For Plato...

For Plato, this does not mean (as some later Christian thought held) that God is the ground of moral goodness; rather, whatever is good is good in an of itself. God must be a first cause and a self-moved mover otherwise there will be an infinite regress to causes of causes. Plato is not committed to monotheism, but suggests for example that since planetary motion is uniform and circular, and since such motion is the motion of reason, then a planet must be driven by a rational soul.

These souls that drive the planets could be called gods. Aristotle made God passively responsible for change in the world in the sense that all things seek divine perfection. God imbues all things with order and purpose, both of which can be discovered and point to his (or its) divine existence. From those contingent things we come to know universals, whereas God knows universals prior to their existence in things.

God, the highest being (though not a loving being), engages in perfect contemplation of the most worthy object, which is himself. He is thus unaware of the world and cares nothing for it, being an unmoved mover. God as pure form is wholly immaterial, and as perfect he is unchanging since he cannot become more perfect. This perfect and immutable God is therefore the apex of being and knowledge. God must be eternal.

That is because time is eternal, and since there can be no time without change, change must be eternal. And for change to be eternal the cause of change-the unmoved mover-must also be eternal. To be eternal God must also be immaterial since only immaterial things are immune from change. Additionally, as an immaterial being, God is not extended in space. The Neo-Platonic God of Plotinus (204/5-270 A. D). is the source of the universe, which is the inevitable overflow of divinity.

In that overflow, the universe comes out of God (ex deo) in a timeless process. It does not come by creation because that would entail consciousness and will, which Plotinus claimed would limit God. The first emanation out of God (nous) is the highest, successive emanations being less and less real. Finally, evil is matter with no form at all, and as such has no positive existence. God is an impersonal It who can be described only in terms of what he is not.

This negative way of describing God (the via negativa) survived well into the middle ages.