"The vocabulary and leading ideas of Catholic bioethics have developed out of the moral work of the great scholastic theologians, most notably from the moral analyses of St. Thomas Aquinas. This tradition of moral thought is often called “natural law theory” or the “natural law tradition” after a dominant component of Aquinas’s time, with notable highlights in the work of the 16th century Spanish scholastics, the 17th century causists, the 18th century synthesis of St. Alphonsus Ligouri, and the revival of Thomistic study in the ate 19th and 20th centuries. The working method throughout this period has been a form of casuistry: new and difficult cases were compared and contrasted with clearer, paradigm cases to illuminate their morally important properties so as to allow their correct moral classification is compatible with the absolutism that characterizes catholic moral analysis: the morally important properties of actions, once revealed by casuistry shows a certain form of intervention in pregnancy involves an intention to end or, more precisely, to shorten the life of the fetus, then the intervention is excluded by the exceptionless prohibition against intentionally killing the innocent."