166. A being which does not think has no consciousness of itself: the stone exists, but does not know that it exists, neither would man himself in a similar case, were all his intellectual and sensible faculties in complete inaction. We easily conceive the difference of these two states by calling to mind what occurs, when from waking we pass into a profound sleep, and again when we awake from it. The first starting-point of our cognitions is this intimate presence of our internal acts, abstraction made of the questions which may be raised upon their nature. If every thing existed as at present, and there also existed, besides the world which we see, infinite other worlds, not even then would any thing exist for us, had we not those internal acts of which we are speaking. We should be like an insensible body placed in the immensity of space, which would suffer no mutation were every thing around it to disappear, and would perceive no change even if it were itself to sink into the abyss of nothing. On the other hand, if we suppose every thing to be annihilated except this being within us which feels, thinks, and wills, there still remains a point whereon to base the edifice of human cognitions: this being, though alone in immensity, would render itself an account of its own acts to the extent of its ability, and might go into numberless combinations having for their object the possible though not the real.
167. The famous principle of Descartes, _I think, therefore I am_, has been often attacked, and justly and conclusively so, if this philosopher really understood his principle in the sense which the schools are accustomed to give it. If Descartes presented it as a true argument, as an enthymema with an antecedent and a consequent, the argument was clearly defective in its foundation. For when he said, "I am going to prove my existence with this enthymema: I think, therefore I am:" this objection might have been made; your enthymema is equivalent to a syllogism in this form: whatever thinks, exists; but I think; therefore, I exist. This syllogism, in the supposition of a universal doubt, excluding even the supposition of existence itself, is inadmissable in its propositions and in their connection. In the first place, how do you know that whatever thinks exists? Because nothing can think without existing. How do you know that? Because what does not exist, does not act. But how in its turn do you know this? Supposing every thing to be doubted, nothing to be known, these principles are not known; otherwise we fall short of the supposition of universal doubt, and consequently go out of the question. If any one of these principles must be admitted without proof, it is just as well to admit your own existence and save yourself the trouble of proving it with an enthymema.