Understanding that consciousness is the substantive of the three states is understanding of non-duality in the waking experience.

 There is non-duality experience as in deep-sleep, as everyone experiences - that is same in yogic Samadhi too. Deep sleep and yogic Samadhi are identical, but they are not the state derived from non-dual wisdom. Non dual wisdom is realizing the true self is the soul and the nature of the soul is formless and non-dual. Consciously becoming aware of the non-dual nature of the soul in the midst of waking experience is  natural state of the self  attained though non dual wisdom. 

 Everyone  is in free of experience of duality (waking or dream) in deep sleep.  One can speak of the deep sleep experience only in waking, thus one must become aware of the formless non-dual  nature of the soul in waking, by discovering the fact that, the experience of duality is created, sustained by the soul and finally merges itself as soul, which is the true self.   formless  soul alone is real. Soul is the innermost  self and it  is present in the form of consciousness. Realizing the fact that , the  Soul or consciousness alone is real  and   everything else is falsehood in the midst of waking experience, leads to non-dual Self-Awareness.

 

What is lacking is the understanding of the non-duality that one experiences. Hence without perfect understanding one cannot  have non-dual wisdom. Through non dual wisdom one becomes aware of the fact that,  the duality (waking or  dream)and non-duality (deep sleep)are one in essence.  Seeker should understand that all three states   are made fundamentally of the soul or consciousness , which is the innermost self.

Understanding that  consciousness is the substantive of the three states is understanding of non-duality in the waking experience. 

Wisdom is meaningful only so long as it bases on only un-contradictable truth, in the sense that it must not be contradictble. The truth must be such that it must be accepted universal truth.

In other words, non-duality must not be opposed to the presence of duality. If there is such an opposition, non-duality would become the dualistic opposite of duality - when duality comes, non-duality goes and vice-versa.

Where there is duality, there would be no non duality and vice-versa. Thus, being limited by the presence of duality, it would effectively become a kind of duality in its own right - an oxymoron.

Therefore, non-duality in the spiritualistic sense implies freedom from (or transcendence of) duality rather than absence of duality. Non dual wisdom implies "freedom from ignorance" rather than "absence of ignorance" - the freedom from ignorance must necessarily include the freedom to take on any and all ignorance.

  Another way to understand this is that absence of dualistic attributes implies the presence of its dualistic opposite. True freedom from attributes requires freedom from both the opposing attributes, which effectively implies the freedom to include both the opposing attributes. Only such an attribute can imply true non-duality. Only when one becomes aware of the fact that the attributes of duality is dependent on the non-duality and non-duality is independent and can remain with or without the dualistic attributes then he will be able to judge what is permanent and what impermanent, and what is real and what is unreal. 

Similarly, one may consider the usage of the word non-duality. Non-duality is not opposed to duality, but inheres in and through duality.  To understand non duality, seeker must recognize that the whole experience of duality (waking or dream) and make the formless witness (non-duality) itself an opposite of duality leads to freedom from experiencing the duality as reality.

The sky,  the star, planet ,sun , the moon, the earth,  the mountain , the ocean  and the person are all soul  or consciousness , but soul  or consciousness   is not specifically any of these while simultaneously being all of these. This is because while soul, the innermost self  is free from   the sky, the star, planet, sun, the moon, the earth, the mountain, the ocean and the person , etc it is  the formless substance and witness of all these.