  If the transcendentals came primarily from Muslim Aristotelians, especially Avicenna, and the three routes to God were opened by Augustine, the last set of materials Bonaventure used to construct his arguments for the existence of God came from Aristotle himself. “Science” consists in knowledge of a limited subject achieved through demonstrating conclusions about it based on un-demonstrated principles. Bonaventure was one of a group of Parisian theologians, including the Dominicans Albert and Thomas, who attempted to set up Christian theology as an Aristotelian science. He therefore approached the issue of the existence of God with a sharp distinction between principles and conclusions in mind. The question he asks is not “Does God exist?” but “Is the divine being so true that it cannot be thought not to be?” This Anselmian formulation offers two options: God’s existence is either a principle or a demonstrated conclusion. Philosophers are inclined to pick one route to God and reject all others, but Bonaventure had learned from Francis, the poor man of Assisi, that the world is filled with signs of God that even the simplest peasant can grasp. Bonaventure’s response to the problem of the existence of God was therefore most unusual. He pursued all three routes to God; and he even ranked them: Illumination arguments make us “certain” of God’s existence; aitiological arguments give us “more certain” knowledge of God’s existence; while ontological arguments show that God’s existence is “a truth that is most certain in itself, in as far as it is the first and most immediate  truth.”[43] Let us look at each of them in turn.