The common objections to mentalism may be summarized in three forms: (1) A thing does not cease to exist when we cease to think about it; thus, Australia is still to be found on the map even when we are not thinking about Australia. (2) The fact that we do not think of a thing does not prevent such a thing coming into existence. (3) Our awareness of things is largely quite involuntary; we do not choose to think them into existence--they just are there. The answer which mentalism makes to these objections, and to all others which may arise, is a simple one. It is this: consider your life as a dream! All possible objections will then have no ground on which to stand. They appear true while we are under the illusion of dreaming, but they are seen to be false as soon as we awake from the dream itself.
-- Notebooks Category 21: Mentalism > Chapter 3: The Individual and World Mind > # 25