Facts, intuitions and uncertainties in the jus ad bellum

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Lawyers disagree about international law governing the resort to force. That much is obvious and evident in numerous posts on this and other sites and in the extensive literature studying controversies in the jus ad bellum. Disagreements between lawyers representing states are easy to attribute to their clients’ clashing interests and ideologies, rather than genuine differences in legal opinions. Yet even highly qualified jurists have sincere disagreements about what the jus ad bellum permits or prohibits in general and in specific cases.

My research, based on systematic textual analysis of scholarly writings and ICJ judgments, and interviews with 31 UK-based international lawyers, suggests there is some validity in the well known explanation that such disagreements are driven by vagueness in the law and differences in lawyers’ interpretive techniques. My research also suggests some role for a less examined explanation: that disagreements are in part driven by the need for lawyers to make factual assessments and forecasts when they determine the lawfulness of resort to force.

‘Vagueness’ and interpretation in the jus ad bellum

International law governing resort to force – codified in three brief paragraphs in the UN Charter, modified by the customary international law processes of opinio juris and state practice, interpreted in sources such as UN General Assembly declarations, ICJ cases and scholarly writings – displays several forms of ‘vagueness’. Using concepts from the philosophy of knowledge, the law can be described as based around ‘paradigms’ of lawful and unlawful uses of force – such as invasion of a state to deprive it of its territorial integrity, or individual or collective self-defence if an armed attack occurs. These paradigms are not defined by a single, simple test, but by what is, in effect a ‘multi-part test’ – made up of multiple sub-tests such as necessity, proportionality, imminence. These sub-tests are overlapping but not entirely co-extensive, can themselves be broken down into further component tests, and can be interpreted in different ways. The very processes of identifying customary international law – parsing individual and collective statements by Governments, assessing the nature and intentions of state behaviour – are similarly multifaceted and open to multiple interpretations. All these features of the law align with a form of vagueness which philosophers have termed ‘supervaluationism’.

Furthermore, the tests which define the jus ad bellum do not in practice define a sharp, binary distinction between lawful and unlawful force. Rather, the categories of lawful and unlawful force are opposing end-points of a continuum of cases, separated by a ‘penumbra of uncertainty’. The indicators of opinio juris and state practice which form customary international law are also often better described as spectra or continuums rather than clearly binary tests. These features of the law align with a form of vagueness which philosophers term the ‘sorites paradox’ – the paradox of the heap, or ‘fuzzy logic’.

For example, figure 1 illustrates my survey of 23 UK-based international lawyers, showing them demonstrating varying levels of disagreement about the lawfulness of ‘hard cases’ of resort to force: anticipatory self-defence, pre-emptive self-defence, self-defence against non-state actors, humanitarian intervention, and use of force to prevent WMD proliferation. The diversity of approaches to international law between legal communities in different states, which for example Roberts has written about, suggests that a more international survey may well reveal different patterns of disagreement.

Figure 1: UK-based lawyers’ disagreements about the use of force

Such disagreements may be in part related to lawyers at least unconsciously conforming to competing ‘interpretive cultures’, holding different views about valid legal tests, how they should be interpreted, and what boundaries distinguish lawful and unlawful force. Olivier Corten and other scholars have observed how lawyers who use formalist, textually-oriented, originalist interpretive techniques tend to favour a more restrictive jus contra bellum. Those who use more creative, purposive, dynamist interpretation techniques tend to propose a more expansionist jus ad bellum. My research suggests there is some correlation between lawyers’ interpretive preferences and views on the legal permissibility of force.

Facts, forecasting and legal uncertainty

The need for lawyers assessing the lawfulness of force to grapple with uncertainty about facts, and the law’s requirement for forecasting may also contribute to these disagreements – a potential cause of uncertainty and controversy in the jus ad bellum which has been less fully investigated. Hard cases engaging the jus ad bellum are usually military crises which are chaotic, fast moving, involving belligerents deliberately trying to deceive and mislead. So factual evidence about such crises is usually patchy, disputed and open to multiple interpretations.

In addition, key tests of the jus ad bellum, such as necessity, proportionality, imminence, require decision-makers to construct and compare multiple forecasts or counter-factual scenarios. Is force the only remaining option to stop an attack, or might non-forceful measures succeed if continued for a few days more? Would using force result in more suffering than not using force? Would using this amount of force be enough to stop the attack? Insufficient? Excessive? Is a state using force in response to a genuine attack or as a pretext for territorial gain or political dominion?

A hypothetical case illustrates some of these dilemmas. Hercules and Thrasymachus lead states with a long history of enmity. Figure 2 illustrates an apparent drone strike by Thrasymachus against Hercules. At what if any point in that chain of events does Hercules have the right to hit back against Thrasymachus? How would you answer if Hercules says he has intelligence that Thrasymachus ordered the drone strike a week earlier? Or if Thrasymachus alleges his people are enduring a bloody insurgency Hercules is sponsoring? Or if Hercules claims Thrasymachus is attempting genocide against those insurgents’ communities? Revealing more factual detail about this complex multi-phase conflict seemed to increase rather than reduce disagreement between my research participants about the lawfulness of force.

Figure 2: Hercules, Thrasymachus and the penumbra of uncertainty

Rules of evidence – such as corroboration from multiple sources, scrutinised for independence, quality, contemporaneity and collection methods – help but don’t eliminate such uncertainties. Because the assessments and forecasts lawyers and other analysts make about conflicts – as political scientists and psychologists have observed – depend on underlying intuitions, assumptions, beliefs and biases about how and why actors behave in conflicts. In effect, those assessing uncertain facts and making forecasts rely on at least implicit politico-strategic and ethical theories of how the world works and how it ought to work – reasoning which might be described as ‘extralegal’.

Such extra-legal intuitions shape not only lawyers’ assessments of specific hard cases of force, but also their conclusions about the desirability and validity of different interpretations of the law more generally. Does force never, sometimes, or almost always stop attacks by malign states and terrorists? Reduce deaths from state sponsored genocide or non-state insurgency? Cause more short and long term harm than good to wider international peace and security? My research suggests there are correlations between lawyers’ opinions on such factual questions and their views on the legal permissibility of force. In effect, lawyers may align with competing ‘strategic cultures’, operationalising different beliefs, intuitions, and biases about the reality and normativity of military force.

Managing uncertainty in the jus ad bellum?

Such disagreements may be irresolvable precisely because they reflect deeply internalised psychological characteristics. But researchers in forecasting and intelligence analysis have developed multiple methods to help decision makers expose their assumptions and biases and navigate such uncertainties. One technique is the analysis of competing hypotheses. Figure 3 illustrates a loose interpretation of the technique analysing Nato’s 1999 intervention in Kosovo. Similar techniques could be used to analyse competing legal justifications, and to assess their risk of attracting or withstanding legal challenge. I argue that more could be done to adapt such techniques to assist legal analyses of hard cases engaging the jus ad bellum.

Figure 3. Analysis of competing hypotheses

Of course, lawyers cannot always prevent political leaders from advancing absurd legal justifications for force. For example, a leader might claim a right to anticipatory self defence against a weaker neighbouring country, alleging it is run by Nazis and about to join a hostile alliance as prelude to aggressive war. Nor will lawyers be able to eliminate the less bad faith sources of uncertainty described in this blogpost.

As Koh and others have argued, the decentralised nature of adjudication and enforcement in international law means international lawyers have particular professional responsibilities. They need to balance their role as ‘counsel’ – enabling clients to navigate the law to achieve legitimate objectives; and ‘conscience’ – encouraging clients to adapt their behaviour to obey the law.

But by acknowledging the existence and nature of uncertainty in the law governing the resort to force, and the role of their own cognition in creating and perpetuating it, lawyers can do more to develop ways to reduce and manage its impact. That can only serve to reinforce a jus ad bellum that is undeniably under pressure, and yet still makes a vital contribution to international peace and security.

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Dr Sam Selvadurai says

November 4, 2022

My sincere thanks to all those who have assisted me in my research so far. To learn more about this work, and take part in the next phase of this study if you wish, please contact me at samuel.selvadurai@kcl.ac.uk or follow this link: https://www.surveymonkey.co.uk/r/2JXJNVW