In his famous book Just and Unjust Wars, Michael Walzer articulates a thesis he calls the “Moral Equality of Soldiers,” namely, the principle that combatants have an equal right to kill other combatants in war, regardless of the justice of the cause for which they are fighting. The Moral Equality Thesis, as I shall call it, is an essential component of traditional Just War Theory, in that it provides the basis for distinguishing the jus in bello from the jus ad bellum. It also plays a crucial role in identifying the nature of the difference between combatants and civilians. The Moral Equality Thesis has recently come under attack by scholars of Just War Theory, notably philosopher Jeff McMahan, on the grounds that killing for immoral purposes cannot be justified, and so it cannot be true that combatants all have an equal right to kill, regardless of the justice of their cause. In this essay, I defend the Moral Equality Thesis in its traditional formulation. Without it, I argue, the rule of law would not apply in war. The failure to recognize the equal right of combatants to kill in war, I suggest, creates an inconsistency between the rules of war and basic concepts in the law and morality of self-defense, an inconsistency that McMahan himself would think undesirable. I argue that McMahan’s argument applies more compellingly to armed conflict in asymmetrical warfare. Arguably, the Moral Equality Thesis does not apply in an armed conflict between combatants and unlawful combatants. In that context, the divergence from the law and morality of self-defense is less of a concern.

Can two individuals, each of whom needs a certain resource for his survival, have equal and conflicting rights to that resource? If so, is each entitled to try to exclude the other from its use? An old chestnut of moral and legal philosophy raises the problem. Following a shipwreck, two men converge simultaneously on a plank floating in the sea. There is no other plank available and no immediate hope of rescue. Unfortunately the plank can support only one; it sinks if two try to cling to it. Is it permissible for each to attempt to secure his own survival by pushing the other off the plank?

The literature on rights in both moral and legal philosophy is voluminous, so voluminous that there may seem to be little justification for one more symposium to swell its ranks. But the discussion of rights has been fairly tightly organized around several narrow topics of debate, among them whether rights should be explained in terms of interests or choices,The traditional debate is between the “Interest Theory” and the “Will Theory.” For a discussion of this, see A DEBATE OVER RIGHTS (Kramer et al. eds., Clarendon Press 1998). whether rights are strictly correlative with duties,See L.W. SUMNER, THE MORAL FOUNDATIONOF RIGHTS §2.2 (Clarendon Press 1987) for a discussion of this point. and the relation between rights and utility.See, e.g., RONALD DWORKIN, Rights as Trumps, in THEORIESOF RIGHTS 153–68 (Jeremy Waldron ed., Oxford University Press 1984). The inspiration for the present symposium is the sense that one topic of central importance has generally been given short shrift: the question of whether rights can conflict. There is, of course, a perfectly good explanation for why this topic has received so little attention; namely that contemporary rights theorists have generally assumed that rights cannot conflict.Notable exceptions include JUDITH JARVIS THOMSON, THE REALMOF RIGHTS (Harvard University Press 1990) (who allows that rights can conflict without specifically discussing the point); JEREMY WALDRON, Rights in Conflict, in LIBERAL RIGHTS: COLLECTED PAPERS 1981–1991 (Cambridge University Press 1993). But this assumption seems to be out of keeping with the way people commonly speak about rights as well as the way in which rights are usually understood in our constitutional tradition.

Sometimes it is morally permissible to prevent someone from performing a wrongful act by harming him before he has a chance to act. It is permissible, for example, to kill someone you reasonably fear is about to kill you. Under other circumstances, however, it may only be permissible to threaten to harm someone to discourage him from performing a wrongful act. It is not always permissible straightaway to harm him. A military commander, for example, may threaten an enemy with disproportionate retaliation, even though it would not ordinarily be permissible to carry it out.