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Yale Law School




Much post-9/11 scholarship asks whether modern transnational terrorist networks, the increasing availability of catastrophic weapons to nonstate actors, and other novel threats require changes to either or both of the two traditional branches of the law of war: (i) the jus ad bellum, which governs resort to war, and (ii) the jus in bello, which governs the conduct of hostilities. Scant recent work focuses on the equally vital question whether the relationship between those branches-and, in particular, the traditional axiom that insists on their analytic independence-can and should be preserved in contemporary international law. The issue has been largely neglected since Hersch Lauterpacht, the eminent scholar and former judge of the International Court of Justice, published a seminal article on the topic half a century ago. This Article revisits the issue in the twenty-first century. The standard view, the dualistic axiom, holds that the jus in bello applies equally to all combatants, whatever the ad bellum legality or justice of their resort to force. Yet scrutiny of law and practice alike suggest that politically subjective conceptions of the legality or justice of particular conflicts increasingly erode or blur the boundary between ad bellum and in bello constraints on war. The cost of ad bellum-in bello conflation is high: conflation of the two threatens to compromise the efficacy of each. This Article defends the continuing vitality of the dualistic axiom but also tries to refine our understanding of it. It explains the sources and logic of ad bellum-in bello conflation, illustrates its cost (the neglect or improper application of each), and argues that we must consciously resist the axiom's erosion. To adapt Justice Holmes's maxim, the life of the law of war has not been logic but experience. The dualistic axiom should candidly confront serious, though by no means unassailable, objections raised by recent theorists, but it ultimately remains more firmly grounded in experience and an appreciation of the political and moral reality of war. At the same time, for the axiom to operate most effectively, it must adapt to new geostrategic developments, technological advances, and changes in the nature of warfare. The Article concludes by clarifying how the axiom might be conceived and applied today to best serve the values and policies that underwrite it.

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