flourished 0441; 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.