place, that as of the fact of thinking we possess an absolute and indestructible assurance, so also do we possess a similar assurance of the fact of our existence. To think for self is to exist, and, as in thinking there is given a subject of thought, of the existence of self,—of this subject we have an absolute assurance. It is thus that Descartes holds it to be as impossible to doubt of self-existence as of the fact that we think; for, when I doubt whether I exist, I think, and thus even because I doubt of my existence, I, to the extent of this doubt, exist. Were I not existing when I supposed I was not, I should thus not exist by supposition, and yet exist because I supposed. The certainty of our existence is thus not dependent on the certainty of the existence of God, or on the certainty that God is no deceiver, for, even though deceived, though compelled to think and determine falsely, we think, are conscious; that is, exist. This certainty is the fundamental one; the basis and ground of all knowledge and science; the ultimate point on which Descartes, trusting to the potency of thought, seeks to raise the superstructure of science.
Thus far of the nature of the Cartesian Doubt, and its solution. But Descartes does not rest here. From finding somewhat that is above doubt, he proceeds to inquire into the grounds of its certainty, and therefore into the last ground of our assurance of the truth of all individual judgments. He thus seeks the Criterion of truth, or "that through which we may be assured that we possess
