The reader will recognize this as a re-statement of the argument by St. Anselm. As such it raised a tempest of controversy in Descartes’ time, and was attacked from all sides. (b) Two are causal arguments, that is, based on the assumption of the equality of cause and effect. Only one of these arguments will be cited here. This is known as _The Cartesian Argument._ I have an idea of a perfect Being. This idea must have an adequate cause. Therefore God must exist, for only He, and no imperfect being, can be the adequate cause of my idea of perfection. The ontological arguments given by Descartes are evidently deductions from the certainty of self-consciousness. The question which we immediately raise concerning them is, Are they true? As to the causal arguments, Descartes is breaking away from his original assumption, viz., that self-consciousness is the only certainty, and is introducing another assumption, viz., the certainty of the law of cause. The question, then, that the thoughtful student asks, is, Does Descartes really escape from his solipsism? =The Reality of Matter.= It will be seen that Descartes is trying to deduce from the certainty of the idea of self-consciousness the certainty of other ideas, as propositions are deduced in geometry from axioms. The existence of God is an implication of human consciousness. Now Descartes points out that the existence of matter is implied in the existence of God. Descartes is interested in material science, and it is important for him to prove the reality of matter. Here again his scholastic training comes into play. Since God has all the attributes of a perfect being, He must be veracious. If there were no God, but only a deceiving Devil, the external world might be only a fiction, created to deceive us. But God exists, and we can trust that He would not continually deceive men about the existence of nature. An atheist could have no science, but to Descartes, “God’s in His heaven―― All’s right with the world.” Of course, man is constantly in error about the character of physical things, but these errors arise from his misinterpretation of them. Nature in some form lies before man, or else God in His truthfulness does not exist. The essence of matter is extension (see below), and whatever my interpretation of it, something extended lies before me to be interpreted.