Greece

Doctrines and Testimonia

Air, through the processes of rarefaction and condensation, is the single material principle that becomes fire when thinned and becomes wind, cloud, water, and earth in turn as it is progressively compressed.

Anaximenes of Miletus, the third in the Milesian sequence of natural philosophers after Thales and Anaximander, proposed air as the underlying principle of all things, known chiefly through later doxographic summaries in Theophrastus, Aristotle, and Simplicius. His distinctive contribution was a mechanism, rarefaction and condensation, explaining how a single substance could become the many different observed materials of the world: air thinned becomes fire, while air progressively compressed becomes wind, then cloud, then water, then earth, then stone. This appeal to a definite physical process rather than mere assertion of a substance marks an advance in explanatory rigor over both of his Milesian predecessors.

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