Locke denies, and denies with great vigor, the existence of innate ideas. His motives in so doing are practical and theoretical. He sees almost every old idea, every hereditary prejudice, every vested interest of thought, defended on the ground that it is an innate idea. Innate ideas were sacred, and everything which could find no defence before reason was an innate idea. Under such circumstances he takes as much interest in demolishing them as Bacon took in the destruction of the "eidols." But this is but a small portion of the object of Locke. He is a thorough-going empiricist; and the doctrine of innate ideas appears to offer the greatest obstacle to the acceptance of the truth that all the furnishing of the intellect comes from experience. Locke's metaphors for the mind are that it is a blank tablet, an empty closet, an unwritten book. The "innate idea" is only a sentence written by experience, but which, deified by a certain school of philosophers, has come to be regarded as eternally imprinted upon the soul. Such, indeed, is Locke's understanding of the nature of innate ideas. He conceives of them as "characters _stamped_, as it were, upon the mind of man, which the soul has received in its first being and brings into the world with it;" or they are "constant _impressions_ which the souls of men receive in their first beings." They are "truths _imprinted_ upon the soul." Having this conception of what is meant by "innate ideas," Locke sets himself with great vigor, and, it must be confessed, with equal success, to their annihilation. His argument is somewhat diffuse and scattered, but in substance it is as follows: Whatever is in the mind, the mind must be conscious of. "To be in the mind and not to be perceived, is all one as to say that anything is and is not in the mind." If there be anything in the mind which is innate, it must be present to the consciousness of all, and, it would seem, of all at all times, savages, infants, and idiots included. And as it requires little philosophical penetration to see that savages do not ponder upon the principle that whatever is, is; that infants do not dwell in their cradle upon the thought of contradiction, or idiots ruminate upon that of excluded middle,--it ought to be evident that such truths cannot be innate. Indeed, we must admit, with Locke, that probably few men ever come to the explicit consciousness of such ideas, and that these few are such as direct their minds to the matter with some pains. Locke's argument may be summed up in his words: If these are not notions naturally imprinted, how can they be innate? And if they are notions naturally imprinted, how can they be unknown?