Homicide in self-defence has been characterized as unintended killing, and said to be justified under the conditions of the Principle of Double Effect. Those who appeal to this Principle distinguish an effect of an act which the agent intends from an effect which the agent merely foresees. Traditionally, those who have sought to justify homicide in self-defence in terms of Double Effect have maintained that, while as a private person I must not engage in intentional killing, it can be permissible for me to act foreseeing that my act will kill someone, provided I do not intend this effect. On the Double Effect view, because intentional killing is prohibited, the agent's intention is crucial to the permissibility of self-defence when the aggressor's death is foreseen as a certain or highly probable effect. Foreseen homicide in self-defence poses both the most difficult case of self-defence for the Double Effect justification, and the case of self-defence for which, on this view, the Double Effect justification is crucial. Here it is held that, provided the agent intends only to use necessary force to defend him- or herself, the aggressor's death is unintended. As explained so far, the Principle of Double Effect could also permit homicide in defence of others.

THE RELEVANCE OF DOUBLE EFFECT TO SELF-DEFENCE

Numerous philosophical discussions of the Principle of Double Effect have focused, rightly, on whether its distinction between an intended and a foreseen effect of an agent's act is defensible and morally important in problem cases. Direct consequentialists usually dismiss this distinction as confused or morally irrelevant.