Anaximenes of Miletus (ca. 585–525 B.C.)

Anaximenes, fellow citizen and student of Anaximander, was the first to promote a physical interpretation of the change of things, attributing it to the degree of rarefaction or condensation of the primary substance, air. His empirical thought is found at the opposite pole from Anaximander’s abstract mind. Thus, Anaximenes would follow a course more systematic and inductive that would lead him to two basic conclusions. These might lack the intuitive power of his mentor, but would prove extremely fertile for the later development of scientific thought. First, he establishes the continuous and uninterrupted evolution of an infinite primary substance (air) toward the plurality of the world, while its very material essence (air) remains unaltered, and second, he is the first to attribute all qualitative changes to quantitative differentiations.