 The historical origins of the principle of double effect as a tenet of Catholic casuistry might provide a similar explanation for the unity of its applications. If one were to assume that it is absolutely prohibited to cause the death of a human being, then it would not be permissible to kill an aggressor in self-defense, to sacrifice one’s life to protect others, to hasten death as a side effect of administering sedation for intractable pain, or to endanger non-combatants in warfare. If one were to assume instead that what is absolutely prohibited is to cause the death of a human being intentionally, then these cases can be viewed as cases of non-intentional killing. Controversy about the principle of double effect concerns whether a unified justification for these cases of non-intentional killing can be provided and if so, whether that justification depends on the distinction between intended and merely foreseen consequences.