It is a commonplace of scientific teaching to say that without the five senses man would know nothing of an external world. This is true, but only while science remains on a materialistic basis. For when it turns over--as it is now beginning to turn--to a mentalistic one, then it has to admit that both those senses and that of which they become aware are themselves mental products. Once this is grasped then it is possible to grasp why they do function during dreams and why we do know an external world in them.
-- Notebooks Category 21: Mentalism > Chapter 1: The Sensed World > # 13