2. Berkeley does not try to prove the existence of the mind or soul, nor does he attempt to show that we perceive the soul. But in the spirit of the Enlightenment he hardly questions its reality. He takes its existence for granted, and like the philosophers of the period he makes a direct appeal to consciousness. “I know I am conscious of my own being.” Like Locke and Descartes he alleges the direct intuition of the self. In the _Principles_ he speaks of “a notion of our own minds or spirits.” Since the ideas are copies of other ideas, there can be no idea of the soul; but the “notion is like the spirit that knows it.” We have therefore direct knowledge or _notion_ of ourselves in knowing our ideas; we have direct knowledge of something superior to the ideas, an activity whose reality consists not in being perceived, but in perceiving. Indeed, he made the assertion in his _Commonplace Book_, which he began in college, that nothing properly does exist but conscious persons. All other things are not so much existences as signs of the existences of persons. One is absolutely certain of what one means by “I.” 3. Spiritual substances are sufficient and adequate to explain all ideas. There is no difficulty in explaining the images of our own minds, for our minds control them. But what explains the existence of our percepts over which we have no control? What substantial support have they if we remove the “material hypothesis”? Suppose I grant that I exist and have control of my imaginative ideas, and that other minds exist and have control of their imaginative ideas, how then, I ask Berkeley, am I to explain the great world of perceptions over which neither I nor other men have control? Berkeley’s general psychological position must be summarized here in order to answer this important question. It is as follows: (1) All things are nothing more than perceptions. (2) All ideas, both perceptions and images, are passive, and must be caused by something in itself active. (3) Souls are active and the cause of ideas. The question then is, What soul is the cause of our perceptions? Perceptions are ideas, are passive, but they are the ideas of whom? Repudiate the material substance, and what is the cause of perceptions?