International Law
30 April 2018

The Legality of the Use of Force in Armed Conflict and Occupation

Interview with Ka Lok Yip

A recent PhD thesis explores what it really means to say that it is “legal” to kill or capture and confine a person in war. Interview with Ka Lok Yip on “The Law of Force, the Force of Law: The Legality and Ontology of the Use of Force against Individuals in Armed Conflict and Occupation”.

Can you describe your thesis and its major findings?

My thesis tackles one particular, perhaps the core, aspect of armed conflict and occupation, that is, the use of force against people. It examines both its legality and ontology. I remember the first time I mentioned my thesis title to a professor, the word “legality” proved provocative, “How can killing a person be legal? At most there is combatant immunity, but that’s not ‘legal’ as such.” This professor was pointing at the big elephant in the room – is it really “legal” to kill a person in war? The thesis answers this question from the perspectives of international law and international relations/political science and has three major findings.

The first major finding is that there are many different shades to the meaning of the term “legal” and their conflation conveniently facilitates the domination of some laws (and their underlying social rationalities) over others. Many laws govern the use of force against people in war: the law of armed conflicts, international human rights law, the law regulating interstate use of force, international criminal law, domestic law – the list goes on. Does “legal” mean (1) legal under one law, or (2) legal under a law that renders the act legal under another law, or (3) legal under all laws regulating the act? And is it “legal” in the sense of being (4) specifically permitted, or (5) simply not prohibited, or (6) not even regulated?

To clarify, I have established a taxonomy of six concepts of legality corresponding to these six possible meanings as (1) simple legality, (2) compounding legality, (3) system-wide legality, (4) positive legality, (5) negative legality and (6) neutral legality. With this taxonomy, it becomes clear that just because a use of force is “legal” as a matter of (1) simple legality (e.g., under the law of armed conflicts), even if it enjoys (4) positive legality (i.e., it is specifically permitted by the law of armed conflicts), it does not necessarily mean that it is legal as a matter of (3) system-wide legality because the use of force might be illegal under other laws. Conflation between these different concepts of legality could allow for instance the law of armed conflicts and the specific social rationality that underlies it to dominate over other laws and their underlying social rationalities. Clarifying and distinguishing between these six concepts of legality can allow us to concentrate on establishing which of them is referred to in a given requirement in the law and have an intelligent debate about whether a particular use of force is “legal” in the sense required.

The second major finding relates to the fear of the “fragmentation” of international law as a coherent system by regarding a use of force as legal under one law but illegal under another. This fear catalyses the promotion of certain “techniques of legal reasoning” to procure compounding legality – that is, legality under a law that would render the act legal under another law, thereby achieving unity. Two commonly used “techniques” are lex specialis, that is, the special law prevails over the general law, and systemic integration, that is, interpreting one law by taking into account other relevant laws. Under lex specialis, if one law is deemed more “special”, for example because it applies to a narrower situation such as war, legality under this more “special” law should prevail over any illegality under other, more general laws relating to the same subject matter. Under systemic integration, if a law is deemed relevant to the same subject matter governed by another law which is silent on a given point, the latter should be presumed, on that point, not to contradict the former which is akin to being “more special”. The application of both techniques depends on these laws’ relation to the “same subject matter”, which has often been understood as the “same factual situation”, for example war. On this understanding, the law of armed conflicts has often been considered more “special” than other laws with regard to war. The thesis draws on doctrines and jurisprudence from different areas of public international law to demonstrate that the “same subject matter” does not refer to the same “factual situation”, over which different legal norms may serve different regulatory purposes whose priority need not correlate to the underlying norms’ relative speciality. Rather, the “same subject matter” refers to the same “regulatory purpose”, the pursuit of which by different norms enables the inference that the more “special” norm is intended to prevail over, or not be contradicted by, the more general norm. On this understanding, the law of armed conflicts cannot be considered more “special” than other laws because they serve distinct regulatory purposes while governing the same factual situation of war.

The third major finding is that the differences between these laws stem from their different presuppositions about the ontology of the use of force in war in terms of its nature and causes, the neglect of which blinds legal interpretation to social reality while the vindication of which can reconnect them. The thesis demonstrates that the law of armed conflicts accepts as given the structural conditions in war and relies on human individuals to uphold certain minimum standards commensurate with their diminished agency, which explains its different requirements from, for example, those of international human rights law, which seeks to scrutinise, challenge and change these structural conditions. The use of lex specialis to conform the demands of international human rights law to those of the law of armed conflicts thus mistakes the scope of the structural problem addressed by international human rights law for that of an agential problem addressed by the law of armed conflicts. The proposal of revisionist just war theorists to conform the demands of the law of armed conflicts to those of international human rights law underestimates the structural constraints in war and overestimates human agency, thereby mistaking the structural nature of the problem addressed by international human rights law for the agential nature of the problem addressed by the law of armed conflicts. The use of systemic integration to synthesise the law of armed conflict and international human rights law elides the analytic distinction between agency and structure and ends up empowering decision-makers to decide according to their vested interests. Recognising these laws’ different ontological presuppositions vindicates their distinct regulatory purposes and social rationalities and precludes the misconstruction of their differentiation as “fragmentation”.

To sum up, the thesis finds widespread conflation among different concepts of “legality”, serious abuse of “legal techniques” to reach politically convenient outcomes, and a fundamental disconnect between the dominant interpretation of the law and the reality of war that the law tries to regulate.

What made you choose your research topic?

I really like this question because it sounds as if there is something other than “me” that “made me” choose my research topic! And there is some truth to that for I believe it is the numerous constraints I face in my own life, not related to armed conflict or occupation at all, that led me to my research topic. Other than the fieldwork I did towards the end of my thesis, I have had no direct experience with people living in war; yet we share the universal experience of finding ourselves in circumstances not of our own choosing. For example, people who get conscripted into fighting a war may not agree with it, or are not sure whether they agree with it – what is to be done? Object and face the prospects of prosecution, social ostracism and financial ruin? Or just go with the flow and forget their own positions, beliefs and objections? We all face similar constraints, whose severity may vary but whose basic pattern is the same. I am interested in understanding constraints of all kinds, natural, social, legal, structural, cultural, personal, facing people in war and in general, because without a full understanding of these constraints, it is also impossible to fully appreciate and value the powers, strategies and agency that people come up with to react to these constraints in making their ways through their lives. For me, coming to grips with this dialectic between constraints and freedom is as much a quest for understanding others by self-reflection as it is an act of self-exploration through solidarity with others.

What are you doing now?

My thesis examiners raised extremely interesting questions about the ontology of law, which have prompted more research questions that I am working on!

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Ka Lok Yip defended her PhD thesis in International Law on 21 September 2017. Professor Andrea Bianchi presided the committee, which included Professor Andrew Clapham and Professor Thomas Biersteker, thesis codirectors, and Professor Dapo Akande, from the University of Oxford.

Full citation of the PhD thesis:
Yip, Ka Lok. “The Law of Force, the Force of Law: The Legality and Ontology of the Use of Force against Individuals in Armed Conflict and Occupation”. PhD thesis, Graduate Institute of International and Development Studies, 2017.

Interview by Nathalie Tanner, Research Office.
Front picture by Ciberprofe [CC BY-SA 4.0 (], from Wikimedia Commons.