This conception of soul-stuff may have been an important contribution to metaphysics. The doctrine of material substance is reached by abstracting all the qualities of things; but then there would be nothing left, were it not for this venerable idea of something invisible and intangible in things in which qualities may “inhere,” or which may serve as a “support” to them; so that, when it is taken away there is only a shell or semblance of anything left. But such a tenet is uncommon. Along another line of speculation this soul-stuff may become the Soul of the World. When by philosophers spirits are no longer conceived to have bodies, but to be the very opposite of bodies, a spiritual substance must be invented to support their qualities, in order to put them upon an equal footing of reality with corporeal things; but as there is no spirit-stuff ready made by the wisdom of our forefathers, this concept remains uncomfortably empty. To appear as ghosts and to have mechanical energy, spirits may be invested with “soul-stuff” as a spiritual body; but this is only subtle matter. Their own substance must be correlative with their proper attributes as pure conscious beings, the very opposite of bodies; and, therefore, immaterial, unextended, simple, self-identical, according to the “paralogisms of Rational Psychology.” But such speculations are confined to philosophers and theologians: some of whom, however, maintain (as if reverting to the original savage idea) that spirit is the true substance of material things, at least that material things depend upon a spirit, or spirits, for their existence. Monists, again, say there is one substance of both matter and mind, which is not either of these any more than it is the other. Locke very honestly calls it “a supposed I know not what.” In writing of Magic, I have indicated the origin of the notion of force; and if my view is justifiable, it appears that those celebrated abstractions “force” and “matter,” form and substance, spirit and body, may be traced to the savage mind. That savages are incapable of general and abstract ideas we have seen to be an illusion. They are necessary to economy in the organisation of the mind. When a tribe bases its grammatical gender on the distinction of Animate and Inanimate, has it in no sense corresponding ideas? But an abstract idea results from a long process of dissociative growth from its concrete sources, and must exist in some manner at all stages of that growth, before its distinctness is completed by an appropriate name; and it is reasonable to suppose that at every stage of growth it functions and influences the course of thought. Accordingly, it is plain that from very early times thought has been greatly influenced by ideas of force, form, spirit and the rest of them. § 6. GHOSTS AND SPIRITS