It is very clear that there is no difference between waking state and dream state. By no practical reason can one assert any difference between the two. Karika also proves, by several examples, the equivalence in nature of both states.
However, these two states differ fundamentally from the third state of ours i.e. deep sleep. In both the waking and dream state, we have a feeling of ‘I’. This is called jiva or ahamkara or aham-vritti or simply ‘I’-thought. This ‘I’-thought is absent in deep sleep.
Entire waking state and dream state in nothing but thoughts. All these thoughts have a root thought without which they are not possible. This root thought too is the ‘I’-thought. For any thought to happen, this ‘I’- thought is the sine qua non.Therefore, in deep sleep state, where there is no ‘I’- thought, there are no other thoughts either and consequently no world.
It can, therefore, be safely concluded that the world rises and sinks along with the rising and sinking of this ‘I’-thought.
Now, we have a unique statement in Upanishads. This statement states, “I am Brahman”. At the same time, the Upanishads also declare Brahman to be simply beyond intellect and therefore, inconceivable. So, the problem arises as to how to understand the inconceivable. It is like a mathematical equation which states that I = Brahman. We do not know about the right hand side. But the good thing is that we apparently know the left hand side. After all, everyone is aware of his own self ‘I’. We do experience, in the waking state and dream state, an ‘I’- thought.
So, are the Upanishads declaring this ‘I’-thought to be equal to Brahman? Let us inquire.
This ‘I’-thought is not permanent. Rather, it is transient. It is not present in deep sleep state. Something which is not there in all three states has to be unreal and illusory. This ‘I’-thought cannot be, therefore, Brahman. Then what is this ‘I’ which is there in the equation as left hand side?
The goal of spiritual practice is to experience Brahman or ‘I’. It is said by great persons like Ramana Maharishi that this can be done by experiencing the illusoriness of ‘I’-thought. That can happen by seeking the source of it. The moment source of ‘I’-thought is sought to be experienced by concentrating on it to the exclusion of all other thoughts, this ‘I’-thought disappears (and thus its illusoriness is experienced). However, something else also happens at the same time. An unexperienced experience reveals itself. It is said that that is (which is explained as experiencing, experiencer and experienced) the pure ‘I’ and that is, therefore, Brahman.