Xenophanes was one of the materialist philosophers (physiologoi) or naturalistic thinkers who spearheaded the rationalist movement away from the spiritualist thinkers (theologoi) of Greek philosophy.
...Or was he?
Reading The Shape of Ancient Thought (Thomas McEvilley) we discover that "Xenophanes' rejection of the supernatural was accompanied by advances in the empirical theory of knowledge."
"And as to truth, there never was nor will there be anyone who knew the truth about the gods and the other things I am speaking of. Even if someone should once by chance say what is actually the case, he would not be sure of this. For only illusory opinion is available to anyone." (p. 329)
McEvilley goes on to say, "in antiquity the second sentence of this passage was interpreted as meaning, "Even if someone should be speaking the truth he would not really know whether he was or not."
However, he goes on a bit later to say, "A second interpretation emphasizes the crucial Greek verb in the sentence, which is cognate with Latin video and like it originally meant "know by seeing."If the word still meant this for Xenophanes, his fr. 34 should mean, "Even if someone should succeed in telling the truth, if he is not speaking from direct personal experience but from conjecture, then his statement is invalid methodologically, regardless of its correspondence or lack of correspondence with the facts."
In this passage we discover some interesting roots of the Gurdjieffian ideal. Gurdjieff, after all, insisted that inner understanding derive from personal verification through experience—a concept Xenophanes' statement seems to anticipate and encompass. In addition, the idea to know by seeing became—and exists as—a vital extension of Gurdjieff's idea of inner work as expounded by Jeanne de Salzmann. The empirical—whatever that is—must be known inwardly and known through experience.
We might perhaps suggest here that Xenophanes' subtleties were lost on his contemporaries, who did not understand just what kind of seeing he was referring to. An inner seeing verifies qualities invisible to the outer world.
The metaphysical bridge to Xenophanes' avowed materialism is provided by Gurdjieff's adage that everything is material. As such, even the noumenal world of the theologoi has a material basis, though it may be one too subtle for us to understand it wholly. Even God, in other words, has substance; yet as Xenophanes rightly recognized, that substance can never be known by us except subjectively—hence Gurdjieff's world of idiots, which rests its laurels on the premise of the absolute subjectivity of being, subsumed by the objectivity of law, to which even God must bow.
If there was a split in Greek philosophy leading to today's divide between the materialist sciences and religion, the Gurdjieffian model seems, in other words, to effectively bridge the gap.
This idea of gnosis—knowing by an inner seeing—roughly corresponds to Gurdjieff's understanding, which, like Xenophanes' seeing, transcends the idea of correspondence with facts. Understanding, as those with some gnostic experience will already know, comes through vibration, not mere thought.
Seeing in this way is not an intellectual experience—although it is a deeply intelligent one. One can presume that some of the ancient Greek schools knew this, even though the point may be lost on modern philosophers.
May your soul be filled with light.