Meditations - pg. 67

Am I so bound to a body and its senses that without them I cannot exist? --' But I have convinced myself that nothing in the world exists -- no sky, no earth, no minds, no bodies; so am not I likewise non-existent?' But if I did convince myself of anything, I must have existed. But there is some deceiver, supremely powerful, supremely intelligent, who purposely always deceives me.' If he deceives me, then I again undoubtedly exist; let him deceive me as much as he may, he will never bring it about that, at the time of thinking (quamdiu cogitabo) that I am something, I am in fact nothing. Thus I have now weighed all circumstances enough and more than enough; and must at length conclude that this proposition 'I am', 'I exist', whenever I utter it or conceive it in my mind, is necessarily true.