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The Iraq war rekindled debate – debate now further inflamed in discussions of Iran and North Korea-about the legal use of force to disarm an adversary state believed to pose a threat of catastrophic attack, including with weapons of mass destruction (WMD). Coinciding with this debate is the stark fact that intelligence about allegedly hostile states' WMD capabilities is and will remain limited.

This Article aims to develop more fully how an objective reasonableness approach to WMD capability assessments would work, and more generally how the law governing use of force should guide capability assessments. It begins in Part I with an analysis of the debate over the international law regulating uses of force and the way each doctrinal camp purports to operate in a world of WMD proliferation. Part II argues that a key challenge for any doctrinal approach will be inevitable uncertainty about adversaries' WMD capability, and then examines how each approach grapples with the epistemic problem of judging such capability amid informational gaps and distortions. It argues that a reasonable necessity approach to use of force against WMD threats – and with it an objective standard of assessing WMD capability – operating as a narrow exception to formal U.N. Security Council authorization, best balances competing risks in an environment of significant capability uncertainty. However, it also argues that U.N. Security Council-driven processes and an objective necessity approach are not mutually exclusive and can be combined in reciprocally reinforcing ways.

An objective necessity approach prompts the questions: what level of certainty is reasonable, and what evidentiary logic and assumptions should guide that judgment? Part III explores these questions, and reveals how evidentiary principles reflect underlying policy choices about balancing risks and combating proliferation. Even if one remains unconvinced by the objective necessity approach, the evidentiary issues raised in Part III – and forced to the surface through objective reasonableness analysis – are critical to the effective operation of the legal processes advocated by the traditional view and its strict construction of the U.N. Charter.


International Law | Law | National Security Law


National Security Law Program


Center on Global Governance