The fallacy in his system can be briefly exposed. Consciousness is, no doubt, the ultimate ground of certainty of existence for _me_. But though I am conscious of all that passes within myself, I am not conscious of what passes in anything not myself. All that I can possibly know of anything not myself lies in its effects upon me. Any other ideas I may have in regard to the outside world are founded only on inferences, and directly I leave the ground of consciousness for the region of inference my knowledge becomes questionable. It was this defect in Cartesianism which Baruch Spinoza, the great Jewish thinker of Amsterdam, set out to rectify. Spinoza asked himself: What was the reality which lies beneath all appearance? We see everywhere transformations perishable and perishing, yet there must be something beneath which is imperishable and immutable. What is it? In Spinoza's view, the absolute existence is God. All that exists, exists in and by God. Taking the words of St. Paul, "In Him we live and move and have our being," as his motto, he undertook to trace the relations of the world to God and to man, and those of man to society. To John Locke, born at Wrington, in Somerset, in 1632, the problem presented itself in another way. Instead of accepting the validity of clear ideas, as Descartes and Spinoza did, he adopted the Baconian method, and opened the inquiry into the origin and formation of ideas. Separating himself from the philosophers who held that the mind was capable of arriving at knowledge independent of experience, and from the sceptics who maintained that the senses were the only channels of information, he showed that ideas were derived from two sources--sensation and reflection. He was succeeded by George Berkeley, Bishop of Cloyne, born at Kilcrin in Kilkenny, in 1684. He defeated the sceptics on their own ground. There is nothing in the world, he says, except our own sensations and ideas. In order to exist for us, things have to be perceived by the mind; therefore, everything, in order to exist, must exist in the mind of God. But when Berkeley had proved that matter was figment, David Hume, born in 1711, came forward and showed that mind was also an illusion. You know nothing of matter, said Berkeley; you have only perceptions and the ideas based thereon. You know nothing of mind, replied Hume; you have only a succession of sensations and ideas.