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forces) lies underneath the question of the origin of ideas. The point of this paper is to show the inadequacy of the a-priority by which Kant explains the forms of knowledge, whether he considers the negative character of a-priority or independence of experience, or the positive character — spontaneity of the thinking subject. The criteria of irreducibility and necessity are also inadequate. The Kantists can never prove that the matter of thought will with docility take on the forms they want to give it. Nothing but the mere form of identity can be got out of intellectual spontaneity; intellectual spontaneity too instead of explaining causality presupposes it. Whence the activity of thought for Kant? Hegel's creative thought is the natural explanation, but Hegelism is anthropocentric; Kant too is a Ptolemy rather than a Copernicus. In the theory of ideas, as in nature, we must introduce a point of view akin to that of Laplace, which believes in one substance universally extended which includes everything in itself; under form more or less implicit, sensibility and will of ideas are only the condensations in luminous centres and in conscious hearths of that which exists everywhere as sensation and desire; physical movement becomes conscious desire, and nihil est in intellectu quod non prius fuerit in sensu et voluntate. F. at once draws from and embraces Schopenhauer. II. L'Evolutionisme. The cerebral structure may have several origins: 1st. The direct action of environment on the brain and consciousness by means of the senses; 2d. Acquired habit which is then transmitted by heredity; 3d. Natural selection; 4th. The fundamental laws of life; 5th. The universal constitution of elements from the physical and psychical point of view. All systems which neglect one or other of these causes are incomplete, and cannot explain the genesis of cerebral and mental forms. Spencer's theory of the explanation of the structural forms of the brain and thought by association of ideas strengthened by heredity, takes firstly, only account of sensations and not of other mental functions such as emotions and volitions, and secondly, accounts only for superficial mental forms and not for essential forms such as time, space, cause, etc. The second theory of the hereditary transmission of acquired habits is now disputed by some biologists, e.g. Weissmann. Thirdly, we cannot grant that happy molecular accidents suffice to explain the roots of universal and necessary beliefs; the characteristic, too, of the mind is not passivity but reaction — vital necessity is the mother of intellectual industry. We must now show the intimate relations which bind necessary beliefs, chiefly those of identity and sufficient reason, to biological laws of motor reactions, and to psychological laws of desire or volition. Life has for its first law that of preserving itself (root of principle of identity), for its second that of developing itself (root of principle of sufficient reason — every being reacting on