Phenomenism has had its origin in the _Idealism_ which confines the human mind to a knowledge of its own states, proclaiming the unknowability of any reality other than these; and in the _Positivism_ which admits the reality only of that which falls directly within external and internal sense experience. Descartes did not deny the substantiality of the soul, nor even of bodies; but his idealist theory of knowledge rendered suspect all information derived by his deductive, _a priori_ method of reasoning from supposed innate ideas, regarding the nature and properties of bodies. Locke rejected the innatism of Descartes, ascribing to sense experience a positive rôle in the formation of our ideas, and proving conclusively that we have no such intuitive and deductively derived knowledge of real substances as Descartes contended for.(226) Locke himself did not deny the existence of substances,(227) any more than Descartes. But unfortunately he propounded the mistaken assumption of Idealism, that the mind can know only its own states; and also the error of thinking that because we have not an intuitive insight into the specific nature of individual substances we can know nothing at all through any channel about their nature: and he gathered from this latter error a general notion or definition of substance which is a distinct departure from what Aristotle and the medieval scholastics had traditionally understood by substance. For Locke substance is merely a supposed, but unknown, support for accidents.(228) Setting out with these two notions—that all objects of knowledge must be states or phases of mind, and that material substance is a supposed, but unknown and unknowable, substratum of the qualities revealed to our minds in the process of sense perception—it was easy for Berkeley to support by plausible arguments his denial of the reality of any such things as material substances. And it was just as easy, if somewhat more audacious, on the part of Hume to argue quite logically that if the supposed but unknowable substantial substratum of external sense phenomena is illusory, so likewise is the supposed substantial _Ego_ which is thought to underlie and support the internal phenomena of consciousness.