The Principle of Distinction and the Role of Consent

Arthur Ripstein offers a Kantian response to what he calls “Shawcross’s argument”—the argument that the killing of combatants in war is justifiable only where the war is legal. In doing so, he is seeking to provide a moral justification for what may appear to be an incoherence between the two main pillars of modern law of war: On the one hand, the ius ad bellum provides that states may only lawfully resort to war when they have a just cause. On the other hand, the ius in bello specifies rules governing conduct that apply equally to both sides in a conflict—regardless of whether they are waging a lawful or unlawful war. Hence combatants in an unlawful war are entitled to the same immunities from prosecution as combatants in a lawful one. But how can that possibly be morally just? Shawcross rejects that moral equivalence, comparing combatants in unlawful wars to a “lawless robber band.” In the process, Shawcross—and those sympathetic to his view—threaten to upend the modern law of war. Ripstein comes to international law’s defense, though not in terms most international lawyers would find familiar. Ripstein’s effort to morally ground the international legal rules is admirable. Yet the argument provides a moral foundation for the modern rules of war that is incomplete at best. Moreover, it fails to grapple with the voluntary nature of international law, which allows states to agree to further their long-term best interests even at the price of short-term constraints.