“In this it is implied,” says Descartes, “that thought is more certain to me than body. If from the fact that I touch or see the earth I judge that it exists, I must more certainly judge from this that my thought exists. For it may very well happen that I judge the earth to exist, even if it does not exist, but it cannot be that I judge this, and that my mind which judges this does not exist.” (10) That is to say, everything which is for me I may assert to be non-existent; but when I assert myself to be non-existent, I myself assert, or it is my judgment. For I cannot set aside the fact that I judge, even if I can abstract from that respecting which I judge. In this Philosophy has regained its own ground that thought starts from thought as what is certain in itself, and not from something external, not from something given, not from an authority, but directly from the freedom that is contained in the ‘I think.’ Of all else I may doubt, of the existence of bodily things, of my body itself; or this certainty does not possess immediacy in itself. For ‘I’ is just certainty itself, but in all else this certainty is only predicate; my body is certain to me, it is not this certainty itself. (11) As against the certainty we feel of having a body, Descartes adduces the empirical phenomenon that we often hear of persons imagining they feel pain in a limb which they have lost long ago. (12) What is actual, he says is a substance, the soul is a thinking substance; it is thus for itself, separate from all external material things and independent. That it is thinking is evident from its nature: it would think and exist even if no material things were present; the soul can hence know itself more easily than its body: (13)All else that we can hold as true rests on this certainty; for in order that anything should be held as true, evidence is requisite, but nothing is true which has not this inward evidence in consciousness.
“Now the evidence of everything rests upon our perceiving it as clearly and vividly as that certainty itself, and on its so entirely depending from, and harmonizing with this principle, that if we wished to doubt it we should also have to doubt this principle likewise” (our ego). (14) This knowledge is indeed on its own account perfect evidence, but it is not yet the truth; or if we take that Being as truth, it is an empty content, and it is with the content that we have to do.
c. What comes third is thus the transition of this certainty into truth, into the determinate;Descartes again makes this transition in a na?ve way, and with it we for the first time begin to consider his metaphysics. What here takes place is that an interest arises in further representations and conceptions of the abstract unity of Being and Thought; there Descartes sets to work in an externally reflective manner. “The consciousness which merely knows itself to be certain now however seeks to extend its knowledge, and finds that it has conceptions of many things - in which conceptions it does not deceive itself, so long as it does not assert or deny that something similar outside corresponds to them.” Deception in the conceptions has meaning only in relation to external existence. “Consciousness also discovers universal conceptions, and obtains from them proofs which are evident, e.g. the geometric proposition that the three angles of a triangle are together equal to two right angles is a conception which follows incontrovertibly from others. But in reflecting whether such things really exist doubts arise.” (15) That there is such a thing as a triangle is indeed in this case by no means certain, since extension is not contained in the immediate certainty of myself. The soul may exist without the bodily element, and this last without it; they are in reality different; one is conceivable without the other. The soul thus does not think and know the other as clearly as the certainty of itself. (16)Now the truth of all knowledge rests on the proof of the existence of God. The soul is an imperfect substance, but it has the Idea of an absolute perfect existence within itself; this perfection is not begotten in itself, just because it is an imperfect substance; this Idea is thus innate. In Descartes the consciousness of this fact is expressed by his saying that as long as the existence of God is not proved and perceived the possibility of our deceiving ourselves remains, because we cannot know whether we do not possess a nature ordered and disposed to err (supra, p. 226).
