He feels so firmly situated in the physical body that his whole being seems there alone. The first unthought, unanalysed impression supports materialism. But if he remains there he remains an intellectual child. It cannot be said that the brain knows the outside things directly; for it knows them through the intermediary service of the structure of nerves which connects it with the body's eyes, ears, skin, and so on. He hears, touches, or sees a thing or person through the body's senses. But although ear, finger, or eye is involved, analysis shows that in the end the experience is a concept: it is there when he thinks it. Consciousness is involved in the act. For the mere fact that a man is aware of what he does and feels shows that he is a conscious creature in his own right, a mind-being apart from the fleshly form, however much he may be interlocked with it. This perception of the mentalist nature of all our experience of the world opens the way to de-blocking the innate materialism forced upon us by the senses and the thoughts linked with them, a materialism which can be so subtle that even very pious persons are deceived by it.
-- Notebooks Category 21: Mentalism > Chapter 1: The Sensed World > # 57