¹ Grotius observed that “a war may be just in its origin, and yet the intentions of its authors may become unjust in the course of its prosecution.” See Grotius, Hugo, The Rights of War and Peace (1625), trans. A. C. Campbell (London: M. Walter Dunne, 1901), p. 273Google Scholar. But a shift of intention does not entail the disappearance of the just cause. Thus, Grotius goes on to say that “such motives, though blamable, when even connected with a just war, do not render the war ITSELF unjust.”

² Here I am in agreement with Mellow, David, A Critique of Just War Theory (Ph.D. dissertation, University of Calgary, 2003), p. 201Google Scholar.

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

⁴ See McMahan, and McKim, , “The Just War and the Gulf War,” pp. 502, 512–13Google Scholar. There we acknowledge our debt on this point to Thomas Hurka, whose “Proportionality in the Morality of War” is one of the most probing and rigorous contributions to just war theory in recent decades.

⁵ Although I reject competent authority as a necessary condition of a just war, I concede that it is of practical importance to restrict the authority to take certain actions to certain individuals or bodies when we seek to give institutional expression or embodiment to the requirements of a just war. It may be that, once certain institutions are established, some just causes for war can permissibly be pursued only by those with proper authority.

⁶ Walzer, Michael, Just and Unjust Wars (Harmondsworth, U.K.: Penguin, 1977), p. 21.Google Scholar

⁷ For elaboration, see McMahan, Jeff , “ The Ethics of Killing in War ,” Ethics 114, no. 4 (2004 ), esp. pp. 718 – 29.CrossRefGoogle Scholar

⁸ I have argued at length for the claim that those who fight without just cause cannot satisfy the jus in bello requirement of proportionality. See ibid., pp. 708–18.

⁹ Ibid., pp. 712–14.

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

¹¹ Some people accept that if you reasonably but mistakenly believe that I am culpably trying to kill you, you may be morally and legally justified in killing me. Even if this were so (I think it is not, but I cannot argue for that here), this would not imply that I would be liable to be killed. I cannot be made liable by your mistake, even if it is a reasonable one. The basis of moral liability must be some form of responsible action by the person who is liable. For discussion, see Jeff McMahan, “The Basis of Moral Liability to Defensive Killing,” Philosophical Issues 15 (2005, forthcoming).

¹² Grotius, , The Rights of War and Peace, p. 76.Google Scholar

¹³ de Vattel, Emmerich, The Law of Nations (1758), trans. Joseph Chitty (Philadelphia: Johnson & Co., 1863), p. 302.Google Scholar

¹⁴ de Vitoria, Francisco, “On the Law of War,” in Political Writings, Pagden, Anthony and Lawrance, Jeremy, eds. (Cambridge: Cambridge University Press, 1991), pp. 303–304.Google Scholar

¹⁵ Ibid., p. 307. Vitoria seems to accept a subjective account of justification, according to which it is wrong for a person to fight in a war that he believes to be unjust, even if his belief is mistaken (p. 308). This account of justification may not be fully subjective, however, because elsewhere Vitoria suggests that only reasonable belief is sufficient for justification (p. 306). But this means that he accepts that a person can be justified in fighting in an unjust war, provided that he reasonably believes that it is just; and Vitoria suggests that whenever there is uncertainty about whether a war is just, it is reasonable for a citizen to accept the assurance of his government that it is just (pp. 312–13).

¹⁶ Francisco Suárez, “On War” (Disputation XIII, De Triplici Virtute Theologica: Charitate) (c. 1610), in Selections from Three Works, trans. Gladys L. Williams, Ammi Brown, and John Waldron (Oxford: Clarendon Press, 1944), pp. 845–46.

¹⁷ See, e.g., Thomas Nagel, “War and Massacre,” in Charles R. Beitz, Marshall Cohen, Thomas Scanlon, and A. John Simmons, eds., International Ethics (Princeton: Princeton University Press, 1985), p. 69; Anthony Kenny, The Logic of Deterrence (London: Firethorn Press, 1985), p. 10; and Michael Walzer, Just and Unjust Wars, p. 145. Elizabeth Anscombe, another influential contributor to the literature on the just war, is inconsistent on this point. In her justly celebrated pamphlet opposing Oxford's award of an honorary degree to President Truman (on the ground, in effect, that mass murderers ought not to be awarded honorary degrees), she wrote that “‘innocent’… is not a term referring to personal responsibility at all. It means rather ‘not harming.’ But the people fighting are ‘harming,’ so they can be attacked.” (Anscombe, “Mr. Truman's Degree,” in Ethics, Religion, and Politics: Collected Philosophical Papers, vol. 3 [Minneapolis: University of Minnesota Press, 1981], p. 67.) But in a later paper she wrote that “what is required, for the people attacked to be non-innocent in the relevant sense, is that they should themselves be engaged in an objectively unjust proceeding which the attacker has the right to make his concern; or—the commonest case—should be unjustly attacking him.” (“War and Murder,” in the same volume, p. 53.) In this quotation, “non-innocent” means neither “harming or threatening” nor “guilty,” but “engaged in objectively wrongful action.” So when she wrote the second essay, she had reverted to a position more in keeping with the older just war tradition but inconsistent with the contemporary orthodoxy.

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

¹⁹ See, e.g., Grotius, The Rights of War and Peace, pp. 75–76; Vitoria, “On the Law of War,” pp. 302–306; Vattel, The Law of Nations, pp. 301–14; and Samuel Pufendorf, De Jure Naturae et Gentium, Libri Octo (Oxford: Clarendon Press, 1934), p. 1294.

²⁰ I am grateful to Rachel Cohon for calling this to my attention.

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

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

²³ Craig L. Carr, ed., The Political Writings of Samuel Pufendorf, trans. Michael Seidler (New York: Oxford University Press, 1994), p. 259.

²⁴ Vattel, The Law of Nations, p. 310.

²⁵ McMahan and McKim, “The Just War and the Gulf War,” pp. 502–506. In this article we used the terms “sufficient just aim” and “contributing just aim,” rather than the more perspicuous terms “independent just cause” and “conditional just cause”.

²⁶ For a more detailed discussion of these issues, see Jeff McMahan, “Preventive War and the Killing of the Innocent,” in David Rodin and Richard Sorabji, eds., The Ethics of War: Shared Problems in Different Traditions (Aldershot, U.K.: Ashgate, 2005), pp. 169–90. See also Allen Buchanan and Robert O. Keohane, “Governing the Preventive Use of Force: A Cosmopolitan Institutional Proposal,”Ethics International Affairs 18, no. 1 (2004), pp. 1–22.

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

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

²⁹ The Pastoral Letter of the U.S. Catholic Bishops, The Challenge of Peace (London: CTS/SPCK, 1983), p. 27.

³⁰ Coates, A. J., The Ethics of War (Manchester, U.K.: Manchester University Press, 1997), p. 151.Google Scholar

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