René Descartes Quote
But there is I know not what being, who is possessed at once of the highest power and the deepest cunning, who is constantly employing all his ingenuity in deceiving me. Doubtless, then, I exist, since I am deceived; and, let him deceive me as he may, he can never bring it about that I am nothing, so long as I shall be conscious that I am something. So that... this proposition I am, I exist, is necessarily true each time it is expressed by me, or conceived in my mind.
Meditations on First Philosophy (1641)