Prohibited Force: A Symposium on Rethinking the Prohibition of ‘Use of Force’ in International Law

By Essex Law Research Team

Credit: Dr Erin Pobjie

In Prohibited Force: The Meaning of ‘Use of Force’ in International Law (Cambridge University Press, 2024), Dr. Erin Pobjie addresses the ambiguities surrounding the prohibition of ‘use of force’ under article 2(4) of the UN Charter, a foundational rule of international law designed to prevent war and maintain international peace and security. Article 2(4) prohibits States from using force against each other, except in cases of self-defence or UN Security Council authorisation, yet its interpretation is often unclear in complex, real-world situations. Recognizing these challenges, Dr Pobjie introduces her ‘type theory’ framework, which suggests that determining a prohibited use of force should involve a set of contextual requirements and a flexible set of ‘non-essential’ elements – including physical force, effects, gravity, and hostile or coercive intent – that are weighed together, rather than applied rigidly. With this framework, Pobjie brings analytical depth to ambiguous cases, refining our understanding of this cornerstone of international law. Adil Haque describes Prohibited Force as ‘an extraordinary book’ with a ‘striking and rare’ combination of theoretical sophistication and empirical rigour. 

Opinio Juris, a leading blog on international law, recently hosted a symposium to engage critically with Prohibited Force. The discussion opened with Dr Alonso Gurmendi’s introduction, followed by Professor Claus Kreß, who highlighted the book’s potential to strengthen the international legal order. Professor Adil Haque explored its implications for self-determination units, while Ambassador Tomohiro Mikanagi considered its relevance to cases of territorial acquisition. Professor Andrew Clapham underscored the framework’s real-world impact, noting that its insights could affect thousands of lives by shaping legal responses to blockades impacting food and humanitarian supplies in conflict zones like Yemen and Gaza. Professor James Green reflected on the strengths and potential limitations of type theory when applied to complex, borderline cases, and Professor Alejandro Chehtman highlighted the need to balance analytical sophistication with accessibility in practical settings. In her response, Dr Pobjie engaged with each contributor’s insights and critiques, underscoring her framework’s potential to foster richer discourse on the prohibition of force and its role in advancing international peace and security. 

The full symposium can be read here: Symposium on Erin Pobjie’s Prohibited Force: The Meaning of ‘Use of Force’ in International Law – Introduction – Opinio Juris  

Prohibited Force is available open access for all readers thanks to the University of Essex’s Open Access Fund: https://doi.org/10.1017/9781009022897  

Proving online incitement of international crimes: expert evidence in the digital era

By Dr. Matthew Gillett, Senior Lecturer, Essex Law School, Head of the Digital Verification Unit.

Image via shutterstock

Throughout history, grave crimes have been fueled by incitement and inflammatory rhetoric. From the Holocaust to Rwanda, influential leaders have established the psychological and rhetorical antecedents for mass violence. However, in the digital age, a far wider range of potential inciters have access to platforms with instantaneous global reach. Already this new era has seen online incitement to atrocities in Myanmar, Ukraine, and Sudan. These events demand accountability and, as investigations and prosecutions get underway, inflammatory statements are increasingly becoming a critical form of evidence.

Speech acts, whether oral or written are forensically significant in multiple ways. They can demonstrate criminal intent, they can demonstrate instigation, and they can amount to crimes in and of themselves, such as persecution or direct and public incitement to genocide. The relevance of speech acts was evident in the International Court of Justice’s provisional measures order in the Israel-South Africa genocide case. Statements made online by high-level Israeli officials through Twitter/X and other platforms were key evidentiary items cited by the Court in granting provisional measures. And that relevance will continue to grow in future litigation. Whereas the Court’s provisional order did not require a detailed evidentiary assessment, the statements will be subjected to far more exacting scrutiny during the merits phase. Equally, if genocide is charged at the ICC or other courts, incendiary statements will constitute a central focal point for the litigation. This begs the question of how such statements can be entered into evidence and contextualized in the context of international legal proceedings.   

In an article I recently co-authored with Wallace Fan, former student manager at the University of Essex Digital Verification Unit, we explore how online materials can be submitted as evidence before international courts. Published in the Journal of International Criminal Justice in December 2023, the article notes that digital open-source information has become a significant means of proving atrocity crimes charges. It argues that digital materials will typically need to be authenticated and contextualized via expert evidence. Highlighting the challenges that DOSI presents, including the risks of misinterpretation and biases leading to erroneous conclusions, the article proposes a six-factor test to identify digital specialists to serve as expert witnesses. It also encourages the digital open-source community to utilize transparent, accessible and replicable methodologies when conducting online investigations. On a complementary track, I am working with PhD candidate Vanessa Topp on a new version of The Hartford Guidelines on Speech Crimes in International Criminal Law, which I co-authored with Professor Richard Wilson of the University of Connecticut in 2017. The new guidelines will address international speech crimes on social media platforms, disinformation, and other linked topics arising in the digital age.   Building on the analyses in those publications, a key facet of the research is to examine how to analyse and tender online speech acts as evidence. For these purposes, it is clear that expert evidence will be required from a range of specialists. Forensic questions include the authenticity of the statement (excluding deepfakes and identifying alterations to the item), attributing it to the suspect, preserving the native files, measuring the reach of the statement, identifying the influence of the statement maker, and, perhaps most significantly, interpreting the statement’s contents in light of its sociological, temporal and cultural context. Underlying conceptual questions include how to categorize online materials as evidence, how digital materials can shift the truth-discerning moment outside of the courtroom, and how the democratization of access to technology tests the distinction between experts and laypersons for legal purposes. As court proceedings heat up, providing conceptual clarity on these issues will help facilitate the submission, contextualization and interpretation of online materials which may constitute or instigate atrocity crimes including genocide and persecution.