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For more than a thousand years, just war theorists accepted that wars could be launched to punish or avenge wrongdoing, the war itself being an instrument of retribution. Today, this punishment theory of just cause has completely disappeared from international law, which recognizes only individual and collective self-defense as legitimate cause for war. But retributive emotions are as strong today as ever, and the punishment theory is still alive and well in the moral imaginations of modern societies, even if the diplomats and lawyers scrub it from their official pronouncements about the wars their nations fight. Furthermore, intuitions about enemy collective guilt underlie current debates over who counts as a direct participant in hostilities, how voluntary human shields should be treated, and how much risk soldiers must take to minimize casualties among enemy civilians.

This paper addresses two principal questions: how we got from there to here—that is, from just war theories that embraced the punishment theory to its current erasure—and whether the punishment theory may nevertheless be right.

In answer to the first question, the paper traces the punishment theory from its initial formulation in writings of St. Augustine (whose views it examines in detail) through its medieval and early modern defenses, to its rejection by Kant and Vattel. Defenders of the theory, notably Cajetan, viewed punitive war through the lens of criminal justice by which states punish miscreants; they argued that natural reason cannot accept notorious unpunished wrongdoing. Those who rejected the theory did so because it requires one state to judge the conduct of another. This objection raises two distinct issues: violation of sovereign equality, and biased judgment. The paper rejects the sovereignty objection, but elaborates the biased judgment objection by examining the distinction between retribution and revenge.

These arguments lead to five objections to the punishment theory: (1) It places punishment in the hands of a biased judge, namely the aggrieved party, which (2) makes it more likely to be vengeance than retributive justice. (3) Vengeance does not follow the fundamental condition of just retribution, namely proportionality between punishment and offense. (4) Furthermore, punishment through warmaking is collective punishment that punishes the wrong people, and (5) it employs the wrong methods. Ultimately, Cajetan's concerns about unpunished wrongdoing argue for international criminal law, not punitive warfare.