We began this review of dreams with the idea of determining whether the analogy can help us understand the nature of reality, and thereby to respond to the metaphysical viewpoint that only the featureless, unmoving Brahman is real, and all else is an illusion. It has become clear, however, that dreams, one way or the other, whether they accurately or inaccurately represent realities, still have their basis in some real forms in the universe. Sri Aurobindo points out “Even if our images are incorrect, what they endeavour to image are realities, not illusions; when we see a tree or a stone or an animal, it is not a non-existent figure, a hallucination that we are seeing; we may not be sure that the image is exact, we may concede that other-sense might very well see it otherwise, but still there is something there that justifies the image, something with which it has more or less correspondence.”
Turning then to the phenomenon of hallucination, we see that there are several types of hallucinations. There can be a sensory hallucination, whereby we can see things which are not actually there. Another type is a mental hallucination “when we take for an objective fact a thing which is a subjective structure of the mind, a constructive mental error or an objectivised imagination or a misplaced mental image.”
Sri Aurobindo provides 2 classic examples: “An example of the first is the mirage, an example of the second is the classic instance of a rope taken for a snake.”
Once again, however, the concept of hallucination does not take on metaphysical import to explain the imposition of pure illusion on the uniform unmoving existence of Brahman. Even when we see something that is not there, it is nevertheless an image of something that exists in and of itself somewhere or at some time. Both the rope and the snake are things which exist in some form and our confusion of the two does not obviate their existence. Similarly, the mirage pictures a city or an oasis, both of which exist and have their own form in some way, and in some place.
The infinite, unmoving, Absolute cannot be imposed on by an illusion, and thus, the forms created in the universe are the Real Idea of the Infinite and take on a reality of their own.
reference: Sri Aurobindo, The Life Divine, Book 2, Part I, Chapter 5, The Cosmic Illusion; Mind, Dream and Hallucination, 428-430