Descartes On Doubt

Descartes doubted everything, but hitched his epistemological wagon to the existence of his own consciousness: "I think, therefore I am".

But how could he go from certain knowledge as to his own consciousness and personal existence knowing for sure that the external world exists, and that common sense realism is acceptable, that he human perceiver detects things in existence out there as they are?

Here is what Will and Ariel Durant write on Page 639 of their volume, The Age of Reason Begins:"To escape from this 'solipsistic' prison of the self, Descartes appeals to God, who surely would not make our whole sensory equipment a deception. But when did God come into this system that begin so boldly by doubting all beliefs? Descartes cannot prove the existence of God from evidences of design in the external world, for he has not yet shown the existence of that world. So Descartes evolves God out of the knowing self, very much as Anselm has done in the 'ontological proof' six centuries before. I have, he says, a conception of a perfect being, omniscient, omnipotent, necessary and eternal. But that which exists is more nearly perfect than that which does not; therefore, a perfect being must include existence among his attributes. And who could have put that idea in me but God Himself? 'Is it not possible that . . .I should have in myself the idea of a God if God did not veritably exist? For if God were a deceiver He would not be perfect. Therefore he does not deceive us when we have clear and distinct ideas, nor when He allows our senses to reveal to us an external world. 'I do not see how He could be defended from the accusation of deceit if these ideas were produced by causes other than corporeal objects. Hence we must allow that corporeal things exist. So the gap between mind and mater, subject and object, is marvelously closed, and Descartes, by the help of God, becomes a real-ist. . ."

It seems that Descartes was successful at establishing certain knowledge growing out of the conscious self. It remains to be seen if his ontological proof for God's existence and then building an entire cosmology out of that "proving" that objects really exist out there does hold, but I am sympathetic to his grand attempt.