Symposium on Erin Pobjie’s Prohibited Force: The Meaning of Article 2(4) of the UN Charter

[Dr Erin Pobjie is Assistant Professor at Essex Law School and a Senior Research Affiliate at the Max Planck Institute for Comparative Public Law and International Law. She serves as co-Rapporteur of the International Law Association’s Committee on the Use of Force.]

The author writes here in her personal capacity.

Amidst the shadows cast by current global events, there is solace in casting light upon the cornerstone of the UN Charter – article 2(4) – crafted to ‘save succeeding generations from the scourge of war’. As the thoughtful commentators on my book observe, article 2(4) is foundational to the international legal order, yet its application is complex and necessitates a clear, adaptable framework for contemporary challenges. The destabilisation of the geopolitical landscape, including conflicts in Ukraine and Gaza and recent US political developments with far-reaching implications, underscores the urgent need to reinforce shared international norms. 

My curiosity about jus contra bellum, kindled by Noam Lubell and ignited by Claus Kreß, led me to examine the meaning of its central provision: the prohibition of the use of force in article 2(4) of the UN Charter. As a research assistant to Lubell during his tenure as Rapporteur of the International Law Association (‘ILA’) Committee on the Use of Force, I aspired to contribute meaningfully to this dialogue. This intellectual journey has come full circle, as I now have the privilege of serving as Rapporteur of the ILA Committee on the Use of Force alongside James Green. My book, Prohibited Force: The Meaning of ‘Use of Force’ in International Law (Cambridge University Press, 2024) applies a doctrinal approach to the meaning of the prohibition of the use of force, aiming to facilitate clearer analysis and fulfil the potential that Claus Kreß identified to ‘significant[ly] advance in strengthening the international legal order in one of its core components.’

Its relevance shines through in practice, as Adil Haque, Tomo Mikanagi and Andrew Clapham have highlighted with probing questions regarding its application to situations in Gaza, Yemen and Ukraine – with broader implications for food insecurity in Africa –  and to issues such as the right to self-determination, the forcible acquisition of territory, blockade and the protection of merchant vessels on the high seas. I marvel that the jus contra bellum, comprised essentially of a single ‘simple’ rule and two exceptions, continuously unfolds into a kaleidoscope of astonishing complexity. Haque, Mikanagi and Clapham illustrate the innovative potential of the type theory framework of prohibited force to address concrete challenges and reduce harm and suffering. In doing so, they tap rich veins for further exploration. 

Resolving Tensions

Haque raises an important point about whether the prohibition of the use of force extends to actions against self-determination units, highlighting a potential tension between my reliance on the Friendly Relations Declaration and my conclusion that the prohibition applies only between States. As he rightly points out, this is not merely theoretical; it has practical implications for conflicts like the Israeli-Palestinian situation and the lives impacted by the application of international humanitarian law.

Haque presents an intriguing range of interpretive possibilities to reconcile this apparent tension, linking it to the ICJ’s recent advisory opinion on the Legal Consequences arising from the Policies and Practices of Israel in the Occupied Palestinian Territory, including East Jerusalem. The Court found that Israel’s continued presence in the Occupied Palestinian Territory violated the prohibition of forcible acquisition of territory – described as a corollary of the prohibition of the use of force – without determining that Palestine is a State. As Mikanagi notes, ‘[t]here is ambiguity in the term [] “corollary”’ as used by the ICJ. His application of type theory to  determine what constitutes acquisition of territory by force is thought-provoking. While I will not delve deeper here, I agree that ‘there is, at least, significant overlap between the prohibition of acquisition of territory by force and the prohibition of use of force under article 2(4) of the UN charter’. 

The tension that Haque identifies can be resolved by clarifying my position. In my book (p.92), I noted that the text of article 2(4) does not unambiguously require that a State be the object of a ‘use of force’, and that the primary value protected – international peace and security – supports a broad interpretation. However, I observed that there is no State practice extending its interpretation beyond damage to States. Therefore, while a broader interpretation remains textually open, because article 2(4) also protects States’ sovereignty and territorial integrity, it is likely that another State must be the object/target for a ‘use of force’ to be in ‘international relations’ and fall within the scope of article 2(4). I also acknowledged that it is controversial whether, or under what circumstances, a ‘use of force’ against entities falling short of Statehood falls within a State’s ‘international relations’ and the scope of article 2(4) (p.101). For non-State objects that do not have a close association with a State, more is required to bring the act within ‘international relations’ and into the scope of article 2(4) (pp.93 and 101). This allows for reconciliation with Haque’s argument.  

Thus, the tension may be illusory, and there is a way to resolve it. This would require further analysis of the relevant parts of the Friendly Relations Declaration and the identification of subsequent State practice supporting this interpretation. I appreciate Haque’s important question and the opportunity to clarify any ambiguity in my position. This underscores the need for nuanced analysis in interpreting the prohibition of the use of force, especially concerning actions against entities not universally recognised as States.

Balancing Complexity with Clarity

James Green and Alejandro Chehtman highlight that while my approach offers a comprehensive framework for understanding the prohibition of force, it introduces complexities that may challenge its practical applicability. They express concern that the intricate analysis could make it difficult for practitioners to reach clear conclusions in urgent situations.

Regarding Green’s comment on the ‘threshold’ of prohibited force, I agree that type theory does not always yield unambiguous outcomes. However, this complexity reflects the nuanced reality of international relations. Type theory is a tool to facilitate analysis and encourage legal discourse, not to provide absolute answers. It offers precision in discussing how and why we might disagree on particular issues. Green’s analysis of my case studies demonstrates that, even amidst disagreement, we can engage more transparently and constructively.

Chehtman raises valid concerns about the potential for increased complexity to hinder practical application and the possibility that a lower threshold for violations could escalate conflicts. He suggests that introducing more variables into the analysis may make disagreement more likely and intractable, potentially undermining the prohibition’s pacifying function. 

I acknowledge that introducing more variables may lead to disagreements. However, these disagreements would exist regardless of the framework. Without effective tools to engage with them constructively, they may remain shrouded in obscurity and could lead to greater uncertainty. The type theory framework I propose in my book aims to balance comprehensiveness with practicality. It is not designed to complicate the analysis unnecessarily but to provide a precise and transparent framework for legal discourse. By offering a shared language and methodology, we can reflect the complex reality of international relations and strengthen the normative force of article 2(4). Greater sophistication and transparency in our analysis can enhance understanding and promote compliance with international law.

Chehtman also raises the concern that a more complex framework might lower the threshold for violations, potentially escalating conflicts. I understand the importance of maintaining a threshold that prevents unnecessary escalation. However, I believe that clarity in defining what constitutes prohibited force can help prevent misunderstandings and miscalculations that might otherwise lead to conflict.

The Broader Meaning of the Prohibition of the Use of Force

Clarifying the meaning of prohibited force also has value beyond immediate application. As Kreß noted, ‘“military occupation” constitutes another example where [this] analytical framework allows for analysis and explanation of the law, which, perhaps understandably, the ICJ has refrained from providing’. Similarly, Clapham incisively delves into its application to modern blockades. This underscores the framework’s utility in re-examining traditional concepts requiring further legal elaboration.

As Marco Roscini highlighted during my book launch at the Geneva Academy, the type theory framework is helpful when it comes to certain forms of cyber operations, where traditional definitions of force are challenged by new technologies. It also brings clarity to issues in the domain of outer space and has the potential to facilitate UN negotiations on space security by providing a foundation to advance common understandings on a rule that already binds all States, applies in outer space, and enjoys hierarchical superiority both as a peremptory norm and under article 103 of the UN Charter.

These applications reflect that the potential utility of type theory lies not in providing the one correct answer in every specific instance but in opening dialogue and providing a shared language and framework to elucidate the meaning of prohibited force. This can advance its clarity and strengthen the norm, contributing to diplomatic efforts and the development of international law in new domains.

But the prohibition of the use of force carries a symbolic meaning which should not be dimmed by a focus on doctrinal analysis. This is something I sought to convey through my selection of the book’s cover image by the war photographer W Eugene Smith, from his 1945 photograph in Okinawa, Japan, entitled: ‘Some men want to make a distinction as to how other men are killed. They would outlaw poison gas, and the atom bomb–allow the flame thrower, rockets, and block-buster bombs.’

The essence of Article 2(4) of the UN Charter should not be obscured by attempts to justify the use of force through fine distinctions of legality and illegality. While its application to specific instances on the margins is required by its nature as a legal rule – and I believe this analytical precision has its uses – the strength of the norm lies in its essence, which proclaims the value of right over might and infuses the Charter.

I am encouraged to see the breadth and depth of engagement with this work and hope that it will spark renewed interest in and commitment to the prohibition of the use of force and its foundational role in the international legal order. I thank each of the contributors to this symposium, who have enlightened the discussion with their insights, and I look forward to continuing the conversation.