Front Page Titles (by Subject) CHAPTER VI: Concerning the Efficient Cause of War - Commentary on the Law of Prize and Booty
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CHAPTER VI: Concerning the Efficient Cause of War - Hugo Grotius, Commentary on the Law of Prize and Booty 
Commentary on the Law of Prize and Booty, ed. and with an Introduction by Martine Julia van Ittersum (Indianapolis: Liberty Fund, 2006).
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Concerning the Efficient Cause of War
Article I. What is a just efficient cause of private war?
Article II. What is a just efficient cause of public war?
We are told that some of the causes effecting a given result are principal causes, while others are contributory and still others are to be classified as instrumental. Certainly all three kinds of cause are discernible in connexion with voluntary human actions (among which war is included), just as they are in regard to most other things.
In the natural order, as we have already pointed out, every individual is charged with the execution of his own rights. For we have been compounded of mind and body with precisely this purpose in view, namely, that the body may be the servant of the mind.a This very point is borne out by the uses of our bodily members, and particularly by the uses assigned to the hands,b since we defend ourselves by thrusting the hands forward, and claim a thing as our own by laying our hands upon it.
It is also natural for us to do good to one another, and to lend each other aid.c For it is right that we should accord to others the same treatment that we wish to receive when we ourselves are in distress.d It has been well said by those writersa who discuss the subject of duties that, in accordance with God’s Will, nothing—save God Himself—should be more useful to man than his fellow man. Moreover, human beings employ certain terms denoting fellowship; and in obedience to the implications thereof, kinsmen unite for mutual aid, neighbours are called upon in time of needb and all the citizens of a given community are likewise invoked as a whole,c whence there has arisen that well-known line employed on the stage, “Forward, Roman citizens!”d Thus Solon (so we are told) laid down the doctrine that the state wherein each individual regards injuries to others as injuries to himself, will be a happy state. Democrituse has said: ἀδικουμἑνοισι τιμωρει̑ν κατὰ δύναμιν χρὴ καὶ μὴ παριἑναι. τὸ μὲν γὰρ τοιου̑το δίκαιον καὶ ἀγαθόν, τὸ δὲ μὴ τοιου̑τον ἄδικον καὶ κακόν. “It behoves us to defend with all our might the victims of unjust oppression, and not to leave them neglected; for the former course is just and good, whereas the latter is unjust and wicked.” In the works of Aristotle,f too, we find this excellent passage: δει̑ τοὺς ἀδικουμἑνους ὑπὲρ ἑαυτω̑ν πολεμει̑ν, ἢ ὑπὲρ συγγενω̑ν, ἢ ὑπὲρ εὐεργετω̑ν, ἢ συμμάχοις ἀδικουμἑνοις βοηθει̑ν. “If injury has been inflicted upon any person, it is fitting that we should take up arms, whether in self-defence or for the sake of kindred or benefactors; or again, if our allies have been wronged, it is fitting that we go to their aid.” For that matter, even if other bonds are lacking, the universal fellowship of mankind and the communion established by nature, will still cause us to be affected in our turn by ills inflicted upon others. For human beings should not hold themselves aloof from anything that is of human import. Indeed, this maxim holds good to such an extent that great nations, as well as theologians and juristsg of no slight authority, in many cases regard as punishable the negligence of those who have allowed some person to be injured when they could have prevented such injury.
The authors of a deed, however, and their allies, act of their own force (the former, to be sure, on their own behalf, and the latter on behalf of another); instruments, on the other hand, act by the force of him who wields them, not by their own force. For in a certain sense, instruments fall into the category of parts, and a part is naturally the servant of the whole.a Thus the hand is, so to speak, ὄργανον ὀργάνων, “the instrument of all instruments”; and in this connexion the poet Lucretiusb observes:
Conversely, weapons are the hands of the soldier. Nevertheless, when we speak of the instruments of war, we do not wish to be understood as referring to projectile engines, swords, and spears, since these things are scarcely pertinent to the question of justice; we refer rather to the men themselves whose deeds are performed subject to the commands of others. Take sons as an example:c for a son is from the standpoint of nature a part of his father, inasmuch as the former has derived his very existence from the latter. The slave also provides us with an illustration,d because he is in a sense, like any other possession, a part of his owner. For just as a given part does not merely pertain to its whole by virtue of the same relationship in which the latter is the whole corresponding to the said part, but furthermore depends upon that constituent whole for the very fact of existence, even so a possession is essentially a thing pertaining to the possessor himself. Democritusa gives us this advice: οἰκἑτῃσιν ὡς μἑρεσι του̑ σκηνἑος χρω̑ ἄλλῳ πρὸς ἄλλο; “Use your servants as you use the parts of your body: different ones for different purposes.” Nor is Aristotleb mistaken when he says that certain persons are by nature slaves, not because God did not create man as a free being, but because there are some individuals whose character is such that it is expedient for them to be governed by another’s sovereign will[27′] rather than by their own.c Thus a household consists, as it were, in a multitude of bodies directed by one mind; and absolutely every person who serves another is an instrument, wherefore we refer to those whose labour we utilize, as our “hands.” Let us apply the designationSubjects “subjects,” then, to all such persons.
Conclusion V, Article ITherefore, on the basis of the foregoing observations, we conclude that private wars (for these should be dealt with first) are justly waged by any person whatsoever, including cases in which they are waged in conjunction with allies or through the agency of subjects. In this connexion, one may quote the words of Baldus:d “Some persons make war directly, and not through the agency of another; some make war directly in conjunction with another; some do so through another’s agency, without intervening directly, and some do so both directly and through another’s agency.” The three kinds of warfare in question, [warfare by direct personal intervention, with the aid of allies, and through the agency of subjects,] are all clearly exemplified in a single instance drawn from the story of Abraham,e wherein war is waged not only by Abraham himself, but also by his allies (Aner, Eshcol, and Mamre) and, furthermore, by his household slaves, who are called in that story, “the young men.”
Moreover, I except no one from the conclusion set forth in the preceding paragraph. For if a given individual is prohibited from waging war, that prohibition is based not upon a defect in personal qualifications but upon a procedural defect,a or in other words, upon the Ninth Law, the force of which we shall have occasion to discuss elsewhere. It is in the light of this distinction that we should interpret the admonition of Augustine:b “In such circumstances, the chief thought of the just man shall be for this consideration alone, namely: that the war be undertaken by one who may lawfully wage war. For not all persons may lawfully do so.”
To be sure, in the majority of cases where writers employ the term “war,” they are referring not to private but to public war, which is more frequently the subject of discussion.c Let us now turn our attention to this public aspect of war.
Just as the power to wage war privately resides in the individual, so the power to wage war publicly resides primarily in the state,d regardless of whether the subject-matter of the dispute was public from the beginning or whether it has been changed from a private into a public matter through a judicial process.e Now,The State a state must be conceived of as something αὐταρκής, “self-sufficient,” which in itself constitutes a whole entity: something αὐτόνομος, αὐτόδικος, αὐτοτελής, as Thucydides would express it, that is to say, possessed of its own laws, courts, revenue, and magistrates; something endowed with its own council and its own authority, as is explained by Cajetan,f and also by Victoriag in the passage where the latter lays down the doctrine that there is nothing to prevent several sovereign and perfect states from being subject to one prince, or otherwise very closely bound together, by treaty.h But if a given state lacked power to wage war, it would not be self-sufficient for purposes of defence.a Consequently, it was permissible for the Roman people to decree war, as it was also for the Latins, the Etruscans, the Samnites, the Tarentines, and numerous other peoples of Italy who (so we are told) fought against the Romans;b not to mention for the moment the Carthaginians in Africa, the Spartans and Athenians in Greece, and many other nations. The same may be said of the ancient Hebrews, and of all the peoples who have lived sui iuris. Accordingly, Bartolusc (following Cuneo) declares that war is just when waged between two free states, and that possessions captured in such a war become the property of the captors.
The authority to undertake public wars also resides in magistrates.d For when the state has once transferred its will into the keeping of the magisterial will, whatever is permissible for the state on its own behalf is likewise permissible for the magistrates on behalf of the state.e The term “magistrate” should here be understood, of course, as referring to one who has been entrusted with a mandate for the waging of war. In a sense, however, all magistrates have been invested with this attribute, save in those cases that are specifically excepted, since the rendering of judgements and the defence of one’s jurisdiction, the issuance and the execution of decrees, pertain to one and the same office,f and since such functions sometimes cannot be discharged without resort to war. Furthermore, punishment of domestic enemies and punishment of external enemies naturally pertain to one and the same power.g Nevertheless, regard must be had for rank. Thus, in view of the fact that there is nothing which more gravely imperils the welfare of the state than war, there can be no doubt but that the state has willed that the power of making war shall be given into the hands of him in whom it has placed the greatest trust; and since the state has established various grades of magistracies, the clearest possible indication has been given of its will that, in a matter so grave, recourse shall first be had to the supreme magistrate, to the one second in rank if the supreme magistrate is not accessible or fails to discharge his functions, and so on, successively. For at all times the state desires both to be defended and to see justice administered; and care for the common welfare is the function of all magistrates.a
Therefore, in localities where it is not the custom for the people themselves to assemble as a whole, and where they have not decided that such an assemblage would be to their advantage, authority to undertake a war is invested primarily in those persons, or in that person, to whom[28′] all civil power, or the greater part thereof, has been committed. For in some states this power is entrusted to a number of individuals, for example, to a specific portion of the people, or to the aristocrats; while in other states it is entrusted to a single individual who is called the prince. Thus Augustineb says: “The natural order, the order adapted to the maintenance of peace among mortals, demands that authority and discretion for the undertaking of wars should reside in princes.”c In my opinion, however, when the prince is absent or negligent, and when no law exists expressly prohibiting this alternative course, the magistrate next in rank will undoubtedly have power not only to defend the state, but also to make war, to punish enemies, and even to put malefactors to death.d
A paradoxical contentionOn the other hand, there is a dispute as to whether or not, if a case of this kind should arise, the term “public war” would be applicable. I myself see no objection to this application of the term. For such wars are supported by the will of the state; and the state’s will, whether expressly or tacitly indicated, ought assuredly to be regarded as authority for the waging of war, as has been argued not only by Ciceroa but also (among the theologians) by Cajetan,b who bases his contention on what is undoubtedly an ancient formula: “Let the welfare of the people be the supreme law.” Indeed, this very question has been weighed on various occasions, both in Rome and elsewhere. For by the law of the Quirites, it was impossible (generally speaking, at least) for war to be undertaken otherwise than through a decree of the People or of the Senate. Nevertheless, when Gnaeus Manlius made war upon the Galatians, for cause but without any previous declaration of hostilities, he was not only acquitted after being accused; he was even rewarded with triumphal honours. Again, Cato’s opinion was repudiated when he characterized as “private” the war undertaken by Julius Caesar (who had been sent into Gaul with supreme power) against Ariovistus and the Germans, and the war of that same Caesar against the Britons. I, for my part, do not doubt that both Manlius and Caesar could have been defended on this ground, namely, that whenever war has been publicly declared upon any nation, all persons of potential aid to that nation would seem to be tacitly included under the declaration. In fact, it is my belief that even the war waged against Antony by Decimus Brutus, as Governor of Gaul, was a public war. Accordingly, in the light of the foregoing arguments and examples, I am moved to reject the authority of Innocentc and that of Bartolus,d who follows him. Certainly their authority should carry little weight in cases relating to public law or to the law of nations; especially in view of the fact that the opposite opinion does not lack adherents, even among the Spaniards,e a race by no means to be despised in the field of jurisprudence. In particular, it may be noted that there is no one who does not concede the truth of this very opinion in relation to reprisals,a which may be regarded as a form of war.
Now, just as private individuals are rightly drawn into war by other private individuals, so also a given state or magistrate may be joined in warfare not only by such individuals but even by another state or magistrate.b Here we have the origin of allied forces. In regard to this institution, the Greeksc drew a neat distinction, employing the terms ξυμμαχίαν and ἐπιμαχίαν, which refer respectively to alliances established with a view to any cause of war whatsoever, and to those formed for defensive purposes only, in accordance with the First Law.
Subjects (that is to say, those persons who are bound by the laws of a state) likewise serve as instruments of public warfare. This is the sense, in part, of the Seventh and Eighth Laws, and also of the Fourth Rule. Consequently, no subject should be excepted from this category, save perchance on the basis of a special law or because of the customs of the particular state concerned: as slaves, for example, were excepted under Roman law and clerics under pontifical law, though for diverse reasons. But the extent to which subjects participate in public warfare is a matter which will be discussed in another context.d
For the present, our inquiry is concerned solely with the rights of [different classes of] persons [viewed as potential participants in public warfare], and those rights may be summarized as followsConclusion V, Article II: Public wars are justly waged by a state or by a magistrate in accordance with his rank, both in conjunction with an allied state or allied magistrate, and through the agency of subjects.
[a. ]See Rule V and end of Chap. ii, supra, pp. 42 and 50.
[b. ]See discussion of Law II, supra, p. 23.
[c. ]See part before Laws V and VI, supra, p. 28, and compare Rule III.
[d. ]See Second Informal Exposition of Art. I, Concl. I, supra, p. 58; Dig. XVIII. vii. 7.
[a. ]Cicero, following Panaetius, On Duties, II [iii. 11]; ibid. III [vi. 26–7].
[b. ]Doctors, On Dig. XLVII. ii. 7; Code, X. i. 5.
[c. ]See Law VII, Chap. ii, supra, p. 37.
[d. ][Laberius in Macrobius, Saturnalia, II. vii. 4.]
[e. ][In Stobaeus, Florilegium, XLVI. n. 43.]
[f. ]Rhetoric to Alexander, iii [ii, p. 1425 a].
[g. ]See discussion of Rule II; Bartolus, On Dig. I. i. 3, nn. 7, 8; Jason, On Dig. I. i. 3, n. 29; Castrensis, On Dig. I. i. 1, § 4, nn. 10, 11, 12; Bartolus, On Dig. XLIX. xv. 24, n. 9; Innocent, On Decretals, II. xxiv. 29 and ibid. xiii. 12; Panormitanus, On Decretals, ibid. n. 18; Sylvester, on word bellum, [Pt.] II. viii; Th. Aq. I–II, qu. 47, art. 1. See also Genesis, xiv, whole chap.; Proverbs, xxiv. 11; Psalms, lxxxii. 4; Dynus, On Sext, V. xii, rule 19; Sylvester, on word homicidium, [Pt.] I. x; Seneca, Epistles, xcv .
[a. ]Arist., Politics, I. iv [I. ii. 4–5].
[b. ]V .
[c. ]Code, XI. xlviii (xlvii). 22, § 1; Arist., Nic. Ethics, V. x [V. vi. 8–9]; add Code, IX. ix. 4; Seneca, Controversies, I. iv.
[d. ]Add Dig. XXIX. v. 19.
[a. ][In Stobaeus, Florilegium, LXII. 45.]
[b. ]Politics, I. v [I. ii. 13].
[c. ]Plato, Republic, IX [xiii, p. 590 d].
[d. ]On Code, III. xxxiv. 2 [n. 77].
[e. ]Genesis, xiv. 13, 14, 24.
[a. ]See example in exposition of Law XIII, supra, pp. 49–50.
[b. ]Questions on Heptateuch, VI, qu. x, On Joshua, cited in Decretum, II. xxiii. 2. 2.
[c. ]See Laws VII and VIII, supra, p. 37.
[d. ]Agrees with Vict. [De Jure Belli], 5; Cajetan, On II–II, qu. 40, art. 1 and id., Summula Peccatorum, words bellum iniustum.
[e. ]Baldus, Consilia, IV. cvi; Bartolus, On Reprisals, at beginning, n. 6 [qu. 1, ad 2, n. 6].
[f. ]On II–II, qu. 40, art. 1, and Summula Peccatorum, words: bellum iniustum.
[g. ]De Jure Belli, 5 and 7; Henry of Gorkum, De Bello Justo, in Pref.
[h. ]Arist., Politics, II. ii [II. i. 4–5] and ibid. III. ix [III. v. 10].
[a. ]See definition following Rule III, Chap. ii, supra, p. 36. Arist., Politics, VII. iv .
[b. ]See Dig. XLIX. xv. 24.
[c. ]On Dig. I. i. 5 and ibid. XLIX. xv. 24.
[d. ]See discussion of Laws X and XI, Chap. ii, supra, p. 44.
[e. ]See definition, Chap. ii, supra, p. 43.
[f. ]See Dig. VI. i. 68; Bartolus, On Dig. XLIX. xv. 24, n. 11.
[g. ]Cajetan, Summula Peccatorum, word bellum; Fulgosius, On Dig. I. i. 5; Oldradus, Consilium lxx.
[a. ]See Law X, Chap. ii, supra, p. 44.
[b. ]Against Faustus, XXII. lxxiv [lxxv], cited in Decretum, II. xxiii. 1. 4.
[c. ]See 1 Samuel, viii. 20.
[d. ]Vict. [De Jure Belli], 9, at end; Bartolus, On Dig. I. i. 5 [n. 3]; id., On Reprisals, Qu. 3, at beg., ad 2, n. 6; Laudensis, De Bello, Qu. 2.
[a. ]Letters to His Friends, To Brutus, vii [XI. vii. 2].
[b. ]On II–II, qu. 64, art. 3, at end.
[c. ]On Decretals, II. xiii. 12, n. 8; ibid. xxiv. 24, 29, n. 5 and Panormitanus on same chaps.
[d. ]On Dig. XLIX. xv. 24, nn. 11, 12.
[e. ]Vict. De Jure Belli, 9; Ayala, De Iure et Officiis Bellicis, I. ii. 9; add Sylvester, on word bellum [Pt. I.] ii: Sufficit etiam.
[a. ]See Sylvester, on word repressalia, ii.
[b. ]Cicero, On Duties, I [xli. 149]; Ambrose, On Duties, I. xxxvi, cited in Decretum, II. xxiii. 3. 7; Baldus, On Code, VIII. iv. 1, nn. 46, 47 [nn. 35, 36]; Cajetan, On II–II, qu. 40, art. 1, ad 2; Laudensis, Qu. 15; Vάzquez, Ill. Cont. xxii. 6.
[c. ]Thucydides, I [xliv. 2], and the Scholiast thereon.
[d. ]On subject-matter and form.