Berkeley wrote for those who “want a demonstration of the existence and immateriality of God, or the natural immortality of the soul,” and his philosophy was intended to check materialism. The key-note of his works may be found in his declaration: “The only thing whose existence I deny, is that which philosophers call Matter or corporeal substance.” The definition given by Berkeley of matter is one which no materialist will be ready to accept, i.e., “an inert, senseless substance in which extension, figure, and motion do actually exist.” The “Principles of Human Knowledge” is the work in which Berkeley’s Idealism is chiefly set forth, and many have been the volumes and pamphlets written in reply. Whatever might have been Berkeley’s intention as to refuting scepticism, the result of his labors was to increase it in no ordinary degree. Dr. Pye Smith thus summarises Berkeley’s views:—“He denied the existence of matter as a cause of our perceptions, but firmly maintained the existence of created and dependent spirits, of which every man is one; that to suppose the existence of sensible qualities and of a material world, is an erroneous deduction from the fact of our perceptions; that those perceptions are nothing but ideas and thoughts in our minds; that these are produced in perfect uniformity, order, and consistency in all minds, so that their occurrence is according to fixed rules, which may be called the laws of nature; that the Deity is either the immediate or the mediate cause of these perceptions, by his universal operation on created minds; and that the created mind has a power of managing these perceptions, so that volitions arise, and all the phenomena of moral action and responsibility. The great reply to this is, that it is a hypothesis which cannot be proved, which is highly improbable, and which seems to put upon the Deity the inflicting on man a perpetual delusion.”