Suárez, Francisco – Theory of War

Author: Cintia Faraco
Part of: Suárez’s Theory of Law, Politics, Anthropology (coord. by Cintia Faraco)
Peer-Reviewed: Yes
Published: June, 21st, 2025
DOI: 10.5281/zenodo.15574680

This entry is a reworking of Faraco (2013), originally published in Italian

The latest version of this entry may be cited as follows: Faraco, Cintia, “Francisco Suárez, Theory of War”, Conimbricenses.org Encyclopedia, Mário Santiago de Carvalho, Simone Guidi (eds.), doi = “10.5281/zenodo.15574680”, URL = “https://www.conimbricenses.org/encyclopedia/suarez-francisco-theory-war/”, latest revision: June, 21st, 2025.

Introduction and Reconstruction of the theme: Augustine of Hippo and Thomas Aquinas

Francisco Suárez dealt with the issue of warfare in a brief disputatio, included in the broader treatise De Charitate (1587), which, in turn, completes his series of treatises on the three theological virtues.

Even today, this brief essay, which has been subject to extensive discussion among the various scholars who have investigated this matter, is the key issue of a heated debate due to its theoretical implications (see Hamilton 1963; Soder 1973; Torres Campos 1917; see also Cassi 2003, 2012). Therefore, it is precisely within this vast debate on this Suarezian disputatio that I intend to summarise the Jesuit’s position on the theme of war, outlining its most general aspects.

However, in order to be able to reconstruct Suarez’s thought on the theme of war, it is necessary to make first of all a very brief, yet functional, preliminary remark with the purpose of highlighting the theoretical as well as historical elements that converge in the formation of the answer to the issue worked out by the Spanish Jesuit.

Now, the theme of war has always been of significant interest both on a political, legal and economic level, and is substantially inextricably linked to the study of man and his behaviour. In this context, it is a theme that, due to its being closely linked to the use of force, raises the problem of its possible configuration within the scientia iuris (Cassi 2012: 7).

Let us leave aside this problem in the light of Greco-Roman influences, which were also very decisive, to limit ourselves instead to the conceptual reference of two auctoritates. These are, on the one hand, Augustine of Hippo and, on the other hand, Thomas Aquinas, who, among the many authors taken by Suárez as his models and sources of inspiration, can be considered by far the most relevant.

In particular, it should be noted that Augustine of Hippo was historically the first to lay the foundations of reflection on the theme of just war, identifying, among other things, in De civitate Dei the requirements upon which a war can perhaps be defined as lawful. In fact, Tertullian was the one who a few years earlier had already indicated a route for the Church on the subject of war, namely conscientious objection and with it the rejection of war as an instrument of offence. More precisely:

1. The legitimate declaration of a war must necessarily reside in the valid constitution of the authority.
2. War must necessarily be the only means left to respond to an iniuria and, therefore, the only way to restore a broken balance.
3. Finally, it is essential that no malignant feelings intervene (Buzzi 2004: 73-78).

These reflections were already conceived and further developed on several occasions, first by Isidore of Seville and then by the glossators of the Bologna school, and eventually taken up, mutatis mutandis, by Thomas Aquinas, who not only tried to establish a synthesis of these discussions but also, whenever possible, to go even further (Buzzi 2004: 78-79). In fact, in observance of a reading of the Holy Scriptures, which preach evangelical peace, Thomas came to conclusions similar to those proposed by Augustine in De civitate Dei, which would contribute to determining that tradition constantly present in the Second Scholasticism. In short, these conclusions involve:

1. The presence of a legitimate authority, which has been entrusted with the task of defending citizens from internal evildoers and external enemies, therefore a principis auctoritas.
2. The presence of a just cause.
3. Tinally, the presence of the intention to promote good and avoid evil, i.e. a recta intentio (Thomas Aquinas 1949).

Indeed, it should be noted that in the same assumption of the issue of warfare and the resulting definitions, the Jesuit cites the Doctor Angelicus precisely in that part of the Summa Theologiae, where the three requirements just mentioned above can be outlined. However, it should be emphasised that, with the discovery of the Americas, this theme found itself faced with new needs, which resulted in new interpretations of the concept of war. It should be kept in mind that what was at stake was the conquest of new territories already permanently occupied by unknown populations, which also entailed a new evaluation of their characteristics in terms of government.

Suarezian definitions: bellum and pugna

All the foregoing is to be found in the study and in the very forma mentis of Suárez, who, in the usual academic style derived from his scholastic background, starts by enunciating the following definitions, starting from which he would work out the short piece of writing:

Pugna exterior, quae exteriori paci repugnat, tunc proprie bellum dicitur, quando est inter duos principes, vel duas respublicas; quando vero est inter principem et suam rempublicam, vel inter cives et rempublicam, dicitur seditio; quando inter privatas personas, vocatur rixa, vel duellum; inter quae materialis magis quam formalis differentia esse videtur, atque de his omnibus dicemus, de quibus D.Thomas 2.2, q. 40, 1 et 42, et alii infra referendi (Suárez 1857: 737).

What we note from the series of definitions that mark the beginning of the disputatio is first and foremost a precise distinction between two categories of conflict, that the Jesuit defines, respectively, one as exterior and the other – which we could define in opposition to the former – as interior (Please note that the term “interior” was chosen by me, as it is more suitable to show the contrast existing between the various types of conflict that can arise). Now, given the peculiarities of the latter category, which cannot be associated with war, despite the fact that it shares some of properties and evident manifestations of the latter that recall, precisely, real war, it offers some hints that allow us to outline the entire phenomenology of situations of belligerence.

So, let us consider – in the first instance – the second category of conflict, which we have referred to as interior. As for this kind of bellum or pugna, two forms can be identified, namely: the first, which develops through the disagreement between the cives and the princeps or between the cives of two communities coexisting under the same leadership; regarding this first form, we speak of seditio. The second form of pugna interior is the one that does not develop against the constituted authority, but substantially inter privatas personas, and this latter form is referred to as duellum or rixa.

The seditio, i.e. bellum commune intra eamdem rempublicam, quod geri potest vel inter duas partes eius, vel inter principem et rempublicam (Suárez 1857: 759) can be identified in three cases.

The first scenario comes into being in the event that two parts of the community wage war against each other. According to Suárez, this form of seditio is always to be considered an evil whenever we cannot identify the existence of a legitima auctoritas ad indicendum bellum (Suárez 1857: 759) in any specific part of the communitas politica. It can be assumed from this that the aggression of one part against the other part is always mala (ex parte aggressionis); in other words, it is a situation that determines the right to legitimate defence on the part of the opposing party.

The second scenario in which we can identify a situation of seditio comes into being when bellum reipublicae is waged contra principem, which thus includes the case of a revolt of the political body defined here as respublica. In fact, in this case Suárez emphasises that such war non est intrinsece malum”. This stance involves considering the evaluation of a possible unjustified behaviour in the princeps being such as to legitimise the popular revolt.

Besides, as he had already written extensively in the Defensio fidei (Suárez 1872), if the princeps acts as a tyrant, he becomes an aggressor of the communitas politica by waging war against it and its individual members. The consequence is that the entire state community can bello insurgere contra ejusmodi tyrannum (Suárez 1857: 759). Furthermore, it should be emphasised that the Defensio fidei, referring to a usurper, reads as follows:

(…), ideoque si rex legitimus tyrannice gubernet, et regno nullum aliud subsit remedium ad se defendendum, nisi regem expellere, ac deponere, poterit respublica tota, publico et communi consilio civitatum et procerum regem deponere, tum ex vi iuris naturalis quo licet vim vi repellere, tum quia semper hic casus ad propriam reipublicae conservationem necessarius, intelligitur exceptus in primo illo foedere, quo respublica potestatem suam in regem transtulit (Suárez 1872: 290).

These clarifications prove even more insightful if we consider the words of De bello:

quia tunc tota respublica superior est rege; nam cum ipsa dederit illi potestatem, ea conditione dedisse censetur, ut politice, non tyrannice regeret, alias ab ipsa posse depone (Suárez 1857: 759).

Finally, we come to the third scenario of seditio, that Suárez identifies as an outright seditio and the only one of the three scenarios deemed to be intrinsically evil (Pereña Vicente 1956: 125-127). This category of seditio occurs whenever the community rebels against a sovereign whose behaviour has actually given no reason for reaction, nor has he in any way perpetrated an aggression against his own community. The arbitrariness that characterises the behaviour of the political body towards the sovereign therefore appears evident to Suárez and, consequently, this form cannot be the true seditio.

Let us now consider the second category of conflict which, for the sake of convenience, we have indicated as interior in order to differentiate it from the bellum exterior or proprie bellum dicitur (Suárez 1857: 737), that is the duellum or rixa.

Once again, the Jesuit tries to enumerate and group together all the case records on the subject to outline a few rules and certain conclusions, ending up identifying in the duellum or rixa or bellum privatum (Suárez 1857: 759) a form of private war, which he always considers as an evil, except in the case of someone who is driven to commit such a type of deed, intrinsically wicked, by the duty to defend his own honour (Suárez 1857: 760-762).

The reason why the duellum should always be considered intrinsically evil is clarified within the theme of the bellum exterior, where it reads:

vindicatio propria, auctoritate privata, intrinsece mala est, atque eo colore facile excitarentur tumultus et bella in republica; sed jus vindictae, quod habet pars reipublicae, vel privata persona, tantum est imperfectum, et in illo habent haec incommoda majorem locum; ergo non est illi danda haec licentia, nisi solum intra limites justae defensionis (Suárez 1857: 740).

That is to say, if private interest is not justifiable for an exterior war, it is even more condemnable in the case of a situation of conflict within the community. In other words, the duel always ends up being a form of private revenge and, as such, cannot be justified, except before a princeps (Suárez 1857: 762) acting as judge, who will have to establish what motivations led to such a deed by reconstructing the entire event allegata et probate (Suárez 1857: 761).

However, according to the Jesuit there would exist alongside these last two scenarios a third one, which, however, could be considered to be non-negative. In fact, we read:

si auctoritate publica fiat, non est intrinsece mala, sed si alioquin habeat justas belli conditiones, honestari potest (Suárez 1857: 762).

The superior judgment of the authority regarding the legitimacy – justa causa – of the conflict could even justify the conflict itself between two parties, since

moltitudinis personarum non variat honestatem, sive justitiam (Suárez 1857: 762).

This principle also finds further application in the event that someone invested with public authority is killed; in fact,

nam occisio auctoritate publica, et ex justa causa, non est intrinsece mala.

The case of the killing of public authority is, therefore, justified by the presence of a just cause, thus clearly referring to the theories already developed in Defensio fidei which, here, are simply alluded to (Suárez 1872: 285-292).

Well then, already from the analysis of the scenarios that can be occur within a political body, we understand how, for Suárez, the theme of war has an ethical-juridical-political relevance, rather than specifically theological. It can be observed even more clearly – and all the more so in dealing with the war inter duos principes – how it is considered independently of theological evaluations and linked to human philosophical knowledge and always dependent on moral categories (Buzzi 2004: 120).

The reasons for this position find their foundation in natural law and in the Aristotelian philosophy of society, which implies the presence of an authority that has the function of guaranteeing the common good (Buzzi 2004: 118). This is how, for Suárez, the bellum exterior can be differentiated: on the one hand it takes the form of bellum (exterior) defensivum, while on the other hand it takes the form of bellum (exterior) aggressivum.

However, while war waged for defensive purposes is always legitimate, since it takes the form of legitimate defence for the respublica under attack, when it comes to examining the case of aggressive war, the need arises to carefully analyse the different circumstantial situations that can possibly occur.

Bellum etiam aggressivum non est per se malum, sed potest esse honestum et necessarium (Suárez 1857: 738).

This statement highlights a fundamental aspect of the nature of aggressive war according to Suárez’s thought. In fact, the Jesuit motivates his assertion with arguments that, in his opinion, would not have been clear even to Luther, who is directly involved in this regard. In support of his theory, Suárez states that aggressive war can be just

quia tale bellum saepe est reipublicae necessarium ad propulsandas injurias, et coercendos hostes, neque aliter possent respublicae in pace conservari. Est ergo hoc jure naturae licitum, atque adeo etiam lege evangelica, quae in nulla re derogat juri naturali, neque habet nova praecepta divina, praeterquam fidei et sacramentorum (Suárez 1857: 738).

The duty to preserve peace in the nation, therefore, is the ground that legitimises and makes war necessary, to the point that Luther’s theses, which essentially denied such possibility, are even deemed ridiculous:

Quod vero Lutherus aiebat, non licere resistere castigationi Dei, ridiculum est: Deus enim non vult haec mala, sed permittit, unde non prohibet quin juste possint propulsari (Suárez 1857: 738).

Conclusions

From what has been said so far, and fully taking up the Thomistic tradition, which was referred to at the beginning of this work, in order to declare war, wherever the latter is conducted honeste, even if propter multa incommoda quae secum affert, ex iis negotiis est quae male fiunt (Suárez 1857: 739), the guaranteed competition of three elements is required, namely:

1. primum, ut sit a legitima potestate;
2. secundum, ut justa causa, et titulus;
3. tertium, ut vetur debitus modus, et aequalis in illius initio, prosecutione, et victoria, (…) (Suárez 1857: 739).

If for Suárez the first element, namely the legitima potestas, is nothing other than the manifestation of the legitimacy of the prince, who has no one else above him in the respublica, it is clear that the princeps is also the only one to be invested with all the potestas necessary to guide, protect and administer a group. In this connection, the deed that pertinet ad justitiam vindicativam, quae maxime necessaria est in republica ad coercendum malefactors (Suárez 1857: 739) falls within the jurisdictional function. i.e. the potestas jurisdictionis, whereby the Jesuit argues that

sicut supremus princeps potest punire sibi subditos quando aliis nocent, ita potest se vindicare de alio principe, vel republica, quae ratione delicti ei subditur (Suárez 1857: 739).

Actually, should the prince prove to be negligens in vindicanda et defendenda republica, then the entire community could se vindicare et privare ea auctoritate principem, quia semper censetur apud se retinere eam potestatem, si princeps officio suo desit (Suárez 1857: 739).

In Suárez’s opinion, the legitimate potestas in respublica is therefore easily identifiable and, in actual fact, war could not be declared by someone who is not invested with the due legitimate authority, because he would act not only contra charitatem, but also contra justitia etiam adsit legitima causa (Suárez 1857: 741). The reason that Suárez identifies is entirely referable to these conclusions: quia actus ille tunc fit sine jurisdictione legitima; est ergo illegitimus (Suárez 1857: 741).

With regard to the legitimate potestas, then, Suárez makes a digression on the figure of the Pontiff, who non habet directam potestatem in temporalibus extra suum dominium, habere tamen indirectam (Suárez 1857: 740).

Once again – as he had already had the opportunity to highlight in his two major political works, namely: the Tractatus de legibus ac Deo legislatore in decem libros distributus and the Defensio fidei we already mentioned – the Jesuit tries to clarify that the Pontiff is substantially a spiritual authority unable to intervene in all the political matters that concern the most practical life of a kingdom. However, the potestas indirecta grants the head of the Church the power to judge whether the moral ends pursued by a sovereign in pursuit of the bonum commune of his people are consistent or not with the values of the Church. Therefore, the Pontiff will hardly be able to judge a war as just when waged between two Christian kings, although it might “rare” even happen that he sides with one of the two kings involved, while in any case he will always find himself sided against the infidels (Suárez 1857: 740-743). It is clear that the Jesuit could not have been more attentive and suited to the times and to the position he holds.

The second essential element required – according to the Jesuit – to declare war based on reasonable grounds, is found in the justa causa, et titulus. Like all his predecessors, from the examples set by those closest to him, such as Francisco de Vitoria, to those of the older ones, such as Augustine of Hippo, Suárez also identifies in the gravis injuria the only true causa justa et sufficiens to wage war (Suárez 1857: 743). At the same time, however, it is the Jesuit himself who warns against possible errors in the interpretation of situations that could give rise to injuria. Although injuria certainly gives the offended party the right to avenge the offence received, in the event of a justa causa (which is the case in question), it cannot happen instead that both opponents feel simultaneously offended and entitled to defend themselves, since duo enim contra juria non possunt esse justa and, stirring things up even more, Suárez states quod est absurdissimum (Suarez 1857: 744; see also Cassi 2012: 22).

The cause that generates injustice must not, however, be abstract, founded on non-concrete elements and dictated only by the judgement of the princeps; on the contrary, as appears from the text, Suárez is attentive to all the circumstances, even diplomatic ones, that might arise in determining an injuria. In fact, he writes, among the objective elements of injuria, also the following cases should be considered: if the sovereign neget communia jura gentium sine rationabili causa, ut transitum viarum, commune commercium, etc. (Suárez 1857: 744).

In so doing, the Jesuit relaunches a legal-economic approach, precisely by indicating the violation of those fundamental rights of trade and transit (see Cassi 2012: 22-ss. and Buzzi 2007: 120-ss.), ethical-political factors that had been first introduced at the dawn of Spanish Scholasticism.

As he goes on reading the text of the disputatio de bello, Suárez continues to list the various titles, thanks to which the sovereign can declare war. The latter include the possibility – which is worth highlighting here – of waging war in defence of citizens’ rights when these are violated by other sovereigns. Of course, this option had already been pointed out in the Tractatus (Suárez 1868: 161-ss.) and then, more extensively, in the Defensio (Suárez 1872), in which Suárez had deemed it possible, for a community oppressed by a tyrant prince, to request external help. However, in the disputatio under examination, greater emphasis is given to the disagreement existing between the faithful and the infidels, a very delicate issue that had actually involved the Jesuit’s work repeatedly and on several occasions.

Finally, the third part concerns a rather technical aspect of the course of the war itself, not only the princeps as the first leader of armies, but also how the armies themselves should be managed, and even the problem of the soldiers in the pay of the princeps (Suárez 1587: 752-758). I reckon it is not worthwhile to dwell on this third part, since such a discussion would not add any useful element to highlight the general position on the theme of warfare.

In conclusion, the very formulation of the treatise on the three theological virtues dates back to the author’s Roman years, that is, between 1580 and 1585. In those years, in fact, Suárez held an impressive quantity of courses and had the opportunity, also thanks to his friendship with brother Roberto Bellarmino, to study themes that would then undergo a very long gestation, as in the case of the theme addressed here, where even the post mortem publication was edited.

The Jesuit’s casuistic and academic trait is repeated even more so on a theme, such as that of warfare, which gives rise to multiple theoretical – but above all practical – hints. Analysing reality, Suárez, tries to group together the events that, in his opinion, are most likely to happen both outside and inside a communitas politica.

The description not only of the titles, but also of the causes and of the behaviour to be held even at the height of war – which must always be based on weighing up violence with the wrong suffered as a guiding yardstick – is rendered through a harmonious legal and philosophical awareness, capable of clearly recalling the concepts of prudentia and bonum commune, from which all Suárez’s political work draws inspiration.

Besides, Suarez’s entire activity is characterised by constant dialogue with his authoritative teachers as well as with his contemporaries with the aim of projecting himself towards a new interpretation of the themes that, little by little, are brought to his attention in the light of verifying the existence of a solution as close as possible to reality.

Bibliography

Primary Sources

• Francisco Suárez, De triplici virtute theologicae, in Opera Omnia, Parisiis: apud Ludovicum Vivès, 1857.
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• Thomas Aquinas, Summa Theologiae, Bologna: EDS, 1949.

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