A.  Definitions

1  Equity is a polymorphous concept even in the narrow confines of legal language. In its most general meaning it refers to what is fair and reasonable in the administration of justice, a concept that in Roman Law is aptly expressed by the term aequitas. In a narrower and more technical meaning, equity refers to the power conferred on the International Court of Justice (ICJ) under Art. 38 (2) Statute of the International Court of Justice, or on other international courts and tribunals, to decide a case ex aequo et bono, ie without being required to apply rules of law (Judicial Settlement of International Disputes; Peaceful Settlement of International Disputes). Finally, a third meaning of equity refers to the separate system of rules and jurisprudence that has developed in the Anglo-American tradition in parallel with the development of the common law. This latter concept of equity connotes a source of domestic law that has its historical antecedent in the jurisdiction of the Roman praetor. Its evolution is due to the decisions of the Chancery Court in medieval England where the rigidity of the common law, with its limited number of remedies and writs, effectively limited access to justice for potential claimants. A system of general legal principles—dubbed ‘maxims of equity’—was devised in order to avoid the manifest injustices that could arise from the strict application of the prescribed regime, thereby rendering the legal rules more flexible. The following analysis will deal only with the first two types of equity. The third one, in so far as it expresses a peculiarity of the Anglo-American legal tradition, is of interest mainly for comparative law rather than international law (Comparative Law, Functions and Methods).

B.  The Rational-Ethical Foundation of Equity in International Law

2  Preliminary to the consideration of whether equity may constitute a source of international law (Sources of International Law) is the question of whether it is possible to assume the existence of a common sense of justice and fairness in a society that is culturally and politically divided as the international society is today. The profound transformation of the international community in the second half of the 20^th century and the rise to statehood of many peoples and territories hitherto under colonial rule has magnified the complexity and diversity of the international community (Colonialism; Decolonization). Post-colonial studies and critical legal studies have debunked the myth of the universal value of international law (Universality) and have introduced at the epistemological and normative level different perspectives and theories of justice inspired by the needs of the developing world (Developing Countries) and the memory of past injustice and the instrumental use of international law to justify conquest and coercion (see Anghie; Koskenniemi; Kennedy; see also History of International Law, since World War II). Similarly, feminist theories of international law have highlighted its inability to represent the moral and cultural complexity of the human experience because of its failure to include the contribution of women in the institutional structures and normative processes that have shaped the development of the international legal order (Charlesworth and Chinkin; Feminism, Approach to International Law). At the threshold of the 21^st century two developments have the potential to further hinder the conceptualization of a universal theory of justice and equity. The first is the sudden eruption onto the international scene of religious fundamentalism, with the attendant spectre of a ‘clash of civilizations’ and the corresponding emergence, especially in the United States of America (‘US’), of a utilitarian, reductionist view of international law as a pure instrument of State interests (see Goldsmith and Posner; Huntington). The second is the phenomenon of the so-called fragmentation of international law, which puts into question the unity of the international legal order as a consequence of the excessive specialization and compartmentalization in different branches of the law and of the multiplication of institutions and courts responsible for their implementation (see the Report of the Study Group of the International Law Commission ‘Fragmentation of International Law: Difficulties Arising from the Diversification and Expansion of International Law’ [Conclusions] [2006]).

3  Although it is undeniable that the above historical developments and intellectual approaches may disclose real difficulties in reaching agreement on a common definition of equity, nevertheless they cannot logically exclude the existence of a common sense of fairness and equity among different peoples of the world. First, it is precisely because of the pluralism and cultural diversity of the international society that a shared conception of what is just and equitable becomes a condition sine qua non of the overall coherence and unity of the international legal system (see Dupuy). Secondly, modern science is increasingly recognizing the existence of a biological basis for the sense of justice, a basis that is part of the phylogenetic evolution of Homo sapiens, which enables human beings to react to blatant injustice in a way that is similar to the antibody reaction of the cell system in the presence of parasite attack or danger (see Lorenz, Chapter 6). Far from resulting in the resurrection of the metaphysical construct of ‘natural law’ (Natural Law and Justice), this discovery has led to the parallel reconstruction of the structural similarities among the most diverse legal systems of the world as presented by the Common Core Project, developed under the direction of Professor Rudolf Schlesinger of Cornell University in the 1960s and later carried out by the University of Trento as The Common Core of European Private Law Project (see M Bussani and U Mattei ‘The Common Core of European Private Law’ <http://www.common-core.org/> [10 November 2020]), which tends to demonstrate the existence of an innate common perception of what is fair and what is wrong. Indeed, it is germane to note that comparative research has revealed that a large number of so called ‘equitable’ principles, such as good faith and the prohibition of abus de droit, are common to all of the major legal families (Newman; Burke 123–98) (see Good Faith (Bona fide); Abuse of Rights). Thirdly, even if one were to remain skeptical of the biological basis of the sense of justice, a powerful argument in favour of the acceptance of a common sense of equity in international law comes from the historical context in which the problem is posed. We live in an epoch of unprecedented opportunities for contacts, exchange, and communication between individuals and peoples. This entails a process of mutual learning from, and diffusion of, different legal systems and different ideas of justice. This process brings with it the adaptation of human behaviour to the new conditions of exchange and cooperation, and has the reflexive effect of consolidating shared conceptions of justice and equity. This is all the more so in international law, the law that by definition concerns the regulation of international relations and exchanges (see also Cooperation, International Law of) and that, by necessity, has the task of reconciling, not only competing State interests, but also different ethical and cultural views of the peoples of the world.

C.  The Place of Equity in International Law

4  If ethical and cultural diversity are not an insurmountable obstacle to the reception of equity in international law, its precise scope and role among the sources of international norms remains unclear. Art. 38 (1) ICJ Statute does not include equity among the formal sources of international law, ie treaty (Treaties), custom (Customary International Law), and general principles (General Principles of Law). Therefore, it is necessary to examine by which other processes and under which other forms consideration of equity may play a role in the determination, interpretation (Interpretation in International Law), and implementation of international law and in the settlement of international disputes.

5  First of all, equity may become a material source of the law when subsumed under the formal heading of ‘general principles of law’ pursuant to Art. 38 (1) (c) ICJ Statute (Rosenne). In a frequently cited passage of his dissenting opinion in the case concerning the Diversion of Water from the Meuse (The Netherlands v Belgium) (Meuse, Diversion of Water Case [Netherlands v Belgium]), Judge Manley Hudson construed certain maxims of equity as ‘general principles of law recognized by civilized nations’ (at 76). So—he concluded—maxims such as ‘equality is equity’ (ibid 77) and ‘he who seeks equity must do equity’ (ibid), would compel a judge to ensure that ‘where two parties have assumed an identical or reciprocal obligation, one party which is engaged in a continuing non-performance of that obligation should not be permitted to take advantage of a similar non-performance of that obligation by the other party’ (ibid; Reciprocity; see also Separate Opinion: International Court of Justice [ICJ]). Judge Anzilotti went still further in his dissenting opinion, stating that the principle of inadimplenti non est adimplendum (aequitas est equalitas) is ‘so just, so equitable, so universally recognised that it must be applied in international relations … [and is] one of the general principles of law recognised by civilised nations’ (at 50). As Judge Schwebel noted in Military and Paramilitary Activities in and against Nicaragua ([Nicaragua v United States of America] [1986] ICJ Rep 392–94), Anzilotti’s assertion in this regard has never been challenged. The Diversion of Water from the Meuse case itself has been described as equity’s ‘locus classicus’ (Jenks 322).

6  The construction of equity as a material component of the category of general principles of law is also supported by the authoritative opinion of academic writers (see Friedmann; De Visscher; Lauterpacht [1927] para. 48; B Cheng General Principles of Law Applied by International Courts and Tribunals [Stevens London 1953]; Rossi; White). It was clearly also the intention of the drafters of the PCIJ Statute—upon which the ICJ Statute is closely modelled—to include such a construction, albeit for a variety of reasons (see Advisory Committee of Jurists; Burke 103–14).

7  Another uncontroversial role that equity may play in international law is that of an instrumental criterion of interpretation of the applicable law in order to adapt such law to the specific circumstances of the case. In this case equity is not used as a principle endowed with autonomous normativity but rather as a method for infusing elements of reasonableness and ‘individualized’ justice whenever the applicable law leaves a margin of discretion to the court or tribunal which has to make the decision (see Margin of Appreciation). In this sense it is appropriate to speak of equity infra legem, ie within the boundaries of the law (see Frontier Dispute Case [Burkina Faso/Republic of Mali]).

8  Art. 31 (3) (c) Vienna Convention on the Law of Treaties (‘VCLT’ [concluded 23 May 1969, entered into force 27 January 1980] 1155 UNTS 331) prescribes that ‘[t]here shall be taken into account, together with the context: … (c) any relevant rules of international law applicable in the relations between the parties’. As an aspect of the interpretative process, equity must therefore be taken into account alongside, and integral to: Art. 31 (1), the ‘basic rule’ of treaty interpretation—that is, that a treaty is to be interpreted in good faith, with the ordinary meaning given to the terms of the treaty in the light of its object and purpose; Art. 31 (2), the treaty’s context; Art. 31 (3) (a) and (b), subsequent agreements and subsequent practice; Art. 31 (4), any relevant special meaning; and Art. 32, dealing with supplementary means of interpretation. Therefore, if equity may be treated as a sub-category of the general principles source of law, per Art. 38 (1) of the ICJ Statute, it may also be highly relevant in treaty interpretation, as an extraneous legal source.

9  Finally, the hypothesis of equity contra legem or praeter legem, ie in opposition to law or outside the law, is contemplated by Art. 38 (2) ICJ Statute. Resort to this concept of equity, which entails the creation of individualized rules by the judge for the settlement of the dispute ex aequo et bono, requires specific consent by the parties. As is known, no case has been submitted so far to the ICJ in which the parties have granted the Court the exceptional power to decide ex aequo et bono (Pellet and Müller mn 157–75).

D.  Historical Evolution

10  Although in theory the various types of equity outlined above appear well demarcated, in practice the differences between them tend to be blurred. In the early practice developed by arbitral tribunals (Arbitration) and by the Permanent Court of International Justice (PCIJ), the prevailing view of equity is that of a set of principles capable of facilitating a just and fair solution of a dispute within the framework of the applicable law, ie treaty provisions or customary norms (eg Cayuga Indian Claims; Orinoco Steamship Co [United States of America v Venezuela]; Norwegian Shipowners’ Claims Arbitration; Diversion of Water from the Meuse [The Netherlands v Belgium]; Eastern Extension, Australasia and China Telegraph Company Ltd [Great Britain] v United States [1923] 6 RIAA 112; Russian Claim for Interest on Indemnities [Russia v Turkey] [1912] [1961] 11 RIAA 421 [Russian Indemnity Arbitration]; Faber Case [German-Venezuelan Mixed Claims Commission] [1903] [1960] 10 RIAA 438; Dispute between Great Britain and Portugal in the Case of Yuille, Shortridge & Cie [Great Britain v Portugal] [1861] [2011] 29 RIAA 57; ‘Affaire du Capitaine Thomas Melville White, Décision de la Commission Chargée, par le Sénat de la Ville Libre Hanséatique de Hambourg, de prononcer dans la cause du Capitaine Thomas Melville White, date de Hambourg du 13 avril 1864’ in H La Fontaine Pasicrisie internationale 1794–1900: Histoire documentaire des arbitrages internationaux [Nijhoff The Hague 1997] 48; Claim of Finnish Shipowners against Great Britain in respect of the Use of Certain Finnish Vessels during the War [Finland v United Kingdom] [1934] [1949] 3 RIAA 1479; Petroleum Development (Trucial Coast) Ltd v Sheik of Abu Dhabi [1951] [1957] 18 ILR 144 [Abu Dhabi Oil Arbitration]).

11  In this context the relationship between equity and law is one of complementarity and can be characterized as infra legem. A move towards a more autonomous concept of equity, capable of prescribing a settlement outside the applicable rules of law, can be observed in a number of cases decided by the PCIJ in the early 1930s. In the Free Zones of Upper Savoy and the District of Gex (France v Switzerland) (Free Zones of Upper Savoy and Gex Case), the PCIJ was divided on whether the determination of the customs regime of the zone was to be effected exclusively on the basis of the terms of the Treaty of Versailles or by reference to considerations of equity, even though the special agreement between France and Switzerland contained no reference to a decision ex aequo et bono. In the end the majority of the Court, by a casting vote of the president, favoured the application of strict rules of law. However, the door was opened for the debate over the power of the Court to resort to equity principles even in the absence of the power to decide ex aequo et bono. In the subsequent case concerning the Diversion of Water from the Meuse (The Netherlands v Belgium), this possibility was fully seized in the already cited dissenting opinion of Judge Hudson who boldly stated that under ‘Article 38 of the Statute, if not independently of that Article, the Court has some freedom to consider principles of equity as part of international law which it must apply’ (at 77). This statement clarified a point that had remained ambiguous in the Free Zones of Upper Savoy and the District of Gex case, ie that the power to decide ex aequo et bono under Art. 38 (2) ICJ Statute must remain distinct from the inherent power of the Court to resort to equity principles as part of international law and of the normal adjudication process. A cautious confirmation of this approach can be found in the 1937 Resolution of the Institut de Droit international stating that:

12  Individual equitable principles have had important influence in deciding cases before the ICJ and PCIJ. One prominent example is that of estoppel. Lauterpacht (1958) notes that the PCIJ’s early case law was occasionally ‘reminiscent of some of the elements of estoppel in English law’, citing the Treatment of Polish Nationals and Other Persons of Polish Origin or Speech in the Danzig Territory (Advisory Opinion) PCIJ Series A/B No 44, Free Zones of Upper Savoy and The District of Gex, and Greco-Bulgarian Communities (Advisory Opinion) PCIJ Series B No 17 (at 83) cases as prominent examples. In the Chorzów Factory case, it was held that a State could be estopped from pleading that the Court lacked jurisdiction in the case because ‘it is…a principle generally accepted in the jurisprudence of international arbitration, as well as by municipal courts, that one party cannot avail itself of the fact that the other has not fulfilled some obligation, or has not had recourse to some means of redress, if the former party has, by some illegal act, prevented the latter from fulfilling the obligation in question, or from having recourse to the tribunal which would have been open to him’ (Factory at Chorzów [Germany v Poland] [Judgment] PCIJ Series A No 9, 31; see also Burke 216–24). An analogous equitable principle, founded upon the doctrine of legitimate expectation (Legitimate Expectations) was applied in the Legal Status of Eastern Greenland (Denmark v Norway) case (PCIJ Series A/B No 53; Eastern Greenland Case). More recently, the Temple of Preah Vihear Case judgment represented a conspicuous usage of estoppel doctrine by the ICJ ([Cambodia v Thailand] [Merits] [1962] ICJ Rep 6).

13  It is with the ICJ, and in particular with its jurisprudence on continental shelves delimitation that a new and more robust resort to equity praeter legem is inaugurated (Continental Shelf). The locus classicus of this turn is represented by the North Sea Continental Shelf Cases (Federal Republic of Germany/Denmark; Federal Republic of Germany/Netherlands). Here, the Court was confronted with a dispute over the proper method of delimitation of lateral continental shelf boundaries which could have been settled by the application of existing rules of the law of the sea—ie the principle of equidistance. Given the manifestly unjust result that such principle would have produced for one of the parties—namely Germany—due to its concave coastline, the Court resorted to equity, not so much as a general consideration of fairness to bend the law towards a just result, but as a concept capable of generating true legal obligations for the parties to the dispute besides and almost independently of the law. It is true that the Court goes on at length to justify its normative approach to equity in terms of the rule of law requiring the application of equitable principles in matters of continental shelf delimitation. The Court made this point when it stated that it ‘was not applying equity simply as a matter of abstract justice, but applying a rule of law which itself requires the application of equitable principles’ (at para. 85). However, it is easy to see how this argument is simply a rhetorical device permitting the Court to ‘assume’ the existence of a legal norm or principle of international law prescribing the application of equitable principles (General International Law [Principles, Rules and Standards]). In reality, the Court acted as if there was a gap in the law to be filled by a reference to equity. In this sense, one cannot disagree with Judge Morelli’s opinion, which characterized the Court’s decision in terms of a renvoi to equity as a source of principles and criteria outside the scope of the law (North Sea Continental Shelf Cases [Federal Republic of Germany/Denmark; Federal Republic of Germany/Netherlands] [Dissenting Opinion of Judge Morelli] para. 19).

14  Once the concept of equity is freed from the moorings of international law, the consequence and the risk is that of a judicial drifting towards elusive subjectivism with little room left for the necessary guarantee of the objectivity and predictability of the law. This risk was clearly present to the ICJ in Barcelona Traction, Light and Power Co Ltd (New Application: 1962) (Belgium v Spain) (Second Phase) [1970] ICJ Rep 3 (Barcelona Traction Case), which was delivered just one year after the North Sea Continental Shelf Cases. In that case the Court was confronted with the issue of whether the national State of the shareholders had locus standi to extend diplomatic protection to a company whose national State—namely Canada—had chosen not to present a claim (International Courts and Tribunals, Standing). Having found that no such right existed under the applicable rules of customary international law, the claimant State argued that a right of action by the national State of the shareholders should be permitted as a matter of equity. The Court did not dismiss the possibility of a recourse to equity as an alternative to law, thus indirectly confirming the earlier position taken in the North Sea Continental Shelf Cases with regard to the rule of equidistance. However, in this case the Court did not consider that the specific circumstances warranted a departure from the general rule of international law, which authorizes the national State alone to present a claim for diplomatic protection (Barcelona Traction, Light and Power Co Ltd [New Application: 1962] [Belgium v Spain] [Second Phase] paras 92–101). So, equity and equitable principles were not deemed to require a decision different from that dictated by the strict rule of international law. However, the Court did extend the principle of diplomatic protection to corporate entities, which demonstrates a limited conception of equitable flexibility. A different conclusion was reached a few years later by the Iran-United States Claims Tribunal in the case of Harza v The Islamic Republic of Iran where, after recognizing that ‘shareholders such as the claimants ordinarily may not assert claims belonging to their corporation’ the Tribunal concluded that ‘equity requires that they take such claims subject to the defences and counterclaims that could have been raised against the corporation’ (at 110).

15  The high-water mark in the development of a concept of equity praeter legem endowed with its autonomous normativity was reached in the early 1980s in the Continental Shelf (Tunisia/Libyan Arab Jamahiriya) case involving the delimitation of the continental shelf. Here the Court went so far as to construe equity as a self-standing source of legal principles when it stated that:

16  This approach was confirmed shortly thereafter in the decision rendered by a chamber of the Court in the dispute between Canada and the US over the delimitation of maritime boundaries in Delimitation of the Maritime Boundary in the Gulf of Maine Area (Canada/United States of America) (Gulf of Maine Case; Maritime Delimitation Cases before International Courts and Tribunals; International Courts and Tribunals, Chambers). In both cases the use of equity is result-oriented, ie finalized to the attainment of an equitable solution independently of any rule of law. This orientation of the Court and of the chamber was criticized by members of the Court (see, in particular, Continental Shelf [Tunisia/Libyan Arab Jamahiriya] [Dissenting Opinion of Judge Gros] paras 18–19; Delimitation of the Maritime Boundary in the Gulf of Maine Area [Canada/United States of America] [Dissenting Opinion of Judge Gros] paras 41–44 and in literature, eg Weil 134–44). Later case law of the ICJ in matters of land and maritime boundary delimitation reveal a gradual return to a less creative use of equity (Boundaries), as a corrective method to be applied to the relevant norms of international law rather than a substitute of the law (see, in particular, Continental Shelf [Libyan Arab Jamahiriya/Malta] paras 55–58; Continental Shelf Case [Libyan Arab Jamahiriya/Malta]; see also Frontier Dispute Case [Burkina Faso/Republic of Mali]).

E.  Equity contra legem

17  The instances of equity discussed so far fall within the category of equity infra legem and equity praeter legem. In both instances, as we have seen, resort to equity and equitable principles by the judge does not require a special consent by the parties to the dispute since equity simply corrects or supplements the law. When equity, instead, is used as a system of norms and principles that fall outside the scope of the law or are even in antithesis to the law, the question arises of whether special agreement is always necessary to warrant such use of equity. From a formal point of view, one could be tempted to conclude that a clear answer to this question is provided by Art. 38 (2) ICJ Statute which lays down the explicit requirement of the consent of the parties to a dispute for the ICJ to decide ex aequo et bono. But this provision also covers instances in which the judge may decide to make use of equity praeter legem or infra legem, for which no explicit consent by the parties is necessary, as is amply demonstrated by the practice examined in the preceding section. In this sense, Art. 38 (2) ICJ Statute is not conclusive in drawing a line between equity praeter legem, on the one hand, and equity contra legem, on the other. Besides, as is well known, no case has ever been brought before the ICJ under the ex aequo et bono clause of Art. 38 (2) ICJ Statute, so no body of precedent is available to help define the role of consent in this type of adjudication. The answer to this question, therefore, must be more nuanced than a simple ‘no’ based on the clear letter of Art. 38 (2) ICJ Statute. First of all, we must recognize that in international law the relationship of equity to legal rules differs from the same relationship in domestic law, and will never be precisely ‘co-terminus with its role in any national jurisdiction’ (White). In international law, especially customary law, legal rules and principles are very general and with an ambit of application that may be indeterminate and adaptable to different circumstances. This may permit a judge to present resort to equity as a set of considerations and criteria within the law or associated with the law, rather than outside or contrary to the law. Secondly, since customary international law is in constant evolution, what is contra legem at a given time may become consonant to the law at a later stage of evolution of the applicable rules. Equity may therefore anticipate the crystallization of the law and provide the rational and ethical justification for its transformation. Thirdly, since in international law judicial and arbitral decisions do not carry the weight of stare decisis, for the purpose of a more precise definition of the meaning and scope of legal rules, it is more difficult to establish where in a given case the use of discretionary powers by a judge constitutes an application of equity contra legem. Several situations may illustrate the complexity of the question.

18  In the field of the treatment of aliens and foreign investments it is a settled rule of international law that a State expropriating foreign property is bound to provide compensation to the dispossessed owner for the value of the property taken (Investments, International Protection; Property, Right to, International Protection; Expropriation and Nationalization; Expropriation, Indirect). If, as often occurs, the circumstances of the case dictate that application of equity must lead to the determination of an amount of compensation that is less than the market value of the property taken, is this equity contra legem or equity within the law? Similarly, if the collapse of the entire economy of a country leads to the breach of its contractual obligations towards foreign investors, is the reference to equity by an arbitrator in order to alleviate the strict liability of the respondent State in contradiction with an applicable investment treaty, an application of equitable principles underlying the law of treaties or an instance of equity contra legem?

19  Similarly, in the field of humanitarian intervention, are the overriding considerations of humanity (Humanity, Principle of) and equity that may lead the United Nations or other international organization to use force against a State responsible for gross violations of human rights a factor in the interpretation and application of the law or a decision contrary to the law? The answer to this question can be extremely difficult, both because of the never ending debate over the permissible exceptions to the use of force under international law and because of the dynamic evolution of the practice towards the recognition of a positive duty to protect victims of serious human rights abuses (Responsibility to Protect; on this issue, see Francioni [2005 and 2016]; see also Gross and Systematic Human Rights Violations; Use of Force, Prohibition of; Use of Force, Prohibition of Threat). However, recent research suggests that equity—as a palliative series of norms that can temper the rigor of strict law—may indeed have an impact in the humanitarian intervention debate. Rather than having recourse to standards of morality, it has been suggested that equity—as a general principle of law—may impact upon the United Nations Charter regime and customary international law norms concerning the use of force, allowing for a ‘broadening’ of permissible uses of force, in order to include situations where gross human rights abuses are being perpetrated by a State against its own citizens (see Burke 245–46).

20  Finally, the determination of whether equity is contra legem or not may be difficult when its application is in contradiction with a particular rule of law, but, at the same time it may be supported by another rule of positive law. This would be the case if the victim of a serious violation of human rights sought justice before the courts of a foreign State where the rule of sovereign immunity could be invoked by the defendant State to defeat jurisdiction (State Immunity). Access of the victim to remedial process could be argued on the basis of compelling reasons of equity; but at the same time it could be supported on the basis of a restrictive interpretation of the classic rule on immunity and on a liberal construction of international practice which favours the setting aside of immunity in cases of prima facie violations of peremptory norms of international human rights law (Ius cogens).

21  It is clear from the illustrations given above that a demarcation of the use of equity contra legem from equity within the law or associated with the law is extremely problematic, both conceptually and practically. This is further exacerbated by the fact that there have been few studies on equity—or indeed, on general principles—and its role in international law in recent decades, which might add clarity here. The different types of equity we are confronted with in international adjudication represent, rather than separate categories, a continuum along which the international judge or arbitrator exercises varying degrees of discretion in the interpretation, integration, and correction of the applicable rules and principles of international law. In this context, the characterization of whether equity is contrary to the law essentially depends on the construction of the scope and of the evolutive dynamics of the relevant norms. This is an eminently interpretative operation that falls within the discretion of the judge. However, this is certainly not to entirely exclude the potential for equitable principles to act contra legem in very exceptional circumstances, within the framework of equity, qua general principles of law, per Art. 38 (1) (c) ICJ Statute (see Burke 199–245). Such a possibility has been raised, inter alia, by Judge Hudson’s Separate Opinion in Diversion of Water from the Meuse (The Netherlands v Belgium) (76–77).

F.  Equity in Treaties

22  The need to reach a compromise between conflicting interests of different groups of States and even of different generations has led in the past 50 years to frequent reference to equity and equitable solutions in the text of treaties and sometimes of soft law instruments. As noted above (see para. 8), the VCLT makes effective provision for the use of extraneous norms—potentially including equity qua general principles in Art. 31 (3) (c). It would be impossible to furnish an exhaustive inventory of explicit references to equity within treaties within the scope of this article. What follows, therefore, is only a sampling of the role that equity plays in some important categories of treaties, and more particularly in the area of the law of the sea, international economic law, and international environmental law (Environment, International Protection) and sustainable development.

G.  Conclusions

29  Although equity does not constitute a source of international law in a formal sense and within the meaning of Art. 38 (1) ICJ Statute, its use in international adjudication and in the development of treaty law shows that in a substantive sense it has become established as a method of adjudication, even outside the hypothesis of ex aequo et bono authorization under Art. 38 (2) ICJ Statute, and as an element in the progressive development of international law. First, it may infuse basic considerations of fairness and justice into the fabric of the law, so as to adjust the general and abstract rules of international law to the specificities of each individual case. Secondly, it may have an integrating function in the sense of filling gaps in the law by resorting to equitable principles capable of judicial application pursuant to Art. 38 (1) (c) ICJ Statute. Thirdly, it may even perform a contra legem role to the extent that it is used to accompany or support a process of transformation of customary international law under the pressure of new social necessities, thus becoming a catalyst for change and modernization of the law. Its frequent use in international adjudication and in contemporary treaty practice also shows a tendency towards a structuring of the concept of equity as part of applicable law and not as a separate system of concepts and principles. This is important at a time when international law has ceased to be a system of negative obligations of pure coexistence among States and has become a much more complex system of positive obligations whose nuances in content and scope can often be captured by a proper use of equity and equitable principles.