The fifth chapter introduces the diverse, complex, and exciting world of medieval thought and learning. It aims to provide a sketch of the historical development of philosophy and, thus, some specific examples of philosophical reasoning in that period. Central to medieval philosophy is the discussion concerning the existence and nature of God, the meaning of creation, and the nature and purpose of human beings. Augustine, Anselm, Maimonides, Averroes, Aquinas, Bonaventure, and Duns Scotus offered proof of the existence of God. Many eleventh-century philosophers, most notably Anselm, Lanfranc, Peter Damian and Gaunilo, made essential contributions by pursuing a rigorously dialectical method of argument based on rational premises, which led to the twelfth-century flowering of dialectic in the work of Abelard and others. The most famous argument for the existence of God is that of Anselm of Canterbury (1033–1109); variations of this argument can be found in the writings of Descartes, Spinoza, Leibniz, Bonaventure, and Duns Scotus. However, it was rejected by both Thomas Aquinas and Kant, who called it the “ontological argument,” which is an argument that proceeds from a thing's mere conception to its reality or existence, a step that Kant believed to be illegal. Positive theology, riding on the metaphysics of Aristotle, reached its culmination with Thomas Aquinas’ (1225–1274) Summa Theologica. For Aquinas, there are three ways of achieving the knowledge of God: causality, eminence and negation. Our understanding of God is non-comprehensive but possible. As creatures, we can only know that God exists and what God is not. The German Dominican monk Meister Eckhart is another influential medieval Christian mystic and negative theologian. Eckhart emphasizes the significance of losing oneself or being separated. For Eckhart, separateness and purification mean letting to be or releasement, which is “an emptying in which people shake off all their attachments or reach a correct (more pure) surrender.” Nicholas of Cusa is another thinker in our consideration of the notion of apophasis and freedom. Cusa’s philosophy fits well within the broad framework of Plato and Aristotle. Three points are imperative in Cusa's thought to understand how finite beings reflect the Divine. Cusa finds that negative theology is preferable to affirmative theology, pointing out what the Absolute is not. According to him, it is less restrive of God’s being. Cusa prefers negative theology (apophasis) to positive theology (kataphasis), but what is superior to both is what is referred to as copulative theology. Copulative theology combines negative and positive theologies and conceives of God, in accord with the coincidence of opposites, as a being which is no particular thing.