Limiting the Killing in War: Military Necessity and the St. Petersburg Assumption

Over the last decade, conventional just war theory has been systematically and thoroughly unraveled by a group of philosophers sometimes collectively referred to as the “revisionist critics.” Given the antagonism between the conventional and the revisionist camps, it is rarely recognized that their most prominent representatives, Michael Walzer and Jeff McMahan, respectively, share the assumption that the form of the rules of war can be explained by an underlying retention or forfeiture of moral rights by individual persons. Walzer treats combatants on both sides as morally equal—that is, equal in moral rights; and McMahan treats them as morally unequal as a result of their own individual conduct—that is, as displaying different degrees of moral liability to defensive harm as a result of features of their decision to participate in war and of their conduct in that war. Both maintain that there can be a rational connection between the moral status of individuals (moral equality for Walzer and differential “moral liability to defensive harm” for McMahan) and how they are permitted to be treated during combat.

Our argument proceeds in three steps. First, we explain why an ideal typical war cannot be regulated with rules that attach to individuals’ moral status. Second, we propose an alternative framework for regulating the conduct of hostilities that hinges on military necessity and a touchstone for its interpretation that we introduce: the St. Petersburg assumption. Third, we locate our proposal on the just war theory landscape and argue that its deliberate departure from individual rights–based morality notwithstanding, it is morally preferable to either Walzer’s conventional or McMahan’s revisionist approach.

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