How did you come to choose your research topic?
It started with a curiosity about the kind of arguments international lawyers consider to be neutral or objective. I decided to focus on the specific influence of scientific disciplines while I was working for an Assembly member of the ICRC. My impression was that the pragmatism of that institution had integrated certain scientific aspirations and ideals that influenced both my methodology and the kind of arguments I put forward. Legal opinions drafted in this context tended to express a preference for a certain way of practicing international law that included some extent of scientific-like reasoning or phrasing to make it seem concrete, workable and as unbiased as possible.
It seemed to point to a broader intellectual environment than the usual narrative taught in law schools. So I set out to explore the influence of the sciences on legal argumentation. What I found was a fragmented history: a complex succession of different — and often competing — ways of bringing science into legal thinking. It turns out that international lawyers have drawn on very different scientific vocabularies over time. Sometimes they used formal logic to argue against empirical experience, only for that hierarchy to be reversed in other contexts. Elsewhere, they used psychology to relativise what counts as observation; evolutionary thinking against analytical jurisprudence; or even modern physics to rethink natural causation.
What interested me was not simply that these references coexisted, but that they seemed to structure disagreements within the discipline. Over time, I became more attentive to the effects of using scientific references in law. I wanted to understand how these binary forms of reasoning allowed lawyers to push alternative accounts of objectivity aside. How they validated some arguments while marginalising others. Because there seemed to be dark sides to such categorical modes of analysis. Scientific vocabularies have encouraged emotionless styles, but they have historically been tied to asymmetrical ways of seeing the world — whether in the treatment of non-European populations or in gendered practices.
Within the constraints of a doctoral research project, how did you approach your research topic?
I found it helpful to think of scientific references as cultural phenomena. Once they enter the legal discourse, they take on a particular function. Their authority does not really come from scientific demonstration any more. Their meanings are often unstable, and there are so many of them that any strict methodology seems out of reach. What I observed instead is something closer to arguments from authority. Whether they work depends on acceptance by others in the profession. Some styles or analogies stick and become persuasive, others just don’t and are ignored.
From there, I tried to organise the research around a set of questions rather than a single framework. One question concerns the way broader scientific contexts shape what international lawyers consider to be legitimate intellectual work. Another examines the distinction between the scientific and the unscientific, and the role it plays in making certain arguments appear subjective. A third question looks at how these vocabularies function strategically, as resources that international lawyers can mobilise to defend the authority of their discipline.
What are your major findings?
To oppose an “irrational” world of power politics, international lawyers have again and again tried to present their work as compatible with the scientific ideals of their time. Accusations of subjectivity were also used to discredit opposing views inside the discipline. In doing so, lawyers relied on a distinction between what counts as scientific and what does not — even though the content of that distinction changed over time. We find continuity in the structure of these arguments. And these historical configurations still influence contemporary practice. The positions once explicitly defended by references to science are still available: logical coherence is opposed to empirical facts, dynamic evolution to formal stability, psychological representations to material acts, and so on.
More generally, the unstable nature of these oppositions raises a series of broader questions. For example, how we constantly construct “social reality” through legal debates, or how we rely on ideas about evolutionary progress to regularly redefine legal temporality. My goal was not to provide definitive answers. It was more to make visible the role that these scientific references have played — and continue to play — in shaping international legal thought. At the same time, my research situates these developments in specific contexts: the scientific revolution, Victorian Britain, interwar debates, Cold War jurisprudence, and more recent interdisciplinary works.
Can you give examples of issues on which your thesis might shed new light?
Engaging in the tactics I have described has concrete consequences, especially on the identification of custom or treaty interpretation. Some examples are more explicit than others. Consider Article 1(A)(2) of the Convention relating to the Status of Refugees, stating that the status of refugee is dependent on a “well-founded fear of being persecuted”. What is contained in the legal notion of a “well-founded fear”? Should it be established following a fact-based, rational approach that would exist “out there” independently from the applicant, or following a psychological assessment of their subjective representation? Because there is no fixed professional consensus on this question, debates tend to oscillate between these two binary positions. My research suggests that in doing so, lawyers replay an old match about the proper conception of legal concepts: should it be done by way of psychological investigations or empirical facts gathering?
As far as academic debates are concerned, I have focused on the “empirical turn” in international law — or data-driven studies examining how international law operates in practice. This development is often presented as bringing something from outside the discipline — as if it introduced methods that are not properly legal, in an attempt to turn international law into something else than what it is. And indeed, these studies borrow methods from economics, psychology and other social sciences to describe and make propositions about international law. Because data shows that States respond well to non-binding incentives, we should have more of them. Because judges have cognitive biases, we should adapt procedural rules. And so on.
But they are, in many ways, the new manifestations of a long doctrinal tradition. They rely on similar oppositions, and tend to present alternative approaches as subjective. They often want the law to adapt and better reflect what they suggest is the “real world”. What’s interesting is the tension this creates. The more these approaches insist on being empirical and scientific, the more they seem to run into the trap of being one-sided in a plural field. Once again, this leads to old debates about what kind of science could best capture what is objective or subjective in law. Resolving these debates once and for all doesn’t seem possible — or perhaps even desirable. As international lawyers, the language we speak operates within a plurality of scientific traditions. They lead to conflicting understandings of what it means for our law to be objective.
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Thomas Romailler defended summa cum laude his PhD thesis in International Law, titled “Reason against Passion: Scientific Vocabularies in International Law”, on 13 January 2026. Committee members were Professor Fuad Zarbiyev, Thesis Co-Supervisor; Professor Alexis Keller, Thesis Co-Supervisor, University of Geneva; Professor Nico Krisch, President of the Committee and Internal Member; and Professor David Kennedy, Harvard Law School, Harvard University, Cambridge, USA.
Citation of the PhD thesis:
Romailler, Thomas Ludovic. “Reason against Passion: Scientific Vocabularies in International Law.” PhD thesis, Graduate Institute of International and Development Studies, Geneva, 2026.
Access to the PhD thesis:
An abstract of the PhD thesis is available on this page of the Geneva Graduate Institute’s repository. As the thesis itself is embargoed until January 2029, please contact Dr Romailler for access.
Banner image by zackc0rp / Shutterstock.
Interview by Nathalie Tanner, Research Office.