In the Republic the ideas are spoken of in two ways, which though not contradictory are different. In the tenth book they are represented as the genera or general ideas under which individuals having a common name are contained. For example, there is the bed which the carpenter makes, the picture of the bed which is drawn by the painter, the bed existing in nature of which God is the author. Of the latter all visible beds are only the shadows or reflections. This and similar illustrations or explanations are put forth, not for their own sake, or as an exposition of Plato's theory of ideas, but with a view of showing that poetry and the mimetic arts are concerned with an inferior part of the soul and a lower kind of knowledge. On the other hand, in the 6th and 7th books of the Republic we reach the highest and most perfect conception, which Plato is able to attain, of the nature of knowledge. The ideas are now finally seen to be one as well as many, causes as well as ideas, and to have a unity which is the idea of good and the cause of all the rest. They seem, however, to have lost their first aspect of universals under which individuals are contained, and to have been converted into forms of another kind, which are inconsistently regarded from the one side as images or ideals of justice, temperance, holiness and the like; from the other as hypotheses, or mathematical truths or principles. In the Timaeus, which in the series of Plato's works immediately follows the Republic, though probably written some time afterwards, no mention occurs of the doctrine of ideas. Geometrical forms and arithmetical ratios furnish the laws according to which the world is created. But though the conception of the ideas as genera or species is forgotten or laid aside, the distinction of the visible and intellectual is as firmly maintained as ever. The IDEA of good likewise disappears and is superseded by the conception of a personal God, who works according to a final cause or principle of goodness which he himself is. No doubt is expressed by Plato, either in the Timaeus or in any other dialogue, of the truths which he conceives to be the first and highest. It is not the existence of God or the idea of good which he approaches in a tentative or hesitating manner, but the investigations of physiology. These he regards, not seriously, as a part of philosophy, but as an innocent recreation (Tim.).