“ If you don’t go forward, you go back.”<fnref n="1" />

Anyone who has met Gabrielle will be struck by her outspoken and determined personality. She is committed to international law being rooted in social progress and at the service of humanity as a whole. It is only in this way, by ensuring that the law matches to the needs of its users, that we can hope to guarantee the rule of law. In this perspective, law must remain a living substance, up to the challenges of the day, rather than become the fossil of a social and political reality that once existed.

However, this desire can also be faced with opposing currents. With the aim of making a modest contribution to the edifice of progress in law, this contribution will take the opposite tack to Gabrielle’s committed approach. It will aim to present some ways in which international law can develop in the other direction, towards less law and less protection for human beings. The aim is not to encourage this dynamic, but rather to guard against it. It is by being aware of what could be described as negative trends within the field, and of the tools available to counter this erosion, that we can hope to continue to develop international law.

I will begin by discussing the notions of “evolving” and “devolving”, before looking at some of the types of erosion with which international law is confronted, more specifically institutional erosion and language erosion.

<footnote n="1">Barbra Streisand, “Sitting On Your Status Quo” (1962).</footnote>
# I. Evolving and Devolving

One of the first questions that might arise is how to define “evolve” and “devolve.” It is not the intention of this contribution to make objective what is necessarily subjective. There are at least as many definitions of “progress” as there are inhabitants of this planet. So as not to remain in a complete vagueness, I will nevertheless suggest a few elements aimed at circumscribing the notion, for this contribution’s purpose.

Progress is defined primarily by comparison with the past. It is only through the difference between the past and the present or the future that one can establish movement. This movement may or may not constitute progress. The second element involves an appreciation of the past and the way in which we position ourselves in relation to it. Finally, the third and last element is perhaps the most subjective: progress is based on values.<fnref n="2" />

While I am aware of the necessarily subjective nature of what follows, the aim of this contribution is to make a general statement about progress. From this perspective, the values that I will seek to illustrate in the notion of progress will revolve around the broad and vague concepts of justice and humanity.

<footnote n="2">Tilmann Altwicker & Oliver Diggelmann, “How is Progress Constructed in International Legal Scholarship?” (2014) 25:2 Eur J Intl L 425 at 428.</footnote>
# II. Types of Erosion

International law is faced with various types of erosion. I will focus on two examples: institutional erosion and language erosion.

## A. Institutional Erosion

In recent years, we have witnessed institutional erosion. This consists of a gradual weakening of the institutions whose function is to steer us away from unilateralism. I will take two major institutions as examples: the World Trade Organisation (WTO) and the International Criminal Court (ICC).

The challenges facing the WTO have been on public display over the past few years. Among them, the disappearance of the Appellate Body is symbolic of the attempts to weaken institutions whose aim is to move away from unilateralism. The function of the Appellate Body was (and still is, from a strictly legal point of view) to take the final decision on WTO disputes.<fnref n="3" /> Although the formal decision granting legally binding status to a report of the Appellate Body was taken by the Dispute Settlement Body,<fnref n="4" /> in practice it was the role of the Appellate Body to determine who was in the right. In the space of a few years, the consensus-based system that had previously been the hallmark of the WTO and the General Agreement on Tariffs and Trade (GATT) as an institution turned against part of the organisation. Members of the Appellate Body had been elected on a mutual trust basis, allowing for relatively seamless (re)elections. This dispute settlement system was a progress, in that it allowed for a stronger rule of law in international trade. However, the opposition of a WTO Member to certain aspects of the functioning of the Appellate Body put a grain of sand in the gears.

In December 2019, as no consensus could be reached on the renewal of the members of the Appellate Body since 2016,<fnref n="5" /> their number fell below the minimum threshold necessary for its operation. A division must have three members. The two remaining members could thus no longer take on new cases. This created a vacuum that weakened the entire WTO dispute settlement system. Since then, if a WTO Member is dissatisfied with the outcome of Panel proceedings, it can appeal “into the void”, thereby depriving the Panel’s decision of its binding force. In practice, this means that the lack of consensus has removed the consent to a legally binding dispute settlement system for the rest of the WTO member.<fnref n="6" />

The International Criminal Court (ICC) was created by the *Rome Statute* of 1998, which came into force in 2002. It represents a multilateral international effort to prosecute certain crimes (war crimes, crimes against humanity, genocide) when a State is unwilling or unable to do so itself.<fnref n="7" /> It therefore enables the international community to pool its resources in pursuit of a common goal and ideal of justice, which can, I would argue, legitimately be described as “progress.” While it would be misleading to suggest that this initiative benefits from universal support, it does have broad backing with 125 State Parties. However, the ICC sometimes faces the criticism that it lacks legitimacy. Without seeking to explore the primary causes<fnref n="8" /> or the justification for this criticism, it finds an echo when States announce their withdrawal from the ICC. Additionally, the sanctions recently introduced against the institution are designed to undermine its ability to work.<fnref n="9" /> In so doing, the very notion of multilateral justice is being called into question. There thus seems to be a certain resistance within the international community, aiming to roll back the progress made in terms of international criminal justice over the last few decades.

## B. Language Erosion

Language erosion essentially consists of a progressive modification of the discourse surrounding international law. These changes in the discourse can, in turn, lead to a weakening of the law, both in its substance and in its very existence. In the first case, the reduction of the level of protection afforded by the law weakens the law itself. In the second, the very nature of the law may change, losing the status of obligation and becoming more flexible, akin to soft law or political commitment. These changes can occur through both active and passive erosion, which I will examine in turn.

### 1. Active Erosion

The most visible erosion is that actively promoted by certain States. One of the areas in which this tension is present is international humanitarian law (IHL). There is clear opposition between those who advocate limiting or even reducing the protection afforded by international humanitarian law and those who wish to at least maintain the level of protection it currently provides, or even extend it. Two fora can provide some examples of this.

The first concerns international humanitarian law in the cyber domain. What protection does international law offer in the face of the danger posed by certain technological developments? Is the law still relevant if it was developed at a time when certain technological developments were unthinkable? For several years, the United Nations Open-ended Working Group on security of and in the use of information and communications technologies (OEWG) has been discussing how the existing legal framework can take account of these developments.<fnref n="10" /> Some States are taking a position that runs directly counter to the notion of evolutionary interpretation,<fnref n="11" /> suggesting that these new technologies are not regulated.<fnref n="12" /> Indirectly, if implemented, this discourse would have the effect of deregulating what was previously regulated. Certain protections offered by international humanitarian law would disappear. These considerations are not merely hypothetical but correspond to very concrete situations. For example, under this discourse, a computer attack on infrastructure providing essential services to the population (energy, water, health) might not fall within the scope of IHL.<fnref n="13" /> This is not a problem linked to individual rules that could be weakened, but rather to the weakening of the protection offered by an entire body of international law. If the proponents of this vision of international humanitarian law were to prevail, it would entail a considerable regression. Even if the objective promoted were to negotiate a new source of treaty obligations in this area,<fnref n="14" /> the practical, immediate effect would be to reduce the protection currently afforded to protected persons.

Another front in this struggle is the United Nations Security Council, whose large number of products means that tensions can be monitored year after year. This relatively high output for a major international political forum is not without risks. It requires constant attention from the participants to ensure that the products are up to standards. For promoters of international humanitarian law, this has significant practical consequences. In any product dealing with international humanitarian law, the risk of relativisation is present throughout the negotiation process. This can arise in various ways, for example through the refusal of certain states to categorise one or other IHL norm as an obligation. A “must” wording would thus become a “need to” or even a “should”, thereby running the risk of enshrining in *opinio juris* (at least that of the members of the Council) that rules stemming from the Geneva Conventions or customary international law are no longer legally binding.<fnref n="15" /> Another example can be found where the existence of an obligation is recognised in principle, but it is accepted by some members of the Security Council only in a bastardised version. This is the case, for example, when the notion of protected persons is weakened by mentioning civilians but not persons *hors de combat*.<fnref n="16" /> This overall dynamic places a heavy burden on the few States that are actively committed to IHL. They assume de facto responsibility for ensuring that the law does not slip backwards in each and every product of the Security Council. The challenge here is not to ensure that the law progresses, but to prevent it from regressing.

### 2. Passive Erosion

A second type of language erosion occurs through passivity. One such case involves a limited pool of active users of a rule, whose behaviour could change the substance of the rule for the rest of the international community. A blatant example of this is the use of the right to self-defence. Article 51 of the *United Nations Charter*<fnref n="17" /> has traditionally been interpreted as authorising the use of self-defence by States against other States.<fnref n="18" /> Self-defence against non-state armed groups was limited to situations in which the behaviour of the group could be attributed to a state, in particular through the control exercised over the group. Both the International Court of Justice<fnref n="19" /> and the International Criminal Tribunal for the former Yugoslavia<fnref n="20" /> have dealt with the notion of attributing the conduct of armed groups to a State in their case law. In recent decades, however, the use of self-defence has developed in a more liberal manner, with many States justifying interventions against non-state armed groups on the territory of third States without any link of attribution of conduct, nor their consent or an authorisation by the Security Council.<fnref n="21" /> In other words, none of the possibilities for the use of force traditionally permitted by the *Charter* appears to be given.

However, Article 51 of the *Charter* contains a procedural rule that is often glossed over: “Measures taken by Members in the exercise of this right of self-defence shall be immediately reported to the Security Council.”<fnref n="22" /> States more or less willingly comply with this requirement, giving them an opportunity to argue that their action is within the bounds of international law. That said, this reporting system suffers from a lack of publicity, leading in practice to a lack of knowledge on the subject.<fnref n="23" /> The limited awareness of these notifications within the UN system has a perverse effect: only those States that have recourse to self-defence are really involved in shaping the way in which the norm is understood. No debate, no discussion, no reaction to these letters is provided for in UN processes. Depending on the seriousness of the situations and their political significance, meetings of the Security Council could be held to discuss them, but this remains at the discretion of the members of the Security Council.<fnref n="24" /> In these circumstances, States are free to stretch the meaning of Article 51 as they see fit in their communications to the Security Council, sometimes interpreting the article very permissively.<fnref n="25" />

Downstream of these developments, when it comes to observing State practice, only States that have resorted to self-defence are visible, creating a bias in representation. States that might oppose it will remain on the sidelines, respectively will not have access to a centralised channel through which their positions can be collected. As a result, the *opinio juris* to which the world will have access will mainly be that of States that want a permissive interpretation of the right to self-defence.<fnref n="26" /> The way the rule is used therefore shifts the burden onto those States that might wish to remain within a traditional understanding of self-defence and not extend it to concepts such as “unwilling or unable.” The onus will be on them to find ways and fora to express their disagreement with the trend. Their passivity, facilitated by institutional construction, may therefore result in changes to the law.

<footnote n="3">*Understanding on Rules and Procedures Governing the Settlement of Disputes*, 15 April 1994, 1869 UNTS 401, art 17(1), Annex 2 of the *Marrakech Agreement Establishing the World Trade Organization*.</footnote>

<footnote n="4">*Ibid*, art 17(3).</footnote>

<footnote n="5">WTO, *Minutes of Meeting*, WTO Doc WT/DSB/M/389 (2016) at para 13.6, online: WTO <docs.wto.org> [perma.cc/9HHY-2YLC].</footnote>

<footnote n="6">Clément Marquet, “The Appellate Body in Dire Straits: Taking a Step Back on Consent to Jurisdiction” (2018) Society of International Economic Law, Working Paper at 8—13.</footnote>

<footnote n="7">*Rome Statute of the International Criminal Court*, 17 July 1998, 2187 UNTS art 17 (entered into force 1 July 2002).</footnote>

<footnote n="8">See e.g. Christa-Gaye Kerr, “Sovereign Immunity, the AU, and the ICC: Legitimacy Undermined” (2020) 41:1 Mich J Intl L 195.</footnote>

<footnote n="9">United States, “Imposing Sanctions on the International Criminal Court” (6 February 2025), online: <whitehouse.gov> [perma.cc/CAQ5-4MR5].</footnote>

<footnote n="10">*Developments in the Field of Information and Telecommunications in the Context of International Security*, UNGA, 75th Sess, UN Doc A/RES/75/240 (2020).</footnote>

<footnote n="11">On this topic, see Gabrielle Marceau, “L’inteprétation évolutive par le juge OMC: sophisme ou nécessité?” (2018) 122:1 RGDIP 23; Georges Abi-Saab, Kenneth Keith, Gabrielle Marceau & Clément Marquet, eds, *Evolutionary Interpretation and International Law* (Oxford: Hart Publishing, 2019).</footnote>

<footnote n="12">Liina Lumiste, “There and Back Again? Russia’s Quest for Regulating War in Cyberspace” (2023) 43 Polish YIL 239 at 256—57.</footnote>

<footnote n="13">Russian Federation, “Statement by the Representative of the Russian Federation at the Fourth Session of the UN Open-Ended Working Group on Security of and in the Use of ICTs 2021—2025” (7 March 2023) at 3, online (pdf): <docs-library.unoda.org> [perma.cc/39AG-GCB9].</footnote>

<footnote n="14">Russian Federation, “Updated Concept of the Convention of the United Nations on Ensuring International Information Security” (7 March 2023), online: <docs-library.unoda.org> [perma.cc/VR6C-3KYK].</footnote>

<footnote n="15">See also further examples in Switzerland, “International Humanitarian Law in the Security Council: Switzerland’s Lessons learned and How to strengthen IHL while serving on the Council” (2025) at 2, online (pdf): <eda.admin.ch> [perma.cc/W5K7-L4GP].</footnote>

<footnote n="16">*Ibid* at 2.</footnote>

<footnote n="17">*UN Charter*, 26 June 1945, Can TS 1945 No 7 [*Charter*].</footnote>

<footnote n="18">Helmut Philipp Aust, “Article 51” in Bruno Simma et al, eds, *The Charter of the United* *Nations: A Commentary*, 4th ed (Oxford: Oxford University Press, 2024) 1769 at 1791—98.</footnote>

<footnote n="19">*Military and Paramilitary Activities in and against Nicaragua (Nicaragua v United States of America)*, [1986] ICJ Rep 14 at para 115; *Application of the Convention on the Prevention and Punishment of the Crime of Genocide (Bosnia and Herzegovina v Serbia and Montenegro)*, [2007] ICJ Rep 43 at para 400—07.</footnote>

<footnote n="20">*Prosecutor v Dusko Tadić*, IT-94-1-A, Judgement (15 July 1999) at para 120.</footnote>

<footnote n="21">Dustin A Lewis, Naz K Modirzadeh & Gabriella Blum, “Quantum of Silence: Inaction and *Jus ad Bellum*” (2019) Harvard L School Program Intl L Armed Conflict at 8.</footnote>

<footnote n="22">*Charter*, *supra* note 17, art 51.</footnote>

<footnote n="23">Naz K Modirzadeh & Pablo Arrocha Olabuenaga, “A Conversation between Pablo Arrocha Olabuenaga and Naz Khatoon Modirzadeh on the Origins, Objectives, and Context of the 24 February 2021 ‘Arria-formula’ Meeting Convened by Mexico” (2021) 8:2 J Use Force Intl L 291 at 293—94.</footnote>

<footnote n="24">*Provisional Rules of Procedure* *of the Security Council*, UNSC, UN Doc S/96/Rev.7 (1983), Rule 2. If a State that is not a member of the Security Council wants a meeting to be held on a subject important to it, the most common approach is for a sponsor who is a member of the Security Council to request a meeting on its behalf.</footnote>

<footnote n="25">Leonie Brassat, “The Lawfulness of Military Strikes against the Houthis in Yemen and the Red Sea” (19 March 2024), online (blog): <ejiltalk.org> [perma.cc/8V64-XMVA]; Matt Gluck & Maya Nicholson, “US and UK Submit Article 51 Letters to the UN Security Council on Middle East Operations” (2 February 2024), online (blog): <lawfaremedia.org> [perma.cc/G4WU-5JSW]; Russian Federation, *Letter dated 24 February 2022 from the Permanent Representative of the Russian Federation to the United Nations addressed to the Secretary-General*, UNSC, UN Doc S/2022/154 (2022).</footnote>

<footnote n="26">Lewis, Modirzadeh & Blum, *supra* note 21 at 100—90.</footnote>
# III. Pushback and Accretion

With regard to the WTO’s Appellate Body, it is interesting to note that some of the organisation’s members have refused to let this dispute settlement system go gentle into that good night. As early as 2020, the Multi-Party Interim Appeal Arrangement (MPIA) was set up by some forty members. Its aim is to fill the gap left by the practical disappearance of the Appellate Body by offering an alternative appeal route for members who have ratified it. While its success has been limited (just over 50 participants out of 164 WTO members),<fnref n="27" /> the participation of many of the largest exporters (European Union, China, Japan, Mexico, Hong Kong, Canada, United Kingdom)<fnref n="28" /> is an encouraging sign as to the desire for an institutional framework that provides legal certainty by reaffirming the rule of law.

As far as the ICC is concerned, some positive signals can also be identified. For example, a movement among Member States to maintain the ICC’s working capacity has taken shape.<fnref n="29" /> Furthermore, although withdrawals from the ICC are regrettable, it has to be said that they remain rare. They are largely offset by the parallel increase in ratifications. It should be noted that some announcements of withdrawal from the ICC have been followed by limited concrete effects (South Africa rescinded its withdrawal and the Philippines delivered Rodrigo Duterte in 2025 despite the country’s withdrawal). Finally, progressive initiatives have been developed that would tend to align the ICC’s mandate with the general public’s notion of justice. For example, the *Kampala Amendments*, which were adopted in June 2010 and came into force in July 2018, extend the ICC’s jurisdiction to the crime of aggression.<fnref n="30" /> In so doing, the 47 States<fnref n="31" /> that have ratified or accepted the *Kampala Amendments* demonstrate their ongoing commitment to a form of multilateralism, despite the headwinds.

As to the erosion of language, the main tool available to States is what they say. Whether by speaking out in the OEWG or by taking a consistent stance when negotiating products in the Security Council, States that could suffer from the erosion of the norm can take an active stance against this trend. With regard to the development of the right to self-defence, Mexico took the initiative a few years ago. With the aim of raising awareness, it organised an Arria-format meeting to present what seemed to be going on behind the scenes in this area.<fnref n="32" /> In all these situations, however, a major difficulty lies in the budgetary constraints of each State. These necessarily lead to a prioritisation of issues.

<footnote n="27">Geneva Trade Platform, “Multi-Party Interim Appeal Arbitration Arrangement (MPIA)”, online: <wtoplurilaterals.info> [perma.cc/M4PC-TXSE].</footnote>

<footnote n="28">WTO, “WTO trade data”, online: <globaltradedata.wto.org> [perma.cc/Q4PN-7ZR4].</footnote>

<footnote n="29">Afghanistan, Albania, Andorra, Antigua and Barbuda, Austria, Bangladesh, Belgium, Belize, Bolivia, Bosnia and Herzegovina, Brazil, Bulgaria, Cabo Verde, Canada, Chile, Colombia, Comoros, Costa Rica, Croatia, Cyprus, Democratic Republic of the Congo, Denmark, Dominican Republic, Estonia, Finland, France, Gabon, Gambia, Germany, Ghana, Greece, Grenada, Guatemala, Honduras, Iceland, Ireland, Jordan, Latvia, Lesotho, Liechtenstein, Lithuania, Luxembourg, Maldives, Malta, Mexico, Mongolia, Montenegro, Namibia, Netherlands, Nigeria, North Macedonia, Norway, Panama, Peru, Poland, Portugal, Republic of Moldova, Romania, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, San Marino, Senegal, Seychelles, Sierra Leone, Slovakia, Slovenia, South Africa, Spain, State of Palestine, Sweden, Switzerland, Timor-Leste, Trinidad and Tobago, Tunisia, Uganda, United Kingdom, Uruguay & Vanuatu, “Joint Statement—Sanctions International Criminal Court (ICC)” (7 February 2025), online: <government.nl> [perma.cc/7FKD-MF7X].</footnote>

<footnote n="30">ICC, “Crime of Aggression, Amendments Ratification”, online: <asp.icc-cpi.int> [perma.cc/GFB9-SDQZ].</footnote>

<footnote n="31">As of 31 March 2025, see *Amendments on the Crime of Aggression to the Rome Statute of the International Criminal Court*, 11 June 2010, RC/Res.6, online: <treaties.un.org> [perma.cc/6TDG-G7V3].</footnote>

<footnote n="32">Modirzadeh & Olabuenaga, *supra* note 23.</footnote>
# —

A simple hypothesis as to the reason for these erosions is the feeling of certain States that international law does not, or no longer, meet their political needs. This inadequacy can be a factor in both progress and regression. In some situations, it will lead to an evolutionary interpretation to the benefit of the international community and the humans that make it up. In others, a return to unilateralism will be favoured in order to promote the specific wishes of a sub-group of people.

However, this type of thinking can have unforeseen consequences for all concerned. Attempts to turn the clock back or to sabotage certain institutional solutions can generate Ersatz solutions, which are potentially more unpredictable for everyone. To give just a few examples, we can think of the increasing importance of the General Assembly in the event of Security Council deadlocks, the creation of special tribunals to circumvent the occasional lack of jurisdiction of the International Criminal Court, or the development of the MPIA. In turn, these developments entail a risk of fragmentation of international law, with the development of ever more sub-entities within the rules or rules-systems.<fnref n="33" />

This is an opportunity to stress the importance of anticipation in the development of international law and its institutions. The acceptance of certain compromises or constructive ambiguities at the time of negotiation entails risks for future stability. In addition, particular attention should be paid to the capacity of a limited number of states to cause harm. While it is conceivable that some States may wish to give themselves room for manoeuvre in the future, it is more questionable to allow them to deprive all the others of what they have built.

These few developments may leave a rather negative overall impression of the current state of international law. That said, these trends should not obscure the more positive ones that are developing simultaneously. Certain sectoral points have already been identified above, but one can also look at the obvious attraction of international adjudication for a number of States. In addition to the WTO and the creation MPIA mentioned previously, the activity of the International Court of Justice has reached its highest level yet. Interestingly, these include proceedings that can take place even in the absence of consent to jurisdiction. Advisory opinions are at an all-time high, with four proceedings taking place between 2023 and 2025, compared with twenty-seven in the previous three-quarters of a century. In addition, some recent contentious cases have been based on jurisdictional claims that have a tenuous link with the measures that the claimant was actually seeking.<fnref n="34" /> This dynamic underlines the growing need for impartial third parties who can “say the law”, even when this entails the risk of the law being said or clarified in the opposite direction to that desired by the States, with the internal and external political risks that this can entail.

Taken as a whole, the flexibility of the law promoted by Gabrielle has a bright future ahead of it. However, we must not rest on our laurels and ensure that this flexibility is used to serve progress and humanity.

<footnote n="33">Martti Koskenniemi, *Fragmentation of International Law: Difficulties arising from the Diversification and Expansion of International Law*, ILC, 58th Sess, UN Doc A/CN.4/L.682 (2006) at 14.</footnote>

<footnote n="34">See e.g. *Allegations of Genocide under the Convention on the Prevention and Punishment of the Crime of Genocide* *(Ukraine v Russian* *Federation)*; *Application of the Convention on the Prevention and Punishment of the Crime of Genocide in the Gaza Strip* *(South Africa v Israel)*.</footnote>