It is remarkable that any of them were satisfied with the accuracy of their reasonings. We can explain it only by the intellectual habit of the age, and the (misread) traditions of the Stagyrite. They made use, unconsciously, of that intuition which carries us across the gulf, and they misread the process by which they reached the other side. They set down to the credit of their intellect what was due to the necessities of the moral nature, and the voice of the heart. Descartes was the most illustrious thinker, who, at the dawn of modern philosophy, developed the scholastic theism. While inaugurating a new method of experimental research, he nevertheless retained the most characteristic doctrine of mediæval ontology. He argues that necessary existence is as essential to the idea of an all-perfect being, as the equality of its three angles to two right angles is essential to the idea of a triangle. But though he admits that his 'thought imposes no necessity on things,' he contradicts his own admission by adding, 'I cannot conceive God except as existing, and hence it follows that existence is inseparable from him.' In his 'Principles of Philosophy' we find the following argument:-- 'As the equality of its three angles to two right angles is necessarily comprised in the idea of the triangle, the mind is firmly persuaded that the three angles of a triangle _are_ equal to two right angles; _so_ from its perceiving necessary and external existence to be comprised in the idea which it has of an all-perfect being, it ought manifestly to conclude that this all-perfect being exists.'--(Pt. i. sec. 14.) This argument is more formally expounded in his 'Reply to Objections to the Meditations,' thus:-- 'Proposition I. The existence of God is known from the consideration of His nature alone. Demonstration: To say that an attribute is contained in the nature or in the concept of a thing, is the same as to say that this attribute is true of this thing, and that it may be affirmed to be in it. But necessary existence is contained in the nature or the concept of God. Hence, it may be with truth affirmed that necessary existence is in God, or that God exists.'