Physiologoi

The Ionian school, a type of Greek philosophy centred in Miletus, Ionia, in the 6th and 5th centuries BCE, is something of a misnomer. Although Ionia was a center of Western philosophy, the scholars it produced, including Thales, Anaximander, Anaximenes, Heraclitus, Anaxagoras, Archelaus, and Diogenes of Apollonia, had such diverse viewpoints that they cannot all be thought of as having belonged to one particular school of philosophy. Aristotle called them physiologoi, meaning 'those who discoursed on nature', but did not group them together as an "Ionian school". The classification can be traced to the second-century historian of philosophy Sotion. They are sometimes referred to as cosmologists, since they were largely physicalists who tried to explain the nature of matter.

While some of these scholars are included in the Milesian school of philosophy, others are more difficult to categorize.

Most cosmologists thought that, although matter could change from one form to another, all matter had something in common which did not change. They did not agree on what all things had in common, and did not experiment to find out, but used abstract reasoning rather than religion or mythology to explain themselves, thus becoming the first philosophers in the Western tradition.

Later philosophers widened their studies to include other areas of thought. The Eleatic school, for example, also studied epistemology, or how people come to know what exists. But the Ionians were the first group of philosophers that we know of, and so remain historically important.

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