Meditations - pg. xxxvii

The certainty of 'I am', the clearness of 'I think' (I am conscious) resist all the assaults of doubt. No deception can creep into them. The judgment 'I am' is true every time that I make it; it is equally true every time that I make any judgment whatever; every time that I doubt or err. The 'I am' is implied or, more exactly, enveloped in all my judgments, in all my thoughts, in all my acts or states of consciousness. Thought, consciousness, implies and encloses being: 'I am' is an immediate consequence of 'I think' or 'I am conscious'.