International Symposium for Military Ethics 2009

Paper Submission


Grotius’s Two Models of Justice in War


Please do not cite or quote


Pablo Kalmanovitz

PhD Candidate, Political Science

Columbia University

Phone: 347 523 1037


Deep tensions between morality and legality in the theories of just war have been with us since the early times of modern just war thinking. These tensions are, in a sense, Grotius’s legacy. Prior to Grotius, it was mainly the scholastic defenders of natural law who undertook normative work on war, and for them conflicts between positive law and morality, if they appeared at all, were resolved in favor of the latter. Some of Grotius’s fundamental and novel ideas, in particular the idea that rulers’ consent was decisive in determining the content of the law of nations, did not fit well into the scholastic rationalistic and hierarchical model of law and political order. But even though Grotius defended novel and indeed revolutionary ideas about international law and war, he also endorsed the very influential ideas about just war that he inherited from the scholastics. I submit that this dual stance led Grotius to produce two different normative models of war, the first, which I will call the just war model (for short: “just model”), derives criteria of justice from natural law; the other, which I will call the regular war model (for short: “regular model”), obtains criteria of lawfulness from the law of nations.[1] In this paper I want to look closely at these models and their tensions, and discuss some of their consequences. As I hope my discussion will show, some of these tensions appear in contemporary discussions of war and justice.

            The paper is organized as follows. Outlines of the just and regular models appear in Sections 1 and 2 respectively. To anticipate my outline, according to the just model a violation of some particular right is the only justification to wage war, and the aim of the war is to make good for that violation; in just wars the status of a war is established on the basis of ex ante substantive justice, and the belligerent parties are asymmetrically placed: one is in the right, the other in the wrong. The regular model, in contrast, makes due form and not substance the central criterion when it comes to establishing the status of a war: wars duly declared and duly fought are lawful; the belligerent sides are placed symmetrically, their status as lawful combatants being independent from the justice of their cause; here the question whether the cause of the war is substantively just is bracketed and replaced by purely formal ––and more easily established–– criteria. Section 3 will examine the tensions between the two models; most obviously, tensions between the models arise because both justice and lawfulness are held as morally positive statuses, and yet in some cases a lawful war may be unjust, or a just war unlawful. My particular focus will be on arguments that show the superiority of the regular model over the just model.


1.       The just war model

Historians of ideas have often pointed out to Grotius’s large debt to the so-called second scholastic.[2] This debt is clear indeed in the case of the just model, although, as we shall see, things stand quite differently regarding the regular model. In the following presentation of the just model I will rely on this hisotriographic observation and bring in elements from Vitoria’s and Suarez’s writings on war. I will bracket the differences between Grotius, Suarez and Vitoria, significant and important as they may be, so that we can have Vitoria and Suarez’s singular clarity when presenting the basic structure of the just model.

            The central feature of the just model is that it conceives war first and foremost as a judicial action, not as a political act.[3] At the root of a just war there must be a violation of some right, and from this violation the just cause for war arises: wars may be fought either defensively against an impending or ongoing violation, or “offensively”, in order to exact reparations for a violation suffered and/or to inflict punishment to the violators (RWP, II.1.ii). It follows that preventive wars, or wars for the sake of a balance of power, are ruled out by the just model (RWP, II.1.xvii; II.22.v). Sovereign commonwealths are by default the standard war wagers, but under some circumstances public authorities lesser than a sovereign ruler and private persons are authorized to declare and fight wars. Thus, all persons have a natural right to fight defensive wars for the sake of life and property, but in so doing they must abide by criteria of necessity and moderation. Defensive wars are necessary in the sense that they must take place in reaction to an ongoing violation or an imminent and certain danger, which make appeals to a superior authority impossible. The reaction to the danger must be made “in the heat of the moment” (Vitoria, OLW 1.2, §5; Grotius, RWP II.1.xvi) and the proper response to aggression is strictly limited by the immediacy of the threat or injury, and so has to be “waged with a moderation of defense that is blameless” (Suarez, OW i.6). Defensive wars include no authorization to punish or seize back property, for that can be done properly only through appeal to a legitimate judicial authority.

            Offensive wars involve powers and authorizations wider than those of defensive wars, and are generally the privilege of the heads of legitimately constituted sovereign commonwealths.[4] Given the just model’s emphasis on judicial action, it is not surprising that offensive, not defensive, wars are its paradigmatic case. The following passage from Suarez lays out concisely the model’s basic architecture:

Just as within a commonwealth some legitimate power to punish crimes is necessary to the preservation of domestic peace; so in the world, in order that diverse commonwealths may dwell in peace, there must exist some power for punishing injuries inflicted by one upon another. Such a power is not to be found in any superior, for we assume that these commonwealths have no commonly acknowledged superior; therefore, the power in question must reside in the supreme prince of the injured commonwealth, to whom, by reason of that injury, the opposing prince is made subject. Consequently, war of this kind [offensive wars] has been instituted in place of a tribunal administering just punishment. (OW iv.5)


So in the case of offensive wars it is not necessary that an imminent and present danger exist. Wars may be fought in response to violations made in a distant past and the purpose of the war is to rectify them. A violation of right triggers the injured ruler’s jurisdiction over the injuring party, and just as the domestic judicial system aims at public order and the enforcement of rights, so offensive war-making powers aim at a rightful international peace. Although in a limited sense functionally similar to civil lawsuits, in the just model the injured sovereign acts as party, judge and executioner of its own (alleged) rights, which makes the just model structurally unstable.

            There are two important features of the just model that I would like to discuss. The first is its emphasis on substantive rights, which stand at the center of its doctrine of just causes of war, and the second is the asymmetric status it confers on belligerent parties.

            In the just model, the set of rights whose violation could justify a war is in principle open-ended, although limits are imposed by ad bellum criteria such as proportionality (a minor injury does not merit war), necessity (war is the only way to prevent or remedy the violation) and last resort (all alternatives have been exhausted).[5] Above these second-order criteria, the crucial question is really for which rights precisely would a violation justify war.[6] Behind this question lies a profound challenge for the just model, for the model assumes the existence of an agreed-upon basis of substantive rights, while, in practice, disagreements among publicists regarding legal sources, specific rights, and procedural rules were far from rare even during Grotius’s times.[7]

            One may say plausibly that within the set of relevant rights the just model has an undisputed core and a periphery of more contentious rights (and, it should be noted, contentions over rights were often resolved through war). Indeed, some of the rights proposed by Grotius had a strong backing consensus, and eventually became part of the contemporary positive doctrine of human rights. Thus, war may be fought in defense of the rights to life and to bodily integrity (see e.g. RWP, II.1.iii), and also in defense of the right to property and dominium (i.e. territorial integrity, RWP, II.1.xi). On the latter, Vitoria made a crucial contribution in his lecture on the American Indians, where he argued that, tied to the right to political sovereignty or dominion, there is also a right to remedies in cases of wrongful takings, which involves both punishment and compensation. Rights originating in an assumed “natural partnership” of human beings, which are less familiar in contemporary discourses of human rights, arguably belong also in the core. To this class belongs the right to move freely on earth (ius peregrinandi) and to enter relationships, in particular commercial relations, with other human beings (Vitoria, OAI 3.1; Suarez, OW v.2). One may include here also the right to defend the innocent, for example those under subjection of a tyrant (Suarez OW v.2; Grotius, RWP II.20.xl), which is an early version of something like a right of humanitarian intervention.

            The periphery of contention shows clearly how the role of substantive rights in the just model makes its practice highly demanding institutionally. If wars are fought in pursuit of certain rights, then clearly those rights need to be stipulated as clearly and exhaustively as possible, which means that some form of legislative organ is presupposed or required by the model. At Grotius’s time, the grip of natural law ––and the widespread “seriousness of religious convictions”[8]–– was perhaps strong enough to support a belief that the light of reason would be sufficient to produce a consensus over the catalogue of rights. Nonetheless, a cursory look at some of the rights defended by different theorists of the time shows that particular political agendas drove to an important extent the arguments made; controversies and disagreements are proof that religious faith and the light of reason were not reliable enough to guide armies disinterestedly. Vitoria, for example, defended a right to appropriate things that had not been appropriated before and which, he held, belong in common to mankind, for example “gold in the ground or pearls in the sea.” This right was supposed to make war permissible in response to denials of access to unexploited mines or to pearl banks (OAI, 3.1, p. 280). Vitoria was of course considering the question whether the Spanish exploitation of minerals in the Americas was justified, and responding affirmatively, but it did not take long for a rebuttal to appear (could then French miners be sent to Spain to exploit their unproductive mines?)[9]

            As dissenting voices of the time such as Alberico Gentili’s forcefully pointed out, the catalogue of rights at the basis of the just model was itself a matter of dispute, and hence making it hold the main weight of the model was an unhappy move. Moreover, some disputes over rights were in effect resolved by recourse to war (rights of monopolistic commerce, for example), and so in these cases the outcome of the war seemed to dictate in practice the justice of its cause, which is about the inverse situation to what the just model proposed. As we shall see, a considerable advantage of the regular model over the just model is that, by giving up the pivotal role of violations of substantive rights, it sidesteps upfront these questions of legislation and adjudication.

            The second important feature of the just model is that, by giving injuries a pivotal role, it confers asymmetrical status to the warring parties, and in so doing gives derivate status to, and tends to undermine the effect of, jus in bello considerations. Grotius held that the injuring side in a war had no right to defense when he is attacked in a just war; just as domestically a criminal may not resist the police with force, fighting back in a just war would only add to the injuring side’s record of wrongs (RWP II.1.xviii; III.10.iii). Clearly, giving to the unjust side the same titles and protections that the just side has in a war goes against the grain of the model. On the just side, actions that would advance the cause justifying the war are permissible (RWP III.1.ii), which is to say that under the just model necessity is the driving criteria of jus in bello. On the unjust side, as merely fighting in the war was deemed wrong, there was no space for discriminating between allowed and forbidden ways of fighting.

            Under the just model, in bello considerations are derivative from ad bellum considerations, as Suarez precisely showed. In Suarez’s discussion of the proper modes of conducting war, criteria for establishing immunity from being killed in (and after) war are based on complicity in effecting the injury in question. He held that, aside from children, women, persons unable to bear arms, and other few customary immunities, all those who “shared in the crime” that justified the war could be killed in and after war, regardless of whether they were in fact bearing arms (OW vii.15; in some cases, then, civilians could be fair targets in war). Vitoria’s lengthy discussion of excuses for fighting in an unjust side is more nuanced than Suarez’s, but follows a similar spirit. As is well known, the closer he got to granting symmetrical status to belligerents is in cases of doubt in good faith about the justice of a cause, and in cases of what he called “invincible error” (which is close to the legal defense of unavoidable mistake; OLW 2.4). For Vitoria, like for Suarez, blame is the basis of liability to military attack, and it is connected to the cause that justified the war; only in cases of unavoidable mistake or legitimate doubt can there be room for granting any sort of equal status to the warring sides.

            Vitoria’s cautionary caveats notwithstanding, the emphasis on jus ad bellum at the expense of jus in bello came at the cost of depriving the just model of mechanisms that would proscribe ruthlessness in the conduct of hostilities; the righteousness of one of the belligerent sides could easily be taken to justify licenses for the commission of atrocities, if instrumental for pursuing the just cause.[10] This consideration is, as we know, at the center of the defense of Walzer’s well-known “independence thesis,” and was also present in defenses of the regular war model.


2.      The Regular War Model

In contrast to the just model, the regular model gives a pivotal role to formal declarations of war made by a legitimate sovereign ruler (RWP I.iii.4). A declaration need not list the reasons why war is waged ––i.e. the substantive injury that motivates the war––, for its validity depends only on the status of its source (III.iii.5-11).[11] So, in contrast to the just war model, the regular model is agnostic in regard to substantive rights, the violation of which could be offered as a justification for war. Instead of substance, the model makes the formal expression of a sovereign will an unquestionable, necessary condition for a war’s lawfulness. War-making is a prerogative of a sovereign state that may be exercised only by its sovereign ruler.

            We have seen that one important consequence of the just war model’s emphasis on substantive justice is that the injured side appears as righteous and morally superior to the injurer side, who in virtue of its violation gives up protections and rights that it would otherwise enjoy. The regular war model effectively equalizes the warring parties by abandoning the idea of substantive injury and embraces instead the principle of sovereign equality (this principle is sometimes equivocally expressed in the formula “war is just on both sides”, e.g. by Vattel, LN, III.xii §190). The belligerent sides stand symmetrically, as equal moral agents pursuing their differences through war. This implies that any sort of (in bello or post bellum) permission or liability held valid for one side is eo ipso valid for the other. In Christian Wolff’s apt formula, the permissions and protections awarded to the just side in the just war model become in the regular model the common protections and permission of the belligerent parties, so that “the law of nations allows nothing except that which is allowable by the law of nature to a just belligerent” (IG §890; cf. Vattel LN III.viii §137).[12] If the best image to summarize the just war model’s conception of war is a trial involving a judge/prosecutor and a criminal, a suitable image for the regular model is a duel in which two sides “agree” to solve their dispute through force ––or, to use Pufendorf’s phrase, the disputants resort to “the dice of Mars” for an adjudication of their conflict.[13]

            The regular model’s state-centered conception of war has several wide-ranging implications, of which I would like to highlight two. First, the overall emphasis on procedure and the equal standing of belligerent parties shifts the model’s central normative focus away from the substantive justice of the cause and into the regulation of the conduct of warfare. As Vattel put it, “we can only arrive at such rules [of warfare conduct] by considering acts of hostilities in the abstract and in their essential character”, that is, without reference to the overall justice that motivates them. Acts forbidden, Vattel continues, are “essentially unlawful and obnoxious, such as poisoning, assassination, treason, the massacre of an enemy who has surrendered and from whom there is nothing to fear” (The Law of Nations, III.ix §173, emphases added). In the case of the principle of military necessity, the only relevant consideration when it comes to assessing the necessity of a military action is its contribution to tactical progress narrowly conceived, not its contribution to an overarching just cause. Whatever permissions or proscriptions are said to govern the conduct of warfare, they apply, in virtue of the belligerents’ symmetry, equally to both sides.

            Second, and again in contrast to the just war model, the regular model has virtually no place for civil wars. As the status of sovereignty is a necessary condition of admissibility, civil wars are seen rather as cases of domestic crime writ large. The only case of civil war that could enter the purview of the model is that of (what initially appears to be) a group of bandits which has such mobilizing power that it gains firm de facto control over a piece land (RWP III.iii.3).[14] If a civil war does not take this internationalized form, the model consigns whatever issues the conflict is about to civil courts and municipal law (cf. Vattel LN II.iv, §56; III.xviii §293.)


3.      In defense of the regular model

In this Section I would like to present and assess the strongest normative case for the regular model. As we shall see, the core of the defense is that, given the structure of international society, the regular model is the best workable normative framework for the regulation of warfare among equal sovereign states. The best institutional model of conflict resolution and rights adjudication may well be a domestic court of law presided by an impartial judge applying pre-enacted law. We have seen that the just model seeks to mimic this ideal and responds to the absence of an international court of law by introducing a system of self-help, in which a sovereign ruler acts as party, judge and prosecutor in the pursuit of his violated rights. In analogy to the domestic ideal, wars are conceived as quasi-juridical acts of rights enforcement, and indeed as second-best versions of the domestic model. The regular model gives up altogether the analogy of the domestic case and rather takes what might be described as a third-best track. Instead of a system of self-help, it defends a procedure of conflict resolution and adjudication ––not justice enforcement–– through war. The closer the regular model comes to making war a pure adjudication procedure, that is, the more war is bracketed and carried on as a limited duel among professional warriors (by, e g., isolating civilian lives and property, limiting warfare to a contest between legitimate armies, etc), the more it realizes its core aim.

            Before considering the model’s justification, the nature of this justification should be defined clearly. At the beginning of his presentation of the regular model, Grotius distinguishes two concepts of permission. An act is morally permissible if it is free of moral reproach, or “right from every point of view”, and it is legally permissible if the law does not penalize it (III.iv.2). So an act may be morally impermissible and nonetheless carry no legal liabilities. If we assume that a wrongful act must (morally) be met retributively, then we may say that when the law contemplates no punishment against a wrongdoer it grants an impunity that stands in need of justification. Permissions in the regular model, Grotius tells us, belong precisely to this kind: they are impunities granted to morally wrong acts. The regular model does not purport to defend the morality of the acts it permits; Grotius states this very clearly in the famous passage that prefaces the temperamenta belli.[15] The true object of the model’s defense is the legal impunity given to such immoral acts. The model, in other words, purports to justify a system of legal rules, not particular actions. (It follows from this, in particular, that in taking up the burden of defending the legal impunities, Grotius cannot see them as a sheer fact of international politics, which is, I think, how Hedley Bull has read him.[16])

            A brief contrast with Hobbes’s well known discussion of obligations from the law of nature may help to bring out what is distinctive of the Grotian approach. The laws of nature, Hobbes tells us, always oblige in foro interno, that is, they bind in conscience “to a desire that they should take place” (Leviathan I.xv.36). Natural laws, however, do not always bind us in foro externo, or in the actuality of our interaction with others, because, lacking the proper external assurances, if we unilaterally abide by them, we would foolishly expose ourselves to preying instead of securing our livelihood and peace (Leviathan I.xiv.5). But if for Hobbes the laws of nature ––and indeed all legality–– are externally suspended pending the institution of an overwhelming enforcer, for Grotius there is an area of law that remains binding in foro externo at the international level, notwithstanding the lack of an overarching enforcer (let me call this area, with Wolff and Vattel, the “external law of nations”). There are for Grotius also other areas of normativity that ar binding only in foro interno, but these, I think, should be seen as belonging in the order of personal morality and not as making reference to any potential or aspirational international legal order.[17] Moreover, among the externally binding laws of nations, some are valid in foro interno and some are not: the just side, and only the just side, may (morally) enjoy the permissions that apply in regular warfare, but a slave is not obliged in foro interno to obey his master, although he can (legally) be compelled in foro externo.[18]

            A defense of the regular model takes the form of a defense of the external law of nations. There are at least two elements in this defense. The first addresses the fact that the law permits seriously immoral acts, and the second addresses doubts regarding the law’s efficacy. The latter doubt, more precisely, is not so much that the external laws have no teeth but rather that they follow power dynamics too closely ––the worry, put differently, is not that the normative bite of these laws may be ineffective but rather that they have no real normative bite.[19]

            That the external laws have some normative bite can be readily seen. The laws aim to regulate inter-state relations regarding, e.g., territorial rights, property rights, rights of neutrality, and the right to make alliances. Cases pertaining to all these rights may eventually land before a domestic court of law, and hence be subject to state coercion.[20] To take two crucial examples: the status of neutrality confers certain rights and imposes certain obligations on a neutral party (e.g. duty to treat both sides impartially, in particular to allow ongoing commerce with both; right to remain free from attack, in particular to be allowed to continue relationships with both sides). There are breaches by which the status of neutrality may be lost, which may carry as a consequence the need to undertake reprisals, even military action. (Why belligerent states would respect neutrality is a different question, to which I believe some answers may be found in Grotius.[21]) The second example, to be discussed at more length at the end, is respect for the territorial boundaries as defined at the end of a war. The regular model, in contrast to the just model, encourages states to respect the “verdict of Mars” and give up the pretension to make justice the criterion on which respect for boundaries is based.

            Cases of the law condoning moral wrongs are of course not absent in domestic contexts either. The enactment of a statute of limitations is an obvious example ––even assuming that irrefutable evidence of wrongfulness becomes available, if it is found beyond the duly set period, the legal system precludes further action––, and criminal justice can furnish a number of additional illustrations.[22] If we grant that an accurate reflection of inter-personal morality is not the only aim of a domestic legal system, then we should be able to see why a mismatch between law and morality may sometimes be justified. I believe that Grotius saw clearly and correctly that international law would have to depart even more than domestic law from inter-personal morality’s principles and intuitions.[23] But, as in the domestic case, the only reason that could justify this departure is that it contributes to preserve other important values. I think this is indeed the sort of argument that Grotius would like to make in defense of the regular model, and a central value that the model aims to preserve, as we shall see presently, is the stability of the international order, or the bracketing and limitation of conflict.

            I submit that the regular model, unlike the just model, seeks to provide a plausible basis for a stable normative equilibrium, in the sense that all parties can be plausibly seen as having an interest in upholding the external laws. In order to establish this, we need of course to make some assumptions about what the parties’ interests are, and most certainly we need to include such interests as claiming and preserving the status of neutrality, freely making alliances, carrying international trade, and generally limiting and moderating warfare. Given its importance, it is worth emphasizing that this equilibrium must be self-sustaining because there is no superior, centralized adjudication and enforcement mechanism. Now, consider the following key passage from Grotius:

The reason why such effects [of regular warfare] met with the approval of nations was this. To undertake to decide the justice of a war between two peoples had been dangerous for other peoples, who were on this account involved in a foreign war. Furthermore, even in a lawful war, from external indications it can hardly be adequately known what is the just limit of self-defense, of recovering what is one’s own, or of inflicting punishments; in consequence, it has seemed altogether preferable to leave decisions in regard to such matters to the scruples of the belligerents rather than to have recourse to the judgment of others… (III.iv.4)[24]


It is clear that this passage does not simply state an existing convention ––as several of Grotius’s followers have observed, it is not clear that there was indeed such convention–– but rather introduces an argument in defense of the regular model (cf. Barbeyrac, p. 1275 [Tuck]). There are two different yet connected lines of argument involved: one is the epistemic line that observes how difficult it is to make accurate judgments for the class of disputes that typically escalate to war, and commends, accordingly, epistemic abstinence. The other argument takes a consequentialist line and holds that the practice of epistemic abstinence will limit the quantity (numbers and extension) of conflicts. By ‘judgment’ Grotius means statements that apply mainly to jus ab bellum considerations ––the reference in the quote to the “just limits of self-defense”, reparations, and punishment exhaust the types of causes for which wars could be fought justly according to (Grotius’s version of) the just model, see RWP II.i.2–– and that carry legal and material implications, such as not recognizing a state’s claim of jurisdiction over a particular territory, or its claims of ownership over particular goods.

            It is remarkable that Grotius did not opt for the simple “equal sovereignty” defense, according to which states should not judge other states’ affairs because they have no authority to do so (cf. Vattel LN Preliminaries §15-16), and said instead that they were not epistemically qualified to judge. The reason is, I think, that he wants to make a dual and stronger appeal, both to the awareness that, indeed, conflicts and wars are highly demanding epistemically, and to reciprocity, in the sense of positing an interest in being left (and leaving) alone when it comes to judging about one’s best interest. The weakness of Grotius’s appeal is those cases in which injustice is blatant, the existence of which, as I said earlier, Grotius himself was ready to recognize. But if we give enough credit to the plausible assumption that such clear cases are exceptional in international affairs, and we share Grotius’s interest in thinking about general guiding rules for state interaction, then we can begin to empathize with the basic motivation of the regular model.

            Grotius’s move may be seen as a choice of sides, on consequentialist grounds, in the trade-off between allowing for across-the-board judgments (as does the just model, which even prescribes third party interventions in cases of injustice) and epistemic abstinence; this trade-off reflects a more basic trade-off between two fundamental values: justice, in the classic sense of giving each his due, and peace, in the sense of minimizing the use of violence in social interactions. The regular model responds to Grotius’s intuition that, in international affairs, justice is too high an aspiration, and that it is consequently better to think about a system of rules that could minimize the uses of violence, even if in some (or most) cases this means giving up ideal justice.

            The premises of the Grotian argument for the regular model need to be unpacked clearly. A central premise is that, in general, there will be reasonable disagreements in international disputes. And as reasonable yet conflicting positions relative to a dispute can coexist, it is unwise to allow position-holders the use force on behalf of their particular stance. In contrast to the just model, which posits the existence of an underlying truth of the matter in all disputes and authorizes the use of force to any sovereign ruler who holds it, the regular model gives up the aspiration to access truths of the matter ––if not the assumption of their existence––, and along with that limits the authorization to use force to the parties directly involved. As a consequence of this metaphysical shift, the model’s orientation moves to give a central role to the consideration of which system of rules could indeed guide behavior effectively in an anarchical context. If we assume that justice is too demanding epistemically to have such guiding role, then it becomes necessary to rethink the import of justice imperatives in state interactions; this is precisely what Grotius’s construction of external justice is meant to do.

            But on what basis could one expect the regular model to be stable and indeed conducive to peace? A few general things may be said in response, but a fully adequate answer has to take into account each particular element in the model. Generally speaking, the regular model assumes that parties are sufficiently moved by their long-term self-interest, one posits that it is in their interest to have a peaceful and social coexistence; this interest would go some way in motivating respect to the limits of warfare and avoidance of total war. Similarly, states have an interest in staying away from conflict unless it affects other vital interests, and hence will claim and support the status of neutrality.

            These observations are admittedly superficial, so I would like to conclude by considering with some more care the case of respect for territorial rights allocated through war. Nations, Grotius wrote, “have decided that the property of enemies should stand to enemies in the same relation as ownerless property” ( According to Grotius’s general theory of property, the first taker of an ownerless object acquired a rightful title to it by the mere act of taking possession (II.ii.2.5).[25] By holding that in war the belligerent parties may treat all involved property (that is, all property belonging to the enemy’s subjects) as res nullius, Grotius implied that war takings were the source of rightful ownership.[26] The far-reaching implications of this “nullification proviso”, as it may be called, can be seen clearly if we compare the regular and the just models on their post-war allocations of goods. As part of its asymmetric treatment of enemies, the just war model gave only the just side a right to appropriate goods in the aftermath of war. When doing so, the just side had to abide by a proportionality principle, which holds that a just winner could only take as much from the loser as would repair the injury that caused the war, and possibly also to cover war costs. In the regular model, an important implication of the nullification provision is that both sides can rightfully appropriate, and also that there is no principle of proportionality limiting the size of takings ––Grotius tells us explicitly that, regardless of which belligerent does it, appropriation in a lawful war is “without limit or restriction” (RWP,

            The particular scope and structure of the nullification proviso in regard to property follows directly from a central justification of the regular model. If third parties were to inquire into the just pedigree of goods acquired in war or its aftermath, they would be, in Grotius’s words, “involved in war against their will” (III.x.5.1), for they would thereby be forced to take a stance on conflictive issues. Nullification is therefore motivated by containment and commercial expediency: in the case of movables, tying the legitimacy of exchanges to the goods’ pedigree would be a recipe for renewing or spreading conflict. In the case of inmovables, not recognizing a state’s de facto possession of a territory amounts to challenging its territorial claims, and hence, likewise, to renewed conflict. The model submits, in sum, that wherever things fall after a war, that is where they should stand. The reason why this element of the model may be taken to be part of an equilibrium of state interests is a posited interest in commercial activity plus an interest in having clearly set jurisdictional and property boundaries. Lingering doubts and unresolved claims relative to territorial rights would upset a global system of commerce that, Grotius plausibly assumed, all states would find in their best interest to uphold and protect.



[1] This terminology follows Peter Haggenmacher definition of two historical “paradigms” of just war theorizing Peter Haggenmacher, 'Mutations Du Concept De Guerre Juste De Grotius À Kant', Cahiers de philosophie politique et juridique 10 (1986), ———, 'Just War and Regular War in Sixteenth Century Spanish Doctrine', International Review of the Red Cross 290 (1992); see also Gregory Reichberg, 'Just War and Regular War: Competing Paradigms', in Just and Unjust Warriors: Moral Equality on the Battlefield, ed. David Rodin and Henry Shue (Oxford University Press, 2008).

[2] There is wide consensus among historians of political thought and international law about the large indebtedness of Grotius to the scholastics, in particular to Vitoria and Suarez. See for example Peter Haggenmacher, 'Droits Subjectifs Et Système Juridique Chez Grotius', in Politique, Droit Et Théologie Chez Bodin, Grotius Et Hobbes, ed. Luc Foisneau (Paris: Kimé, 1997), 117, Brian Tierney, The Idea of Natural Rights : Studies on Natural Rights, Natural Law, and Church Law, 1150-1625, Emory University Studies in Law and Religion No. 5 (Atlanta, Ga.: Scholars Press, 1997), 289, 320-324, Wilhelm Georg Grewe, The Epochs of International Law (Berlin ; New York: Walter de Gruyter, 2000), 24, 191-195. Quentin Skinner, The Foundations of Modern Political Thought (Cambridge ; New York: Cambridge University Press, 1978), 154. For a dissenting view and qualifications see Richard Tuck, 'Grotius, Carneades and Hobbes', Grotiana n.s. 4 (1983), ———, Philosophy and Government, 1572-1651, Ideas in Context (Cambridge England ; New York, NY: Cambridge University Press, 1993), 169-179..

[3] In Grotius’s words, “It is evident that the sources from which wars arise are as numerous as those from which lawsuits spring; for where judicial settlement fails, war begins.” (RWP, I.1.ii). “RWP” stands for Grotius’s Rights of War and Peace. Unless otherwise noted, I will use Kelsey’s translation, in the 1925 Carnegie Endowment Edition.

[4] For Vitoria and Suarez, and of course not for Groitus, ecclesiastical authorities could also wage offensive wars. According to Grotius, private persons in the open sea may wage offensive wars.

[5] According to Vitoria and Suarez, for example, violations of natural law such as adultery, sodomy or cannibalism are not grounds for war-making because they are not politically serious enough, and also because were they made such grounds, wars would multiply and too much instability would follow (Vitoria, OAI 2.5; Suarez, OW v.1). 

[6] This issue, which was already central in early modern debates among theorists of just war, has re-emerged in contemporary discussions of jus ad bellum and human rights. Which violations of human rights can we deem to be so serious that a military humanitarian intervention would be a justified response? In particular, should the alleged human right to democracy be put in the list, as some have argued? See Thomas Franck, 'Legitimacy and the Democratic Entitlement', in Democratic Governance and International Law, ed. Gregory H. Fox and Brad R. Roth (Cambridge: Cambridge University Press, 2000).

[7] In Tuck’s reading of Grotius, one of the central motivations of RWP was precisely to carve out a thin set of unquestionable rights, in a way that would sidestep disagreement and, tied to it, skepticism about universals.

[8] Grewe, The Epochs of International Law, 287.

[9] Likewise, there is what may be called purely Christian rights. Vitoria defended the right to preach and announce the Gospel (ius predicandi) “even against the will” of the audience (OAI 3.2; likewise Suarez, OW v.8). These rights were for Vitoria the best justification for the so-called wars against the American Indians. Grotius did not defend the rights of missionaries but did defend a right “to preach or profess Christianity” (RWP II.xx.44).

[10] See Stephen C. Neff, War and the Law of Nations : A General History (Cambridge ; New York: Cambridge University Press, 2005), 112-119.

[11] Grotius says that in some cases a declaration of war may be “conditional” (i.e. a threat), which is in a sense reason giving (e.g. “You owe me P. Restore P or else I will wage war upon you”). But he goes on to make clear that declarations of war could also be unilateral and absolute (“I bear witness that this people is unjust, and does not give satisfaction” (III.iii.7.2), hence I wage war against it). Wolff says that it is desirable that war declarations state reasons, but they should certainly avoid the expression of passions such as hatred or vindictiveness (Ius Gentium §742).

[12] Strictly speaking, here Wolff runs against Grotius, in whose formulation of the regular model all limitations on the practice of warfare effectively disappear (he said, for example, that regular belligerents may indiscriminately kill all members of the enemy community, including infants and women, see III.iv.9.) As the just war model derives privileges and immunities from jus ad bellum, it seems that for Grotius the elimination of considerations of just cause implied necessarily the elimination of all limits on warfare. There is, however, no logical necessity here, and Wolff held indeed that Grotius’s in bello permissions were at best purely customary, but an evil custom that should be terminated. On this regards, my reconstruction of the regular model takes distance from Grotius and sticks to Wolff’s (and Vattel’s) formula. On the construction of the jus in bello doctrine for regular wars, see Haggenmacher, 'Mutations Du Concept De Guerre Juste De Grotius À Kant', 117-122.

[13] Pufendorf, De Jure Naturae V.ix.3, cited in Neff, War and the Law of Nations : A General History, 157. The idea of war as contract, however, has limitations. The contract would run along the lines of: “We hereby agree to solve our disagreement on issue X by means of war; the winner will dispose of the issue as he sees fit.” The regular model, however, admits wars declared unilaterally and contains no explicit requirement of an ex ante agreement. Grotius was opposed to the idea of war as contract on the grounds that, when justice is ex ante clear, it would be absurd to regard the outcome of the clash of forces as decisive about justice (III.x.5.1). Pufendorf did endorse the idea of a hypothetical war contract, but this leads to the rather preposterous consequence of, e.g., seeing cases in which a mighty aggressor crushes a weak neighbor as a fulfillment of contract (precisely the sort of case that made Grotius resist the image of contract). For the history of this idea of wars as duels, see Haggenmacher, 'Mutations Du Concept De Guerre Juste De Grotius À Kant', 122-124.

[14] Grotius cites Augustine, City of God, IV.iv, where he writes: “If by accessions of desperate men this evil grows to such proportions that it holds lands, establishes fixed settlements, seizes upon states and subjugates peoples, it assumes the name of kingdom.”

[15] Where Grotius writes, “I must retrace my steps, and must deprive those who wage war of nearly all the privileges which I seemed to grant, yet did not grant to them. For when I set out to explain this part of the law of nations I bore witness that many things are said to be ‘lawful’ or ‘permissible’ for the reason that they are done with impunity, in part also because coercive tribunals lend to them their authority; things which, nevertheless, either deviate from the rule of right (whether this has its basis in law strictly so-called, or in the admonition of other virtues), or at any rate may be omitted on higher grounds and with greater praise among good men” (III.x.1.1).

[16] Hedley Bull, 'The Grotian Conception of International Society', in Hedley Bull on International Politics, ed. Kai Anderson (New York: Palgrave Publishers, 2000), 103.

[17] Consider, for example, Grotius’s emphasis on charity as a necessary supplement to strict justice (III.xiii.4.1). Throughout RWP, Grotius tends to dissociate nouns such as humanitas, caritas, bonitas, pudor, modestia, honestum, and pietas from iustitia; see Peter Haggenmacher, Grotius Et La Doctrine De La Guerre Juste, Publications De L'institut Universitaire De Hautes Études Internationales, Genève (Paris: Presses universitaires de France, 1983), 583. Strict justice is the business of courts of law, whereas charity, humanity, generosity, honesty etc, are the business of one’s conscience, and God.

[18] Grotius’s discussion of slavery is not logically tight, however. He says, on the one hand, that it is lawful for a slave to attempt to escape (III.vii.6), but on the other that the slave must always obey his master (III.vii.7). There is in general a constant ambivalence in Grotius’s treatment of actions that are illegal but morally right.

[19] In Rousseau’s well known words, “But what is a right that perishes when force ceases? If one has to obey by force, one need not obey by duty, and if one is no longer forced to obey, one is no longer obliged to do so. Clearly, then, this word “right” adds nothing to force; it means nothing at all here” (SC I.iii.2).

[20] As Grotius writes elsewhere, “in this Question of the interpreting Agreements, we do not enquire what is most commendable, nor what Piety or Religion demands, but what every one may be forced to do; in a Word what is merely of external Right, as we call it in Opposition to the Duty of Conscience.” (III.xx.25)

[21] For a brief historical account of the difficulties involved in the protection and defense of the status of neutrality, see Grewe, The Epochs of International Law, 384-389.

[22] For a classic discussion, see John L. Austin, 'A Plea for Excuses', Proceedings of the Aristotelian Society LVII (1956).

[23] And so I think that, although a righteous Rousseau could write that, in Grotius, “the most frequent mode of argument is always to establish right by fact” (SC I.ii.4), it is nonetheless well worth considering the sort of balance Grotius was trying to strike between international politics and law.

[24] Cf. Vattel: “How could it be determined accurately just how far it was necessary on a given occasion to carry hostilities in order to bring about the successful termination of the war? And even though this may be determined, Nations recognize no common judge, and each decides as to what conduct its duties require of it. Open the door to continual accusations of excesses in the conduct of war, and you will only multiply complaints and embitter more and more the minds of the belligerents; fresh injuries will be continually arising, and the war will not cease until one or the other of the parties be destroyed. Hence, as between Nation and Nation, we must lay down general rules, independent of circumstances and of certain and easy application.” (LN III.ix §173)

[25] This principle of first possession can be found in Gaius’s Institutes, a second century A.D. source of Roman Law. For an insightful discussion and “qualified defense” of the principle, which illustrates its role in contemporary American common law, see Richard Epstein, 'Possession as the Root of Title', Georgia Law Review 13 (1979).

[26] This nullification, however, has a structure particular to wars; the goods it covers are not strictly speaking res nullius because the suspension of titles applies only to the belligerent parties. Third parties could not take war property at will but rather had to treat their belligerent de facto possessors as rightful owners.