The critic may point out that all biology is opposed to mentalism, that when forms attain a particular level of organization they become thinking forms, that inanimate insentient Nature preceded living conscious form in the order of evolution, that the embryonic mind of animals appeared in the universe before the maturer mind of man itself, and that consequently it is quite absurd to suggest that the mind of man could have thought into existence what in fact was already in existence before it had itself appeared. He may finally observe scornfully that these are mere commonplaces of scientific knowledge, which now have long passed the need of being defended. We must give as a reply to our materialistic critic a fundamental counter-criticism. If the world's existence is completely and satisfactorily accounted for by its reactions to the physical senses of the human body, and if this body itself is a consequence of the evolutionary process of the larger world outside it, the materialist's explanation explains nothing, for it falls into a vicious circle. He forgets that if, according to his theory, the appearance of consciousness were the consequence of an evolution of material forms, then the cerebral-nervous structure of the sensory instruments--which are supposed by him to explain the possibility of consciousness--not having yet manifested themselves, no sensations telling of a world's existence could have been possible! This dilemma cannot be got over except by mentalism. The only world of which we can be certain is that constituted by sensations of colour, shape, breadth, bulk, taste, smell, solidity, weight, and so on. But sensations form the experience of individual minds and such experience, being always observed experience, is formed by thought. Hence if we talk of an uninhabited world--that is, of a world utterly devoid of a mind--we contradict ourselves. The error of materialism is to separate things from the thoughts of them. The consequence of this error is that it can speak of a world by itself as though the latter includes no such existence as thought. It forgets that each individual knows only its own world, because it knows only its own sensations, and that the identity between a Man's consciousness and the world of which it is conscious, is complete and indissoluble. We must place the mind inseparably alongside of the world. The world does not precede it in time. This is so and this must be so because, as the psychological analysis of perception shows, it is the constructive activity of the individual mind which contributes toward making a space-time world possible at all. An uninhabited world has never existed outside the scientific evolutionary theory. For sensations have never existed in separated form, as some celebrated metaphysicians of the eighteenth century supposed, but only in the combined form which they take in the individual's own perceptions.
-- Notebooks Category 21: Mentalism > Chapter 1: The Sensed World > # 134