At the centre of it lies what has crystallised in more living shape out of the dry conceptions of the Socratic method--the domain of ideas. Even as Parmenides perceived Being in the eternal All-Existent, accessible to Reason alone, so Plato sees the being of individual things in that which pertains to them in common and as such can be grasped by the Reason. But even as the Eleatic “One” exists even apart from its recognition as an objective being, so these eternal and unchangeable archetypes (_ideai_) live in and by themselves as objective essences which exist wholly apart from the individual objects which partake of their form. These archetypes, like the Eleatic All-Existent, bear the name of unit (monad), only in Plato’s scheme there are many such monads, and their unchangeableness does not exclude the idea of causation. Thus his “ideas” are the “units” of Parmenides in multiplicity and the “conceptions” of Socrates endued by metaphysics with the breath of life. To Socrates the idea of Good and of Virtue lay at the heart of his teaching, and thus the preponderance of the idea of Good is confirmed to his pupil, and in its theological elaboration this abstract idea is converted into the Supreme Reason, the first cause of Being, which is identical with the Deity. As to the Eleatics, the external world was an illusion of the senses, and in any case a thing irrational, so matter and the world of phenomena which occupies the middle place between matter and ideas is hard to grasp, and Plato’s notion of the World-Soul which hovers between the two is as contradictory and obscure as that of the human soul. For with this gifted poet-philosopher there is much that tarries on the threshold of consciousness, and fails to struggle into clear light, a circumstance that harmonises with his own teachings, which find clearness and singleness of purport in the Eternal and Divine alone, obscurity and ambiguity in the intermediate terrestrial sphere of genesis, and utter darkness and inconceivability in the lower sphere of matter and non-existence. These three stages are repeated in his theory of the soul, which from desire rises to courage and ultimately to reason. His ethics and politics, which according to his Hellenic ideas are one and the same, are calculated for three classes of humanity--the iron, the silver, and the golden. The last two, the military and learned classes, are the only ones taken into account in the educational system of his ideal state; for the proletariat there is no need to be concerned, although Antisthenes and his successors regarded this very class as the only one capable of genuine philosophy. But Plato, like the aristocrat he was, has in view an elect type of humanity, exalted by exceptional intelligence above the brute multitude and the solid middle-class element and called by philosophy, _i.e._, the doctrine of ideas, to the helm of the ideal state.