3. From the proposition I think, therefore, I am, the whole nature of the mind may be determined. When we examine who we are who hold every thing to be false that is distinct from ourselves, we see clearly that neither extension nor figure, nor any thing which can be predicated of body, but only thought, belongs to our nature. I am therefore only a thinking being, _i. e._ mind, soul, intelligence, reason. Thought is my substance. Mind can therefore be apprehended clearly and completely for itself alone, without any of those attributes which belong to body. Its conception contains nothing of that which belongs to the conception of body. It is therefore impossible to apprehend it through any sensuous representation, or to make an image of it: it apprehends itself only through the pure intelligence. 4. From the proposition _cogito ergo sum_, follows still farther the universal rule of all certainty. I am certain that I am a thinking being, what now is involved in the fact that I am certain of any thing? Whence comes this certainty? From no other source than the knowledge that this first proposition contains a clear conception of that which I affirm. I know of a certainty that I am, and I know any thing else only when I know it as certainly as I know that I am. Hence I may regard it as a universal rule, that every thing is true which I know clearly and determinately. 5. This rule, however, is only a principle of certainty, not of knowledge and of truth. We apply it therefore to our thoughts or ideas, in order to discover what is objectively true. But our ideas are partly innate, partly acquired, and partly self-originated. Among those of the first class we find the idea of a God. The question arises, whence have we this idea? Manifestly not from ourselves; this idea could only be implanted within us by a being who has the fulness of all perfection in himself, _i. e._ only by an actually existing God. If I ask now the question, whence have I the faculty to conceive of a nature more perfect than my own? the answer must ever come, that I have it only from him whose nature is actually more perfect. All the attributes of God, the more I contemplate them, show that their idea could not have originated with myself alone. For though there might be in me the idea of substance because I am a substance, yet I could not of myself have the idea of an infinite substance, since I am finite; such an idea could only be given me through a substance actually infinite. Moreover, we must not think that the conception of the infinite is to be gained through abstraction and negation, as we might gain darkness through the negation of light; but I perceive, rather, that the infinite contains more reality than the finite, and that, therefore, the conception of the infinite must be correspondingly antecedent in me to that of the finite. Since then I have a clear and determined idea of the infinite substance, and since