Plato's metaphysics grew out of that of Parmenides, together with a strong feel for Heraclitus's account of the physical world as a world of incessant change. His ethics were deeply inspired by Socrates, but his views on the soul also pick up on motifs that emerge in Pythagoras.

Presocratic Philosophy: A Very Short Introduction (2004) - Ch. 4 : Reality and appearance: more adventures in metaphysics