A. 1. Is It Always Sinful to Wage War?
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In ST II–II, Q. 40, A. 1, Thomas asserts that waging war can be justified if three conditions are satisfied: (1) that legitimate authority makes the decision to wage war; (2) that there is a just cause to wage war; (3) that those waging war have a right intention, namely, to wage only for the sake of justice.
In ST II–II, Q. 64, Thomas holds that it is never lawful to kill an innocent human being (A. 6), that it is lawful for private persons to kill another in necessary self-defense of their lives but unlawful for the persons to intend the resulting death (A. 7), and that one killing another accidentally is not guilty of homicide, that is, murder or manslaughter (A. 8).
[This question is divided into four articles, one of which is translated here.]
We thus proceed to the first inquiry. It seems that it is always sinful to wage war, for the following reasons:
Obj. 1. Punishment is inflicted only for sin. But the Lord declares that those who wage war will be punished, as Mt. 26:52 says: “Those who take to the sword will perish by the sword.” Therefore, all wars are unlawful.
Obj. 2. Everything contrary to a divine precept is a sin. But waging war is contrary to a divine precept, since Mt. 5:39 says: “I tell you not to resist evil,” and Rom. 12:19 says: “Do not defend yourselves, dearly beloved, but leave it to [God’s] wrath.” Therefore, it is always sinful to wage war.
Obj. 3. Only sin is contrary to a virtuous act. But war is contrary to peace. Therefore, war is always a sin.
Obj. 4. Every exercise regarding something lawful is lawful, as is clearly the case with scientific exercises. But the church prohibits the warlike exercises in tournaments, since the church denies those who die in such contests Christian burial. Therefore, war seems to be absolutely sinful.
On the contrary, Augustine says in a sermon on the centurion’s servant: “If Christian teaching were altogether to condemn war, the soldiers in the {165} Gospel who sought salutary advice [Lk. 3:14] would have been told to cast aside their arms and abandon military service altogether. But Christ told them: ‘Do violence to no one, and be content with your pay.’ And if Christ commanded them to be satisfied with their pay, he did not forbid military service.”1
I answer that three things are required for a war to be just. Indeed, the first requirement is that the ruler at whose command the war is to be waged have the lawful authority to do so. For it belongs to no private citizen to initiate war, since private persons can pursue vindication of their rights through the decisions of their superiors. Likewise, it belongs to no private citizen to initiate war, because no private citizen can call on the people to wage war, which has to be done in wars. Rather, since the care of the commonweal has been committed to rulers, it belongs to them to protect the commonweal of the city or kingdom or province subject to them. And they lawfully use physical weapons to defend the commonweal against domestic rebels when they punish malefactors, as the Apostle says in Rom. 13:4: “He [the ruler] does not carry a sword without cause, since he is God’s servant, an avenger to execute wrath on the evildoer.” Just so, it also belongs to rulers to use weapons of war to protect the commonweal against foreign enemies. And Ps. 82:4 tells rulers: “Rescue the poor and free the needy from the hands of sinners.” And so Augustine says in his work Against Faustus: “The natural order conducive to peace among mortals requires that the legitimate authority to undertake war, and deliberation regarding war, be in the hands of rulers.”2
Second, there needs to be a just cause to wage war, namely, that the enemy deserve to have war waged against it because of some wrong it has inflicted. And so Augustine says in his Questions on the Heptateuch: “We usually define just wars as those that avenge wrongs, when peoples or political communities need to be punished either because they have failed to rectify wrongs committed by their subjects, or because they have failed to restore property unjustly seized.”3
Third, those waging war need to have a right intention, namely, an intention to promote good or avoid evil. And so Augustine says: “For true worshipers of God, wars waged with zeal for peace and not out of desire for gain or out of cruelty, wars waged to restrain the wicked and assist the good, are also conducive of peace.”4 But even if legitimate authority {166} declares war, and the cause is just, wars may be unlawful because they are waged with a wicked intention. For Augustine says in his work Against Faustus: “Desire to harm, vengeful cruelty, insatiate and implacable animus, savagery in renewing combat, lust for dominance, and the like are justly condemned in the matter of waging war.”5
Reply Obj. 1. Augustine says in his work Against Faustus: “They take to the sword who take up arms against the life of another without any superior or legitimate authority either commanding or allowing it.”6 But those who use the sword by the authority of a ruler or judge, if they be private citizens, or out of zeal for justice and by the authority of God, as it were, if they be public officials, do not themselves “take to” the sword. Rather, they “use” the sword committed to them by another. And so they do not deserve punishment.
Still, even those who use the sword sinfully are not always slain by the sword, although they always perish by their own sword, since they are eternally punished for their sinful use of the sword unless they repent.
Reply Obj. 2. As Augustine says in his work On the Lord’s Sermon on the Mount,7 human beings should always observe such precepts in readiness of spirit, namely, that they be ready, if necessary, not to resist and not to defend themselves. But one sometimes should act otherwise for the sake of the common good, and also for the good of those against whom one is fighting. And so Augustine says in a letter to Marcellinus: “We should also do many things to those whom we punish with a kindly severity against their will. For they are beneficially vanquished who are snatched from the licentiousness of sin, since nothing is more miserable than the happiness of sinners, which feeds a punishable licentiousness and, like an internal enemy, strengthens an evil will.”8
Reply Obj. 3. Even those who wage just war strive for peace. And so they are only contrary to the evil peace that the Lord “did not come to send upon the earth,” as Mt. 10:34 says. And so Augustine says in a letter to Boniface: “We do not seek peace in order to wage war. Rather, we wage war in order to achieve peace. Therefore, be peacemakers in waging war, so that you may in winning bring those against whom you war to the benefit of peace.”9
Reply Obj. 4. Not all military exercises by human beings are forbidden. Rather, only disordered and dangerous military exercises that give rise to {167} slayings and plunderings are forbidden. And the ancients took part in military exercises without such risks. And so the ancients called them “military exercises” or “bloodless wars,” as Jerome makes clear in one of his letters.10
1Letter 138, to Marcellinus, c. 2, n. 15 (PL 33:531).
2Against Faustus XXII, 75 (PL 42:448).
3Questions on the Heptateuch, q. 10, on Jos. 8:2 (PL 34:781).
4Actually, Gratian, Decretum II, causa 23, q. 1, c. 6.
5Against Faustus XXII, 74 (PL 42:447).
6Ibid., 70 (PL 42:444).
7On the Lord’s Sermon on the Mount I, 19, nn. 58–9 (PL 34:1260).
8Letter 138, to Marcellinus, c. 2, n. 14 (PL 33:531).
9Letter 189, to Boniface, n. 6 (PL 33:856).
10Actually, Vegetius, Institutes of Military Affairs I, 9–28; II, 23.