gods as oxen, horses, or lions. This critique was not limited to the looks of gods but also their behaviour. Greek mythology, mostly shaped by the poets Homer and Hesiod, attributed moral failures such as jealously and adultery to the gods. Xenophanes opposed this. He thought gods must be morally superior to humans. Xenophanes, however, never claimed the gods were omnipotent, omnibenevolent, or omniscient. Xenophanes also offered naturalistic explanations for phenomena such as the sun, the rainbow and St. Elmo's fire. Traditionally these were attributed to divine intervention but according to Xenophanes they were actually effects of clouds. These explanations of Xenophanes indicate empiricism in his thought and might constitute a kind of proto-scientism. Scholars have overlooked his cosmology and naturalism since Aristotle (maybe due to Xenophanes' lack of teleology) until recently but current literature suggests otherwise. Concerning epistemology, Xenophanes questioned the validity of human knowledge. Humans usually tend to assert their beliefs are real and represent truth. While Xenophanes was a pessimist about the capability of humans to reach knowledge, he also believed in gradual progress through critical thinking. Xenophanes tried to find naturalistic explanations for meteorological and cosmological phenomena. Ancient philosophy historian Alexander Mourelatos notes Xenophanes used a pattern of thought that is still in use by modern metaphysics. Xenophanes, by reducing meteorological phenomena to clouds, created an argument that "X in reality is Y", for example B32, "What they call Iris [the rainbow] that too is in reality a cloud: one that appears to the eye as purple, red, and green. This is still use[d] today 'lightning is massive electrical discharge' or 'items such as tables are a cloud of micro-particles'." Mourelatos comments that the type of analogy that the cloud analogy is remains present in scientific language and "...is the modern philosopher's favourite subject for illustrations of inter-theoretic identity". According to Aristotle and Diogenes Laertius, Xenophanes was Parmenides' teacher; but is a matter of debate in current literature whether Xenophanes should also be considered an Eleatic. Heraclitus The hallmark of Heraclitus' philosophy is flux. In fragment DK B30, Heraclitus writes: This world-order [Kosmos], the same of all, no god nor man did create, but it ever was and is and will be: everliving fire, kindling in measures and being quenched in measures. Heraclitus posited that all things in nature are in a state of perpetual flux. Like previous monist philosophers, Heraclitus claimed that the arche of