We have now been able to discover that our ordinary sense of self is a muddled one, confusing thought and thing, mind and body. It may be thought that the statement of mentalism contradicts our natural belief in the solidity of the material world. But as a matter of fact it does not really contradict either of the aforementioned beliefs; it merely corrects them. For it does not deny that the world is external to the body, and it does not deny that all tangible things are solid to the touch. What it does say is that the world is internal to the mind and that its solidity is likewise present in the mind alone.
-- Notebooks Category 21: Mentalism > Chapter 2: The World As Mental > # 17