just war theory a set of conditions justifying the resort to war (jus ad bellum) and prescribing how war may permissibly be conducted (jus in bello). The theory is a Western approach to the moral assessment of war that grew out of the Christian tradition beginning with Augustine, later taking both religious and secular (including legalist) forms. Proposed conditions for a just war vary in both number and interpretation. Accounts of jus ad bellum typically require: (1) just cause: an actual or imminent wrong against the state, usually a violation of rights, but sometimes provided by the need to protect innocents, defend human rights, or safeguard the way of life of one’s own or other peoples; (2) competent authority: limiting the undertaking of war to a state’s legitimate rulers; (3) right intention: aiming only at peace and the ends of the just cause (and not war’s attendant suffering, death, and destruction); (4) proportionality: ensuring that anticipated good not be outweighed by bad; (5) last resort: exhausting peaceful alternatives before going to war; and (6) probability of success: a reasonable prospect that war will succeed. Jus in bello requires: (7) proportionality: ensuring that the means used in war befit the ends of the just cause and that their resultant good and bad, when individuated, be proportionate in the sense of (4); and (8) discrimination: prohibiting the killing of noncombatants and/or innocents. Sometimes conditions (4), (5), and (6) are included in (1). The conditions are usually considered individually necessary and jointly sufficient for a fully just war. But sometimes strength of just cause is taken to offset some lack of proportion in means, and sometimes absence of right intention is taken to render a war evil though not necessarily unjust. Most just war theorists take jus ad bellum to warrant only defensive wars. But some follow earlier literature and allow for just offensive wars. Early theorists deal primarily with jus ad bellum, later writers with both jus ad bellum and jus in bello. Recent writers stress jus in bello, with particular attention to deterrence: the attempt, by instilling fear of retaliation, to induce an adversary to refrain from attack. Some believe that even though large-scale use of nuclear weapons would violate requirements of proportionality and discrimination, the threatened use of such weapons can maintain peace, and hence justify a system of nuclear deterrence. See also POLITICAL PHILOSOPH. R.L.H.