Whatever the universe be in human experience, it is, in important ways, like a dream. That is, we must grant existence to a dream world as an indubitable fact because it is a perceived and experienced world; but at the same time we must refuse its form ultimate existence, and hence enduring reality, because it is neither perceived nor experienced after we awake from sleep. This twofold character of the dream world also belongs to the familiar and so-called real universe. It is plain, yet paradoxical at the same time. For this reason, ancient Tibetan philosophers declared the world to be both existent and non-existent. To the unenquiring mind it vividly is what it seems to be, but to the awakened insight of the sage its form presents itself like a more enduring version of the transient form of a dream world. Both forms are thought-constructions. Both have Mind as their underlying "substance." Therefore Mind is their reality. Apart from Mind the world could not even exist, just as apart from the dreamer his dream could not exist.
-- Notebooks Category 19: The Reign of Relativity > Chapter 1: The Cosmos of Change > # 34
-- Perspectives > Chapter 19: The Reign of Relativity > # 42