I shall proceed by setting aside all that admits of the slightest doubt, just as if I had discovered it to be absolutely false; and I shall continue always in this track until I shall find something that is certain.
I suppose, accordingly, that all the things which I see are false; I believe that none of those objects which my fallacious memory represents ever existed. I suppose that body, figure, extension, motion, and place are merely fictions of my mind. What is there, then, that can be esteemed true? Perhaps this only, that there is absolutely nothing certain.
But I was persuaded that there was nothing at all in the world: that there was no sky, no earth, no minds, no bodies. Was I not, therefore, at the same time persuaded that I did not exist? Far from it. I assuredly existed, since I was persuaded. But there is a deceiver, I know not who, who is constantly employing his ingenuity in deceiving me. Doubtless, then, I exist, since I am deceived; and let him deceive me as much as he will, he can never bring it about that I am nothing, so long as I shall be conscious that I am something. So that it must, in fine, be maintained that this proposition, I am, I exist, is necessarily true each time it is expressed by me, or conceived in my mind.
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