For details, the reader is referred to Zeller's fuller account of these pre-Platonic elements.[471] But we may summarize as follows: the physical elements to which the Hylicists had in turn attributed finality Plato united into Pythagorean matter, which remained as an element of Dualism. The world of nature became the becoming of Heraclitus. Above that he placed the Being of Parmenides, in which the concepts of Socrates found place as ideas. These he identified with the numbers and harmonies of Pythagoras, and united them in an Eleatic unity of many, as an intelligible world, or reason, which he owed to Anaxagoras. The chief idea, that of the Good, was Megaro-Socratic. His cosmology was that of Timaeus. His psychology was based on Anaxagoras, as mind; on Pythagoras, as immortal. His ethics are Socratic, his politics are Pythagorean. Who therefore would flout Plato, has all earlier Greek philosophy to combat; and whoever recognizes the achievements of the Hellenic mind will find something to praise in Plato. When, therefore, we are studying Platonism, we are only studying a blending of the rays of Greece, and we are chiefly interested in Greece as one of the latest, clearest, and most kindred expressions of human thought. If however we should seek some one special Platonic element, it would be that genuineness of reflection, that sincerity of thought, that makes of his dialogues no cut and dried literary figments, but soul-tragedies, with living, breathing, interest and emotion. Plato thus practised his doctrine of the double self,[472] the higher and the lower selves, of which the higher might be described as "superior to oneself." In his later period, that of the Laws, he applied this double psychology to cosmology, thereby producing doubleness in the world-Soul: besides the good one, appears the evil one, which introduces even into heaven things that are not good. It was only a step from this to the logical deduction of Xenocrates that these things in heaven were "spirits" or "guardians," both good and evil, assisting in the administration of human affairs.[473] Such is the result of doubleness introduced into anthropology; introduced into cosmology, it establishes Pythagorean indefinite duality as the principle opposing the unity of goodness. The next step was taken by Plutarch. The evil demons, had, in Stoic phraseology, been called "physical;" and so, in regard to matter, they came to stand in the relation of soul to body. Original matter, therefore, became two-fold; matter itself, and its moving principle, "the soul of matter." This was identified with the worse World-soul by a development, or historical event, which was the ordering of the cosmos, or, creation.