Anaximenes

Anaximenes (ăn'əksĭm`ĭnēz), Greek philosopher, 6th cent. B.C., last of the Milesian school founded by Thales. With Thales he held that a single element lay behind the diversity of nature, and with Anaximander he sought a principle to account for diversity. He believed that single element to be air. The principle of diversification he taught was rarefaction and condensation. Different objects were therefore merely different degrees of density of the one basic element. Anaximenes anticipates the spirit of modern scientific practice that seeks to explain qualitative differences quantitatively.

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Anaximenes

(flourished c. 545 BC) Greek philosopher of nature. With Thales and Anaximander, he is one of three Milesian thinkers (see Miletus) traditionally considered the first philosophers of the Western world. He defined the essence of matter as aer (“air”) and explained the densities of various types of matter in terms of varying degrees of condensation of moisture. His writings no longer exist except as quoted by later authors.