successfully invoked if the United States’ actions amounted to an unlawful use of force.Footnote ⁶⁴ The Court considered that it was therefore competent to determine whether the actions in question were an unlawful use of force ‘by reference to international law applicable to this question, that is to say, the provisions of the Charter of the United Nations and customary international law’, and it proceeded to determine that the United States’ actions ‘constituted recourse to armed force not qualifying, under international law on the question, as acts of self-defence’.Footnote ⁶⁵

In support of its view that the Article XX(1)(d) defence could not be invoked if the United States’ actions were an unlawful use of force, the Court referred to Article 31(3)(c) of the VCLT. However, the Court did not explain how international law on the use of force was relevant to interpreting Article XX(1)(d) (‘measures … necessary to protect its essential security interests’).Footnote ⁶⁶ It is questionable whether these external rules were relevant to interpreting Article XX(1)(d).Footnote ⁶⁷ Indeed, as Judge Higgins stated, ‘the actual provisions of Article XX, paragraph 1(d), are put to one side and not in fact interpreted at all’.Footnote ⁶⁸ But, even if international law on the use of force were relevant to interpreting Article XX(1)(d), the Court used those external rules in a way that cannot be defended by reference to Article 31(3)(c): the Court directly applied external rules on the use of force to the facts of the case.

A. Unexplained Uses of Applicable Law

In practice, courts and tribunals exercising jurisdiction under compromissory clauses apply external rules in circumstances that go beyond the situations identified in the previous section. The Chagos proceedings provide an example of such an ‘unexplained’ use of external rules.Footnote ⁶⁹

In Chagos, the Annex VII tribunal upheld its jurisdiction with respect to Mauritius’ fourth submission. In that submission, Mauritius claimed that the Marine Protected Area declared by the United Kingdom was incompatible with the United Kingdom's obligation under Article 56(2) of UNCLOS, among other provisions.Footnote ⁷⁰ Article 56(2) requires a coastal State to have ‘due regard’ for the ‘rights’ of other States when the coastal State is exercising its UNCLOS rights in its exclusive economic zone. To determine whether the United Kingdom had breached its obligation to have due regard for Mauritius’ rights, the tribunal first had to determine whether the so-called ‘Lancaster House Undertakings’ created rights for Mauritius, which was disputed between the two States.Footnote ⁷¹ It stated that it would ‘establish the nature and scope of the United Kingdom's undertakings’.Footnote ⁷² The tribunal ultimately determined that the United Kingdom was estopped from denying the binding effect of the commitments that it had made in the Lancaster House Undertakings, and the tribunal stated that it would treat the commitments ‘as binding’.Footnote ⁷³ The tribunal proceeded to find that the United Kingdom had not had due regard to Mauritius’ ‘rights arising from the Lancaster House Undertakings’ and that the United Kingdom had breached Article 56(2).Footnote ⁷⁴

The Chagos tribunal used external rules in a way that goes beyond the situations discussed in the previous section. Article 56(2) refers to external ‘rights’ and so can be seen as an example of a provision that refers to external rules (the second situation discussed in the previous section). However, the Chagos tribunal did not merely apply external rules or rights referred to in a provision of UNCLOS. It also dealt with an antecedent issue. The tribunal determined whether the external rights invoked by the applicant existed. It did not explain on what basis it was competent to determine the existence (or not) of rights said to be found outside of UNCLOS.Footnote ⁷⁵

B. An Argument for the Making of Incidental Determinations

Decisions such as the above can be explained on the basis that courts and tribunals exercising jurisdiction under compromissory clauses are competent to apply external rules in a fourth situation and to make what are referred to in this article as ‘incidental determinations’.

Recently, three UNCLOS tribunals have made statements to the effect that they are competent to determine ‘incidental’ or ‘ancillary’ issues. When dealing with a different submission made by Mauritius, the Chagos tribunal stated that the jurisdiction of an UNCLOS tribunal ‘extends to making such … ancillary determinations of law as are necessary to resolve the dispute presented to it’.Footnote ⁷⁶ In Coastal State Rights, the tribunal recalled this statement and applied it, finding that the external issue in question in those proceedings—sovereignty over territory—was not a ‘minor issue ancillary to the dispute concerning the interpretation or application of the Convention’.Footnote ⁷⁷ The tribunal explained that this was not an ancillary issue because, ‘[o]n the contrary, the question of sovereignty is a prerequisite to the Arbitral Tribunal's decision on a number of claims submitted by Ukraine’.Footnote ⁷⁸ In the Enrica Lexie proceedings, the tribunal held that the external issue raised in those proceedings—the immunity of certain marines—was a question ‘preliminary or incidental’ to the application of UNCLOS.Footnote ⁷⁹ The tribunal explained that it ‘could not provide a complete answer [to the parties’ dispute] without incidentally examining whether the Marines enjoy immunity’.Footnote ⁸⁰

Two key questions are raised by these awards. The first is: what exactly do these tribunals mean when they refer to ‘incidental’ and ‘ancillary’ issues? It is not entirely clear, including because the statements made by the different tribunals are not consistent. The Chagos tribunal stated that an ancillary determination is one ‘necessary to resolve the dispute presented’ to the tribunal; that is, it is a determination that is a prerequisite for the tribunal's decision. The Coastal State Rights tribunal stated the opposite. It found that the external issue in those proceedings was not an ancillary issue precisely because its determination was a ‘prerequisite’ to ruling on claims under UNCLOS.

In this article, an external issue is said to arise ‘incidentally’ where: (i) the court or tribunal in question has jurisdiction over a claim under the relevant compromissory clause (such as a claim that an obligation under the relevant treaty has been breached); and (ii) the claim cannot be disposed of unless the court or tribunal decides the particular external issue. In short, an incidental issue is an issue that a court or tribunal has to decide for it to be able to rule on a claim within its jurisdiction. This article argues that courts and tribunals exercising jurisdiction under compromissory clauses can determine incidental issues so defined.

This fourth situation in which it is suggested that courts and tribunals can apply external rules is in fact an overarching situation, which encompasses the first and second situations discussed in the previous section. For example, the first situation discussed above recognises courts and tribunals as being competent to determine one subset of incidental issues: it recognises courts and tribunals as being competent to determine external issues under secondary rules that they have to decide to be able to rule on a claim within their jurisdiction. Indeed, in practice, when courts and tribunals apply secondary rules they often highlight that they are doing so for the purpose of resolving a claim within their jurisdiction. In the Bosnian Genocide proceedings, for example, the Court stated that it would have recourse to secondary rules ‘[i]n order to determine whether the Respondent breached its obligation under the [Genocide] Convention’.Footnote ⁸¹ The suggested fourth situation in which courts and tribunals can apply external rules is broader and covers incidental determinations in general, not only incidental determinations under secondary rules or incidental determinations under rules referred to in the relevant treaty (the second situation discussed above).Footnote ⁸²

The second question raised by the three UNCLOS awards mentioned above is: why are courts and tribunals competent to make incidental determinations? None of the three tribunals explains why UNCLOS tribunals can determine what they refer to as ‘incidental’ or ‘ancillary’ issues. In support of their statements to the effect that UNCLOS tribunals are competent to determine such issues, the three tribunals simply cite a passage from the PCIJ's judgment on preliminary objections in the Certain German Interests proceedings,Footnote ⁸³ proceedings brought by Germany against Poland under the compromissory clause in the 1922 German–Polish Convention relating to Upper Silesia (the Geneva Convention). The passage cited provides as follows:

In their awards, none of the three UNCLOS tribunals went beyond citing this passage. In the Enrica Lexie proceedings, two of the arbitrators dissented—Judge Robinson and Dr Rao—and, in their opinions, those arbitrators did enter into a discussion of the Certain German Interests proceedings. But the dissenting arbitrators only discussed the PCIJ's use of Article 256 of the Treaty of Versailles, mentioned in the passage quoted above.Footnote ⁸⁵ The PCIJ's use of that provision does not provide support for the existence of a general competence to make incidental determinations. In its judgment on the merits in Certain German Interests, the PCIJ did interpret and apply Article 256. However, the Geneva Convention—the treaty on which the Court's jurisdiction was based—explicitly referred to Article 256.Footnote ⁸⁶ That is, the Court's use of Article 256 in the Certain German Interests proceedings is an example of an incidental determination being made under an external rule referred to in the relevant treaty (the second situation discussed in the previous section).Footnote ⁸⁷

Notwithstanding this, the PCIJ's use of other external rules in the Certain German Interests proceedings does provide some support for the existence of a general competence to make incidental determinations. In the proceedings, Germany claimed that, in introducing a domestic law, Poland had acted in a manner contrary to the Geneva Convention.Footnote ⁸⁸ Poland responded that the law in question gave effect of its rights under other treaties, including the Armistice Convention and the Protocol of Spa.Footnote ⁸⁹ In the course of considering, and rejecting, Poland's argument, the Court interpreted and applied those two other treaties, neither of which is referred to in the Geneva Convention. The Court determined that Poland was not a contracting party to either treaty, that there was no subsequent ‘tacit adherence or accession’ by Poland to the treaties and that the treaties created no rights in favour of Poland.Footnote ⁹⁰ The Court ultimately concluded that ‘no title of international law has been cited by Poland which enables [the Polish law] to be regarded as the exercise of a right overriding her obligations under … the Geneva Convention’.Footnote ⁹¹ In short, the Court made determinations under external primary rules that were not referred to in the relevant treaty; the Court applied external primary rules in circumstances going beyond the situations discussed in the previous section.

While the Certain German Interests proceedings therefore do provide some support for the existence of a broader competence to determine external issues, the PCIJ's judgments in those proceedings do not explain the theoretical basis for this competence. A competence to determine incidental issues (as that term is used in this article) could potentially be justified on a number of bases, such as on the basis that the competence is an inherent power,Footnote ⁹² on the basis that it is an implied power,Footnote ⁹³ or on the basis of the principle of effectiveness in treaty interpretation.Footnote ⁹⁴ However, the soundest basis for the competence appears to be the doctrine of implied powers.Footnote ⁹⁵

The doctrine of implied powers is applied primarily in relation to international organisations.Footnote ⁹⁶ But there does not appear to be any reason why the doctrine could not also be applied to international courts and tribunals. The rationale for implied powers is that it is not possible to spell out in a constituent instrument of an international organisation every specific power that the organisation will need to perform its functions, including because it is not possible to foresee what specific powers will be needed in an uncertain future.Footnote ⁹⁷ This rationale is equally applicable to the constitutive instruments of international courts and tribunals. Indeed, others have taken the view that the doctrine of implied powers can also be applied to international courts and tribunals or, at least, that an equivalent doctrine can be applied to them. For example, Elihu Lauterpacht stated that ‘the implication of powers for the International Court is comparable in legal justification and method to the implication of powers for any other international organ operating on the basis of a constitutive instrument’.Footnote ⁹⁸

There are two views regarding the scope of the doctrine of implied powers.Footnote ⁹⁹ The narrower view sees an international organisation as possessing the implied powers necessary or essential for the exercise of its express powers.Footnote ¹⁰⁰ The broader view sees an international organisation as possessing the implied powers necessary or essential for the achievement of the functions of the organisation.Footnote ¹⁰¹ An implied power to make incidental determinations could be justified in line with either view.

Regarding the narrower view (implied powers are those necessary for the exercise of express powers), courts and tribunals exercising jurisdiction under compromissory clauses are expressly granted jurisdiction over disputes concerning the interpretation or application of a particular treaty.Footnote ¹⁰² That is, they have the express power to rule on disputes concerning the interpretation or application of a particular treaty, such as claims that an obligation under the treaty has been breached. To be able to exercise that express power and rule on such claims, it is necessary for the court or tribunal to also have the power—an implied power—to determine the issues that must be determined before ruling on the claims. That is, it is necessary for there to be an implied power to make incidental determinations.

Regarding the broader view (implied powers are those necessary for the achievement of a court or tribunal's functions), courts and tribunals can be seen as having multiple functions.Footnote ¹⁰³ One of those functions, and the one most relevant when exercising jurisdiction under a compromissory clause, is the function of dispute settlement:Footnote ¹⁰⁴ specifically, the settlement of disputes referred to the court or tribunal and within its jurisdiction, such as claims that an obligation under the relevant treaty has been breached. Again, for a court or tribunal to be able to fulfil its function of settling such disputes, it is necessary for it to have an implied power to make incidental determinations.

The implied power to make incidental determinations could of course be limited.Footnote ¹⁰⁵ For example, as noted already, the applicable law clause in UNCLOS states that UNCLOS tribunals shall apply ‘other rules of international law not incompatible with this Convention’.Footnote ¹⁰⁶ An UNCLOS tribunal could not make an incidental determination that required some rule ‘incompatible’ with UNCLOS to be applied.

C. Incidental Determinations and Recent Decisions of the ICJ

Two recent decisions of the ICJ—the 2019 judgment on preliminary objections in the Certain Iranian Assets proceedings and the 2020 judgments in the ICAO Qatar Appeals—can be seen as consistent with the view that courts and tribunals exercising jurisdiction under compromissory clauses are competent to make incidental determinations.

In Certain Iranian Assets, another claim made by Iran was that the United States had violated Article III(2) of the 1955 Treaty, which grants Iranian companies a right of ‘freedom of access’ to US courts.Footnote ¹⁰⁷ Iran argued (among other things) that, by abrogating in proceedings before the US courts the immunities that certain Iranian companies are entitled to under customary international law, the United States had violated the companies’ right of freedom of access to the US courts.Footnote ¹⁰⁸ Iran's claim would have required the Court to determine whether the companies are entitled to immunities under customary international law and whether those immunities had been abrogated. In substance, Iran argued that these were incidental determinations that the Court could make when exercising jurisdiction under the compromissory clause in the 1955 Treaty.Footnote ¹⁰⁹ As the Court stated in relation to this claim and other claims made by Iran:

The Court ultimately held that it had no jurisdiction over Iran's claim. The Court did not accept the link between Article III(2) and immunities suggested by Iran, finding nothing which suggested that the obligation to grant Iranian companies freedom of access to US courts entails an obligation to uphold any applicable immunities.Footnote ¹¹¹ Nonetheless, the Court appears to have accepted that, in principle, it can make incidental determinations. At the outset of its consideration of Iran's claim, the Court stated:

The Court clearly stated that, even though Article III(2) does not refer to external rules regarding immunities (the second situation discussed in the previous section), that is not the end of the matter. The Court contemplates some other situation in which it can make determinations under external primary rules (in this case, rules regarding immunities). Indeed, the Court suggests that, if Iran had been correct, and a breach of immunities ‘would constitute a violation’ of the obligation under Article III(2), then the Court could have ‘examine[d] the question of sovereign immunities’. In other words, if the issue of immunities had been incidental to Iran's claim that the obligation under Article III(2) had been violated, then the Court could have determined that issue.

Regarding the ICAO Qatar Appeals, as discussed above,Footnote ¹¹³ in relation to the substance of Qatar's claims, the Quartet contend that the wrongfulness of their actions is precluded because their actions constitute lawful countermeasures. This contention is in turn based on an argument that Qatar breached certain primary rules found outside of the two treaties in question. In the appeals before the Court concerning the ICAO Council's jurisdiction, the Quartet argued that Qatar's claims before the ICAO Council are inadmissible on grounds of judicial propriety. Specifically, the Quartet argued that Qatar's claims are inadmissible because their resolution ‘would necessarily require the ICAO Council to take a view on whether the airspace restrictions can properly be justified as lawful countermeasures, which in turn would involve the ICAO Council adjudicating on … whether Qatar has breached its international obligations in relation to matters outside the scope of the Chicago Convention’.Footnote ¹¹⁴

In its July 2020 judgments, the Court rejected this argument. As noted above,Footnote ¹¹⁵ the Court effectively held that Qatar's claims are within the jurisdiction of the ICAO Council because they are claims that obligations under the relevant treaties have been breached. In rejecting the Quartet's argument regarding judicial propriety, the Court appears to have recognised that the ICAO Council can determine external issues for the purpose of disposing of Qatar's claims of breach. The Court stated:

That is, the Court appears to have recognised that the ICAO Council can make incidental determinations.

A. Res Judicata

In the ICAO Qatar Appeals, the Quartet argued that, if the ICAO Council were to have jurisdiction over Qatar's claims, in the course of determining those claims, the ICAO Council would decide the external issues relating to terrorism and non-intervention with res judicata effect. The Quartet stated that the ICAO Council would ‘issue a decision which either side might claim—in any and all fora—is final and binding in respect of matters concerning terrorism and interference in the affairs of other States’.Footnote ¹¹⁹

Such concerns are misplaced. A good argument can be made that incidental determinations do not have res judicata effect, because res judicata only attaches to rulings made by a court or tribunal in the dispositif of any judgment or award that it renders. As stated by Judge Anzilotti when discussing the res judicata effect of two judgments rendered by the PCIJ under a compromissory clause, ‘binding effect attaches only to the operative part of the judgment and not to the statement of reasons’.Footnote ¹²⁰ More recently, in Delimitation beyond 200 Nautical Miles, Judge Greenwood stated that ‘it is only the dispositif of a judgment which can have the force of res judicata’.Footnote ¹²¹ As discussed above,Footnote ¹²² in a dispositif, a court or tribunal can only rule on matters within its jurisdiction. In the context of proceedings brought under compromissory clauses, this includes claims that obligations under the treaty in question have been breached. It does not include incidental determinations made under external rules forming part of the applicable law. Incidental determinations cannot be included in a dispositif and do not have res judicata effect.

To be sure, there is conflicting authority to the effect that res judicata attaches not only to a dispositif, but also to findings made in the body of a judgment or an award.Footnote ¹²³ However, the better view is that res judicata only attaches to a dispositif. There is a lack of clarity regarding what methodology is to be used for deducing the existence and content of general principles of law,Footnote ¹²⁴ such as res judicata.Footnote ¹²⁵ But it is clear that: (i) general principles of law are, as their name suggests, general principles found in domestic systems, as opposed to specific rules; and (ii) to be a general principle of law, a general principle found in domestic systems must be transposable, and transposed, to the international level.Footnote ¹²⁶ Regarding the first of these points, in some domestic legal systems there is a specific rule under the umbrella of res judicata that recognises findings made by courts and tribunals in their reasons as having res judicata effect (common law issue estoppel).Footnote ¹²⁷ But the general principle of res judicata that is recognised across domestic legal systems is reflected in the two maxims interest reipublicae ut sit finis litium (it is in the public interest that there should be an end of litigation) and nemo debet bis vexari pro una et eadem causa (no one should be proceeded against twice for the same cause).Footnote ¹²⁸ It is this general principle which must be transposed to the international level.

Regarding the second of the above points, when this general principle is transposed to the international level, it is transposed into a legal system in which dispute settlement is based on consent. In the context of a system based on consent, the general principle of res judicata should only attach to determinations that States have consented to courts and tribunals ruling on. In the case of compromissory clauses, States have consented to the adjudication of, and courts and tribunals have jurisdiction to rule on, claims relating to the interpretation or application of the relevant treaty, such as claims that an obligation under the treaty has been breached. It is the rulings on such claims, which can be reflected in the dispositif, that res judicata should attach to.

In any event, even if one takes the view that res judicata does attach to findings made in the reasons supporting a judgment or an award, such as incidental determinations, incidental determinations would at most have res judicata effect in relation to the particular dispute or case in the context of which the determination was made. This follows from the constitutive instruments of the Court and UNCLOS tribunals. Regarding UNCLOS tribunals, Article 296(2) of UNCLOS provides that any decision rendered by an UNCLOS tribunal ‘shall have no binding force except between the parties and in respect of that particular dispute’ concerning the interpretation or application of UNCLOS (emphasis added). Regarding the Court, Article 59 of the Statute of the Court provides that the ‘decision of the Court has no binding force except between the parties and in respect of that particular case’ (emphasis added). In short, even if one were to take the view that res judicata attaches to findings made in the reasons supporting a judgment or an award, an incidental determination would be, at most, a final and binding determination of the relevant external issue for the purpose of the dispute or case adjudicated upon. An incidental determination cannot be invoked in other contexts, or ‘in any and all fora’, as a final and binding determination of the particular issue.

B. Abuse of Process and Abuse of Right

The Chagos tribunal appears to have had concerns regarding the purpose for which Mauritius brought some of its claims in those proceedings. The tribunal considered that the true object of Mauritius’ second submission was ‘to bolster Mauritius’ claim to sovereignty over the Chagos Archipelago’.Footnote ¹²⁹ It is understandable that there would be concerns if States were to bring claims under compromissory clauses for the purpose of obtaining incidental determinations; that is, if, for the purpose of circumventing a lack of consent to settle disputes relating to some particular issue, a State manufactured a claim under a compromissory clause that would require the relevant court or tribunal to determine that issue as an incidental matter. However, to address such concerns it is not necessary to invent new analytical approaches, such as the ‘characterisation’ approach adopted by the Chagos tribunal. Concerns about States bringing claims under compromissory clauses for the purpose of obtaining incidental determinations can be addressed by applying the prohibitions of abuse of process and abuse of right.

Abuse of process is a special application of abuse of right.Footnote ¹³⁰ An abuse of right can occur when a State exercises a right ‘for an end different from that for which the right was created’.Footnote ¹³¹ Abuse of process more specifically concerns the abuse of a procedural right by a party to a dispute.Footnote ¹³²

The Court and UNCLOS tribunals appear to have accepted that the right to submit a dispute to judicial settlement under a compromissory clause could be exercised in such a way as to amount to an abuse of process or an abuse of right. Regarding the Court, to date the Court has not found any particular exercise of the right to seek judicial settlement of a dispute to be abusive.Footnote ¹³³ However, in a number of proceedings, the Court appears to have accepted that, in principle, the exercise of the right to submit a dispute to judicial settlement under a compromissory clause could amount to an abuse of process.

In Immunities and Criminal Proceedings, for example, France argued that Equatorial Guinea's seisin of the Court constituted an abuse of process.Footnote ¹³⁴ The Court seems to have accepted that claims could be inadmissible on this basis, but rejected France's argument on the facts.Footnote ¹³⁵ Similarly, UNCLOS tribunals seem to have accepted that, in principle, the exercise of the right to submit a dispute to judicial settlement under the compromissory clause in UNCLOS could amount to an abuse of process or an abuse of right. For example, in the South China Sea arbitration, the tribunal considered whether the Philippines’ initiation of the arbitration was an abuse of right contrary to Article 300 of UNCLOS,Footnote ¹³⁶ noting that the allegedly abusive conduct in question—the fact that the arbitration was initiated unilaterally—did not itself constitute an abuse of right.Footnote ¹³⁷ In Mauritius/Maldives, the Special Chamber of ITLOS considered the Maldives’ argument that Mauritius’ claims were an abuse of process, but rejected that argument on the facts.Footnote ¹³⁸

While the Court and UNCLOS tribunals appear to have accepted that the right to submit a dispute to judicial settlement under a compromissory clause could be exercised in such a way as to amount to an abuse of process or an abuse of right, neither the Court nor any UNCLOS tribunal has considered more specifically whether exercising this right for the purpose of obtaining an incidental determination would be abusive.Footnote ¹³⁹ Nonetheless, a credible argument could be made that claims brought in such circumstances are abusive. If a State were to exercise its right to refer a dispute to judicial settlement under a compromissory clause, not for the purpose of obtaining rulings on the claims brought themselves, but for the purpose of obtaining an incidental determination, so as to further its position in respect of another dispute that the opposing State has not consented to settle, it could be said that the right to refer the dispute to judicial settlement has been exercised ‘for an end different from that for which the right was created’.Footnote ¹⁴⁰ Indeed, Lowe has stated that abuse of process ‘might, for instance, be deployed to defeat attempts by states to manufacture entirely artificial disputes in order to avail themselves of the jurisdiction of a convenient tribunal, to which the respondent happens to have submitted’.Footnote ¹⁴¹

The threshold for establishing an abuse of process or abuse of right is high. As the Court stated in Immunities and Criminal Proceedings, where a State has established a valid title of jurisdiction, it is only in ‘exceptional circumstances’ that the Court should reject a claim on the ground of abuse of process, and the Court should only do so with ‘clear evidence’ of abuse of process.Footnote ¹⁴² Notwithstanding that the threshold is high, an attempt to circumvent a lack of consent to dispute settlement could be an ‘exceptional circumstance’ in which a court or tribunal would find an abuse of process or abuse of right, provided of course that there was ‘clear evidence’ that the relevant claims had been brought for the purpose of circumventing a lack of consent and obtaining an incidental determination.Footnote ¹⁴³ Alternatively, claims brought in these circumstances might not be considered to meet the threshold for an abuse of process or abuse of right. But, if they do not meet the threshold, then the claims are not abusive and should be allowed to proceed.