In referencing his own existence he acknowledged no contingent fact about himself but only what was necessary, namely the pure possibility of being. Even if he were to be annihilated, it was clear that the possibility of his restoration at a succeeding point of time could not be annihilated, the possibility of waking up again. This very possibility belonged to him in a special way, since if the same context of possibility of being were to yield up any other, formally equivalent self, this would not be himself and therefore the context of possibility could not have been identical. All the arguments equating self, as distinct from mind, to brain function, founder on this. It is harder than the hard problem. Any physicalist version of the self is by definition perfectly reproducible, but the self is not reproducible. There is only one self, can only be one self. He could arise again with an entire set of different characteristics, as a different mind, but the self can only be one, there are not two copies. If others truly exist and are not just dreamed figures, they must have exactly the same self, including the one reading this now. The only kind of plurality that is admissible is the one experienced in temporal seriality, all of whose mysteries are immanent mysteries.