Obligations Erga Omnes ( Partes ) and the Participation of Third States in Inter-State Litigation

This article addresses the role of third States in public interest litigation – i.e., ongoing proceedings concerning interests which they share with the international com - munit y. It scrutinizes third-State intervention in inter-State cases through the prism of rules and principles arising in public interest litigatio n, and aims to clarify the limits of such participatio n. Having synthesized the relevant law and doctrine of intervention practice before the ICJ and other institutional court s, it considers the extent to which third-State interests find expression through Articles 62 and 63 of the ICJ Statut e. It examines the invocation of international legal responsibility on the basis of obliga - tions erga omnes and erga omnes partes , as well as the prospect of intervention on this basi s. It then identifies and addresses jurisdictional and procedural questions arising in these and other instances of “public interest” interventio n. It concludes by envisag - ing the prospective institutional development of multilateral participation in public interest litigatio n.


Introduction
Public interest litigation -in which actions are taken before courts and tribunals to safeguard interests shared with the international community1 -is a curious notion in the context of inter-State proceedings.Although the International Court of Justice (ICJ, the Court) routinely receives submissions from many States during its advisory proceedings2 (often supporting different outcomes in the name of the public interest), this mass participation has not historically featured in the Court's treatment of contentious cases.Because such proceedings concern live disputes between sovereigns, derive from consensual jurisdiction, and bind the parties with res judicata force, they are conducted with greater respect to principles such as the autonomy of parties in adversarial proceedings, and the free choice of means embodied in the UN Charter.3As such, inter-State courts and tribunals have ensured an equality of parties wherein neither party lays claim to "civil society" or the public interest.4 The problem of how these judicial and arbitral bodies may take the public interest into account in contentious proceedings -within the confines of inter-State procedural rules and principles -is thus built into the very architecture of such proceedings.By contrast, no such problem is inherent to the design of investor-State arbitration, for example.Unlike contentious proceedings before the ICJ and inter-State courts, such systems of dispute settlement have notably  (1994), 235 (observing that "it is easier to describe the content of community interests than to define their subjects and points of reference"); Giorgio Gaja, "The Protection of General Interests in the International Community", 364 R.C.A.D.I. (2011), 20 (observing that "for an interest to be general, the fact that it concerns more than one or two States is clearly required", and that such an interest "goes beyond the individual States or entities immediately concerned by a breach").Characterizing the concept of "civil society" as similarly "chimerical, in particular in an international law context", see Farouk El-Hosseny, Civil Society in Investment Treaty Arbitration: Status and Prospects (2018), 8.
developed amicus curiae practices to reflect the interests of civil society.5 Non-governmental submissions have also been accepted in some specialized systems of inter-State dispute settlement, as seen in the practice of the World Trade Organization (WTO).6 In this light, the present article frames public interest litigation by third States as participation in ongoing proceedings concerning interests which it shares with the international community.It scrutinizes third-State participation in inter-State cases through the prism of rules and principles arising in public interest litigation.As a practical matter, this inquiry serves to clarify whether limits exist as to which States can participate, under which circumstances, and through which means.It draws reference to ongoing developments in the ICJ's intervention practice, as seen in two pending cases instituted under the Genocide Convention: The Gambia v. Myanmar7 and Ukraine v. Russia.8As this article focuses on specific substantive and procedural rules which may determine the admissibility and scope of third-State participation, it does not examine recent developments in the limited inter-State practice of human rights courts (where this may instead be determined solely as a matter of judicial discretion).9 The present article begins by introducing the statutory mechanisms which govern intervention before the ICJ, and the doctrine which has developed in this practice (Part 2).In particular, we shall see that the general form of mcgarry lape 22 (2023) 273-300 intervention found in Article 62 of the ICJ Statute -which provides that a State may request to intervene in a contentious case if it "consider [s] that it has an interest of a legal nature which may be affected by the decision in the case"raises a more intriguing array of questions in public interest litigation than the form of intervention found in Article 63 of the Statute (which is limited to third-State observations on questions of treaty interpretation).
Having recalled the scope of the "interest of a legal nature" criterion for intervention under Article 62 -and the absence of similar elements when applying Article 63 -this article examines the invocation of international legal responsibility on the basis of obligations erga omnes10 and erga omnes partes,11 and the prospect of a third State intervening on the same basis (Part 3).The article then identifies and addresses jurisdictional and procedural questions arising in instances of "public interest" intervention (Part 4).The author concludes by considering the prospective institutional development of multilateral participation in public interest litigation between States (Part 5).

Relevant Law and Doctrine in Intervention Practice
In contentious cases before the ICJ and other inter-State courts, an Applicant instituting proceedings must demonstrate the existence of a dispute between the parties concerning the rights or obligations submitted to the court.12Separate from this requirement of a bilateral dispute, an Applicant may -in claims which do not concern obligations of an erga omnes character13 -also be required to demonstrate judicial standing, or locus standi, on the basis of a direct injury or other unique interest in bringing the case before the court.These customary requirements may be informed or removed altogether by treaties applicable in the case (such as those with compromissory clauses referring any "difference of opinion" to the Court,14 or those vesting all contracting States with a right to invoke another contracting State's obligations erga omnes partes).
While such requirements may be relevant to the court or tribunal's exercise of jurisdiction in the case at hand, they are not equally applicable vis-à-vis third States which wish to appear therein.This is quite sensible -non-party interveners in ICJ practice do not seek substantive remedies, nor a declaration that the Respondent has breached international legal obligations toward that In the context of treaty relations, an "interest of a legal nature" in the ICJ's interpretation of a given convention might thus be viewed as an interest inter partes, held by all contracting parties to the treaty in question.There may be overlap as well between the interests of the Article 63 intervener and a party in such a case.Indeed, many treaty compromissory clauses providing for ICJ jurisdiction encompass disputes arising from the "interpretation or application" of the treaty.22 The ICJ has imbued the vague phrase "interest of a legal nature" in Article 62 with limitations in its case law as well as in its Rules of Court, including the requirement in Article 81(2)(b) thereof that an application to intervene under Article 62 of the Statute must set out "the precise object of the intervention".In the first instance of a successful Article 62 application, El Salvador/Honduras, Nicaragua's stated object of intervention was to "inform the Court of the nature of the legal rights of Nicaragua which are in issue in the dispute".23  possessed a unique legal interest in the proceedings, stemming from the central role of its judiciary in the case.25 This repeated formulation of the "object of intervention", and the particularization of the "interest of a legal nature" to the third State's uniquely held rights and obligations, is no accident.It follows a consistent practice dating to the ICJ's first judgment on an Article 62 application.In Tunisia/Libya, the Court flatly rejected Malta's general objective to "submit its views to the Court on the issues raised in the pending case".26The Court was unable to find that such a generic object of intervention "is really based on an interest of a legal nature which may be affected by the decision in the Tunisia/Libya case".27 The Article 62 intervener thus does not serve to inform the ICJ of legal areas to which it has no unique connection -a task reserved to the Court, as implied by the principle of jura novit curia.28In this sense, the commonly held interest associated with "public interest" litigation -while potentially sufficient for the institution of a new case -may fail to meet the threshold of an "interest of a legal nature" under Article 62 of the Statute.Under Article 63 of the Statute, however, the third State's "interest" in the proceedings is rather inconsequential to the Court's analysis of the admissibility of its declaration of intervention, and does not substantially impact construction of the underlying convention in cases where the erga omnes character of the applicable rules is not itself in question.By contrast, an interest in the fulfilment of an obligation erga omnes may be critical to the third State's multiplication of the proceedings by instituting a new case against the same Respondent.29This functional distinction between judicial standing in public interest liti- the identification of sources of obligations erga omnes partes, as well as the Court's potential influence on third-party practice in other inter-State fora.

3
Intervention and the Invocation of Obligations Erga Omnes

Third States and Common Interests
The ICJ has famously developed a lineage of case law since the 1970 Barcelona Traction Judgment which recognizes the locus standi of all States in respect of breaches of obligations concerning genocide and aggression, slavery and racial discrimination, and the basic rights of the human person.30In East Timor, the Court confirmed that this list includes breaches of the right of self-determination.31The Court's tendency to make such pronouncements in obiter dicta is evident in Bosnia and Herzegovina v. Serbia and Montenegro, where it recalled that "the rights and obligations enshrined by the [Genocide] Convention are rights and obligations erga omnes".32 The customary requirement of a direct injury for locus standi in inter-State proceedings developed over the course of the twentieth century, as reflected in the International Law Commission's (ILC) 2001 Articles on the Responsibility of States for Internationally Wrongful Acts (ARSIWA).33Among these reflections of modern customary international law, Article 42 can in large part be seen as a reflection of the traditional requirement of direct interest, such as arises from a unique injury.Yet whereas Articles 42(a) and 42(b)(i) respectively refer to injuries which "individually" or "specially" affect a particular State, Article 42(b)(ii) refers to the breach of an obligation which radically changes the position of "all other States" to which it is owed.
The lack of requirement of "specially affected" status to invoke breaches of international obligations under Article 42(b)(ii) appears to find closer kin in Article 48 of the ARSIWA, which concerns obligations whose "principal purpose will be to foster a common interest, over and above any interests of States concerned individually", such as for the protection of a group of people.34In this light, Articles 42(b)(ii) and 48 are distinguishable by the characterization of members of "the international community" as "injured" in the former, and non-injured -yet still entitled to invoke responsibility -in the latter.As suggested above, such distinctions are merely academic in regards to intervening non-parties before the ICJ, which need not demonstrate injury per se (and which cannot in any event seek substantive remedies).
Article 42(b)(ii) especially recalls the twenty-first-century development in ICJ case law of erga omnes partes doctrine, given the origins of this provision in the law of treaties.35Notably, while the ILC's Commentary frames Article 42 as encompassing non-treaty obligations in theory, the only examples of Article 42(b)(ii) provided therein derive from treaty systems -"a disarmament treaty, a nuclear-free zone treaty, or any other treaty where each party's performance is effectively conditioned upon and requires the performance of each of the others".36The Commentary makes particular reference to the Antarctic Treaty in this light as well.37In each of these instances, the obligation is "integral", or interdependent, meaning that its performance by the responsible State is a necessary condition of its performance by all the other States.38Some ICJ Judges have characterized rules concerning the invocation of State responsibility as giving rise not only to locus standi to institute proceedings, but also an "interest of a legal nature" for purposes of intervention under Article 62 of the Court's Statute.Judge Cançado Trindade encouraged intervention to "contribute to the progressive development of international law […] when matters of collective or common interest and collective guarantee are at stake".39In his Hague Academy course on the protection of general interests in the international community, Judge Gaja observed that "[w]hatever 'interest of a legal nature' is required in Article 62 […], it cannot be higher than the one that justifies bringing a claim before the Court".40He highlighted in this regard a 2005 resolution of the Institut de Droit International produced under his rapporteurship, which advocates that the ICJ "should give a State to which an obligation erga omnes is owed the possibility to participate in proceedings pending" before it.41 Yet the rubric of "higher" and "lower" degrees of interest fits awkwardly with Article 62's framing and practice.The reference to "legal" nature therein concerns a kind of interest, of which any observable degree is in principle sufficient for the purposes of this criterion.On this point, the Court's interpretation of "legal" in its Article 62 practice is consistent with its broader use of the term.42For contrast, one can find an example of a standard of degrees of interest in the WTO Dispute Settlement Understanding, which permits intervention by WTO Members which possess a "substantial" interest in the proceedings.43 Most fundamentally, the standing to institute new proceedings, and the statutory requirements for incidental proceedings such as intervention, remain juridically distinct concepts with very different practical consequences.Indeed, as Judge Gaja acknowledged, third-State submissions in cases raising obligations erga omnes would amount to a "new form of participation" -a point reflected in the aspirational language of the Institut's resolution noted above.44 No such possibility currently exists under Article 62 of the ICJ Statute.45 Despite the ARSIWA's characterization of nuclear treaties as giving rise to collective interests, it is notable that the first Article 62 application before the ICJ -filed by Fiji in Nuclear Tests -based its "interest of a legal nature" solely on direct injuries, such as "radioactive fallout […] deposited on Fiji territory".46By contrast, the Applicants in Nuclear Tests had each pleaded their own unique injuries and, in the alternative, the interests of the international community.47Both Australia and New Zealand showed clear deference to "specific" interests (i.e.direct injury or other unique interest, as seen in Article 62 practice), while also referring to more general interests in the interpretation of treaty rules (as arise in Article 63 practice).48 While Rather, these statements characterize the motivation of the States concernedor, as framed in Article 62 practice, the "object of intervention" -rather than the requirements or purpose of Article 63.The Article 63 intervener's right to seek to influence the Court's interpretations remains unaffected by the State's political interests in the underlying dispute, and the scope of its participation remains similarly unaffected by the nature of the legal interests reflected in the relevant convention.In principle, it may intervene under Article 63 to offer its interpretation of any convention to which it is party, regardless of whether its treaty obligations bear an erga omnes partes character.
As such, the entitlement to invoke State responsibility in accordance with Article 42(b)(ii) or 48 of the ARSIWA does not provide a recognized basis for third-State intervention under the ICJ Statute.Although the erga omnes partes character of a treaty obligation may of course influence how such a rule is interpreted, the declarations drafted in Ukraine v. Russia -according to an apparently shared template -have illustrated the unrealistic expectation that dozens of States might identify dozens of distinct interpretative angles.Now that the Court has admitted intervention in this case, it will thus be instructive for future practice to closely examine how it limits their observations to questions of treaty interpretation.

3.2
Relevant Treaty Rules and Subject-Matter Even if one accepts the prospect of a third State possessing an "interest of a legal nature" in proceedings concerning obligations erga omnes or erga omnes partes, the question arises as to which treaty instruments actually contain such obligations.The ILC observed in its ARSIWA Commentary that "collective obligations" may concern, for example, "the environment or security of a region (e.g., a regional nuclear-free zone treaty), or a regional system for the protection of human rights".50Judge Crawford suggested that even a rule that generally sets forth bilateral obligations could protect a collective interest in the case of a breach of a certain degree of seriousness.51 A State which has not been injured, but which may invoke the responsibility of the wrongdoing State, may be said to do so essentially in the exercise of collective interest.Judge Gaja found that "this could be the case of a State which, even if its coastal and maritime areas are not affected by the consequences of pollution in the high seas, incurs expenses to combat pollution".52By conditioning this example on the State having "incur[red] expenses", however, he thus nevertheless ascribes injury to the invoking State in environmental disputes -a remote injury, but a measurable and compensable injury nonetheless.
Such issues have been discussed in the aftermath of the Whaling in the Antarctic case -the most recently admitted ICJ intervention as of January 202353 -in which Australia alleged Japan's breaches of the International Convention for the Regulation of Whaling (ICRW).The Court was reluctant to take up Australia's argument that the primary object and purpose of the ICRW concerned conservation.54For his part, however, Judge Cançado Trindade considered that the legal nature of the ICRW had been transformed into that of an "environmental treaty" over time.55 In Crawford's view, by instituting proceedings under the ICRW, "Australia invoke[d] Japan's obligations erga omnes partes under the [ICRW]".56  It is thus all the more notable that, after being asked by Judge Bhandari "[w]hat injury, if any, has Australia suffered as a result of Japan's alleged breach of the ICRW",58 Burmester (arguing for Australia) referred in passing to "the fact that some of the JARPA II take is from waters over which Australia claims sovereign rights and jurisdiction", while much more emphatically stressing that it "is seeking to uphold its collective interest, an interest it shares with all other parties [to the ICRW]".59Boisson de Chazournes (arguing for the same) similarly focused her response on Australia's "intérêt commun" in maintaining the integrity of the regime deriving from the ICRW.60 Australia and New Zealand had shown greater willingness to assert their status as specially affected States in Nuclear Tests.In the applications instituting those proceedings, each State emphasised the right to vindicate general interests, but also stressed the Applicant's special position,61 as noted above.As such, Fitzmaurice62 and Tams63 have framed Whaling as a logical follow-up to the 2011 Judgment in Belgium v. Senegal, expanding the doctrine of erga omnes partes into environmental disputes.
In the broader context of the law of the sea, we might consider the prospect of a third State raising interests in judicial proceedings concerning environmental obligations under the UN Convention on the Law of the Sea (UNCLOS).64In the light of public interest litigation, it may be particularly salient to determine whether the environmental damage or risk at issue concerns a coastal State's claimed exclusive economic zone or continental shelf, as opposed to the shared resources of the high seas or the International Seabed Area.As the Seabed Disputes Chamber of the International Tribunal for the Law of the Sea observed in Activities in the Area, obligations to preserve the environment of those common spaces may be owed to the international community as a whole, or owed "to a group of States [providing] that the obligation is established for the protection of a collective interest of the group".65 If we turn our gaze upwards to treaty frameworks governing the use of airspace, we may note that the phrasing of the 1944 Chicago Convention's compromissory clause envisages an inclusive, multilateral dispute settlement practice (providing for submission of "any disagreement between two or more contracting States […] on the application of any State concerned in the disagreement").66Some have gone so far as to link the Chicago Convention's safety obligations to fundamental human rights and international humanitarian law.67 Drawing inspiration from the ICJ's pronouncements in Belgium v. Senegal (regarding the Convention Against Torture),68 commentators on the 2021 diversion of a commercial flight by Belarussian authorities have considered that the 1999 Montreal Convention's69 erga omnes character is reflected in Article 7's "extradite-or-prosecute" obligation.70Affording erga omnes character to certain Montreal Convention rules might alternatively find support through analogy between the freedoms of the sea and the skies.Indeed, the Court in Corfu Channel likened "the freedom of maritime communication" to "elementary considerations of humanity, even more exacting in peace than in war".71The Court has not specifically resolved the question of locus standi in disputes concerning nuclear arms, although it was pre-emptively raised by the Marshall Islands as Applicant in the Nuclear Disarmament cases, with relatively innovative reference to Article 42(b)(ii) of the ARSIWA.72The United Kingdom, as one of the nuclear-armed Respondents, did not object to the Applicant's arguments in regards to Articles 42(b)(ii) and 48(3) of the ARSIWA.Instead, it persuasively refocused the Court's attention on the continued requirement of a bilateral dispute, even in cases arising from collective interests.73Yet this question may arise in future proceedings before the ICJ and other inter-State bodies.

3.3
Cross-Fertilization in Practice The Court's emphasis on direct and particular interests in ICJ intervention practice has not yet been clearly adopted by those inter-State courts and tribunals which it has traditionally influenced.For example, there have been zero attempts thus far to intervene in contentious cases before the International Tribunal for the Law of the Sea (ITLOS).Reliance on the ICJ's guidance in any such future practice may seem logical, given that Articles 31 and 32 of the ITLOS Statute import the terms of Articles 62 and 63 of the ICJ Statute nearly verbatim.Yet there has been cause to doubt such cross-fertilization since the Tribunal's establishment in 1996, when it consciously departed from the ICJ's intervention doctrine while drafting its Rules of the Tribunal.74 In inter-State arbitration, the closest cousin to intervention thus far has been the granting of "observer" status in the South China Sea case administered by the Permanent Court of Arbitration (PCA).In this manner, several coastal States with competing sovereignty claims in the region requested (and received) access to written and oral pleadings -key entitlements of the ICJ intervener.75Indeed, the tribunal fashioned the role of the observer only after Vietnam tentatively reserved "the right to seek to intervene if it seems appropriate and in accordance with the principles and rules of international law".76 In truth, such requests are not entirely novel.The ICJ has at times received requests to admit and recognize a delegation of observers from a third State, without the possibility of submitting views to the Court.77However, since hearings are generally made open to the public (with places reserved for diplomatic corps), there is no logistical need for this recognition.In practice, an observer State is not entitled to rights or recognition in contentious proceedings akin to those permitted through Articles 62 and 63 of the Statute.Nor does it receive access to documents outside of the general procedure prescribed in the Rules of Court.78 Yet the participation of observer States in the inter-State arbitral context appears to be an innovation.Following Vietnam, several neighbouring States submitted requests and received permission from the South China Sea tribunal to attend the jurisdictional hearings in the case.79Some of these States had sovereignty claims in the disputed area, while others (such as Singapore) did not.The window between the issuance of the October 2015 award on jurisdiction and the November 2015 hearing on the merits was very tight, and resulted in an influx of eleventh-hour requests from a wider range of States than previously seen.80 It is notable that the tribunal granted observer status to the United Kingdom despite the absence of British sovereignty claims in the region, as this suggests a low threshold for the interest required to justify observer status.However, the rejection of the United States' request on the basis of its status as a non-party to the Convention is far more intriguing.By rejecting the United States' request, the tribunal may appear to imply that States need an inter partes treaty link mcgarry lape 22 (2023) 273-300 with the parties (i.e., by ratifying UNCLOS).81If the tribunal drew here from the requirement of inter partes treaty membership underlying Article 63 of the ICJ Statute, however, this was not made explicit.Such an approach would, in any event, appear to obviate the need for the tribunal to have evaluated each of the other States' statements of uniquely held interests in the case, as opposed to simply permitting them to observe on the basis of their status as contracting parties to UNCLOS.82 The most straightforward way to interpret the tribunal's approach is that it construed its ability to grant observer status in terms of its jurisdiction ratione personae.In this sense, the tribunal's discretion was guided by an analogy between the admission of third-State participation and the use of similar criteria in the evaluation of applications instituting proceedings.Yet this reflects a departure from ICJ practice, where Applicants instituting proceedings face preliminary questions which States seeking to intervene do not -and where no intervener has yet been required to demonstrate a jurisdictional link to the case at hand.While many of the Court's procedural doctrines have influenced arbitral tribunals, the South China Sea arbitration thus illustrates the challenge of importing the intervention practices of courts to institutionalized arbitration.
While any analogy between ICJ intervention and the participation of observer States is itself subject to certain limitations, the considerations noted above remain particularly salient to the possibility of intervention in UNCLOS arbitration.The premise of unilaterally instituted arbitration between States raises the spectre of the Respondent's non-participation in these proceedings.Moreover, the prospect of mass intervention in public interest arbitrations -as evoked in the cascade of observer requests filed in the South China Sea casearguably increases the likelihood of non-appearance in this system.
When the day inevitably comes where a third State seeks to intervene in such proceedings, the tribunal in question may yet turn away from the ICJ's construction of its Statute.For better or worse, it may instead seek guidance in the standards devised by the South China Sea tribunal to determine whether to admit an observer application.Yet as explored below, it has at time appeared even less clear how international courts and tribunals should draw guidance Yet this question appears even more vexed in the practice of Article 62, a mechanism which the Court has construed as providing two distinct channels of participation.A State may intervene by meeting the express requirements of Article 62, but if it does so with a jurisdictional link to the parties -encompassing the subject-matter of the case -it can intervene as a full party in its own right.This latter channel has been formally (and unsuccessfully) attempted only by Honduras in Territorial and Maritime Dispute.86Every State which has actually intervened in a case before the Court has therefore done so in the capacity of a non-party to the case -i.e., as a guest making written and oral submissions on a circumscribed set of issues.
As with the Court's jurisprudence concerning another incidental proceeding, the institution of counter-claims, it remains an open question whether the ICJ may admit Article 62 intervention as a party using a jurisdictional link which is different from the instrument on which the parties have founded the Court's jurisdiction.Such situations may arise when the Court has exercised jurisdiction under a compromissory clause in a convention, while a third State seeks to intervene on the basis of the three States' respective declarations filed pursuant to Article 36(2) of the ICJ Statute (the so-called "Optional Clause").87While it ultimately attracted intervention under Article 63, Whaling illustrates the potential for multiplicity in this regard, as such declarations were used to provide the Court with jurisdiction concerning the interpretation of a separate legal instrument, the ICRW.
In such instances where the parties have founded the Court's jurisdiction upon Optional Clause declarations, the question arises as to whether such instruments are capable of conferring jurisdiction over the parties in public interest litigation.The question was not raised before the ICJ in Belgium v. Senegal,88 where the Court was given both the compromissory clause of the Convention Against Torture and the Optional Clause as potential bases of jurisdiction, and addressed only the former.Some commentators view cases instituted under Article 36(2) of the ICJ Statute as requiring direct injury or other unique interest.Noting that the treaty bodies of human rights treaties had considered that similar clauses in those conventions established reciprocal rights, Törber considers that "this must hold true for the [ICJ] Optional Clause, too".89Others have taken the opposite view,90 and may see support in Australia's framing of its collective interest-based locus standi in the oral phase of Whaling (a case founded upon Optional Clause declarations).
Whichever approach is eventually adopted by the Court in respect of parties, it may be expected that a third State which intervenes as a full party will be held to the same jurisdictional standard.Yet the question remains interesting for public interest litigation, because key jus cogens conventions contain ICJ compromissory clauses (notably, the Genocide Convention91 and the Convention Against Torture).Given the wide ratification of these jurisdictional bases, a case which is instead instituted under Article 36(2) of the ICJ Statute is unlikely to concern a jus cogens such as genocide or torture.This suggests that such questions surrounding Optional Clause practice are likely to arise only in regards to murkier terrain in public interest litigation, concerning certain subject-matter which -unlike jus cogens -may possess a less clearly erga omnes character (such as those found in the conventions discussed in Section 3.2 above).
When assessing the relationship between intervention and the ICJ's jurisdictional determinations, it is worth recalling that the Court had never admitted an intervening State during the preliminary objections phase of a case until 2023.Indeed, even the "right to intervene" under consideration of El Salvador's Article 63 intervention without a hearing (and dismissing it upon deciding to apply customary international law, rather than the conventions raised in the application instituting proceedings).92This aversion to non-party intervention during jurisdictional phases appeared particularly sensible in light of the merits-oriented assessment of the "interest[s] of a legal nature" proffered by Article 62 interveners,93 and the Court's procedural practice of joining to the merits any objections which lack an "exclusively preliminary character".94 In its June 2023 order admitting Article 63 intervention during the preliminary objections phase of Ukraine v. Russia, the Court ensured consistency with this prior case law by recalling that El Salvador had "failed to identify the provisions of any convention the interpretation of which, in its view, would be in question at the stage of the proceedings concerning the jurisdiction of the Court and […] referred to conventions that could only concern the merits of the case".The Court also emphasized the incidental and limited function of Article 63 intervention explained above, circumscribing participation in several key respects.95 If a State moreover applies to intervene as a party to the case, the timing of this decision risks exposing a significant lacuna in the ICJ's Rules of Court.In particular, while that State would have until "the closure of the written proceedings" on the merits of the case to apply under Article 62 of the Statute96 -and thus to furnish its jurisdictional link with the parties -the Court may well have exercised its jurisdiction under a separate basis by that point, leaving no particularly orderly options for the Court to deal with this eventuality.For this reason, it would be prudent for the ICJ to fill this gap by supplementing its Rules of Court on this point.In this manner, the Court would formally codify its doctrinal distinction between non-party and full-party intervention under Article 62.97 What would remain to be determined in practice, however, is whether intervention as a party will invite analysis of the third State's locus standi using the same rubric applied to the Applicant in the case.Alternatively, the Court might assess the request solely based on the requirements of Article 62 and the presence of a jurisdictional link, thus reinforcing the "incidental" character of intervention.98In practice, however, this question may be easily resolved in cases concerning obligations erga omnes partes, insofar as the third State has asserted the same collective interest pleaded by the Applicant.

4.2
Locus Standi and Proprio Motu Judicial Power It is notable that Belgium v. Senegal and Whaling were unitary proceedings, meaning that the question never arose as to whether the Court may address locus standi -and, in Whaling, intervention -at a preliminary phase.The Court has since determined that it has jurisdiction under the Genocide Convention in The Gambia v. Myanmar.99While the question of The Gambia's locus standi was raised by Myanmar in the form of a Preliminary Objection, it remains unclear whether or when the Court would have determined this question in the absence of any objection on this point.
In this context, a question of particular significance in public interest litigation concerns whether locus standi is waivable by a Respondent, or whether an inter-State court or tribunal may nevertheless decide this question proprio motu.The question is at once novel and fundamental to one's view of the scope of party autonomy and the judicial function in inter-State dispute settlement.Moreover, one may consider this narrow corner of the case law alongside questions raised above concerning the relative powers of courts and parties in intervention proceedings.
In Whaling, Japan focused its objections elsewhere, and did not directly challenge Australia's standing as Applicant in the case.In the present author's view, the case should in this sense be contextualized within the Court's broader procedural rules.As a general matter, parties must raise in the written phase all distinct arguments on which they rely and wish the Court to consider.100A response to a question posed from the ICJ bench during the oral phase -regardless of whether the answer itself is written or oral -thus needs to be predicated on arguments asserted in the written phase to serve as a basis for the Court's ruling on a legal question.In Whaling, Australia had no strategic reason to pre-emptively defend its locus standi in its Memorial, and Japan's Counter-Memorial gave it no basis to assert and rely upon any such defensive arguments during the oral proceedings.101Indeed, as noted above, Judge Crawford, as well as Professors Fitzmaurice, Tams, and Tanaka have soundly inferred that the Court's decision was not based on any direct and particular interest of Australia, despite passing reference to such interest in its oral pleadings.
This does not necessarily imply that the Court took locus standi into account by deciding the merits of the case.Rather, this specific question comes down to whether one considers that locus standi is waivable by the Respondent, or else rests with the Court proprio motu.As noted above, Judge Crawford and Professors Fitzmaurice, Tams, and Tanaka have each taken the position that the Court in this manner affirmed Australia's locus standi on the basis of its collective interest in ensuring respect for obligations erga omnes partes.Such scholars thus necessarily presume that the Court may decide this question proprio motu -i.e., that it could have dismissed the case as a check against actio popularis, and tellingly declined to do so.This view could be said to find some analogical support in the ICJ's 2007 Genocide102 and 2016 Nicaragua v. Colombia103 doctrine on questions implicitly resolved in jurisdictional decisions (there, questions of res judicata).
Yet the present author respectfully disagrees with this particular interpretation of the Court's silence.If, as in Whaling, the Respondent does not raise the question of locus standi, there is no clear basis to infer a statement on the matter where the Court's Judgment says nothing.Locus standi is a doctrine which ultimately serves to safeguard Respondents.104A Respondent is free to raise or otherwise waive this objection as a matter of party autonomy (as Japan did here).Through this waiver, a Respondent may "cure" defects which might otherwise prove fatal to a case.105There may be good reasons -litigation strategy, political optics -why a Respondent chooses not to raise every potentially successful objection.The present author's view defers to this sovereign prerogative, respects the parties' commitments to dispute settlement under the UN Charter,106 and poses no threat to the Court's judicial function or the rights of third States.
Indeed, the a contrario position that this objection was not Japan's to waive in Whaling can give rise to perverse judicial policy consequences.If a Respondent appears in contentious proceedings and does not object to an Applicant's lack of direct injury or unique interest in its claims, a more judicially conservative international tribunal than the current composition of the ICJ might rely upon the scholarly authorities noted above to nevertheless dismiss the case on this very basis.
In South West Africa, the ICJ, in a single operative clause, found in 1962 that it had jurisdiction to adjudicate upon the merits of the dispute.107In its infamous Second Phase, the Court in 1966 dismissed the case by finely slicing a distinction between locus standi ratione personae -a question it acknowledged as decided in the preliminary objections phase -and locus standi ratione materiae, a fatal defect in the Applicants' case (in the opinion of an equally finely sliced majority of the Court).108In Rosenne's view, the absence of argumentation on mcgarry lape 22 (2023) 273-300 locus standi in the parties' pleadings on the merits indicates that the question was "raised by the Court proprio motu".109 In the present author's view, however, the Court's actions in South West Africa do not support this finding of proprio motu power to raise questions of locus standi.Such questions were clearly argued by the parties during the preliminary objections phase.110South Africa cannot be seriously deemed to have deliberately restricted its objection during that phase to locus standi ratione personae, as this extraordinary juridical distinction was created by the Court from whole cloth years later, in its 1966 Judgment.
The decision is better understood as the ICJ itself frames it: a question undecided in its Judgment on preliminary objections.The Court did not find that locus standi had not been effectively argued by the Respondent.Rather, the Court considered that it had implicitly bifurcated this question, joining the substantive question of locus standi ratione materiae to the merits of the case.Like Rosenne's view, this interpretation may have the whiff of legal fiction, but it gains credence in light of the still-primordial state of the ICJ's procedural law prior to the comprehensive 1978 revision of its Rules of Court (its first major advance over the PCIJ's 1936 Rules of Court).111It also bears the virtue of caution, as opposed to relying upon the most maligned Judgment in the Court's history to assert a general power of international courts and tribunals to determine locus standi questions proprio motu, in the absence of any express findings of the Court on this point in the half-century since.

Conclusion
The raison d'être of Article 48 of the ARSIWA (as well as Article 42(b)(ii)) serves to prevent a horror vacui -situations where impunity would reign because, in the absence of direct injury, no State would be permitted to bring the perpetrator State to justice.Importantly, this objective is satisfied as soon as one State brings a justiciable case.In other words, the object and purpose of these rules are not furthered by adding more States to ongoing proceedings.As such, these rules provide questionable grounds for pursuing third-State intervention.This is consistent with the ICJ's jurisprudence requiring a particularized "interest of a legal nature" to intervene as a non-party under Article 62, the relative inconsequentiality of State interests to Article 63 intervention, and the Court's general distinction between incidental proceedings and the admissibility considerations which attach to applications instituting new cases.It remains less clear whether an application to intervene "as a party" under Article 62 should lead the Court to scrutinize the third State's locus standi using the same rubric applied to the Applicant in the case.As discussed above, this question could be easily resolved in cases concerning obligations erga omnes partes, insofar as the third State has asserted the same collective interest pleaded by the Applicant.
While the standing of parties and third States are distinct judicial constructs, the ICJ's doctrinal development of locus standi in cases arising from obligations erga omnes partes is not on its face dissimilar to the inter partes character of Article 63 intervention.The collective nature of States' interest in such cases does not necessarily problematize the core requirement of Article 63: shared membership in a convention which the Court is called upon to interpret.Article 63 intervention -on the basis of this limited "interest" in the construction of the relevant convention -thus remains available to each concerned State in such cases.On the other hand, the ARSIWA Commentary's reference to "legal interest[s]" arising under both Articles 42 and 48 thereof112 does not invite us to equate this basic term with an "interest of a legal nature" under Article 62 of the ICJ Statute -a lex specialis mechanism governing incidental proceedings.
When a State has already instituted proceedings in respect of a collective interest recognized under either Article 42(b)(ii) or 48 of the ARSIWA, the residual interest possessed by other States is thus in informing the Court's interpretation of the obligation erga omnes partes.This recalls the propriety of Article 63 intervention in such cases, as well as the present article's repeated distinction between the collective interest and the Article 62 interest of a "legal" nature.
Contemporary proceedings such as the currently pending Genocide Convention cases of The Gambia v. Myanmar and Ukraine v. Russia may further clarify the possibilities and confines of third-State participation in public interest litigation.Yet The Gambia v. Myanmar in particular might also illustrate a need for a treaty-based mechanism which confers each Member with judicial mcgarry lape 22 (2023) 273-300 standing to raise claims or complaints on behalf of stateless peoples.113More broadly, the legal and practical challenges of intervention in such cases -as seen in the ad hoc managerial techniques adopted by the Court in response to the unprecedented flood of Article 63 declarations filed in Ukraine v. Russiashould lead States to consider developing new institutional forums for the multilateral settlement of disputes arising from obligations erga omnes.
In conclusion, the premise of intervention in respect of interests held by all States reflects twenty-first century conceptions of international justice and accountability.Articles 62 and 63 of the ICJ Statute, however, have in general remained statutorily and doctrinally anchored in a twentieth century vision of international adjudication.While Article 63 is currently enjoying a period of relative rediscovery, it offers a fairly limited form of participation.The bolder possibilities of Article 62 intervention in public interest litigation, on the other hand, may require the third State to navigate unique conceptual and practical challenges.
Tanaka has similarly observed that "the Whaling judgment appears to demonstrate that the erga omnes partes character of treaty obligations can be indirectly recognized through the establishment of the […] admissibility of the Applicant State's claims".57mcgarry lape 22 (2023) 273-300 For an in-depth assessment of the Court's advisory function in the context of public interest litigation, see further Jane A. Hofbauer, "Not Just a Participation Trophy?Advancing Public Interests in Advisory Opinions at the International Court of Justice" (in this Volume).3 Charter of the United Nations (San Francisco, 26 June 1945), Art.33. 4 On the challenges of identifying the interests of the international community, see Bruno Simma, "From Bilateralism to Community Interest in International Law", 250 R.C.A.D.I.
1 See South West Africa, Second Phase (Ethiopia v. South Africa; Liberia v. South Africa), Judgment, I.C.J. Reports 1966, p. 6, para.88 (defining actio popularis as a "right resident in any member of a community to take legal action in vindication of a public interest").Recalling the development of this practice, see Christine M. Chinkin, "Symposium: The East Timor Case before the International Court of Justice", 4 E.J.I.L. (1993), 217. 2 State in particular.15Article 63 of the ICJ Statute and its nearly-verbatim predecessor in the Statute of the Permanent Court of International Justice (PCIJ) are rooted in the consent-based origins of international arbitration.In other words, Article 63 invites States to inform the interpretation of treaties to which they have voluntarily acceded whenever that treaty's "construction […] is in question".Given this requirement of prior treaty-based consent, it is thus unsurprising to find clear antecedents for Article 63 in an 1875 Resolution of the Institut de Droit International,16 the 1899 and 1907 Hague Conventions establishing the Permanent Court of Arbitration,17 and the 1907 draft convention and 1910 draft protocol of the International Prize Court.18Article 63 in principle requires only that the Court is tasked with interpreting a convention to which these States are treaty parties.Article 62 of the ICJ Statute, by contrast, provides that any State may request to intervene in a contentious case if it "consider[s] that it has an interest of a legal nature which may be affected by the decision in the case".While there is thus no requirement of being a party to a convention invoked in the case (other than the ICJ Statute itself), there is evident overlap between Articles 62 and 63.According to its travaux préparatoires, the Hague Committee of Jurists -the 14 See Farid Ahmadov, The Right of Actio Popularis before International Courts and Tribunals (2018), 139-140.15 All States which have intervened under Articles 62 and 63 have done so as "non-parties" to the case at hand, although the ICJ has indicated the possibility of intervening as a full party under Article 62. See discussion infra.legal minds assembled to draft the PCIJ Statute, for consideration by the Council of the League of Nations -foresaw in 1920 that an interest in treaty interpretation is also an "interest of a legal nature".19This overlap has manifested in practice since the first PCIJ case (where Poland's Article 63 intervention in S.S. Wimbledon was initially filed under Article 62),20 and is also evident when interventions are filed under both provisions.21 vention for the Pacific Settlement of International Disputes (The Hague, 1907).18 Convention relative to the Establishment of an International Prize Court (The Hague, 18 October 1907); Additional Protocol to the Convention relative to the Establishment of an International Prize Court (The Hague, 19 September 1910).mcgarry lape 22 (2023) 273-300 body of eminent Reports 1999, p.1029 ("to inform the Court of the nature of the legal rights and interests of Equatorial Guinea that could be affected by the Court's decision […]").
While the ARSIWA Commentary credits the notion of "integral" obligations to Sir Gerald Fitzmaurice's work as ILC Special Rapporteur on the Law of Treaties, that earlier work had more clearly distinguished integral from interdependent obligations.
34 See James Crawford, Chance, Order, Change: The Course of International Law (2014), 278.For a typology of such interests in this context, see, generally, E. Benvenisti and G. Nolte, "Community Interests Across International Law: Introduction", in E. Benvenisti and G. Nolte (eds.),Community Interests Across International Law (OUP, 2018), 3. On the role of the PCIJ in this area, see A. Tzanakopoulos, "The Permanent Court of International Justice and the 'International Community'", in C.J. Tams and M. Fitzmaurice (eds.),Legacies of the Permanent Court of International Justice (Brill, 2013), 339 (referring to Greco-Bulgarian "Communities", Advisory Opinion of 31 July 1930, P.C.I.J. Series B, No. 17 (1930), p. 4).For Sir Gerald, the force of "integral" obligations are "self-existent, absolute and inherent for each party, and not dependent on a corresponding performance by the others".Third Report on the Law of Treaties, by Mr. Gerald Fitzmaurice, Special Rapporteur, A/CN.4/115 (1958), pp.27-28.Downloaded from Brill.com 05/30/2024 09:27:56AM via Open Access.This is an open access article distributed under the terms of the CC BY 4.0 license.https://creativecommons.org/licenses/by/4.0/mcgarry lape 22 (2023) 273-300 general interests have not found clear application in Article 62 practice -as seen in the absence of Article 62 applications among the deluge of declarations filed in Ukraine v. Russia -nor does this pending case indicate any legal significance to the incantation of shared interests in Article 63 practice.49 mcgarry lape 22 (2023) 273-300

72
On the disuse of this provision in inter-State dispute settlement during the years following the ARSIWA's adoption, see Simon Olleson, "The Impact of the ILC's Articles on Responsibility of States for Internationally Wrongful Acts: Preliminary Draft", British 104tion and intervention as a party under Article 62 of the ICJ Statute; cf.ITLOS Rules of the Tribunal, Arts.103(4),104(3) (making clear that interveners do not exercise party autonomy, since they cannot appoint judges ad hoc or object to the discontinuance of the case).Downloaded from Brill.com 05/30/2024 09:27:56AM via Open Access.This is an open access article distributed under the terms of the CC BY 4.0 license.https://creativecommons.org/licenses/by/4.0/ Article 63 of the ICJ Statute did not prevent the Court in Military and Paramilitary Activities from deferring 89 See Gunnar Törber, The Contractual Nature of the Optional Clause (2015), 36-37 (finding that under the European Convention on Human Rights and the Inter-American Convention on Human Rights, judicial review is not "considered as a common good or as a part of the common ordre public.All considerations are based on the effectiveness of human rights and the actio popularis for the benefit of the individuals.With good reasons the Optional Clause has been considered as something different as it primarily allows states to enforce their own rights only.As far as the [UN Human Rights Committee] considers Article 41 [of the International Covenant on Civil and Political Rights] as establishing reciprocal rights this must hold true for the Optional Clause, too") (citing Convention for the Protection of Human Rights and Fundamental Freedoms (Rome, Downloaded from Brill.com 05/30/2024 09:27:56AM via Open Access.This is an open access article distributed under the terms of the CC BY 4.0 license.https://creativecommons.org/licenses/by/4.0/