The task of the Rationalists was rendered the more difficult because, for the first time in the history of European thought, the inner and outer worlds had been completely sundered. For the first time do we meet with a clear-cut and positive dualism. The history of the growth of this dualism had been a long one, and to it the Greek Sophist, the Stoic, and the Christian had each contributed his share. However, Galileo and his fellow scientists in this period of the Renaissance had so reconstructed the old “world of nature” that it had become irreconcilable to the “world of grace.” These scientists believed that nature must be made to explain itself; its events must be conceived as necessitated; its processes as having the inevitableness of a machine. From the revolutions of the planets to the circulation of the blood, the movements of nature can be measured. The law of nature, that is conceived to underlie all this science, is mechanical causation. The researches of the scientists of the Renaissance had yielded a rich world of brute, inevitable, and scientific facts, and these stood in absolute fundamental contrast to the world of spiritual facts which were embodied in the church dogma. Apparently the problem of reconciling the “world of nature” and the “world of grace” had been solved by St. Thomas Aquinas in mediæval times. Now, however, the “world of nature” had been so reconstructed that the question was re-opened. How is the new “world of nature” to be brought into harmonious relation with that old, persistent, and settled dogma of the church? How can the newly conceived mechanism of nature be harmonized with the realm of free conscious spirits, without giving up the conception of God as a rational being, and also without depriving the soul of its power of initiation? The new science had therefore made it especially difficult on the one hand to reconcile a mechanical universe with an omnipotent God, and on the other to reconcile the mechanical human body with the free soul.