But if a psychologist takes appearances for things in themselves, then as a materialist he may take up matter into his doctrine, or as a spiritualist he may take up merely thinking beings (namely, according to the form of our inner sense) as the single and sole thing existing in itself, or as a dualist he may take up both; yet through misunderstanding he will always be confined to sophistical reasonings about the way in which that which is no thing in itself, but only the appearance of a thing in general, might exist in itself.