=The Central Principle of Thomas’s Doctrine――The Twofold Truth.= The life-purpose of Thomas was to bring Christianity into closer relation with civilization and science. He sought to give all departments of knowledge their rights and at the same time to protect the ascendency of religion. This was to him the same as bringing Christianity and Aristotle together, for Aristotle meant to him the entire product of ancient civilization. To the mediæval world of grace he added a world of nature, and, fully dominated by the mediæval love of order, he unfolded so comprehensive a view of life that he included all its problems. He felt that the natural and the revealed must not become a contradiction. To accomplish this Thomas found in Aristotle his own ideal estimate of things. Looking at Aristotle through his own neo-Platonism, he naturally found in Aristotle more of the inner and religious estimate of nature than the facts will allow. Yet it was evident to Thomas that there was in Aristotle a great interest in nature and a great reserve on ultimate questions. Nature was, according to Aristotle, an essence unfolding in a system of grades. This became the central principle of Aquinas in this form: _Nature is a sketch in outline of the world of grace_. Before the eye of the religious mind these two truths should appear: (1) the world of faith and the world of nature are two properly distinct worlds; (2) the world of faith is a continuation of the world of nature. The world of grace and the world of nature are two grades of the whole of existence. Nature is the lower stage of development, and the point of contact between it and the world of grace is the soul of man. Religion and philosophy thus have different spheres, but they are not contradictory. Grace does not destroy, but it perfects nature. Nature is subordinate to grace as man is subordinate to the Christian, the state to the church, the Emperor to the Pope.[63]