We are conscious of a world outside through the knowing faculty, the mind. The various ideas which we form of the world are simply states of the mind. These ideas are not separate from the mind itself and could not be. If they were, then we would have to become conscious of them, as we are of the world, through other ideas, through other states of the mind.
-- Notebooks Category 21: Mentalism > Chapter 2: The World As Mental > # 132