There is a need to analyze the three states, in order to realize the existence of the formless witness of the three states.

The term thought must be used differently from the term experience. A thought is any passing fancy or any feeling or any desire which comes and goes within the waking or dream. The thought belongs to individual within the waking or dream.

An experience is not a thought in the above sense but a sensation of some object which is apparently outside the true self. Thus the experience is prior to the thought.   The thought rises within the experience (waking or dream).

 Seeker has to observe the fact that the dreamer may imagine himself to be hunting, ruling or flying when in waking life he never does any of these. Hence his dream ego is entirely a concocted one, fictitious and superimposed on reality. Precisely the same applies to the waking ego. 

The waking experience includes the others because it is only when one is awake that he knows dream and sleep exists. During dream itself he takes it for the time being as though it was waking, and he is unable to know otherwise.

The necessary contrast to enable one to distinguish between the dual and non dual experiences can only be effected whilst awake, when only he can perceive that waking is only an experience that comes and goes; he cannot perceive this during dream or sleep. Hence realization can only be effected in the waking experience. Hence There is a need to analyze  the  three states,  in order to realize the existence of the formless witness of the three states. 

When in a dream, if one is  aware that all the forms, phantasms etc. that he sees are of the same stuff as the essence of the mind; it is knowledge; the dream ceases to be a dream (with its reality) and it comes and goes as mere experience.  The experiencer is formless.

 When my mind is present dream or waking experience is there; when it ceases (as in sleep) the waking disappears. Therefore one has to infer by comparison and agreement that the existence of the waking or dream is connected with the duality of the mind.

The attributes of the mountain one sees in dream i.e. its hardness, sizes form etc. is in the mind. Thus mind is waking or dream.  Similarly in this world the attributes of the various people and objects, are in the mind, the formless substance and witness of the mind is conciousness.  Mind ceases to exist in deep sleep and death but its basis still continues and must continue.