1. Introduction
It is now traditionally accepted that jus ad bellum, defining the conditions under which states are entitled to use force against each other, and jus in bello, defining the obligations of the belligerents once they are engaged in an armed conflict, are two separate branches of international law in the sense that the (extent of the) application of the latter is not dependent upon the respect of the former.Footnote 1 This position is one of the main achievements in the evolution of jus in bello. Indeed, under the just war theories, dating back to the Middle Ages, the emerging laws of war were generally considered to be applicable to each of the belligerents depending upon the justice of their resort to war.Footnote 2 This idea – whereby belligerents pursuing an unjust cause of war did not enjoy all the rights provided under jus in bello or belligerents fighting for a just cause were not bound by all the rules of jus in bello – remained debated even until the beginning of the second half of the twentieth century,Footnote 3 and it basically involved a clear subordination of jus in bello to jus ad bellum. This was firmly criticised as undermining the protection of persons under jus in bello Footnote 4 and, more generally, the development of this body of law.Footnote 5 The Preamble to the 1977 Additional Protocol I to the 1949 Geneva Conventions now unambiguously reflects the evolution towards the general acceptance of equal applicability of jus in bello to belligerents irrespective of the question of the legality of their use of force under jus ad bellum. The Protocol, indeed, reaffirmsFootnote 6 that
the provisions of the Geneva Conventions of 12 August 1949 and of this Protocol must be fully applied in all circumstances to all persons who are protected by those instruments, without any adverse distinction based on the nature or origin of the armed conflict or on the causes espoused by or attributed to the Parties to the conflicts.
This principle of equal application of jus in bello is now generally and firmly supported in legal literatureFootnote 7 and international case law.Footnote 8 Although some scholars are reconsidering this cardinal principle, as they argue for a limited subordination of jus in bello to jus ad bellum,Footnote 9 such a view remains isolated and most scholars often seem to take the position de lege ferenda. Footnote 10 More interestingly, some recent legal literature argues against the separate nature of the two bodies of law but in another way. Jus in bello should not be seen as subordinated to jus ad bellum but, on the contrary, the latter should be considered as subordinated to the former.Footnote 11 This position is notably based on the claim of a particular relationship between the notions of proportionality which are provided for under both jus ad bellum and jus in bello.
It is true that proportionality is a common concept to these two branches of international law. Under jus ad bellum, it is claimed that proportionality is applicable to any use of force, be it legally controversial, such as humanitarian intervention,Footnote 12 or classically admitted, like resort to force authorised by the UN Security Council (UNSC).Footnote 13 Although there is room for arguing in this sense, especially regarding the UNSC military enforcement measures,Footnote 14 it is only with respect to self-defence that the applicability of proportionality is incontestably and clearly established in light of state practiceFootnote 15 and international case law.Footnote 16 Under jus in bello, legal literature is also divided regarding the precise matter to which proportionality is applicable. It could be argued on the basis of Article 8(2)(b)(iv) of the ICC StatuteFootnote 17 that proportionality applies to attacks on the natural environment in humanitarian law. This Article indeed mentions, among the list of war crimes committed in international armed conflicts, the attacks causing ‘long-term and severe damage to the natural environment which would be clearly excessive in relation to the concrete and direct overall military advantage anticipated’.Footnote 18 However, proportionality is not traditionally conceived as relating to the natural environment. Neither Additional Protocol I to the Geneva Conventions nor any other international convention provides a rule that prohibits excessive damage to the natural environment. Article 8(2)(b)(iv) of the ICC Statute must rather be seen as establishing a special regime in this respect, which is only applicable before the International Criminal Court (ICC) and cannot be considered as being part of customary international humanitarian law (yet).Footnote 19 Some scholars also support the idea that the rule prohibiting the use of means that cause superfluous injuries or unnecessary suffering to combatantsFootnote 20 – which is provided for in several jus in bello conventionsFootnote 21 – entails a proportionality requirement. However, this is far from being a common agreed position. Proportionality is most generally referred to in legal literatureFootnote 22 as well as in international case law,Footnote 23 in relation to civilians and civilian objects, as requiring that attacks do not cause excessive damage to the latter in comparison with the direct and concrete military advantage anticipated from the attacks.Footnote 24
In short, it is only with respect to self-defence and attacks on civilians and civilian objects that proportionality is commonly and incontestably referred to under jus ad bellum and jus in bello, respectively. It is precisely between these two notions of proportionality that some debatable interrelations are claimed to exist. The Israeli intervention in Lebanon in 2006 is mentioned as a typical precedent evidencing such interrelations, since – as argued by scholarsFootnote 25 – many states considered that the Israeli intervention was disproportionate in light of the law of self-defence – and, therefore, not justified – because of the excessive damage caused to civilians and civilian infrastructure.Footnote 26 In addition, reasons given by states in order to justify the evaluation as disproportionate of the Israeli intervention under jus ad bellum were similar to those advanced by the same or other states in order to explain the evaluation as disproportionate of the intervention under jus in bello.Footnote 27 In fact, practice shows that states have frequently criticised the disproportionate nature of the self-defence action by emphasising the excessive damage caused by this action to the civilian population.Footnote 28 International case law and – to a lesser extent – the work of the International Law Commission (ILC) have also been interpreted as evidencing the existence of particular interrelations between proportionality under jus ad bellum and jus in bello. In the Nuclear Weapons Advisory Opinion, the International Court of Justice (ICJ) stated that ‘a use of force that is proportionate under the law of self-defence, must, in order to be lawful, also meet the requirements of the law applicable in armed conflict which [encompasses the principle of proportionality]’.Footnote 29 Some scholars have argued that this statement meant that ‘in order for self-defence to be proportionate, it must respect international humanitarian law [including the principle of proportionality]’.Footnote 30 It has been asserted in the same way that the term ‘lawful’, which qualifies the measure of self-defence that precludes the wrongfulness of an act of a state under Article 21 of the ILC's Articles on State Responsibility,Footnote 31 makes the proportionate nature of an action in self-defence dependent upon the respect of the jus in bello rules on the conduct of hostilities, including the principle of proportionality provided by those rules.Footnote 32
According to those interpretations of state practice, international case law and the ILC's work on state responsibility, proportionality under jus ad bellum and proportionality under jus in bello are to be seen as interrelated in such a way that the latter must be considered as part of the assessment of the former. Basically, this means that jus ad bellum would be subordinated to jus in bello to the extent that any action taken under the law of self-defence could only be judged as proportionate under this law if it also conforms to proportionality under jus in bello. This position is allegedly motivated by the increasing concern regarding the protection of civilian populations during war – protection that would be better ensured if the requirement of proportionality under jus in bello was considered as being part of proportionality under jus ad bellum.Footnote 33
This article seeks to analyse such a position and, more generally, to clarify the relationship between the two notions of proportionality, those notions being understood here as those commonly and indisputably used in legal literature and international case law – that is, as referring to proportionality under the law of self-defence and proportionality in relation to attacks on civilians and civilian objects, respectively. The article is divided into two parts. The first part (Section 2) develops the main argument, which is in line with the traditional position regarding the relationship between jus ad bellum and jus in bello. It is argued that, although sharing common features and being somewhat interconnected, the notions of proportionality provided under these two separate branches of international law remain separate and independent of each other, mainly because of the existence of what it is referred to in the article as a ‘general versus particular’ dichotomy. This means that, under the law of self-defence, proportionality is concerned with the armed operation as a whole, whereas, under jus in bello, proportionality regulates individual attacks launched in the framework of this operation.
The second part of the article (Section 3) addresses the particular situations in which the application of the above-mentioned dichotomy, upon which the independent nature of the two notions of proportionality is founded, may be problematic. Such situations are those which involve only one or a few military operations – that is, situations in which it is logically no longer possible to distinguish between the individual military attacks and the military operation as a whole. It is acknowledged that such situations may increase the risk of conflating the assessments of the two independent notions of proportionality.
2. Two Independent Notions
Although they share basic common features, proportionality under jus ad bellum and proportionality under jus in bello remain two independent notions, this independent nature ultimately deriving from their different rationales.
2.1 Basic Common Features
It is undoubtedly the case that proportionality under jus ad bellum and proportionality under jus in bello share common features. The most obvious of these is that their field of application is similar. They simultaneously govern the conduct of hostilities while also serving as a restraint upon such activity. This role is particularly clear with respect to proportionality under jus in bello. The latter forms part of the rules regulating the conduct of hostilities, and it is well known that the general principle behind those rules is that the means and methods of warfare are not unlimited.Footnote 34 Yet, proportionality under jus ad bellum also has a role to play ‘as a restraint upon the conduct, as opposed to the initiation, of hostilities’.Footnote 35 Damage caused to the aggressor state (or even third states and the environmentFootnote 36) by the defensive action (including the targets of this actionFootnote 37), as well as the means used by the state acting in self-defenceFootnote 38 and the duration of the whole military operation,Footnote 39 are all factors which are included in the assessment of proportionality under the law of self-defence.
Another fundamental feature that the two notions of proportionality have in common is the nature of the balance exercise that they both entail as well as the general factors that take part in such an exercise. Indeed, the two notions of proportionality do not actually require striking a balance between two similar quantities, as any proportionate balance normally does. They rather require putting an action in relation to its aim: this action, which includes the damage that it causes, is required not to exceed what is necessary to achieve the intended aim. Basically, this is a teleological balance exercise, which results from the application of a necessity test. In this sense, the two notions of proportionality have a close relationship with necessity. The relation between this test and the notion of proportionality under jus in bello is more obvious. According to scholars,Footnote 40 it may be argued that the notion of proportionality under jus in bello is misleading as it requires less equilibrium between two similar quantities than a teleological balance exercise consisting of assessing whether the attack launched by the belligerent, including the effect of such attack on civilians and civilian objects, does not exceed what is necessary for achieving the military advantage anticipated.
The link between necessity and proportionality under jus ad bellum is more complex. Proportionality under the law of self-defence has usually been conceived by statesFootnote 41 and the ICJFootnote 42 as requiring a quantitative equilibrium between the action in self-defence and the armed attack and, more particularly, a balance between the damage caused and the military means used by the attacker and the damage caused and the military means used by the state acting in self-defence. However, the vast majority of scholars disagree with such a conception. They consider that a state defending itself against an armed attack may require the use of broader means than those resorted to by the aggressor state. As a result, they argue that proportionality implies a teleological balance exercise requiring that the action in self-defence does not exceed what is necessary for the state to defend itself against an armed attack.Footnote 43 This latter approach entirely conflates proportionality with necessity. The most convincing answer to this debate seems to consider the quantitative proportionality test as a means for assessing prima facie the necessity of the action in self-defence.Footnote 44 As rightly emphasised by one author, ‘[p]roportionality thus seems to be one way to evaluate whether a measure is necessary…. The disproportionality seems here to be the mark that the State supposedly acting in self-defence was pursuing some other end than merely riposting to an attack’.Footnote 45 In short, proportionality under jus ad bellum is intrinsically linked to necessity as it is an easy tool for assessing whether the action in self-defence is necessary.
2.2 Relations
The two above-mentioned features – the same field of application and a similar teleological balance exercise – could suggest that proportionality under jus ad bellum and proportionality under jus in bello actually merge. Yet, there is a fundamental distinction between the two notions of proportionality which makes them separate and independent notions. This key distinction is referred to as the ‘general versus particular’ dichotomy. Indeed, according to the position generally upheld in the scarce literature on the subject,Footnote 46 proportionality under jus ad bellum only regulates the conduct of hostilities in a general perspective, since it is concerned with the military operation in self-defence as a whole, whereas proportionality under jus in bello only regulates the conduct of hostilities from a more particular view, as it is concerned with individual military attacks launched in the framework of this operation. This dichotomy must be clearly understood. It does not imply that proportionality under jus ad bellum, envisaged as more general, encompasses proportionality under jus in bello and that, contrary to what is argued in this article, the relationship between the two notions of proportionality would be that of inclusion of the latter in the former. It rather means that, although they share a similar field of application, as they both apply to a similar reality – the conduct of hostilities – proportionality under jus ad bellum and proportionality under jus in bello have a distinct scope of application: the former applies to the hostilities as a whole, whereas the latter applies to the specific incidents of targeting which occur in the framework of those hostilities. Basically, the above-mentioned dichotomy reveals the existence of a clear-cut separation and relation of independence, rather than of inclusion, between the two notions of proportionality.
Admittedly, this does not have an impact on the fact that these two notions have a close relationship with the necessity test and that they both entail a similar teleological balance exercise between an action and its aim. Yet, this radically changes the nature of the general factors which take part in the proportionality equations. As correctly stated by one author, ‘in current times, the dual proportionality [tests] incorporate a consideration of the same general factors but with a different emphasis’.Footnote 47 First, the aim against which the action is to be assessed is entirely different. As far as proportionality under jus ad bellum is concerned, the military operation will be assessed in balance with a general objective, the ultimate goal of the operation – that is, defending itself against an armed attack or, if one admits the right to anticipatory self-defence,Footnote 48 averting an (imminent) threat of armed attack. As a result, proportionality under jus ad bellum can be considered as determining the form of the whole military operation which is necessary for achieving a general objective: repelling (or preventing) an armed attack. By contrast, as far as proportionality under jus in bello is concerned, the objective in relation to which each individual military attack is to be balanced is more specific. Indeed, according to the clear wording of the proportionality requirement under jus in bello,Footnote 49 the proportionate nature of the individual attacks cannot be measured against the defensive military objective of the operation as a whole, but only against the concrete and direct military advantage anticipated from these attacks.Footnote 50 In this sense, proportionality under jus in bello can be considered as determining the form of individual military actions undertaken within the context of the whole operation, which are necessary for the realisation of the corresponding specific military objectives.
It is true, in this respect, that some interconnection may be claimed to exist between the two notions of proportionality given the objectives against which these two notions are to be assessed. Indeed, since proportionality under jus ad bellum determines, as stated above, the form of the military operation as a whole, which is necessary for a state to defend itself against an armed attack, it plays a role in identifying all the specific military objectives that such defensive operation may legally pursue and against which proportionality under jus in bello is to be evaluated. In other words, the definition of the specific military objectives, against which such proportionality is to be tested, must theoretically not exceed what is necessary for the state to defend itself against the armed attack, according to proportionality under jus ad bellum. This evidences a link between the two notions of proportionality, which mainly results from the unavoidable ‘subordination’ of all the particular military objectives to the general defensive goal of the entire military action. That having been said, this link only entails that proportionality under the law of self-defence will be violated not if the rule of proportionality under jus in bello is infringed but if the particular military objectives are not correctly determined. In this sense, such a link merely evidences some overlapping between criteria taking part in the assessment of the two conditions of proportionality and does not make one of these conditions dependent upon the other.
The second general term against which the two notions of proportionality are to be assessed is the forcible action which has been launched. In accordance with the ‘general versus particular’ dichotomy argued above, all the general aspects of this action must be considered as relevant factors when assessing proportionality under jus ad bellum. Those factors include, as already indicated above, damage caused by the action in self-defence to the aggressor state, including its civilian population and armies, the targets and duration of this action as well as the means used on that occasion. Under jus in bello, factors are more limited. Proportionality is assessed mainly in light of the means used for the attack and the damage that this attack caused to civilians and civilian objects.
Again, it is true in this respect that some factors, mainly the damage caused to the civilian population, appear to be common to the two notions of proportionality. This may explain why some authors, such as those commenting on the 2006 Israeli intervention in Lebanon,Footnote 51 have interpreted declarations in which states have criticised the disproportionate nature of the action in self-defence because of the excessive damage caused to the civilian population as also evidencing the violation of proportionality under jus in bello. It is precisely such an interpretation which has led those authors to argue for the position that the jus in bello proportionality is included in the assessment of the jus ad bellum one. Admittedly, it may be argued that the violation of proportionality under jus in bello can be used as an indication that proportionality has also been violated under jus ad bellum. Yet, this does not imply that the violation of one condition of proportionality necessarily entails the violation of the other. This only means that a prima facie assessment may be made with respect to such violation, especially because of similar factors being taken into consideration in the evaluation of the two conditions. Such prima facie assessment must, nonetheless, be conducted in greater depth in order to establish whether it is founded. An in-depth scrutiny will have to assess each notion of proportionality by measuring it against the relevant – general versus particular – action and objective, and this may provide a different assessment result. In short, contrary to the interpretation supported by some authors with regard to state reactions to the 2006 Israeli intervention in Lebanon, emphasis put by states on the excessive damage caused to civilians by the self-defence action as a basis for asserting the violation of proportionality under jus ad bellum does not necessarily imply that proportionality under jus in bello has also been (considered to be) violated.
All of this indicates that the two notions remain independent of one another. This involves two main consequences regarding the assessment of the legality of any use of force. First, it is perfectly possible that a use of force is legal under jus ad bellum but illegal under jus in bello because it is disproportionate according to this law, and vice versa.Footnote 52 Secondly, the two conditions of proportionality must be separately but cumulatively complied with for any resort to force to be legal.Footnote 53 It is in this sense that the aforementioned ICJ conclusions in the Nuclear Weapons Advisory Opinion, as well as the ILC commentary on Article 21 of the Articles on State Responsibility, must be interpreted – that is, as meaning that ‘in order for any use of force to be legal, it must respect both the jus ad bellum limit of proportionality and the principles of jus in bello’.Footnote 54 As a result, there is no fear, contrary to what is voiced by authors who support the inclusion of the jus in bello proportionality in the assessment of proportionality under jus ad bellum,Footnote 55 that the particular protection afforded by jus in bello would not be taken into account, since respect for proportionality under jus in bello will necessarily take part in the general assessment of the forcible action.
2.3 Different Rationales
The fundamental distinction between the two notions of proportionality and the independent nature which derives from such distinction may be explained by the different rationales that underlie those notions. Although both notions serve as a limitation to any resort to force, the logic behind this limitation is radically different. Proportionality under jus ad bellum is fundamentally linked to the maintenance of international peace and security.Footnote 56 It is true that its immediate purpose is to prevent the state acting in self-defence from using a measure of force beyond that which is necessary to repel (or avert) an armed attack. However, by doing so, proportionality precludes this state from acting unilaterally in order to achieve an objective which normally falls within the exclusive competence of the UN Security Council and requires a collective decision in accordance with the UN Charter provisions concerning the maintenance of international peace and security. More concretely, its aim is to avoid any escalation of violence at the international level and any expansion of the already occurring disturbance of the international social order. In other words, although resorting to self-defence is allowed as an acceptable provisional disruption of international peace and security, the requirement of proportionality ensures that such a level of disturbance remains at the level authorised by the UN Charter. This has been validly summarised by one author, who stated that, ‘[while] assigning priority to the defensive needs of the attacker, proportionality [under jus ad bellum] remains an instrument for social control of unilateral resort to force’.Footnote 57 It is therefore logical that the major criteria for assessing it relate to the general aspects of the military operation as a whole, including ‘the level of destruction of enemy territory and the infrastructure of the State; overall collateral civilian damage and combatant casualties; and the impact of the use of force on third States’.Footnote 58
It is only incidentally that humanitarian considerations – namely the suffering caused to civilians and combatants – are taken into consideration in the proportionality equation under jus ad bellum, since they are merely part of the requirement not to cause excessive damage to the aggressor state. It is only in this sense that one may consider, as some authors do, that proportionality under jus ad bellum ‘could limit [the] territorial and temporal dimensions [of war so as to] reduce suffering for both civilians and combatants’.Footnote 59
The logic behind proportionality under jus in bello is entirely different. Its primary concern is not the maintenance of international peace and security but rather the protection of humanitarian values,Footnote 60 in particular the limitation of the suffering of non-combatants in situations of armed conflict. More precisely, its purpose is to conciliate such a limitation with the military necessities that may be legally pursued by each belligerent, by prohibiting that such necessities could justify the launching of an attack causing excessive damage to civilians or civilian objects. Although such damage, as emphasised above, is also a factor for assessing proportionality under jus ad bellum, it is viewed from a different perspective under jus in bello. It is not assessed as part of the damage caused to any particular state, but as damage caused to individuals as such. The suffering of non-combatants is an inherent part of the proportionality equation under jus in bello. As rightly emphasised by one author, whereas the self-defence conditions ‘focus on damage to the enemy state as an abstract entity apart from its individual inhabitants, by taking into account such factors as … the general destruction caused to the state and its population … in [jus in bello], it is the effect of a weapon on civilians … as individuals that requires assessment’.Footnote 61
3. Blurred Situations?
The independent nature of the two notions of proportionality is founded mainly upon the ‘general versus particular’ dichotomy referred to above. Yet, there are situations in which this dichotomy does not seem applicable, such as those which involve only one or a few military measures, including a limited self-defence response to sporadic attacks. In such situations, the teleological balance exercise which characterises the two notions of proportionality is likely to be based on similar elements. Indeed, when there is only one or just a few military actions, it logically becomes impossible to distinguish between the individual attacks and their particular military objectives, against which proportionality under jus in bello is to be assessed (if it applies),Footnote 62 from the military operation as a whole and its general objective, against which proportionality under jus ad bellum is to be measured. In addition, the aspects of the action to be taken into account in the assessment of the two notions of proportionality – namely the means used and the damage that it causes – may entirely overlap. In short, as based on similar elements, the teleological balance exercise that the two notions of proportionality entail could provide a similar assessment result. This does not challenge the theoretical position that the two notions of proportionality remain independent from one another. Yet, this emphasises that making a distinctive assessment between the two notions of proportionality may be very difficult in practice, especially in situations involving one or a few military actions.Footnote 63
It is indicative – although admittedly not entirely conclusive – to observe that considerations regarding proportionality under jus ad bellum and jus in bello have always been confusing or at least problematic in cases in which the ICJ has been called upon to rule on an action allegedly undertaken in self-defence and limited to one or just a few military operations. One may first mention in that respect the Oil Platforms case,Footnote 64 in which the question of the legality of only two military operations under the law of self-defence was put before the Court. It is interesting to note that the United States justified the proportionate nature of its action in self-defence by referring to considerations pertaining, as emphasised by Iran itself,Footnote 65 to jus in bello – namely that the choice of the military target of its action (the oil platforms) was motivated notably by the desirability to limit to the greatest possible extent the number of civilian casualtiesFootnote 66 – as required by proportionality under jus in bello.
One may also mention the Wall case and the considerations held in that case by some judges of the Court as well as by some states. The Court asserted that Israel had invoked the law of self-defence in order to justify the building of the wall – that is, to justify the legality of what could be viewed as one particular military operation.Footnote 67 The Court dismissed this argument mainly because Israel did not prove that the alleged armed attacks came from outside the territory that it controlled.Footnote 68 Some judges and states have nevertheless considered the argument. Observations held in that respect evidence some confusion between the two classically separated branches of international law. Indeed, the reasons for which Judge Kooijmans qualified the building of the wall as disproportionate under jus in bello Footnote 69 were largely identical to those referred to by Judge Higgins in order to support the disproportionate and non-necessary nature of this building under jus ad bellum.Footnote 70 More generally, after having recalled that the law of self-defence was regulated by the conditions of necessity and proportionality, some states seem to have argued that these conditions had not been respected by referring to humanitarian law considerations,Footnote 71 including the absence of any distinction between civilians and combatants, the excessive damage caused to the civilian Palestinian population,Footnote 72 and (other) specific violations of humanitarian law.Footnote 73
Finally, one must refer again to the Nuclear Weapons Advisory Opinion. Indeed, the conclusions reached by the Court in that case have certainly given rise to the liveliest debates on the distinction between jus ad bellum and jus in bello. It is well known that, after having stated that nuclear weapons were ‘generally contrary to humanitarian law’,Footnote 74 the Court concluded in a very ambiguous statementFootnote 75 that
in view of the current state of international law, and of the elements of fact at its disposal, [it] cannot [however] conclude definitively whether the threat or use of nuclear weapons would be lawful or unlawful in an extreme circumstance of self-defence, in which the very survival of a State would be at stake.
The Court, therefore, did not exclude that, in such circumstances, the threat or use of nuclear weapons could be lawful. The Court's reasoning and, more particularly, the relationships between its first jus in bello conclusion and its following jus ad bellum statement have given rise to different interpretations. It has been argued that the Court (possibly) meant that nuclear weapons could be used in some extreme self-defence situations even if violating jus in bello.Footnote 76 According to this interpretation, the Court has asserted that a state which would lawfully resort to self-defence in order to protect its survival would not be obliged to respect humanitarian law rules regulating the conduct of hostilities, including the principle of proportionality provided by those rules. Basically, the Court would have endorsed the idea that jus ad bellum could override jus in bello in some cases. This interpretation is not an isolated one. It has been considered by several judges of the Court as the correct,Footnote 77 or at least a possible,Footnote 78 interpretation of the Opinion. Judge Koroma has argued in this sense that the Court ‘create[d] … a new category called the “survival of the State”, seen as constituting an exception to … the principles and rules of humanitarian law’.Footnote 79 Similarly, Judge Fleischhauer assertedFootnote 80 that the Court's findings meant that,
although recourse to nuclear weapons [was] scarcely reconcilable with humanitarian law applicable in armed conflict as well as the principle of neutrality, recourse to such weapons could remain a justified legal option in an extreme situation of individual or collective self-defence in which the threat or use of nuclear weapons is the last resort against an attack with nuclear, chemical or bacteriological weapons or otherwise threatening the very existence of the victimized State.
Yet, this interpretation does not seem founded for several reasons. First, it implies that the Court has adopted a solution which is contrary to the now undisputable principle of equal application of the laws of war between belligerents, something which would dramatically undermine the whole application of humanitarian law. Secondly, it is contrary to the statement that the Court itself had made in this case and according to which, as interpreted above, any use of force must respect both jus ad bellum and jus in bello in order to be lawful.Footnote 81 Thirdly, it would go beyond what the nuclear states themselves requested of the Court – that is, merely not to rule that the use of nuclear weapons is unlawful in any circumstance. Finally, in this interpretation it is forgotten that the Court has not considered nuclear weapons to be always prohibited under humanitarian law but only as generally contrary to this law.
Those considerations are actually crucial in interpreting the Court's reasoning. Indeed, it means that nuclear weapons could be used lawfully under humanitarian law. Read together with the subsequent jus ad bellum statement of the Court and the principle that any use of force must comply with both jus ad bellum and jus in bello, the Court's statement arguably implies that the only case in which the threat or use of nuclear weapons by a state could possibly be lawful under both the law of self-defence and humanitarian law is when the survival of this state is at stake. Why is it the most likely case? Certainly, as far as jus ad bellum is concerned, it is because this circumstance threatens the most important purpose for which the right of self-defence has been designed – the continued existence of its beneficiary – and could, therefore, legitimise the use of the most powerful and damaging defensive means, including atomic bombs. In other words, the objective to defend itself against an armed attack that threatens its survival is the only potential case in which the use of any means (including nuclear weapons) which is likely to cause severe damage, may be seen as not exceeding that which is necessary to achieve that objective according to the condition of proportionality. Basically, the use of exceptional defensive means would be justified, in this case, by the very significant threat to the state.
But how could it also be consistent with jus in bello? Although, admittedly, it is difficult to answer this question comprehensively, an answer may at least be given when the use of nuclear weapons, in the circumstances mentioned by the Court, consists of only one or a few military operations. Indeed, it is precisely in such a situation that the distinction between the assessments of the two notions of proportionality may fade away. The respective factors for assessing these two notions, including the distinct – general versus particular – objectives of the use of nuclear weapons, are likely to overlap entirely. In other words, if the use of nuclear weapons is judged as being proportionate under jus ad bellum in such a situation, it is likely also to be judged as proportionate under jus in bello, and vice versa. It is in light of these considerations that the position upheld by some judges of the Court can be understood. In her dissenting opinion Judge Higgins interestingly did not exclude the possibility that the use of nuclear weapons in compliance with jus ad bellum in a situation of extreme self-defence ‘might of itself exceptionally make such a use compatible with the humanitarian law’.Footnote 82 This comes after she arguesFootnote 83 that
in order to meet the legal requirement that a military target may not be attacked if collateral civilian casualties would be excessive in relation to the military advantage [that is, in order to meet the requirement of proportionality under jus in bello], the ‘military advantage’ must … be one related to the very survival of a State [which is part of the assessment of proportionality under jus ad bellum].
Those considerations conflate the factors for assessing the two notions of proportionality, in particular, the respective objectives pursued by the use of nuclear weapons under jus ad bellum and jus in bello; this is logically conceivable if the use of nuclear weapons involves only one or a relatively small number of attacks.
4. Conclusion
Proportionality is a concept which is provided under both jus ad bellum and jus in bello. Although traditionally these two branches of international law are considered to be entirely separate bodies of law, some scholars argue that proportionality under jus ad bellum is dependent upon the respect for proportionality under jus in bello, the latter being envisaged as an element of the assessment of the former. This position is ultimately motivated by the aim of strengthening the protection of persons in armed conflicts and is mainly based upon recent state practice, including reactions to the 2006 Israeli intervention in Lebanon.
This article does not share such a position. The two notions of proportionality are clearly distinct. Although applying to a similar reality, they regulate this reality with different emphases: proportionality under jus ad bellum focuses on the military operation as a whole, which must be assessed in relation to a general objective – that is, defending against an armed attack; proportionality under jus in bello is concerned with individual military attacks launched during this operation, which must be measured in relation to the concrete and direct military advantage anticipated from the attack. Accordingly, they operate independently of each other but both must be fulfilled in order for any use of force to be considered lawful under international law. In this respect, there is no reason to argue for the inclusion of the jus in bello proportionality in the requirement of proportionality under jus ad bellum as the most ‘likely development given the current focus on the law in war and on the suffering of the civilian population during war’.Footnote 84 Such specific protection will indeed always be taken into account when assessing the legality of any use of force.
The fundamental distinction between proportionality under jus ad bellum and jus in bello also implies that, although some of the factors for assessing these two notions are similar – which involves mainly damage caused to civilians and civilian infrastructure – those factors are taken into account in a different way. First, they are measured against the general objective of the military operation as a whole under jus ad bellum, and against the particular military advantage of the individual attack under jus in bello. Secondly, they are only taken into consideration as part of the overall damage caused to the aggressor state as far as the assessment of the jus ad bellum proportionality is concerned, whereas they are the primary focus in the proportionality equation under jus in bello. All of this indicates that when states criticise the disproportionate nature of an action in self-defence by emphasising the excessive damage caused by this action to the civilian population – as states often do and did so especially regarding the 2006 Israeli intervention in Lebanon – one must not necessarily interpret that proportionality under jus in bello has also been (considered as) violated. Those state reactions are, therefore, not conclusive for the position that proportionality under jus in bello is part of the assessment of proportionality under jus ad bellum.
The fundamental distinction between the two notions of proportionality actually derives from the distinct rationale underlying each of them: the principal aim of proportionality under jus ad bellum being to minimise the disturbance of the international social order, while proportionality under jus in bello directly pursues humanitarian ends, in particular to limit the suffering of non-combatants in armed conflicts. Such a distinction is clear in theory. Yet, it proves to be far from easy to make distinct assessments between the two conditions of proportionality in practice, especially when the use of force to be assessed involves only one or a few military actions. In such situations, one can hardly distinguish between the general versus particular aspects of the actions and, therefore, the respective factors for assessing the two conditions, which basically increases the risk of complete overlap between the evaluations of these conditions.
