As to the generation(363) of the doctrine of Ideas, Aristotle states it as the common product of the doctrine of Heracleitus that everything which meets the senses is subject to change and flux, and of the Socratic view of the conception. From Socrates Plato learnt that when once this is rightly formed, it can be held fast unchangeably: he would not then apply it to anything which meets the senses, but inferred that there must be other beings which are the objects of the knowledge acquired by the conception, and these objects he named Ideas. The filiation,(364) then, between Socrates and Plato is this: Socrates was the first to require that all knowledge and all moral dealing should proceed from the knowing of the conception, and endeavoured to execute this by his inductive process, while with Plato the same conviction formed the starting-point of a philosophical system: so that what with Socrates was simply a rule of scientific procedure was carried out by Plato to an objective intuition, and when Socrates said, Only the knowing of the conception is true knowledge, Plato added, Only the being of the conception is true being.
Thus in Plato we have a man of great original mind attempting with this instrument of induction and definition to form a scheme of the universe, which divides under his hand into a triple aspect of ethics, physics, and dialectics.(365) No doubt his main intention was to offer to the cultured and reflective few,--that inner circle to which his teaching and his writings were directed,--a philosophy which should serve them as a religion,(366) which should fill up the gaps and remove the anomalies of the existing worship, purifying and restoring it, while it preserved amity with it notwithstanding. Such being his intention, the manner in which he treats the doctrine of the Divine Being is the more remarkable. Instead of basing his philosophy upon it, and showing its relation as a part of his system of physics, ethics, and dialectics, he speaks of it frequently indeed, but always incidentally.(367) It is not so with other doctrines which he has at heart. Three of his finest dialogues are dedicated to setting forth as many aspects of his doctrine as to the soul's immortality; the Phædrus treats of its preëxistence; the Banquet of the influence of immortality on the relations of the present life; the Phædo of death as the means of a happy futurity.(368) But no one collects together and lucidly exhibits his view of the divine nature. This has to be picked out of his writings, a bit here, and another there, and put together by the student. No doubt he felt, as he has said,(369) "with regard to the Maker and the Father of this universe it is hard to find him out, and when you have found him impossible to describe him to all men." He was intimately convinced that the great mass of mankind was quite unsuited to receive the conception of the Divine Being which he had formed. But I believe there to have been another reason of greater force with him for his not having presented as a whole his conclusions on this central doctrine of all. It was not merely that the fate of his master Socrates was ever before him,(370) but the singular position which he held with regard to the established worship. He wished to correct, not to destroy it; he wished to reduce it to monotheism, and yet to preserve polytheism. The two are bound together in his mind. If then his writings be carefully analysed, and every reference to the Supreme Being put together into a sort of mosaic,(371) we should find the following picture. The everlasting essence of things, with which Philosophy deals, is the highest object. Ideas are those everlasting gods after the pattern of which the world and all things which are in it are formed, and the Godhead, taken absolutely, is not distinct from the highest Idea. Plato sets forth the causality of Ideas and the sway of reason in the world together with the impossibility to explain what is generated save by an Ingenerate, motion save by a soul, and the ordered disposition of the world, working out a purpose, save by reason; and in all which he declares respecting the Godhead, the Idea of Good, of the highest metaphysical and ethical perfection, is his guiding-point. As this highest Idea stands at the head of all Ideas as the cause of all being and knowledge, so the one everlasting invisible God, the Former and Father of all things, stands at the head of all the gods, alike difficult to find and to describe. Just as the above Idea is distinguished by the conception of the Good, so Plato selects goodness as God's most essential attribute.