That which is neither internal consciousness nor external consciousness nor both together, which does not consist solely in compact consciousness, which is neither conscious nor unconscious, which is invisible, unapproachable, impalpable, indefinable, unthinkable, unnameable, whose very essence consists of the experience of its own self, which absorbs all diversity, is tranquil and benign, without a second, which is what they call the fourth state—that is the âtman. This it is which should be known.

~ Mândûkya Upanishad