General Ideas Socrates had spoken about concepts, and had affirmed their existence in the field of logic and morality. But he had said nothing of the nature of concepts and of their origin. Plato, his greatest disciple, not only inherited his master's doctrine on concepts, but sought to complete it, giving it a metaphysical foundation. For Plato, the concepts of which Socrates had spoken are representative of a metaphysical world which really exists. Ideas, for Plato, are subsistent realities, distinct both from the mind that possesses them and the material objects in which they appear.
Ideas are eternal, immovable.
Opposed to the world of Ideas there is Chaos , the element which receives the form. And between the worlds of Ideas and Chaos there are Demiurge and souls . Demiurge infuses the soul in the Chaos and, working upon it, makes possible this visible world, the world of becoming, of which Heraclitus had spoken. Another important characteristic of the speculation of Plato, one which he had inherited from Socrates, is that philosophy is conceived of in its practical order. This was the philosophic labor, the quest in which Plato spent his whole noble existence, and it explains the great influence his philosophy has exercised on all ages up to the present day.