Number was the sacred and unchangeable principle by which the universe was regulated; and there was a "music of the spheres;" and that the soul itself was a harmony imprisoned in the body: while his contemporary Democritus, "the first materialist," held that by some law of necessity countless atoms had moved together in the void of space, and so produced a world.
Lastly, the Eleatics took higher ground, and conceived the idea of one eternal and absolute Being which alone exists, while non-existence is inconceivable. Plurality and change, space and time, are merely illusions of the senses. This doctrine is set forth at some length by Parmenides, the founder of this school of thought, in an epic poem, in which he has been commissioned, he says, by the goddess of wisdom, "to show unto men the unchangeable heart of truth." Plato, who always speaks of him with respect—"more honoured than all the rest of philosophers put together"—has given his name to one of his Dialogues, in which he introduces him as visiting Athens in his old age, in company with Zeno, his friend and pupil, and there discussing his theories with Socrates, then a young man of twenty.
The Dialogue turns upon the difficulties involved in the famous Eleatic saying, that "the All is one, and the many are nought;" but, by an easy transition, the argument in the first part of the Dialogue discusses the doctrine of Ideas—the key-stone of Plato's philosophy. This doctrine seems to have grown upon him, and engrossed his mind; and his poetic feeling is continually suggesting additions and embellishments to it, just as
