This paper investigates the mechanisms used by the "halakhah" to defuse this tension in Jewish law. It also examines similar tension between the provisions of the criminal law and rational morality in Islamic jurisprudence and the defense of necessity in the Common Law. Some rabbinical authorities have sought a formal basis for prohibiting feticide in existing "halakhah." Their suggestions include assault and the notion of potential life. Others have simply indicated the existence of the tension and left the matter there. The paper discusses the killing of a terminally ill person, monarchial corrective criminal jurisdiction in Jewish and Islamic law, and sacrificing a terminally ill person for the sake of saving a viable one. Abortion and the treatment of the terminally ill are dynamic areas of Jewish law as a result of the dialectical nature of that system and its long history of casuistic reasoning. Notes