Ius ad bellum Proportionality is More Complicated Still: A Response to David Kretzmer

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Thomas Liefländer is a doctoral candidate at St Hugh’s College, University of Oxford

Any attempt to come to terms with the notion of proportionality, be it in the context of the use of force in self-defence or anywhere else, has to grapple with a number of questions. First, what is the nature of the applicable proportionality test? Possible answers include ‘tit-for-tat’, ‘not-more-than-necessary’ or the ‘narrow proportionality test’ which assesses whether the ‘good’ effects of a measure outweigh its ‘bad’ effects. Secondly, once this question is settled, a more precise definition of the various factors going into the proportionality equation and how they interrelate is needed. Finally, how is each factor to be assessed under the conditions of epistemic and normative uncertainty that exist in the real world? Depending on the context, the answer to any one of these questions can be straightforward or very difficult. In self-defence, it seems, they are mostly difficult.

Professor Kretzmer’s recent EJIL article tackles some of these questions. He focuses, in particular, on the definition of the legitimate ends of self-defence and how they impact on the proportionality test. In summary, he first suggests that the definition of legitimate goals can determine whether a ‘tit-for-tat’ or ‘not-more-than-necessary’ test is applicable. Secondly, identifying the legitimate aims is crucial for being able to apply both the ‘not-more-than-necessary’ and the ‘narrow proportionality’ test, as both relate action taken in self-defence to the good (ie the legitimate ends) it intends to achieve. In these two respects, Professor Kretzmer’s contribution is outstanding. His work will certainly focus the discussion on the centrality that the definition of legitimate ends has both for self-defence in general and the issue of proportionality in particular. However, in stressing this particular aspect Professor Kretzmer may have downplayed the role of the remaining questions to some degree. I shall outline the important questions that Professor Kretzmer’s article essentially leaves open. In doing so, I will briefly touch on (1) the status of the ‘narrow proportionality’ test, (2) the ‘means’ side of the ‘means-end/not-more-than-necessary’ test, and finally (3) on the more general issue of proportionality-assessments under epistemic and normative uncertainty. My intention is not so much to challenge Professor Kretzmer’s arguments, but rather to extend – but not complete – the picture of what it is that we argue about when proportionality is in issue.

‘Narrow Proportionality’

In the abstract to his article, Professor Kretzmer indicates that he would “argue that […] there is still place for assessing narrow proportionality” (p. 235) in the ius ad bellum. In the main text, however, he does not take a position regarding whether or not defensive force is ultimately subjected to this test, or whether it should be. Instead, he simply observes that “[i]ssues of ‘narrow proportionality’ in jus ad bellum have not been subjected to much academic analysis” (p. 278) and suggests a number of reasons why this may be so. Whether there is or should be a ‘narrow proportionality’ test in the law of self-defence thus remains open.

Answering this question is important, since the applicability of a ‘narrow proportionality’ test may determine the legality of a state’s use of force in self-defence. To give an extreme (and admittedly extremely theoretical) example for the purpose of illustration, where only a ‘not-more-than-necessary’ proportionality test is in place, a state could use extreme force (such as a nuclear weapon) to repel a relatively ‘minor’ attack (eg, the occupation of a remote and uninhabited island), provided that it factually has no other means of achieving this result. The reverse is, of course, that if a ‘narrow proportionality’ test applies, a situation might arise where a state has to suffer the consequences of an attack without being allowed to respond, despite being able to, simply because the only effective means it has at its disposal are ‘too extreme’.

There are two distinct issues at hand here, neither of which Professor Kretzmer really tackles. First, is there currently sufficient evidence to conclude that the law on the use of force includes a ‘narrow proportionality’ criterion? There is much discussion, and approval, of this notion of proportionality among moral philosophers writing on the ethics of war, but not so much among lawyers. The best indication that this notion of proportionality might be used in ius ad bellum as a matter of law can be found in the ICJ’s controversial Nuclear Weapons opinion. While the Court’s main focus was on the ius in bello, its finding that the use of nuclear weapons may be lawful “in an extreme circumstance of self-defence, in which its very survival would be at stake” (para 97) could be read as relating to the ius ad bellum as well (especially when read in conjunction with para 43). In this reading, the Court would suggest that the ‘bad’ effects of nuclear weapons can only ever be justified when a particularly important ‘good’ is at stake. Justifying the ‘bad’ would then not only depend on whether the ‘good’ can be reached in a less harmful way (the ‘not-more-than-necessary’ test), but also on whether or not the ‘good’ is important enough. Apart from this pronouncement, there is however little clear evidence for the applicability of the ‘narrow proportionality’ test in international law.

The second, and probably both more decisive and divisive issue, is whether international law should include such a test. Imposing a ‘narrow proportionality’ test would ultimately signify that a state’s right to defend itself is subject to an overall utility calculus, in which the interests of third states or even the aggressor state itself could – theoretically – outweigh the attacked state’s interest in defending itself. Has the international community reached a stage of integration in which it can credibly be maintained that the ultimate interest of the community as a whole can sometimes override each state’s right to defend itself? Or is the right to self-defence so absolute that it can justify imposing any cost whatsoever, if that cost is unavoidable to achieve the legitimate ends of self-defence? These are hard normative questions that deserve attention.

The ‘Means’ Side of a ‘Means-Ends’ Test

It emerged from Professor Kretzmer’s analysis – and I agree fully in this respect – that in most cases of self-defence the primary test under the label of proportionality is one of ‘means-ends’ rationality, focusing both on whether a particular use of force is effective in achieving the legitimate ends at stake and whether a “less drastic”alternative is available (p. 277). While Professor Kretzmer focuses extensively on the ‘ends’ part of this equation, the difficulties that lie in the ‘means’ part are not explored in any depth. However, deciding whether a particular use of force was really necessary is by no means straightforward, even if agreement can be reached on the legitimate ends. The two primary issues in this respect are the qualification of two measures as alternatives and determining which one is the “less drastic”.

To start with the first, let us assume a state plans defensive action by drawing up two campaigns. One may involve a fully-fledged invasion, with a high chance of obtaining the legitimate objectives quickly, and another is based on a combination of targeted bombings and commando operations, with a lower probability of achieving the legitimate objectives and later in time. Assume for now that the invasion is considered more “drastic” than the second option (more on this later). Under the ‘means-ends’ proportionality test, would the defending state be obliged to opt for the second campaign, even though it is less likely to succeed and will take longer? There are two possible answers: the first one would be to consider that in order for these two measures to count as alternatives, they need to achieve at least the level of effectiveness the defending state desires. In this case, the defending state would be free to choose either of the two operations, provided that both implied levels of effectiveness fall within the range of legitimate ends (that this is possible is easily illustrated by the fact that a state is always perfectly allowed to pursue a lower level of effectiveness than it would maximally be allowed to). If it chooses the first one, the second is insufficiently effective; if it chooses the second, the first is disqualified by being too drastic. It could, however, also be argued that the defending state must accept a certain loss of effectiveness if the harm thus avoided is more significant. The balance drawn between the loss of effectiveness and the harm avoided is effectively a form of ‘narrow proportionality’. This option is defended by just war theorists (see for instance this excellent piece by Professor Hurka). The position of international law, on the other hand, is rather unclear.

The second question relates to what counts as “less drastic”. We can assume that as the condition of proportionality relates to curbing the harm a defending state is allowed to cause in pursuit of its legitimate objectives, a state that has two alternatives to choose from must select the less harmful one. There are, again, two sub-issues involved here. First, what counts as harm? It is clear that the ius ad bellum calculus is wider than the one involved in ius in bello proportionality, in that also damage to enemy combatants and military objects is counted as relevant harm, and that one must look at the whole campaign rather than individual operations. But just how inclusive is the definition of harm (the same question is of course relevant to any ‘narrow proportionality’ test)? While just war theorists have argued about this problem extensively, the issue has received little attention in international law.

The picture becomes even more complex when the harmful factors are given a dimension of weight. To return to our two campaign options, let us now assume that the envisaged invasion will lead to massive losses of combatant lives on both sides, whereas the bombing/commando scenario would entail a higher loss of civilian lives, but much fewer combatant deaths on both sides. Which operation is less harmful? How many combatant lives equal one civilian life? Is the defending state’s wish to minimize its own combatant casualties a relevant factor? Many of these questions are well-known in the context of ius in bello proportionality; my point here is to show that they may apply similarly under the ius ad bellum proportionality test (although the selection and weighing of factors is not necessarily identical in the two regimes).

Epistemic and Normative Uncertainty

A brief final point relates to the conditions of epistemic and normative uncertainty that are involved at various stages in the proportionality calculus. By epistemic uncertainty I refer to the fact that comparative analyses of alternative measures, whether ex ante or ex post, involve counterfactuals and ‘what-if’ questions that can never be answered with full certainty. Can we say with anything approaching certainty whether one strategic option is more likely to be effective than another or predict with precision which option will cause more harm, especially given the inherent dynamism of developing conflicts? Professor Kretzmer mentions epistemic limitations of this sort only with respect to self-defence against imminent attacks (p. 271), but it seems to me that they are always involved, to one degree or another. Normative uncertainty, on the other hand, relates to the old chestnut of incommensurability. How can the overall good of defensive force be weighed against the overall bad in the absence of fixed scales of values? How can it be decided how many combatant lives equal that of a civilian? As seen, issues of incommensurability arise not only if a general ‘narrow proportionality’ test is accepted, but are ingrained in the ‘not-more-than-necessary’ test as well.

The point about raising these problems is not to call for a solution – that seems to be ultimately impossible. Rather, the question is how to deal with them. Deciding whether what is ultimately at stake is the “reasonableness”of the measure (see, eg, Myres McDougal and Florentino Feliciano, Law and Minimum World Public Order (Yale UP 1961), at p. 218) or whether the assessment of necessity/proportionality must be “strict and objective, leaving no room for any ‘measure of discretion’” (Oil Platforms, para 73) is eventually more important than debating the theoretical solvability of the uncertainty conundrum. In short: finding an answer to the legal question of whether any given use of force in self-defence has complied with the proportionality condition depends as much on the applicable standard of review and burden/standard of proof as it does on the actual content of the condition itself, especially (but not only) when a court is to decide.

Professor Kretzmer only touches on this point very briefly, when he states that as far as balancing the various factors involved in ‘narrow proportionality’ is concerned, “[c]ourts and other decision-making bodies do not seem equipped to decide between the conflicting perspectives” (p. 279). Does this mean that hard questions of proportionality of defensive force are ultimately unreviewable under law / non-justiciable and open only to political assessments? Is the context of self-defence really so different from, say, the ius in bello or general human rights law that a legal reviewer cannot come to terms with the unavoidable uncertainties? I personally think that self-defence is perfectly reviewable and that the problems posed by uncertainty can be tamed (rather than overcome) by marrying conceptual clarity with a stronger focus on decision making processes and review procedure.


Professor Kretzmer himself suggests that with his article he may have “replaced one area of uncertainty and indeterminacy with another” (p. 282). It is certainly true that his analysis takes the debates on proportionality from a state of diffuse uncertainty to a more precisely confined form of uncertainty. Maybe this is all that good scholarship can achieve in such difficult areas of law. My intention in this short comment was not to challenge this undoubtedly important achievement, but rather to show that further fields of difficulty exist. To my mind, Professor Kretzmer’s article should then not be understood as defining exhaustively what it really is that we argue about when it comes to proportionality, but rather as highlighting and exploring in depth one of various pieces of a complex jigsaw. As simple as the notion of proportionality is on its face, close attention reveals many complex problems with deep normative implication that will likely keep international lawyers occupied for a long time to come.

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