In 1625, Hugo Grotius argued that “war must be carried on with not less scrupulousness than judicial processes are wont to be.” Grotius' views form the normative ground for both modern Just War theory and contemporary international legal theory. In this Chapter, I will begin to discuss one principle that has often been seen as a cornerstone of both of these theories, the principle of discrimination, or distinction – namely that war tactics must not be employed that fail to distinguish the group of combatants from that of noncombatants, refraining from attacking noncombatants but justifiably attacking combatants. I will offer various reasons to reject the traditional principle of discrimination, on both conceptual and moral grounds. At the end of the chapter, I will offer an amended principle. It is my contention that if we follow Grotius' injunction that this principle be followed with minute scrupulousness, fewer military tactics will be justified than is normally thought.

Just War theorists contend that tactics are illegitimate unless they can be used in such a way as to distinguish combatants from noncombatants. Contemporary international legal theory also draws heavily on the principle of discrimination. The Geneva Convention IV, as interpreted in the Second Protocol of 1977, says, “The civilian population as such, as well as individual civilians, shall not be the object of attack. … Indiscriminate attacks are prohibited.”