Avasthatraya(avastha – state; traya – three) refers to the analysis of the three states that we as human beings pass through every day, namely the waking state, dream state and the deep sleep state, which is employed typically in Advaita philosophy. Such analysis is meant to bring home the fact that we are not the body and mind that we take ourselves to be now but rather pure being-consciousness that we ordinarily feel ourselves to be when we assert “I am” if somebody questions the reality of our existence.
While “I am” (“I” – being or existence; “am” – consciousness) is our true Self, we superimpose on that pristine and nondual reality our identification with the body and mind, in thinking and feeling “I am the body” or “I am this” and “I am that” in the waking and dream states, thereby getting caught in the duality of the world. So, “I am” is present in both waking and dream states but mixed up with “the body” and “this” and “that”. In sleep, however, we are devoid of the body and mind, but we exist in sleep, otherwise we cannot wake up with the memory of having slept blissfully. So, we were present in sleep as the pure “I am”. Since the body and mind exist in only two of the three states, namely, waking and dream [that, too, with the body in waking being different from the body in dream], but the awareness of “I am” exists in all three states, the pure “I am” must be our real self and not the transitory body and mind.
An objection might be raised at this point that we were unaware in sleep or unconscious. However, what was absent was not consciousness because we were aware that the body and the world do not exist for us. It is much like a normal-sighted person in a dark room. Though the room is dark it cannot be said that he does not see. It is true that he does not see the objects in the room but he sees the darkness around because he has sight. That is, he is aware of the darkness. In a similar situation, a blind person would not see or be aware of even the darkness. So, in sleep we are like the normal-vision person in a dark room and not the blind person in a dark room, in that we are aware that the body and world do not exist for us.
Thus, it stands to reason that we are not the body and mind, but pure “I am” or pure consciousness, also often referred to as Self or Brahman.