"If there is a single element within Catholic casuistry that characterizes its analyses, it is the doctrine of the double effect. This doctrine originates in Aquinas’ claim that killing in self-defense need not involve the intent to end the assailant’s life. Thus, killing in this case does violate the prohibition of intentional killing this doctrine can be applied to many issues in bioethics, including mutilations whose intent is not to destroy bodily function but to save the patient’s life, terminations of pregnancy where there is no intent to kill or harm the fetus (or even precisely to end the pregnancy); decisions to withhold treatment whose intent was not to shorten life but to avoid other evils; and actions in which support is given to wrongdoing, but not for the sake of fostering wrongdoing. Recent analysis of the case of the conjoined twins of Malta, for example, makes use of the doctrine of double effect to determine whether the loss of one twin’s life, in an operation to separate the two, was intended as a means, or accepted as a side effect. There has been much dispute over the doctrine of the double effect among Roman catholic theologians since the debates over contraception began in the 1960s (Boyle, 1993, pp. 11-18). These are part of the larger controversy over moral norms and the conduct of Catholic casuistry, which has dominated catholic moral theology for the last sixty years. The view of the Vatican on these matters has been stated in Pope John Paul II’s Veritatis Splendor (1993, pp. 108-127)."