Des Cartes was of opinion that his demonstrations of the existence of God "equal or even surpass in certitude the demonstrations of geometry." In this opinion we must confess we cannot share. He has already told us that the basis of all certitude is consciousness--that whatever is clearly and distinctly conceived, must be true--that imperfect and complex conceptions are false ones. The first proposition, all must admit, is applicable to themselves. I conceive a fact clearly and distinctly, and, despite all resistance, am compelled to accept that fact; and if that fact be accepted beyond doubt, no higher degree of certainty can be attained, That two and two are four--that I exist--are facts which I never doubt. The _Cogito ergo Sum_ is irresistible, because indubitable; but _Cogito ergo Deus est_ is a sentence requiring much consideration, and upon the face of it is no syllogism, but, on the contrary, is illogical. If Des Cartes meant "I" am conscious that I am not the whole of existence, he would be indisputable; but if he meant that "I" can be conscious of an existence entirely distinct, apart from, and external to, that very consciousness, then his whole reasoning from that point appears fallacious. We use the word "I" as given by Des Cartes. Mill, in his "System of Logic," says, "The ambiguity in this case is in the pronoun I, by which in one place is to be understood _my will_: in another _the laws of my nature_. If the conception, existing as it does in my mind, had no original without, the conclusion would unquestionably follow that '1' had made it--that is, that the laws of my nature had spontaneously evolved it; but that my _will_ made it would not follow. Now, when Des Cartes afterwards adds that I cannot unmake the conception, he means that I cannot get rid of it by an act of my will, which is true; but is not the proposition required. That what some of the laws of my nature have produced, other laws, or those same laws in other circumstances, might not subsequently efface, he would have found it difficult to establish." Treating the existence of God as demonstrated from the _a priori_ idea of perfection and infinity, and by the clearness of his idea of God's existence, Des Cartes then proceeds to deal with the distinction between body and soul. To prove this distinction was to him an easy matter. The fundamental and essential attribute of substance must be extension, because we can denude substance of every quality but that of extension; this we cannot touch without at the same time affecting the substance.. The fundamental attribute of mind is thought; it is in the act of thinking that the consciousness of existence is revealed; to be without thought would be to be without consciousness.