Xenophanes (c. 570–475 BC)
Xenophanes was a Greek philosopher and native of the city of Colophon. He is best known for having traveled around Greece reciting poetry and as a social critic concerned with how the Greeks conducted themselves. He had a particular gripe against the anthropomorphism of popular religion. Why, he asked, did people suppose their gods to be human in appearance? Wouldn't cows, if they were inclined to pray, worship bovine gods? Xenophanes was one of the first philosophers to promote monotheism in Greece, and was the founder of Eleatic philosophy – the belief that above everything in the world there is an unchanging, everlasting "One."
Xenophanes urged that people should stop assuming they were the center of cosmic attention or that either they or the Earth were unique. To him the idea of unlimited worlds was irresistibly attractive, and he added a new possibility – that the Moon might support life.
The early Milesian philosophers believed that there is a fundamental principle (arche) of the world. They disagreed whether it was water, air, or something without elemental properties (the apeiron). In Xenophanes opinion, two substances, earth and water, worked together. He saw the interplay of wet and dry capable of explaining all the events of the natural world.