Thus, whereas the Ionians, confounding the unity and the plurality of the universe, had neglected plurality, and the Pythagoreans, contenting themselves with the reduction of the variety of nature to a duality or a series of dualities, had neglected unity, Parmenides, taking a hint from Xenophanes, made the antagonistic doctrines supply one another's deficiencies; for, as Xenophanes in his theological system had recognized at once the unity of God and the plurality of things, so Parmenides in his system of nature recognized at once the rational unity of the Ent and the phenomenal plurality of the Nonent.
The reaction against anthropomorphism begins in Greek philosophy with the satirical spirit of Xenophanes (540 B.C.), who puts the case as broadly as any.
With them came philosophical poems, such as those of Xenophanes and Empedocles; the epical history of Herodotus; the dramatic philosophy of Plato.
Aristotle, in a passage already cited, Metaphysics, A5, speaks of Xenophanes as the first of the Eleatic unitarians, adding that his monotheism was reached through the contemplation of the oupavos.
Thus, whereas in his writings, so far as they are known to us, Xenophanes appears as a theologian protesting against an anthropomorphic polytheism, the ancients seem to have regarded him as a philosopher asserting the unity of Being.
The silence of the extant fragments, which have not one word about the unity of Being, favours the one view; the voice of antiquity, which proclaims Xenophanes the founder of Eleaticism, has been thought to favour the other.
Unlike the Hindu, Xenophanes inclined to pantheism as a protest against the anthropomorphic polytheism of the time, which seemed to him improperly to exalt one of the many modes of finite existence into the place of the Infinite.
The earliest mention of the name of Homer is found in a fragment of the philosopher Xenophanes (of the 6th century B.e., or possibly earlier), who complains of the false notions implanted through the teaching of Homer.
Whether Xenophanes was a monotheist, whose assertion of the unity of God suggested to Parmenides the doctrine of the unity of Being, or a pantheist, whose assertion of the unity of God was also a declaration of the unity of Being, so that he anticipated Parmenides - in other words, whether Xenophanes's teaching was purely theological or had also a philosophical significance - is a question about which authorities have differed and will probably continue to differ.
But, while he thus stood aloof from philosophy, Xenophanes influenced its development in two ways: first, his theological henism led the way to the philosophical henism of Parmenides and Zeno; secondly, his assertion that so-called knowledge was in reality no more than opinion taught his successors to distinguish knowledge and opinion, and to assign to each a separate province.