In several passages in Śańkara’s Commentary on Gaudapāda’s Kärikäs and in the Nineteenth Chapter of the verse section of the Upadeśa Sahasrī we find ‘acosmic’ doctrines buttressed by theoretical arguments as well as by upanishadic quotation. They are associated with a world-view in which the external world is reduced to the ‘oscillation’ of the mind (citta-spandana).
In some places the Self is represented as imagining the individual soul, who then proceeds to imagine his own private worlds, a waking-world which recurs, and dream-worlds which differ from the waking-world and from each other.
From the waking standpoint, it is clear that dreams are illusory. But for their part, the dream-worlds exhibit all the characteristics of the waking-world, including a kind of Alice-in-Wonderland time-space-causation framework of their own.
More important still, from Śańkara’s point of view, is the fact that they contain a distinction between physical and mental (external and internal) and between real and unreal. This parallel between the (admittedly) false dreaming-worlds and the waking-world is used to bring home to the mind the falsity of the latter. Both worlds are the mere play of false ideas consequent upon ignorance of the true nature of the Self.
And a critique of the whole conception of causality is developed, aimed partly at refuting the natural and common conviction that dream-experience is an illusory ‘effect’ arising from waking-experience conceived as a real cause. In these passages there is a tendency to emphasize the irrational and spontaneous character of the experiences of both the dream and the waking states.
Outside the above-mentioned two works, Śańkara rarely if ever attacks the notion of causality, or establishes the irreality of waking-experience from the parallel with dream. He inherited this line of teaching from Gaudapāda, who was himself largely indebted for it to Mahāyāna Buddhist teaching. If Sankara made little use of it outside his commentary on Gaudapāda’s Kārikās, it may be that he considered it suitable only for a particular kind of pupil.
It has been argued that he was initiated into Advaita as a pupil of a Teacher of Gaudapāda’s line and that he later gradually emancipated himself from the acosmic and subjectivist views of Gaudapāda under the influence of other traditional Vedanta teaching.
Whatever be the truth here, he and his great pupil Sureśvara express a reverence for Gaudapāda which they nowhere retract, so that the texts in which he expresses the kind of views we more specifically associate with Gaudapāda deserve to be represented.
~Alston, Creation, p.244