Platonism is named after the Greek philosopher Plato and his philosophy. Plato was one of Socrates' students and since Socrates himself never wrote anything down, we only know what others wrote about him. Plato wrote dialogues in which Socrates more often than not played the leading role.

In these dialogues he spoke to his students, or sometimes to complete strangers, about almost every conceivable subject. However, when people talk about Platonism, they are usually referring to the metaphysical dialogues written by Plato and later expanded upon by others, including Aristotle.

The most complete description of Plato's metaphysics is found in the Timaeus, a book that is the culmination of his life's work.

According to the Timaeus, the universe was created by a transcendent god called the Craftsman. He gave the universe a body in the form of a sphere by fashioning it from four elements, Fire, Air, Water and Earth. The visible and tangible body of the universe was made possible by binding these elements together in the right proportions.

The Craftsman also created the World Soul to provide movement for the universe. The World Soul was created from three parts — Sameness, Difference and Existence — which were bound together in exact proportions. Two strips of the World Soul's substance were formed into rings that crossed each other in the shape of an X.

Within these rings, the Craftsman created seven planetary rings or spheres, whose distance from the Earth depended on their apparent speed of motion. The Moon was closest, followed by the Sun, Venus, Mercury, Mars, Jupiter and Saturn. These planets became the heavenly gods, subordinate to the Craftsman.

In creating the planets, the Craftsman also created time itself, since the planets controlled the days, months and seasons. The traditional gods of the Greeks, Plato supposed, were created by the planetary gods, whose existence was more certain since they could actually be seen.

The Craftsman also created the souls of men from the same ingredients used for the World Soul, one for each star in the sky. These souls are implanted into bodies according to the dictates of Necessity and if a person lives a righteous life by controlling the passions that have been imposed upon him, his soul travels back to his consort star after death. Since the Craftsman could only create perfect, immortal things, the bodies of human mortals had to be made by the planetary deities, who were also tasked with governing and guiding humanity.

The mortal body is then formed by the gods who borrow from the elements for this purpose. This loan must be repaid when the person dies. Here we see the origin of the idea that humans could look forward to an afterlife in heaven, an idea that would displace the older view of an afterlife in the underworld.

Like the God in Genesis, Plato's Craftsman was a benevolent being who had made the cosmos good by endowing it with soul and reason. Thus the entire cosmos functioned according to the Craftsman's foresight, called Providence. The only allowance for evil was that human souls were implanted in bodies that had to overcome various earthly influences in order to live righteously.

Plato created a metaphysical framework that became extremely popular. While the average farmer or peasant probably didn't care much for it, for other philosophers it became virtually synonymous with philosophy itself. Through Hellenization — Alexander the Great's conquest of much of the Middle East, including Judea — it also had a major influence on Judaism and later Christianity and Islam.