The materialist argument is essentially that mental function varies with bodily condition, that alcohol can convert the coward for a time into a brave man, that the increase in size and weight of the brain as man passes from infancy to maturity runs parallel with the increase of mental capacity, and that therefore mind is nothing else than a product of body. Mentalism says these facts are mostly but not always true but that even granting their truth, the materialistic conclusion does not necessarily follow. It is just as logical to say that mind uses brain as a writer uses a pen, that the body is merely instrumental and the limitations or changes in the instrument naturally modify or alter the mentality expressed. The thoughts and feelings, the ideas and memories, the fancies and reasonings which constitute most of our mental stock can be detected nowhere in the brain, can be seen by nothing physical, and can only be observed by the mind itself as acts of consciousness.
-- Notebooks Category 21: Mentalism > Chapter 1: The Sensed World > # 67