Proportionality and Necessity in Jus in Bello Page 1 of 27 PRINTED FROM OXFORD HANDBOOKS ONLINE (www.oxfordhandbooks.com). (c) Oxford University Press, 2015. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single chapter of a title in Oxford Handbooks Online for personal use (for details see Privacy Policy). Subscriber: OUP-Reference Gratis Access; date: 12 April 2016 Proportionality and Necessity in Jus in Bello Jeff McMahan The Oxford Handbook of Ethics of War Edited by Seth Lazar and Helen Frowe Abstract and Keywords In this chapter, the author explores the requirement of proportionality in the killing of civilians in war. The work first examines the general notion of proportionality in defensive harming. It then explores proportionality in the resort to war and explains why the traditional theory of just war claims that proportionality in individual acts of war must be different. The author argues that the traditional theory’s claim is a mistake and that when a war lacks just aims, individual acts of harming can seldom be proportionate. Finally, the author considers proportionality as a constraint on violence in a war with just aims, claiming that, in some instances, judgments of proportionality in the conduct of war can be surprisingly precise, though much depends on assumptions about certain fundamental issues in moral theory, such as whether there is an ‘agent-relative permission’ to give some degree of priority to one’s own life. Keywords: proportionality, necessity in defence, jus in bello, jus ad bellum, just war, collateral damage, civilian immunity 1. Introduction In the traditional theory of the just war, the requirements of proportionality and necessity appear twice, once among the principles governing the resort to war (jus ad bellum) and again among the principles governing the conduct of war (jus in bello). The theory insists, in other words, not only that a war itself be proportionate and necessary but also that each individual act of war be proportionate and necessary. Subject: Philosophy, Social and Political Philosophy Online Publication Date: Apr 2016 DOI: 10.1093/oxfordhb/9780199943418.013.24 Oxford Handbooks Online