The System of the Vedanta according to Badarayana's Brahma-Sutras and Cankara's Commentary c7.s3.t7.26

c7.s3.t7.26

When, further, those who deny external objects maintain that, as in the case of perceptions in dream, so also perceptions of pillars, etc., in waking, arise without an external object, because the two cannot be separated, as both are perceptions [p. 576], we answer: Perceptions in waking cannot arise as do perceptions in dream. Why? Because they are of a different nature. For between dream and waking, there is a difference of nature. In what does this difference of nature consist? In the refutability or irrefutability. For that which is apperceived in dreams, refutes itself; for he who is awakened, says: ‘In error I apperceived a large assembly of people, for there is no large assembly, only my ‘soul was confused by sleep, hence this error arose.’ In the same manner, all illusions of the senses are refuted, according to their character. On the other hand, there is no condition in which the existence of an object perceived in the waking state, a pillar, for example, can be refuted. A dream-face is only a remembrance, whilst seeing in the waking state is apperception. The difference between remembrance and apperception is evident, and is felt of itself; for it consists in the fact that a person is either separated, or not separated, from an object; when, for example, a beloved son is remembered, he is not apperceived, but we wish to apperceive him. [p. 577] As this is so, we cannot maintain that what is perceived in the waking state deceives, because, like apperception in the dreaming state, it is [only] apperception. For the difference between the two makes itself felt. And that which is felt by pretended sages cannot be denied by them. But just because their feelings protest, and they cannot demonstrate to themselves the groundlessness of waking perception, therefore they wish to prove it by its relation with dreaming perception. But a quality that is not in a thing in itself, will not be put there by relating it to another thing. For when we feel that fire is hot, it does not become cold because [as an element] it is related to water. And we have demonstrated the difference between dream and waking.”