=The Character of the Realism of the Nineteenth Century.= We have already discussed the nature of the Realism of ancient civilization as it appeared in Plato’s theory of Ideas; and we also have reviewed the variation of Plato’s doctrine in mediæval times. Both ancient and mediæval societies give expression through Plato to Realistic conceptions――ancient society to an æsthetic Realism, mediæval to an ecclesiastical Realism. Now in the modern period we find a still different kind. _The Realism of the nineteenth century has been that of natural science._ The question of the nineteenth century has been, What degree of importance has the scientific conception of phenomena in our total conception of life? German Idealism had taken up the natural science of the Renaissance and the Enlightenment, and had made it a part of a world conceived as cosmic Reason. But in the nineteenth century the conception of the cosmic Reason and that of nature part company. The two conceptions begin to stand in antithesis. Nature is conceived as a reality existing in sublime independence. Democritus wins his victory over Spinoza. There are two reasons for this: (1) The ideas of science are expressed with a clearness and distinctness that is in marked contrast with the ideas of German romanticism. Natural science is formulated mathematically and demonstrated in experience, and natural science moreover does not require the labor of interpretation. (2) Natural science proves its usefulness, thereby responding to the imperative needs of the economic changes of the nineteenth century.