just Cause For War - Rutgers University · “Operation Just Cause ... War,” Philosophy &...

Perhaps it should be rather hearten-ing that democratic leaders whowish to take their countries to war

are now obliged to advertise the war ashaving a “just cause.” Politicians nowroutinely invoke this rather quaintphrase drawn from the traditional theoryof the just war. Indeed, when the admin-istration of George H. W. Bush decided toinvade Panama, it christened its war“Operation Just Cause,” thereby appro-priating a label that George W. Bushmight later have found serviceable had itstill been available. But despite theincreasing prominence of the notion ofjust cause in political discourse, there arefew serious discussions of it, and thosethere are tend to be perfunctory. Theusual practice is to offer a simple charac-terization of the requirement of justcause—for example, that it is the require-ment that there be a good or compellingreason to go to war—and then to observethat, at least until quite recently, contem-porary just war theory and internationallaw have recognized only one just causefor war: self- or other-defense againstaggression. It is then often noted that theconsensus on this point is currently beingchallenged by those who claim that theprevention of large-scale violations ofpeople’s human rights by their own gov-ernment also provides just cause for war.Occasionally, skeptics of just war theorywill also, for satirical effect, cite instancesfrom the classical literature of causes forwar that are now rejected but were once

widely accepted as just, such as the pun-ishment of wrongdoing and the spread ofthe Christian religion.

In this essay I advance a conception ofthe requirement of just cause that is revi-sionist in the context of contemporaryjust war theory, but that has roots in anolder tradition of thought about the justwar with which contemporary theoristshave lost touch to a considerable extent.This revisionist conception has variousheterodox—indeed, heretical—implica-tions that I will highlight and defend: forexample, that a just cause is necessary forthe satisfaction of any of the other condi-tions of a just war, that there can be var-ious just causes for war other thandefense against aggression, that bothsides in a war can have a just cause, andso on. The conception of just cause forwhich I will argue must ultimately beassessed by reference to the moral plausi-bility both of these implications and ofthe larger understanding of a just war inwhich the conception is embedded. As Iwill make clear below, I mean by a justwar something more than merely amorally justified war.

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Just Cause for WarJeff McMahan*

*I am deeply grateful to Christian Barry, AllenBuchanan, David Lefkowitz, Larry May, RonMcClamrock, David Mellow, and Derek Parfit forpenetrating comments on an earlier draft of thisessay, and to Thomas Hurka for illuminating discus-sion.

RESORT TO WAR, CONTINUATIONOF WAR, AND TERMINATION OFWAR

In the just war tradition, just cause is one ofthe requirements of jus ad bellum—that is,one of the conditions of justification for theresort to war. Contemporary just war theo-rists often assume, therefore, that therequirement of just cause applies only to theinitial resort to war, and that after war hasbegun all that matters is how the war is con-ducted. But this cannot be right. It is possi-ble that a war can begin without a just causebut become just when a just cause arisesduring the course of the fighting and takesover as the goal of the war. When this hap-pens, it would be absurd to say that an unjustwar has concluded and a new, just war hasbegun. Rather, one and the same war maycease to be unjust and become just—just asa war that begins with a just cause may con-tinue after that cause has been achieved orhas simply disappeared on its own.1 But if awar in progress can either acquire or cease tohave a just cause, then the requirement ofjust cause must apply not only to the resortto war but also to the continuation of war.2

A just cause is, indeed, always required forengaging in war. Just cause specifies the endsfor which it is permissible to engage in war,or that it is permissible to pursue by meansof war.

One important implication of the ideathat any engagement in war requires a justcause is that when the just cause of a war hasbeen achieved, continuation of the war lacksjustification and is therefore impermissible.Just cause thus determines the conditionsfor the termination of war.

There are, however, complexities here ofwhich it is important to be aware. Althoughtheorists in the just war tradition often writeas if just cause were always a single, unitary

goal, such as collective self-defense, there isno reason to suppose that a war may haveonly one just cause. Even if the requirementof just cause applied only to the resort towar, there could in principle be two or morejust causes. It is even possible that, if therewere two or more just causes, no one on itsown would be sufficiently important tomake the resort to war proportionate,though all together would be. And assumingthat the requirement of just cause appliesnot only to the initial resort to war but alsoto the continuation of war, it is also possiblefor there to be different just causes for thesame war at different times. Consider, forexample, a war that has self-defense againstunjust aggression as its initial just cause. Itmight be justifiable to continue the war evenafter the initial aggression had been defeatedin order to protect people in a justly occu-pied area or to ensure the effective disarma-ment of the aggressor. These would be justcauses that, while not part of the justifica-tion for the recourse to war, may legitimatelybe pursued by the continuation of the war.

The idea that war may not be continuedin the absence of a just cause explains why itcannot be permissible to demand that anadversary surrender unconditionally. Forthe idea that it could be permissible todemand unconditional surrender presup-poses that the denial of any condition thatthe other side might set for surrender would

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1 Grotius observed that “a war may be just in its origin,and yet the intentions of its authors may become unjustin the course of its prosecution.” See Hugo Grotius, TheRights of War and Peace (1625), trans. A. C. Campbell(London: M. Walter Dunne, 1901), p. 273. But a shift ofintention does not entail the disappearance of the justcause. Thus, Grotius goes on to say that “such motives,though blamable, when even connected with a just war,do not render the war ITSELF unjust.”2 Here I am in agreement with David Mellow, A Critiqueof Just War Theory (Ph.D. dissertation, University ofCalgary, 2003), p. 201.

itself be a just cause for the continuation ofwar. And that cannot be the case. Supposethe enemy insists on something perfectlyreasonable as a condition of surrender—forexample, that the victors pledge not to killthe prisoners of war they are holding. If itwere permissible for the victors to insist onunconditional surrender and to continuethe war until they secured it, that would pre-suppose that it is permissible for them toassert by means of war their alleged right towithhold a pledge not to kill prisoners.

This of course leaves open the question ofwhat may be done when an adversary whohas fought without justification demands asa condition of surrender something towhich they are not entitled, yet the demandis also of a type that it would not be permis-sible to resist by means of war. Suppose, forexample, that an adversary who has beenlargely defeated militarily demands as a con-dition of surrender that they be allowed tocontinue certain unjust domestic practices,such as certain forms of religious discrimi-nation (for example, providing state fund-ing for schools that promulgate the statereligion, but not for others). Just as it may benecessary for an individual not to resist cer-tain forms of wrongdoing when the onlyeffective response would be inappropriate orexcessive in relation to the offense, so it maybe necessary in war to grant certain unde-served concessions when the only alterna-tive is to continue to fight without sufficientjustification.

THE MORAL PRIORITY OF JUSTCAUSE IN JUS AD BELLUM

It is not only unjust aims that cannot per-missibly be pursued by means of war. Thereare also many good or legitimate aims thatcannot permissibly be pursued by means ofwar. The requirement of just cause is not

simply that war must have a just or worthygoal. Nor is it a requirement that there be aworthy goal, the achievement of whichwould outweigh the bad effects of war. In thejust war tradition, the task of assessing thecomparative importance of the goal or goalsof war is assigned to the independent jus adbellum requirement of proportionality. Pro-portionality requires, roughly, that the rele-vant bad effects attributable to the war mustnot be excessive in relation to the relevantgood effects.3 According to the view I accept,it might in principle be possible for consid-erations of proportionality to be fully sub-sumed within the requirement of just cause.Many just war theorists would resist thissuggestion, however, because they believethat the goods that count in the proportion-ality calculation are not restricted to thosespecified by the just cause. But unless justcause fully accounts for considerations ofproportionality, it ought not to say anythingabout the scale, magnitude, or comparativeimportance of the goods to be achieved bywar. For it would be uneconomical andindeed pointless to divide the work ofweighing and measuring values betweentwo requirements—for example, by havingjust cause stipulate that the goal of a warmust be to achieve some very great good,while proportionality would require that the

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3 This is not, as some have supposed, a requirement thatthe bad effects, or expected bad effects, not exceed thegood. A war might kill more people than it saves andstill be proportionate if, for example, the majority ofthose killed are combatants who fight without a justcause, so that the war achieves a net saving of the livesof those who are fully innocent in the relevant sense. Iwill not pursue these complexities here. For discussion,see Thomas Hurka, “Proportionality in the Morality ofWar,” Philosophy & Public Affairs 33 (2005), pp. 34–66;and Jeff McMahan and Robert McKim, “The Just Warand the Gulf War,” Canadian Journal of Philosophy 23,no. 4 (1993), pp. 506–18.

good be great enough to outweigh the rele-vant bad effects of the war.

I suggest, therefore, that just cause saysnothing about considerations of scale ormagnitude, but functions entirely as arestriction on the type of aim or end thatmay legitimately be pursued by means ofwar. It does not require that there be a greatdeal of good to be gained from war; nor doesit imply that if there is a great deal of good tobe gained, there is therefore a just cause.

This way of understanding the require-ment of just cause parallels commonsensebeliefs about the morality of individualaction. Consider killing, for example, whichoccurs on a large scale in war. Suppose—toalter the details of Dostoyevsky’s Crime andPunishment only slightly—that by killingthe miserly and misanthropic old money-lender, Raskolnikov could have divided herwealth among a large number of poor peo-ple, bringing significant benefits to each thattogether would have greatly outweighed theharm to her. Most people think that this isnot even the right kind of justification forkilling. It is widely held that only certaintypes of aims—such as self-defense againstan unjust attack—can provide a justificationfor killing. In the same way, there are numer-ous worthy and important goals that cannotjustify the resort to war, or the practice ofwar. It cannot, for example, be a justificationfor going to war against a people that itwould stimulate the world economy, nomatter how great the economic benefitswould be.4

I will soon turn to the question of howthose types of goal that might provide a justcause for war may be distinguished fromthose that cannot. For the moment I will saymore about the relation between just causeand proportionality.

Because just cause is only a restriction onthe type of aim that can justify war, the pro-

portionality requirement may have a largerrole than many people suspect. Suppose, forexample, that the defense of a state’s territo-rial integrity against even partial annexationby another state is a just cause for war, asmany people believe. If just cause is not amatter of scale, then there would be a justcause for war if a neighboring country wereabout to capture an acre of our territory onits border—an acre that it regards as a holysite, but that we are using only as a garbagedump. In this case, the reason why it wouldbe wrong for us to go to war to retain ourpossession of that acre is not that our aimwould be too trivial to constitute a just cause;it is, rather, that our just cause would be tootrivial for war to be proportionate. (Some-thing of this sort might have been arguedwith respect to Britain’s resort to war whenArgentina seized the Falkland Islands—though defenders of that war argued that theproportionality calculation had to take intoaccount the importance of deterring evenlimited acts of aggression in order to upholdthe principle of territorial integrity.)

If this is right, there is a sense in which justcause does less work than many have sup-posed, while proportionality does more. Butthere is also a sense in which just cause has akind of priority over all the other require-ments of jus ad bellum. In most statementsof the traditional theory, the followingrequirements are included among the prin-ciples of jus ad bellum: just cause, competentauthority, right intention, reasonable hopeof success, necessity, and proportionality.The satisfaction of each is held to be neces-

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4 See McMahan and McKim, “The Just War and theGulf War,” pp. 502, 512–13. There we acknowledge ourdebt on this point to Thomas Hurka, whose “Propor-tionality in the Morality of War” is one of the mostprobing and rigorous contributions to just war theoryin recent decades.

sary in order for the resort to war to be jus-tified. And in that sense all the requirementsare of equal importance. But I believe thatjust cause has priority over the other validrequirements in this sense: the others can-not be satisfied, even in principle, unless justcause is satisfied.

Admittedly, this is not true of the tradi-tional requirement of competent authority,but I reject that component of the tradi-tional theory for reasons I will not presenthere.5 I also think that the plausible ele-ment in the requirement of “reasonablehope of success” is subsumed by the pro-portionality requirement.

That leaves right intention, necessity, andproportionality. Although it is not obviousto me that right intention is a valid require-ment, suppose for the sake of argument thatit is. It requires that war be pursued for thereasons that actually justify the war. It insiststhat those reasons not simply serve as acover for the pursuit of other aims. Whatthis means is that right intention is therequirement that war be pursued in order toachieve the just cause. Without a just cause,therefore, there are no reasons that canproperly motivate the resort to war.

There is, it might be argued, one way inwhich right intention could be satisfied evenin the absence of a just cause: if people falselybelieved that there was a just cause andfought with the intention of achieving it. Yetit seems to me that this would clearly not bethe right intention in the circumstances,though it might well be a good intention.

Consider next the requirement of neces-sity. This requirement demands that war bea necessary means of achieving the justcause. The claim that war is necessary forsomething other than the achievement of ajust cause has no justificatory force.

In the case of proportionality, there is anequally simple argument. If just cause indi-

cates the range of goods that may permissi-bly be pursued by war, then no goods thatfail to come within the scope of the justcause, or are instrumental to achieving it,can count in the proportionality calculation.If they did, that would imply that a war isjustified, at least in part, by the fact that itwould achieve certain goods that cannotpermissibly be achieved by means of war.(For those who are unconvinced by this sim-ple argument, I will say more on this pointin a later section on just cause and propor-tionality.)

JUST CAUSE AND JUS IN BELLO

I have argued that none of the valid require-ments of jus ad bellum can be satisfied in theabsence of a just cause. I also believe some-thing even more controversial, which is thatthe requirements of jus in bello also can-not—except in rare instances—be satisfiedin the absence of a just cause. This is a highlyunorthodox claim. It is an axiom of con-temporary just war theory that whetheraction in war is permissible or impermissi-ble does not depend on whether there is ajust cause. Just cause, on this view, governsonly the resort to war. It is an ad bellumrequirement, and as such has no role in theaccount of jus in bello. For the requirementsof jus in bello and those of jus ad bellum are,as Michael Walzer puts it, “logically inde-pendent”; hence, just as a war that one is jus-tified in fighting may be fought in an unjustmanner, so a war that is itself unjustified

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5 Although I reject competent authority as a necessarycondition of a just war, I concede that it is of practicalimportance to restrict the authority to take certain actionsto certain individuals or bodies when we seek to give insti-tutional expression or embodiment to the requirementsof a just war. It may be that, once certain institutions areestablished, some just causes for war can permissibly bepursued only by those with proper authority.

may nevertheless be fought in a just manneror, as Walzer says, “in strict accordance withthe rules.”6 The requirements of jus ad bel-lum are, moreover, thought to apply only tothe political leaders, those with the authorityto commit a people to war, and not to thosewho do the actual fighting. On this view,there is a moral division of labor that makessoldiers responsible for adherence only to theprinciples of jus in bello, which must there-fore be satisfiable whether or not their warmeets the conditions of jus ad bellum. Itwould be intolerable to suppose that all sol-diers who are commanded to fight in anunjust war, or who fight in such a war with-out knowing that it lacks a just cause, are forthat reason criminals or even murderers.

It may seem obvious, in any case, that atleast some of the requirements of jus in bellocan be satisfied even by those who fightwithout just cause. The requirement of dis-crimination, for example, requires only thatcombatants restrict their attacks to militarytargets—that they target only other combat-ants and not noncombatants. This isimplicit in the widely used alternative labelfor the requirement: the “requirement ofnoncombatant immunity.”

But this is in fact just one interpretationof the requirement of discrimination, whichin generic terms is simply the requirementto discriminate between legitimate and ille-gitimate targets and to make deliberateattacks only on the former. In my view,which I have defended elsewhere, the dis-tinction between legitimate and illegitimatetargets does not coincide with that betweencombatants and noncombatants. Rather,what discrimination requires is that soldierstarget only those who are morally responsi-ble for an unjust threat or for some othergrievance that provides a just cause for war.If that is right, soldiers who lack a just causealso lack legitimate targets.7

Similarly, if soldiers lack a just cause, thereare no goods that they are justified in pursu-ing by means of war. So even if there aregoods for which belligerent action is neces-sary, they are not goods that can permissiblybe achieved in that way. And when there areno goods that may be pursued by means ofwar, there are no goods that can properly beweighed against the bad effects that an act ofwar would cause; therefore, no act of warcan be proportionate in the absence of a justcause.8 In short, when there is no just cause,acts of war can be neither discriminate, nec-essary, nor proportionate.

There is, I concede, a small class of excep-tions to this general claim. These are acts ofwar by those who lack a just cause that arenecessary to prevent their adversaries fromacting in ways that would be seriouslywrong—for example, to prevent those fight-ing with a just cause from pursuing it by ille-gitimate means, such as by attacking peoplewho are innocent in the relevant sense as ameans of coercing those people’s govern-ment to surrender.9

This concession necessitates that we dis-tinguish between a just cause for war, whichcan contribute to the justification for goingto war and may legitimately be pursued bymeans of war, and what I will call a discretejust aim, which cannot contribute to the jus-tification for the resort to war or for its con-tinuation, but may legitimately be pursuedby means of war if war is in progress. Suchaims are “discrete”because they occur in iso-

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6 Michael Walzer, Just and Unjust Wars (Har-mondsworth, U.K.: Penguin, 1977), p. 21.7 For elaboration, see Jeff McMahan, “The Ethics ofKilling in War,” Ethics 114, no. 4 (2004), esp. pp. 718–29.8 I have argued at length for the claim that those whofight without just cause cannot satisfy the jus in bellorequirement of proportionality. See ibid., pp. 708–18.9 Ibid., pp. 712–14.

lation and are unconnected with the largeraims of the unjust war of which they are apart. The permissibility of pursuing a dis-crete just aim by means of war is doublyconditional: it may be pursued if war isalready in progress and if the wrong to beprevented cannot be avoided by surrender-ing on morally acceptable terms.

In general, however, a just cause is neces-sary for an act of war to be justified. It is forthis reason that war must cease once the justcause has been achieved. Soldiers may notcontinue to fight once the aims that justifiedtheir fighting have been achieved. And if thisis true, it should also be true that they maynot fight at all if there are not and never wereany aims that justify their being at war. Justcause is necessary not only for it to be per-missible for political leaders to resort to war;it is also necessary for it to be permissible toparticipate in war.

This is not to say that those who partici-pate in war without a just cause are neces-sarily culpable or deserving of punishment.Just as in the law a person may be fully excul-pated for action that is objectively in breachof a statute, so most soldiers who fight with-out a just cause may have a variety of excusesthat partially or even fully exculpate them.And even if the excuses that soldiers have forfighting in an unjust war never fully excul-pate them, it is possible, and almost certainlyhighly desirable, not to treat mere participa-tion in an unjust war as punishable underinternational law.

THE CONNECTION BETWEEN JUSTCAUSE AND MORAL LIABILITY TOATTACK

These claims about the dependence of jus inbello on just cause deviate substantially fromthe currently orthodox understanding of thejust war. I will now advance a view about

what types of aim can be just causes for warthat is also heretical, given the consensus thathas developed between international law andcontemporary just war theory that defenseagainst aggression is the sole just cause forwar (with the possible exception of the pre-vention of large-scale violations of humanrights, such as genocide). The view aboutwhat may be a just cause for war that I willdefend does, however, have roots in the writ-ings of earlier just war theorists and earliertheorists of international law.

Thomas Aquinas, for example, was closeto the truth when he wrote that “a just causeis required, viz. that those who are to bewarred upon should deserve to be warredupon because of some fault.”10 This claim is,however, in one respect too narrow and inanother too broad. It is too narrow in itsinsistence that it is necessary for just causethat those attacked should deserve to beattacked. I take the claim that a persondeserves to be harmed to imply that there is amoral reason to harm him even when harm-ing him is unnecessary for the achievementof any other aim—for example, when harm-ing him would not prevent, deter, or rectifyany other harm or wrong. In this sense, peo-ple seldom if ever deserve to be warred upon.

The notion I would substitute for desert isliability. To say that a person is liable to beattacked is not to say that there is a reason toattack him no matter what; it is only to saythat he would not be wronged by beingattacked, given certain conditions, thoughperhaps only in a particular way or by a par-ticular agent. This notion is broader than

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10 Thomas Aquinas, Summa Theologiae, IIaIIae, q. 40,art. 1, resp., quoted in Jonathan Barnes, “The Just War,”in Norman Kretzmann, Anthony Kenny, and Jan Pin-borg, eds., The Cambridge History of Later MedievalPhilosophy (Cambridge: Cambridge University Press,1982), p. 777. Since the only citation is to the Latin text,I assume that the translation is Barnes’s own.

desert in that, while desert implies liability,liability does not imply desert.

Although liability to attack usually orperhaps always arises from action that iswrongful, there is no necessary connectionbetween liability and punishment or retri-bution. To say that a person is liable to beharmed even though he does not deserve tobe harmed is just to say that if it is unavoid-able that someone must be harmed, there isreason that he should be the one who isharmed and that he will not be wronged bybeing harmed.

Substituting the notion of liability forthat of desert, we can say that there is justcause for war only when those attacked havemade themselves liable to be warred upon.But Aquinas’s claim that the basis of theirliability is fault, or culpability, may be bothtoo broad and too strong. It is possible toread his claim as implying that any fault thatmight make a person deserving of harmcould be a basis of liability to attack, inwhich case it would be too broad. For therelevant fault must be specifically for awrong that war against the perpetratorswould prevent or redress. And the insis-tence on fault, or culpability, may in princi-ple be too strong in that it is possible—though not likely—that a people couldmake themselves liable to be warred uponby being morally responsible, though fault-lessly, for a wrong that war against themwould prevent or redress.11

Here, then, is a statement of the formalconcept of just cause. There is just cause forwar when one group of people—often astate, but possibly a nation or other organ-ized collective—is morally responsible foraction that threatens to wrong or hasalready wronged other people in certainways, and that makes the perpetrators liableto military attack as a means of preventingthe threatened wrong or redressing or cor-

recting the wrong that has already beendone.

The connection I am claiming betweenjust cause and liability may be found, thoughnot altogether explicitly, in the work of someof the earlier jurists writing in the just wartradition. These writers typically insistedthat just cause is founded in an injury, bywhich they meant a wrong or a violation ofrights. Hugo Grotius, for example, notedwith approval that “St.Augustine, in definingthose to be just wars, which are made toavenge injuries, has taken the word avenge ina general sense of removing and preventing,as well as punishing aggressions.”12 Similarly,Emmerich de Vattel claimed that “the foun-dation, or cause of every just war is injury,either already done or threatened. . . . And, inorder to determine what is to be consideredas an injury, we must be acquainted with anation’s rights. . . . Whatever strikes at theserights is an injury, and a just cause of war.”13

But the most explicit of the classical writersis Francisco de Vitoria, who argued that a political leader “cannot have greaterauthority over foreigners than he has over hisown subjects; but he may not draw the swordagainst his own subjects unless they havedone some wrong; therefore he cannot do so against foreigners except in the same

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11 Some people accept that if you reasonably but mis-takenly believe that I am culpably trying to kill you, youmay be morally and legally justified in killing me. Evenif this were so (I think it is not, but I cannot argue forthat here), this would not imply that I would be liableto be killed. I cannot be made liable by your mistake,even if it is a reasonable one. The basis of moral liabil-ity must be some form of responsible action by the per-son who is liable. For discussion, see Jeff McMahan,“The Basis of Moral Liability to Defensive Killing,”Philosophical Issues 15 (2005, forthcoming).12 Grotius, The Rights of War and Peace, p. 76.13 Emmerich de Vattel, The Law of Nations (1758), trans.Joseph Chitty (Philadelphia: Johnson & Co., 1863), p.302.

circumstances. . . . It follows from this thatwe may not use the sword [that is, resort towar] against those who have not harmed us;to kill the innocent is prohibited by naturallaw.”14 It is an implication of this view thatthose who fight by permissible means in ajust cause are innocent and may not permis-sibly be attacked.

To kill the innocent,Vitoria says, is imper-missible. And the innocent are those whohave done no wrong; they are those whohave done nothing to make themselvesmorally liable to be killed. This, as Vitoriarecognizes, supports the view for which Iargued above—that the requirement of dis-crimination cannot be satisfied in theabsence of a just cause. For a war that lacksa just cause is a war fought against those whohave not made themselves liable to attack. Itis a war fought against the innocent. Vitoriatherefore concludes that if a person is cer-tain that a war is unjust, he must not fight init, even if he is commanded to do so by alegitimate authority. For “one may not law-fully kill an innocent man on any authority,and in the case we are speaking of the enemymust be innocent. Therefore it is unlawful tokill them.”15 This view—that only those whofight in an unjust war are liable to attack—isshared by Francisco Suárez, who asserts that“no one may be deprived of his life save forreason of his own guilt”; thus, the innocentinclude all those who “have not shared in thecrime nor in the unjust war.”16

Contemporary just war theorists thinkthat this is a crude mistake. “Innocent,” theypoint out, contrasts in this case with “threat-ening,” not with “guilty” or “culpable.” Any-one who poses a threat is noninnocent, andtherefore soldiers on both sides are nonin-nocent in the sense that is relevant for deter-mining liability to attack.17 This, after all, iswhat gives the distinction between combat-ants and noncombatants its moral signifi-

cance: combatants pose a threat to others;noncombatants do not. Thus, because all

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14 Francisco de Vitoria,“On the Law of War,”in Political Writ-ings, Anthony Pagden and Jeremy Lawrance, eds. (Cam-bridge: Cambridge University Press, 1991), pp. 303–304.15 Ibid., p. 307. Vitoria seems to accept a subjectiveaccount of justification, according to which it is wrongfor a person to fight in a war that he believes to beunjust, even if his belief is mistaken (p. 308). Thisaccount of justification may not be fully subjective,however, because elsewhere Vitoria suggests that onlyreasonable belief is sufficient for justification (p. 306).But this means that he accepts that a person can be jus-tified in fighting in an unjust war, provided that he rea-sonably believes that it is just; and Vitoria suggests thatwhenever there is uncertainty about whether a war isjust, it is reasonable for a citizen to accept the assuranceof his government that it is just (pp. 312–13).16 Francisco Suárez, “On War” (Disputation XIII, DeTriplici Virtute Theologica: Charitate) (c. 1610), in Selec-tions from Three Works, trans. Gladys L. Williams,Ammi Brown, and John Waldron (Oxford: ClarendonPress, 1944), pp. 845–46.17 See, e.g., Thomas Nagel, “War and Massacre,” inCharles R. Beitz, Marshall Cohen, Thomas Scanlon, andA. John Simmons, eds., International Ethics (Princeton:Princeton University Press, 1985), p. 69; Anthony Kenny,The Logic of Deterrence (London: Firethorn Press, 1985),p. 10; and Michael Walzer, Just and Unjust Wars, p. 145.Elizabeth Anscombe, another influential contributor tothe literature on the just war, is inconsistent on thispoint. In her justly celebrated pamphlet opposingOxford’s award of an honorary degree to President Tru-man (on the ground, in effect, that mass murderersought not to be awarded honorary degrees), she wrotethat “‘innocent’ . . . is not a term referring to personalresponsibility at all. It means rather ‘not harming.’ Butthe people fighting are ‘harming,’ so they can beattacked.” (Anscombe, “Mr. Truman’s Degree,” inEthics, Religion, and Politics: Collected PhilosophicalPapers, vol. 3 [Minneapolis: University of MinnesotaPress, 1981], p. 67.) But in a later paper she wrote that“what is required, for the people attacked to be non-innocent in the relevant sense, is that they should them-selves be engaged in an objectively unjust proceedingwhich the attacker has the right to make his concern;or—the commonest case—should be unjustly attack-ing him.” (“War and Murder,” in the same volume, p.53.) In this quotation, “non-innocent” means neither“harming or threatening” nor “guilty,” but “engaged inobjectively wrongful action.” So when she wrote thesecond essay, she had reverted to a position more inkeeping with the older just war tradition but inconsis-tent with the contemporary orthodoxy.

soldiers are noninnocent, even those whohave a just cause are not wronged when theyare killed by those who lack a just cause. Sim-ply to be a soldier is to make oneself liable tobe killed.

But this is an implausible understandingof the basis of liability. If simply posing athreat were a basis of liability to attack, thoseindividuals who engage in justified self-defense would thereby make themselvesliable to preemptive counterattack by thosewho have wrongfully attacked them. Andpolice would not be wronged by being pre-emptively attacked by those whom theywere about to attack in order to preventthem from committing crimes.

Why, then, do most contemporary justwar theorists think that such an account ofliability is appropriate in the case of war? Isuspect that it has to do with their convic-tion that most ordinary soldiers are notcriminals, even if they fight in a war thatlacks a just cause. They believe that it is rea-sonable to absolve ordinary soldiers ofresponsibility for determining whether awar is just or unjust. That responsibility lieswith others. Soldiers may thus see them-selves and their adversaries as engaged in anactivity dictated by goals for which they arenot responsible and over which they have nocontrol. They are bound by a code of honorthat is suited to and distinctive of their roleas warriors, but they are not holy warriorswith a mandate to eradicate evil. They mustnot, for example, take vengeance on prison-ers or seek to punish the vanquished. This isthe only fair way for soldiers to view andtreat other soldiers, given the various pres-sures and constraints under which they allmust act. And, it is often argued, this way ofunderstanding the morality of war alsoworks out far better in practice than a viewthat treats those who fight with a just causeas innocent in the way their civilian popula-

tion is innocent, but treats those who fightwithout a just cause as wrongdoers. Toregard the liability of soldiers as a functionmerely of their role as combatants not onlylimits their liability to matters of jus in bello,and thus rules out the legitimacy of punish-ment merely for fighting on the wrong side,but also has as a corollary the prohibition ofdeliberate attacks on civilians. The separa-tion of jus in bello from the question of justcause thus effectively limits or constrains thesavagery of war.

What this view leaves out, however, is theinsight of the classical jurists—that peopleare treated unjustly if they are deliberatelykilled without having done wrong. The cur-rently orthodox view, which holds that themoral status of soldiers is unaffected bywhether they have a just cause, implies that aperson who takes up arms to defend himselfand others from a threat of unjust aggressionthereby makes himself morally liable to bekilled by the aggressors, who then act per-missibly, and do him no wrong, if they go onto kill him. It is very hard to believe that thiscould be right. Moreover, at least some of thepractical benefits that are attributed to thisorthodox view may be attained just as well byregarding some of those who fight without ajust cause as excused for rather than asmorally justified in fighting.

The contemporary theory of the just warseems, in short, to be less concerned than thetradition it claims to represent with what isjust and unjust in war, and is instead moreconcerned with the consequences of warand the conventions that are useful in con-trolling those consequences.18

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18 For an argument that it is necessary for the law of warto diverge from the underlying, nonconventionalmorality of war, see Jeff McMahan, “The Laws of Warand the Morality of War,” in David Rodin and HenryShue, eds., Just and Unjust Warriors (forthcoming).

A SUBSTANTIVE ACCOUNT OF THEREQUIREMENT OF JUST CAUSE

Thus far I have offered only a formalaccount of the requirement of just cause,claiming that there is a just cause for waronly when those attacked are liable to bewarred upon. A substantive account of justcause has to go further by providing a crite-rion for determining what sorts of actionengender liability to military attack.

The classical jurists to whom I havereferred typically offer a short list of justcauses for war. The jurists tend to agree thatthe just causes for war are basically these:defense against unjust threats; recovery of orindemnity for what has been wrongfullytaken, or compensation for the violation ofrights; and punishment of wrongdoing, notsolely for the purpose of retribution but toprevent or deter further wrongful action bythe culprit or by others.19 These suggestedjust causes for war are all consistent with theinsistence that, for war to be just, thoseattacked must be morally liable to attack.But a unified account of the morality of warought also to explain why certain forms ofaction give rise to liability to attack whileothers do not. In this section I will offer apreliminary sketch of a method for deter-mining whether a certain goal can be a justcause for war.

War involves killing and maiming; or,rather, war that involves killing and maim-ing is what requires a just cause. In principleand even in law, there might be a whollynonviolent war—for example, one declaredby opposing belligerent powers but termi-nated by agreement before their forcesengage. That is not my topic. War, as Iunderstand it here, necessarily involveskilling and maiming, typically on a largescale. A just cause, then, has to be a goal of atype that can justify killing and maiming.

Contrary to what I wrote earlier, this givesconsiderations of scale a role in the conceptof just cause.20 Only aims that are suffi-ciently serious and significant to justifykilling can be just causes. Beyond this, how-ever, considerations of scale are irrelevant tojust cause.

Let us assume that people can makethemselves liable to be killed (for example,in self-defense or as punishment) only byvirtue of seriously wronging or threateningto wrong others. On this assumption, thejust causes for war are limited to the preven-tion or correction of wrongs that are seriousenough to make the perpetrators liable to bekilled or maimed.

If this is right, it does not automaticallygenerate a list of just causes, but it does pro-vide some much-needed guidance in identi-fying what may be a just cause for war. Wecan, in particular, consult our beliefs—which are quite robust and stable—aboutwhich kinds of wrong are sufficiently seriousthat the killing or maiming of the perpetra-tor could be justified if it were necessary toprevent or correct the wrong. Most peopleagree, for example, that one person may per-missibly kill another if that is necessary toprevent the other person from wrongfullykilling, torturing, mutilating, raping, kid-napping, enslaving or, perhaps, imprisoningher. Many people would also accept that itcan be permissible to kill in defense againstunjust and permanent expulsion from one’shome or homeland, and even, perhaps, indefense against theft—though here ques-tions of scale are obviously relevant to pro-

just cause for war 11

19 See, e.g., Grotius, The Rights of War and Peace, pp.75–76; Vitoria,“On the Law of War,” pp. 302–306; Vattel,The Law of Nations, pp. 301–14; and Samuel Pufendorf,De Jure Naturae et Gentium, Libri Octo (Oxford:Clarendon Press, 1934), p. 1294.20 I am grateful to Rachel Cohon for calling this to myattention.

portionality. It is only when theft wouldthreaten extreme and protracted deprivationthat killing could be a proportionate meansof defense. Perhaps what we should say is notthat it can be permissible to kill to preventtheft, but that it can be permissible to kill toprevent any sort of act that would wrongfullyreduce a person to utter destitution.

If each of these types of wrong is suchthat its prevention—or, when possible, itscorrection—can justify killing, then its pre-vention or correction can also be a justcause for war. There are, of course, com-plexities and complications involved inextrapolating from the individual to thecollective level. Except for heuristic pur-poses, we cannot rely on what Walzer callsthe “domestic analogy,” applying the princi-ples that govern relations between individ-uals to relations between collectives, as ifcollectives were individuals. For a collectiveis not an individual: it does not have a sin-gle will, a single set of desires, or a unitarygood. Extrapolation has to proceed by com-position rather than by analogy, but eventhe most reductive form of individualismmust take account of distinctively collectivegoods, such as collective self-identificationor collective self-determination, and thusrecognize that there may be wrongs that arenot entirely reducible to wrongs againstindividuals because they have a collective astheir subject. I cannot pursue these compli-cations here.

Instead, I will explore in the followingsection a few of the implications of the viewI have sketched.

JUST AND UNJUST CAUSES

Recovery of Goods Lost to Prior AggressionIn morality, if not in law, just cause is notlimited to self-defense against armed aggres-sion. It is, for example, possible for an offen-

sive war to be just. This is clearest in cases inwhich defense against wrongful aggressionfails and the aggressor achieves its aim—forexample, by seizing and occupying territory,or by imposing an alien or collaborationistgovernment that will do its bidding. In suchcases it would be absurd to suppose that thevictims lose their rights when they lose theirwar of defense. If it later becomes possiblefor them (or third parties acting on theirbehalf) to reassert through armed rebellionthe rights that were violated by the earlieraggression, and thereby to recover the terri-tory or political independence of which theywere unjustly deprived, they will not wrongthe aggressor if they do so. Successfulaggressors remain liable to attack as long asthey retain the spoils of their wrongfulaggression. (Recall that just cause is not thesole condition of a just war. War must alsobe, among other things, necessary. Unjustoccupation or political subordination mayoften be more effectively defeated, and withfar fewer casualties, by means of nonviolentresistance, particularly when the occupier isa democratic society with a free press—as,for example, Israel is.21)

There is, however, a moral statute of lim-itations here, particularly with respect toterritorial rights. If, following an unjustseizure of territory, enough time passes for anew society with its own infrastructure toarise within the territory, the members ofthat society may acquire an increasinglystrong moral claim to stay, particularly as

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21 I believe, though this cannot be proven, that if thePalestinians had produced a leader like Gandhi ratherthan Arafat, they could have had their own state decadesago and could now be free and prosperous, and thatthis, by removing one potent source of grievance andhumiliation among Arabs and Muslims, could in turnhave helped forestall some of the worst instances ofrecent terrorism. Palestinian terrorism has, in short,been not only morally shameful but also self-defeating.

new generations who are entirely innocentof the initial aggression establish their ownlives there. This is why Israeli settlementsoutside the borders Israel was assigned bythe UN are properly regarded as instru-ments of insidious territorial aggression.The longer the settlers stay, the more theybuild, and the more children they have, thestronger their moral claim to the landbecomes. Consequently, Israelis who moveto the settlements voluntarily are morallyresponsible participants in unjust aggres-sion, and as such are morally liable to defen-sive attack—though their young childrenare not. Even when they do not themselvesbear arms, which they usually do, their pres-ence in the occupied territories is possibleonly because of a background threat of mil-itary protection. There is, therefore, a casefor regarding them as having combatant sta-tus and thus as being liable, even accordingto the orthodox theory of the just war. Ifthere are those who refuse to bear arms, theyare morally like civilians who make them-selves liable by voluntarily acting as shieldsfor combatants engaged in territorialaggression, and who thereby facilitateaggression by forcing the other side to haveto kill civilians in order to resist.

Humanitarian InterventionGovernments sometimes gravely wrongtheir own citizens, particularly members ofethnic or other minorities or political dissi-dents. These wrongs may make their perpe-trators liable to attack for purposes ofdefense or correction. Just as resistance tothese wrongs may in rare instances lead tojustified civil war by the victims against theperpetrators, so military intervention bythird parties may also be justified on behalfof the victims. There are, of course, variousconditions that must be met if humanitar-ian intervention is to be permissible. It must,

for example, either be requested, or theremust at least be compelling evidence thatthe intended beneficiaries would welcomerather than oppose intervention by the par-ticular intervening agent or agents. (Onereason why the American invasion of Iraq in2003 was not a justifiable instance ofhumanitarian intervention is that there wasno evidence that ordinary Iraqis wanted tobe freed from the Ba’athist dictatorship bythe United States—a country that a littlemore than a decade earlier, and under theleadership of the current president’s father,had bombed their capital, decimated theircivilian infrastructure, and successfullypressed for the institution and perpetuationof sanctions that subsequently resulted inmany thousands of deaths among civilians.)

Many people have thought that consider-ations of national self-determination mili-tate against humanitarian intervention.This objection is often specious, however,when the intervention is desired by the vic-tims of governmental persecution. For insuch cases the gulf between victims and per-petrators is typically so wide that there is nolonger (if there ever was) a single collective“self ” whose autonomy is threatened, butrather two or more distinct collective selves,one of which is engaged in wrongful actionthat is not protected by its right of self-determination.22 There are various otherobjections to humanitarian intervention,but the most serious are of a pragmaticnature, having to do with such considera-tions as the likelihood of self-interestedabuse of any norm recognizing the legiti-macy of war for altruistic reasons. But nosuch objections show that certain aims of

just cause for war 13

22 For detailed discussion, see Jeff McMahan, “Inter-vention and Collective Self-Determination,” Ethics �International Affairs 10 (1996), pp. 1–24.

humanitarian intervention cannot be justcauses for war.

The Prevention of Future Aggression It is highly contentious whether the preven-tion of future aggression can be a just causefor war. By prevention of future aggression Imean action taken to address a threat ofunjust attack that is neither in progress norimminent, but temporally more remote.Whether this can be a just cause for war isobviously central to the issue of the legiti-macy of preventive war.

Many theorists of the just war accept thatthe prevention of future aggression can be alegitimate aim of war once war is already inprogress. Samuel Pufendorf, for example,writes: “It is permitted to apply force againstan enemy not only to the point where I haverepelled the danger which he threatensagainst me, or where I have recovered orwrested from him that which he has unjustlyseized from or refused to furnish me; but Ican also proceed against him in order toobtain a guarantee for the future. So long asthe other allows this to be wrested from himthrough force, he gives sufficient indicationthat he still intends to injure me even there-after.”23 Similarly, Vattel acknowledges thatprevention through forcible disarmamentcan be permissible once aggression hasoccurred. But he insists on a prior injury as acondition of legitimacy: “For an injury givesus a right to provide for our future safety, bydepriving the unjust aggressor of the meansof injuring us.”24 Here Vattel echoes his pred-ecessor, Vitoria, who, as I noted above in thediscussion of moral liability to attack,asserted that violence may be done only tothose who have “done some wrong.” If, asthese writers claim, the prevention of futureaggression can be a legitimate aim of waronce war is already in progress, that implies,on the understanding of just cause for which

I have argued, that it can be a just cause forwar. For a just cause is any aim that may legit-imately be pursued by means of war; it mayjustify only a phase of a war or even just a sin-gle act of war without justifying the resort towar or the war as a whole.

I once thought, as these classical writersimply, the prevention of future aggressioncould not on its own be a just cause for war.In a paper drafted during the Gulf War of1990–91, Robert McKim and I drew a dis-tinction between an independent just cause,which could justify war or the resort to waron its own, and a conditional just cause,which could contribute to the justificationfor war, but only when triggered or activatedby the presence of an independent justcause.25 I thought at the time that the pre-vention of future aggression could be only aconditional just cause—that is, that it couldlegitimately be pursued only when war wasalready justified by reference to an inde-pendent just cause arising from a wrong thathad been done, was being done, or was onthe verge of being done. I thought that onlyan act that made a country liable to attackfor some reason other than preventioncould also make it liable to preventive attack.I now think that this view is mistaken.

It is true that when the prevention offuture aggression is a just cause for war, it isin most cases because a country is alreadycommitting a wrong—for example, isengaged in an act of unjust aggression—thatmakes it simultaneously liable to both

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23 Craig L. Carr, ed., The Political Writings of SamuelPufendorf, trans. Michael Seidler (New York: OxfordUniversity Press, 1994), p. 259.24 Vattel, The Law of Nations, p. 310.25 McMahan and McKim, “The Just War and the GulfWar,” pp. 502–506. In this article we used the terms “suf-ficient just aim”and “contributing just aim,”rather thanthe more perspicuous terms “independent just cause”and “conditional just cause.”

defensive and preventive attack. In thesecases, a single wrongful act makes theoffending country liable to attack for morethan one reason. But all that is necessary forprevention of future aggression to be a justcause is that a country should have donesomething to make itself liable to beattacked as a means of preventing it fromcommitting a wrong in the future. And thekind of action that engenders this form ofliability need not engender liability to attackfor any other reason. In other words, theprevention of future aggression may, insome cases, be the sole just cause for war. Inthese cases, the country that is liable to pre-ventive attack may be guilty of no wrongother than the kind recognized in the area ofcriminal law concerned with conspiracy: thekind of wrong that involves collaboratorsmanifestly intending and actively preparingto commit a crime. In order for this kind ofactivity to constitute a just cause for war, theintended wrong must be grave enough thatits prevention could justify killing andmaiming.26

Just War as One Type of Morally Justified WarConsider now a different kind of case. Sup-pose that country A is about to be unjustlyinvaded by a ruthless and more powerfulcountry, B. A’s only hope of successfuldefense is to station forces in the territory ofa smaller, weaker, neighboring country, C, inorder to be able to attack B’s forces from pre-pared positions as they approach A along theborder between B and C. A’s governmentrequests permission from the governmentof C to deploy its forces on C’s territory forthis purpose, but C’s government, foreseeingthat allowing A to use its territory in this waywould result in considerable destruction,denies the request. Suppose that C is withinits rights to deny A the use of its territory but

that, all things considered, it is nonethelessjustifiable for A to avoid an otherwiseinevitable defeat at the hands of B by goingto war against C in order to be able to deploytroops there, provided that it will withdrawimmediately after fighting off the invadingforces from A. (One historical case thatapproximates this scenario is Russia’s waragainst Finland in 1939–40. The Russiangovernment believed that control of Finnishterritory within artillery range of Leningradwas necessary to protect the city from Nazibombardment. It offered the Finns anexchange of territory, but the offer wasrefused, and the Russians then went to warto capture the territory they thought wasnecessary as a buffer against the Nazis. Onereason this is only an approximation of myhypothetical example is that the Finns hadgood reason not to trust Stalin’s assurancesthat Russia’s aims were limited, since, amongother things, Russia had only a short timeearlier collaborated with the Germans incarving up Poland.)

Given that C is not morally required tosacrifice its territory for the sake of A, itseems that C does nothing to make itselfliable to attack by A. On the account I haveoffered, therefore, A does not have a justcause for war against C. Yet if A is neverthe-less morally justified in going to war againstC, it must be possible for there to be warsthat are morally justified yet unjust. A war isjust when there is a just cause and all otherrelevant conditions of justification are also

just cause for war 15

26 For a more detailed discussion of these issues, see JeffMcMahan,“Preventive War and the Killing of the Inno-cent,” in David Rodin and Richard Sorabji, eds., TheEthics of War: Shared Problems in Different Traditions(Aldershot, U.K.: Ashgate, 2005), pp. 169–90. See alsoAllen Buchanan and Robert O. Keohane, “Governingthe Preventive Use of Force: A Cosmopolitan Institu-tional Proposal,” Ethics � International Affairs 18, no. 1(2004), pp. 1–22.

satisfied. But, while all just wars are morallyjustified, it seems that not all morally justi-fied wars are just wars. As the example of A,B, and C suggests, there seem to be wars thatare morally justified despite their requiringthe targeting of those who are innocent inthe relevant sense, so that at least some nec-essary phases of the war, and perhaps indeedall of its phases, lack a just cause. The formof justification in these latter cases is famil-iar: in rare circumstances, considerations ofconsequences override constraints on actionthat would otherwise be decisive. It is com-monly recognized, for example, that it can inprinciple be permissible intentionally toharm or kill an innocent person if that isnecessary to avert some great disaster. Thenecessity of preventing the disaster out-weighs the grave injustice done to the indi-vidual victim.

If war may be justified in the absence of ajust cause, one may wonder how significantthe notion of just cause can be.27 The answeris that the presence or absence of a just causehas a dramatic effect on the stringency of theproportionality requirement. When there isno just cause, all those who are targeted inwar are innocent. And harms inflicted onthe innocent weigh more heavily against thegoals of a war than harms inflicted on thosewho are liable. The burden of justification istherefore very substantially greater in theabsence of a just cause.

DeterrenceDeterrence is problematic as a just cause forthe same reason it is problematic as the soleaim of punishment. In both cases it seemsobjectionable because it uses the harming ofsome as a means of influencing the action ofothers. So, for example, even if a govern-ment’s systematic violations of the humanrights of some of its citizens are sufficient tomake it liable to attack for the purpose of

stopping the violations, they do not obvi-ously make that government liable to fur-ther or harsher attacks intended to warnother governments of the penalties for vio-lating human rights. And certainly the vio-lation of its citizens’ human rights cannotmake a government liable to attack as a showof force intended to deter other countriesfrom engaging in the different crime ofaggression.

Yet deterrence of others can be a just causeand thus contribute to the justification forwar if the wrong committed by the countrythat is attacked would itself otherwiseincrease the probability that other countrieswould commit wrongs of a sort that wouldconstitute a just cause for war. For in that casethe country’s wrongful action would make itto some degree responsible for the increasedrisk of further wrongful action by others.That responsibility makes it liable to belliger-ent action necessary to deter the wrongs thatits own action had made more likely. Sup-pose, to take a historical example, thatArgentina’s seizure of the Falkland Islands, ifunopposed, would have emboldened othercountries wrongfully to seize by force certainterritories to which they believed they had ahistorical claim. In that case, the aim ofrestoring the deterrence of such ambitions toprevious levels could have contributed to thejustification for Britain’s going to war and forits action during the war.

Although deterrence may thus be a justcause, it is, unlike the prevention of futureaggression, unlikely ever to be the sole justcause for war. For any action that is suffi-cient to make a country liable to be used asa means of deterring others will almost nec-essarily be the sort of action that gives rise toanother just cause as well. For example, it

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27 Thanks to Jon Mandle for pressing me on this point.

seems that a country can make itself liable toattack as a means of deterring others fromengaging in aggression only by itself engag-ing in aggression, in which case defenseagainst that aggression will also be a justcause. And the same seems true for otherwrongs that may make a country liable to beattacked for the purpose of deterrence.

DemocratizationThe Bush administration has contendedthat war can be justified as a means of bring-ing democracy to people who lack it—thatis, that democratization can be a just cause.But one does not even need a substantiveaccount of just cause to rule this out; it isruled out by the formal claim that just causeis always correlated with liability to attackon the part of those targeted for attack. Forpeople cannot be liable to killing and maim-ing simply for failing to organize their inter-nal affairs in a democratic manner, even ifdemocracy would be better for them and fortheir relations with others.

There might be a just cause for war if apeople were being forcibly prevented by atyrannical government from organizingthemselves democratically, for then the gov-ernment itself might be liable to attack forwronging its citizens. A war to stop the sup-pression of a people’s democratic aspira-tions would not be a war for the promotionof democracy, but would instead comewithin the category of humanitarian inter-vention, as its fundamental aim would be tostop a government from violating the rightsof its citizens.

This admittedly presupposes a concep-tion of humanitarian intervention that israther more expansive than the prevailingconception. If the concept of humanitarianintervention is insufficiently elastic toinclude interventions that are necessary todefend the right of a people to democratic

self-government from suppression by atyrannical regime, this suggests the need fora further category of intervention—namely,intervention that is necessary for the defenseof the rights of a people against violation byothers within their own state, particularly bytheir own government. But note that whatis really at issue here is not the concept ofhumanitarian intervention or the right todemocracy, but the permissibility of mili-tary intervention to defend a people’s rightto collective self-determination. Such inter-vention might be justified even if what peo-ple want is not democracy but rule by whatthey perceive to be the law of god, while theirgovernment insists on subjecting them tosome different form of rule instead. Oneimportant question here is whether inter-ventionary war could be justified even whena people’s aspirations for self-determinationwere being suppressed not by force butmerely by a threat of force. If what I haveclaimed earlier is right, the way to thinkabout this is to ask whether those who areresponsible for the suppression therebymake themselves liable to be killed if that isnecessary in order to end it. A useful test isto consider whether the people whose rightsare being violated would be justified inresorting to armed rebellion in defense ofthose rights. If they would be, that suggeststhat external military intervention on theirbehalf would be justified as well, otherthings being equal.

JUST CAUSE ANDPROPORTIONALITY

I claimed in the earlier section on the moralpriority of just cause that only the achieve-ment of aims that are specified by a justcause can contribute to the satisfaction ofthe ad bellum proportionality requirement.No other goods that might be realized by

just cause for war 17

war may weigh against the bad effects thatwould be attributable to the war in deter-mining whether war would be proportion-ate. In light of the formal and substantiveelements of the account of just cause I havesketched, it may now be clearer why this isso. A just cause is necessarily connected withmoral liability to attack on the part of thosetargeted for attack. The basis for liability ismoral responsibility for a wrong that bel-ligerent action would either prevent orsomehow rectify. The substantive compo-nent of the account specifies the types ofwrong that may permissibly be prevented orcorrected by means of war—namely, wrongsthat are sufficiently serious to make thoseresponsible for them liable to be killed ormaimed, if necessary, in order to prevent orcorrect them.

To see that only the prevention or cor-rection of wrongs can weigh against theevils of war in the proportionality calcu-lation, consider what would follow ifother desirable goals were allowed tocount as well. I am assuming that peoplecan become morally liable to be killed ormaimed only by virtue of action (which Itake to include knowingly allowing thingsto happen) that wrongs or threatens towrong others. If that is right and weassume that desirable goals unconnectedwith the prevention or correction ofwrongs can count in the proportionalitycalculation, it follows that the achieve-ment of these goals could justify (or con-tribute to the justification for)deliberately killing or maiming innocent(that is, nonliable) people. Although Ihave conceded that this may be true inextreme cases in which the alternative tokilling the innocent would be a catastro-phe involving substantially greater harmto the innocent, I have also claimed that awar fought in this way would not be a just war.

It seems, therefore, that the only goodsthat can count in the ad bellum propor-tionality calculation involve the preventionor correction of wrongs for which thosewarred against are responsible (for again itwould be obviously unjust to prevent orcorrect a wrong by going to war againstpeople not responsible for that wrong). If,moreover, war could be expected to preventor correct wrongs that are insufficientlyserious to make those responsible for themliable to killing or maiming, it seems thatthose good effects must also be excludedfrom the proportionality calculation. Oneargument for this claim invites us to sup-pose, to the contrary, that good effects ofthis sort—that is, the prevention or correc-tion of wrongs that do not rise to the levelof just cause for war—could figure in theproportionality calculation and thus con-tribute to the justification for the war. Sup-pose, for example, that the prevention oralleviation of certain forms of religiousoppression, such as coercing women towear veils, cannot be a just cause for war.Yet suppose there is a just cause for waragainst a certain country, and that going towar against that country could be expectedalso to mitigate the harshness of the reli-gious oppression that many of its citizenssuffer. It may seem that the expectation ofalleviating religious oppression could con-tribute to the justification for war byweighing against the bad effects in the pro-portionality calculation, at least if thosewarred against were responsible for theoppression. But this seems to imply that thepursuit of an end that is insufficient to jus-tify killing and maiming—namely, alleviat-ing religious oppression— can contributeto the justification for an activity—war—that necessarily involves killing and maim-ing. And that makes no sense. It seems,therefore, that the only ends that can weigh

18 Jeff McMahan

against the bad effects of war in the propor-tionality calculation are those specified bythe just cause or causes for war.

There is, however, a forceful challenge tothis argument. Not all of the bad effects ofwar involve killing or maiming. There aremany lesser types of bad effect. Even if therelief or mitigation of minor religiousoppression cannot justify killing or maim-ing, perhaps it can weigh against, and there-fore justify, the infliction of some of thelesser bad effects of war. If that is so, per-haps certain expected good effects that donot rise to the level of just cause can countin the proportionality calculation, providedthat they are weighed only against lesserexpected harms and not against theinevitable killing and maiming. Only thosegoods specified by a just cause can beweighed against the killing and maiming.

If good effects beneath the threshold ofjust cause can weigh only against the lesserbad effects of war, it follows that in certaincases some such effects cannot count at all.If, for example, a war would have twice asmany good effects beneath the level of justcause as it would have lesser bad effects, halfthe good effects would count in cancelingout the bad, but the other half would haveno justificatory role at all.

This understanding of the proportional-ity calculation may, however, require com-parisons of expected effects that are toofine-grained to be possible. It seems unreal-istic to suppose that we could separate boththe good and bad expected effects of warinto two categories and compare theexpected effects in one category only withthe expected effects in the correspondingcategory. So assuming that this challenge tothe claim that only goods specified by a justcause can count in the proportionality cal-culation is correct, its practical significancemay be negligible.

CAN MORE THAN ONEBELLIGERENT HAVE A JUST CAUSE?

I noted in the introduction that the receivedview in international law and contemporaryjust war theory is that the only just cause forwar is defense against aggression. This ispleasing to orthodox theorists because itcoheres well with the traditional view that atmost one side in a war can have a justcause.28 But if, as I have argued, there aremore just causes than defense againstaggression, and if, as seems obvious, a coun-try can pursue both just and unjust causes inthe same war, then it is clearly possible forboth sides in a war to have a just cause.

Here is what I take to be a clear case inwhich two opposing belligerents both have ajust cause. A and B both plot to conquer ter-ritory belonging to the other. A seizes a pieceof B’s territory and B seizes a piece of A’s ter-ritory—not as a reprisal but in accordancewith plans formulated in advance. Both arepursuing unjust causes, but each side’sunjust cause gives the other a just cause:namely, self-defense or the recovery of cap-tured territory. But neither is simultane-ously fighting two wars, one of aggressionand another of defense; rather, each is fight-ing one war on two fronts. Each has the aimof defeating the other militarily, thereby

just cause for war 19

28 In answering the question “whether war can be juston both sides,” Vitoria writes that “except in ignorance,it is clear that this cannot happen.” The exception hemakes for ignorance is a mistake. After correctly notingthat “invincible error is a valid excuse,” he then con-cludes that those who fight in good faith, erroneouslybelieving their cause to be just, are justified in fighting.But excuse excludes rather than entails justification.(Vitoria, “On the Law of War,” pp. 312–13.) Vattel tooasserts that “war cannot be just on both sides,” but says,more plausibly, of a party fighting an unjust war, that “ifhe acts in consequence of invincible ignorance or error,the injustice of his arms is not imputable to him.” (Vat-tel, The Law of Nations, p. 306.)

enabling itself to reclaim its own territory,but also to annex the coveted part of theother’s territory.

This kind of example forces us to recon-sider what might be meant by the assertionthat a war as a whole is either just orunjust. For what this case shows is that atleast in some instances a war may have ele-ments or phases that are just even thoughother elements or phases are unjust. It isnot clear how these can be aggregated toyield an overall judgment of a war as awhole. One coherent question is, of course,whether the war is such that it is better thatit be fought than not. But that question,even if we take account of considerationsof justice in answering it, is not equivalentto the question of whether the war as awhole is just.

“COMPARATIVE JUSTICE”

The idea that both sides in a war may simul-taneously or sequentially pursue both justand unjust causes is different from the viewof the U.S. Catholic Bishops that both oppo-nents in a war may have some degree of jus-tice on their side, and that just cause istherefore a matter of “comparative” ratherthan absolute justice. On their view, justcause is a matter of “the comparative justiceof the positions of the respective adversariesor enemies. In essence: Which side is suffi-ciently ‘right’ in a dispute. . . ?”29 A similarthough more carefully worked out view isadvanced by A. J. Coates. He argues thatboth sides can have just cause (what he calls“bilateral justice”), though it may be thatonly one is justified in fighting. “Thoughnever absolute or unilateral, there may besuch a preponderance of justice on one sideand injustice on the other as to constitutejust cause, and even sufficient perhaps tojustify recourse to war.”30

But the plausible idea that neither sidemay be absolutely right and the otherabsolutely wrong—the idea that both sidesmay have legitimate claims and griev-ances—does not belong in our conceptionof just cause. Certainly both sides in a warmay have legitimate complaints and griev-ances. But to suppose that just cause is com-pounded out of all these elements is topresuppose an overly broad conception ofjust cause.

Compare individual self-defense. Prior toa conflict, both parties may have legitimategrievances or claims and each may be guiltyof wrongful provocations. But this is com-patible with one having a right of self-defense and the other having no right at allin the conflict—for example, if one partyunjustifiably succumbs to provocation andattacks the other as a means of resolvingtheir disputes. It is the single act of aggres-sion that makes the aggressor liable andgives the defender a right of self-defense.The same may be true in war.

THE PLURALITY OF CAUSES ANDTHE MORAL STATUS OFCOMBATANTS

There are many cases in which one side in awar has no just cause at all. All of its waraims are unjust. There are also cases inwhich one side in a war has one or more justcauses but still ought not to be fighting atall—for example, because its war is dispro-portionate, or because it is simultaneouslypursuing a larger unjust cause that all its actsof war tend to advance. It is also possible thata country may have a just cause or set of just

20 Jeff McMahan

29 The Pastoral Letter of the U.S. Catholic Bishops, TheChallenge of Peace (London: CTS/SPCK, 1983), p. 27.30 A. J. Coates, The Ethics of War (Manchester, U.K.:Manchester University Press, 1997), p. 151.

causes sufficient to justify its being at war,but that this country also and simultane-ously pursues other aims—either aims thatare laudable but inappropriate for pursuit bymeans of war or aims that are positivelyunjust. These cases, which may even consti-tute the great majority of cases in which wehave been inclined to judge that a war wasjust overall, pose a number of problems. Iwill close by mentioning just one of theproblems that I think is particularly impor-tant. Recall that I argued earlier that a sol-dier’s moral status and what he maypermissibly do—his immunities andrights—both depend on whether he has ajust cause. The problem is that one and thesame soldier may at one time act to serve ajust cause but at another act to serve anunjust cause, and may not himself evenknow which is which. Or it may well be thata single act by this one soldier will serve botha just and an unjust cause.

In these cases, what is that soldier’s status?Is he liable to attack when his action serves anunjust cause but not when it advances a justcause? And what presumptions are soldierson the other side entitled to act on, given thatin practice they cannot have knowledgeabout whether a particular adversary’s actionsupports a just or unjust cause? Matterswould be clearer if we could assume that all

soldiers on one side have a just cause while allthose on the other side do not.

One thing we can say is that those whofight in a war that is unjust overall might bemorally liable to attack even at a time whenthey are pursuing a just cause, because theywill soon revert to the pursuit of the largerunjust cause or causes that give the war itsoverall status as unjust. When they are pur-suing a just cause they are nevertheless at thetime engaged in fighting an unjust war—justas they are while they are asleep.

There is a great deal more to be said aboutthis vexed set of issues, but here is not the placeto try to say it. I hope, however, to haveadvanced and defended a conception of justcause for war that ties it closely to an adver-sary’s liability to attack as a result of a wrongfor which that adversary is or, in the absence ofdefensive action, would be responsible. I havetried to show that this conception, which hasdeep roots in the work of classical theorists inthe just war tradition but is in many ways anti-thetical to contemporary just war theory, hasradical implications for our thinking about themorality of war. I hope to explore these impli-cations further in future work.31

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31 Most comprehensively in a book called The Ethics ofKilling: Self-Defense, War, and Punishment (New York:Oxford University Press, forthcoming).