Diogenes of Apollonia c. 460 BC – c. 390 BC

Diogenes of Apollonia was a Greek pre-Socratic natural philosopher of the late fifth century BC and the last great representative of the early Ionian tradition of inquiry into the principles of nature. Working in Athens during the high classical period, he revived and refined the thesis of his Milesian predecessor Anaximenes that air is the principle of all things, arguing that this single underlying substance, when differentiated by greater and lesser thickness, produces every visible body, and that the intelligence ordering the cosmos is itself a modulation of air. His doctrine of the universal kinship of breath shaped Hellenistic and early Christian thought on the world-soul.