In the midst of war, combatants are at every turn confronted with the overwhelming demands of military necessity. Not following them will most definitely give the enemy an advantage in the struggle for victory and can in extremis put an immediate end to a combatant’s life. The social, legal and emotional consequences of killing or maiming another human being in war, to the contrary, are uncertain and remote. In the presence of a threatening enemy combatant, an actor’s commitment to the notion that all human life is worthy may appear abstract, his self-conception as a compassionate person fanciful. Yet few actors will fail altogether to perceive imperatives for action arising from humanitarian concerns, even though those imperatives may interfere with the pursuit of victory or survival.

IL can make a difference for behaviour by providing an actor faced with the task of making a decision with an acceptable compromise between his normative beliefs and instrumental considerations in a certain situation. When it comes to warfare, norms and interests as defined here tend to present directly opposite imperatives for action. Urgent requirements of the situation at hand (interests) in war will often centre on self-preservation and defeat of the adversary. Principled beliefs about war tend to revolve around concerns for the protection of human life beyond one’s own. This chapter introduces the definition of a legitimate target of attack according to international treaty law. The definition’s complicated architecture and considerable contingent indeterminacy bear testimony to the difficulty of balancing utility and appropriateness during the conduct of hostilities.