All our experience is ordinarily confined to what the five senses present us--that is, to the sounds touches smells tastes and colours which are their objects. All these may conveniently be called our "sensations." These are what we really know, they are ours individually, and anything which we believe we know beyond them--such as separate and independently existent material objects--are mere suppositions and inferences. Therefore, there must be something in us which projects them so as to appear outside or interprets them as caused by something outside--which amounts to the same thing. Both projection and interpretation are governed by conditions of space and time. The obscurity in which all these operations are carried on does not cancel out the operations themselves. The world does not exist outside of our mind.
-- Notebooks Category 21: Mentalism > Chapter 2: The World As Mental > # 50