As a character in a dream you can rehearse the cogito: "I think..." - but is it really thinking that you are doing in the dream, or does it only seem that way since logic is suspended? And can you universally doubt with sufficient irony, since you really are at the mercy of an evil genius, or alien biological process? - "... therefore I am" - This is the kicker, because even though on waking you might agree that the dreamer existed in some legitimate sense, the 'being' that his "I am" was pointing to was utterly fictitious, was precisely not being. Granted this, doesn't exactly the same argument apply to the cogito in the waking state: you "I am" is correct in some abstract sense, but the being it points to is imaginary. In other words, all your thoughts drift around in a shadowy realm since they refer only to other thoughts and can never complete a circuit, and so it is absurd to claim that a certain thought or thought of certainty crosses over to truth. As an individual your consciousness takes place between one degree and another on a scale that extends further in both directions. The scale itself is subject, but the being in which it is grounded is inconceivable.