Its element of truth is the fact that these affections of the percipient mind are the conditions of our knowledge. Its error is in denying that through these and in these we know that which exists independently of our consciousness. The idealism of the present day is mainly a materialistic idealism. It defines matter and mind alike in terms of sensation, and regards both as opposite sides or successive manifestations of one underlying and unknowable force. Modern subjective idealism is the development of a principle found as far back as Locke. Locke derived all our knowledge from sensation; the mind only combines ideas which sensation furnishes, but gives no material of its own. Berkeley held that externally we can be sure only of sensations,—cannot be sure that any external world exists apart from mind. Berkeley’s idealism, however, was objective; for he maintained that while things do not exist independently of consciousness, they do exist independently of _our_ consciousness, namely, in the mind of God, who in a correct philosophy takes the place of a mindless external world as the cause of our ideas. Kant, in like manner, held to existences outside of our own minds, although he regarded these existences as unknown and unknowable. Over against these forms of objective idealism we must put the subjective idealism of Hume, who held that internally also we cannot be sure of anything but mental phenomena; we know thoughts, feelings and volitions, but we do not know mental substance within, any more than we know material substance without; our ideas are a string of beads, without any string; we need no cause for these ideas, in an external world, a soul, or God. Mill, Spencer, Bain and Tyndall are Humists, and it is their subjective idealism which we oppose.