"The study and the reaching of Christian philosophy."'are both beset with many difficulties . . . (this) author's experience suggests that students often fail to find their way in the teaching of the common Doctor for lack of a proper mastery of fundamental principles or elements. We call here "elements' those key notions and doctrinal positions that are not always explicitly stated in the discussion of each particular problem, but whose knowledge is required for a complete understanding of St. Thomas' answers. Such are: first and foremost, the specific nature of the way in which the theologian uses philosophy according to the view of St. Thomas; second, the Thomistic notion of being, including the consequences it entails for the doctrine of the transcendentals; last, not least, the impact of this same notion on many philosophical problems in whose date it is included-God, substance, efficient causality, creation, the structure of finite being, the nature and unity of than, the soul, the human intellect and its object. These and other key notions are so many basic doctrines that need to the correctly understood before the student attempts to face the colossal array of particular questions and answers) objections and replies, that make up the body of the Christian philosophy of St. Thomas Aquinas.