The state of consciousness, which is beyond limitation, and hence is beyond the cognizer, cognition and cognized. It is thus a state of unconsciousness.
The Secret Doctrine speaks of it as “the dark mystery of non-Being; unconscious, yet absolute Consciousness; unrealizable, yet the one self-existing reality” (SD I:2). It is spoken of as the state attained in Nirvana, a state “in which all sense of individuality is merged in the whole” (Esoteric Buddhism, 189).
