8 War Crimes and Immoral Action in War Jeff McMahan I. The Traditional Theory of the Just War War crimes are grave violations of the legal principles of jus in bello, the principles governing the conduct of war, for which individual combatants may be punished. In international humanitarian law, these principles are found in the Hague Conventions and the Geneva Conventions. They have subsequently been absorbed, though with some modifications, into inter- national criminal law. As in domestic criminal law, the ideal in the law of war is that all and only those acts that harm their victims and are seriously morally wrong should be criminal, and thus punishable. The law ought, within certain limits, to deter by threat of punishment all acts that are morally impermissible and inflict wrongful harm. Yet it ought not to punish people for acting in ways that are morally permissible. Ideally, therefore, the category of war crimes should include all forms of morally wrong action in war that inflict serious harms on their victims. In this chapter I will argue that there are insurmountable obstacles to achieving this ideal. I first offer a brief account of the way that jus in bello is conceived both by the traditional theory of the just war and by the law. I next indicate why jus in bello so conceived cannot be right as a matter of morality and then sketch a revisionist account of the morality of jus in bello. Yet I also argue that the requirements of this revisionist account cannot in general be satisfied by those who fight without a just cause. Because in bello law has as one of its purposes the effective constraint of the action of those who fight without a just cause, it cannot simply declare that all their acts of war are impermissible. It seems, therefore, that in bello law cannot be modelled directly on in bello morality. In bello law and in bello morality must be substantially divergent. I conclude by considering what the criterion, or OUP CORRECTED PROOF – FINAL, 5/1/2013, SPi