11. The Atomism of Anaxagoras. -- Born 500 B.C. at Clazomenae, a contemporary of Leucippus and Empedocles, ANAXAGORAS spent most of his life at Athens, where his great learning secured for him the friendship of many illustrious men. Towards the end of his career, however, owing to political revolutions, he was forced to leave Athens, and settling down at Lampsacus he died there in 428.

The atomism of Democritus, more scientific in its tendencies than that of Empedocles, had neglected the question of the efficient cause of movement. To Anaxagoras belongs the notable merit of having sought the source of material movement in an immaterial, intelligent being. The moving and guiding agency is intelligence, -- mind, endowed with simplicity and the power of knowledge. This is the agency which unites and separates the material particles with set purpose and design. Anaxagoras did not pass beyond the cosmic point of view in studying this intelligence; nor is it likely that he endowed it with the attributes of personality.

Not less remarkable is the difference between his notion of the original matter and the view of his predecessors. He regards it as composed of parts constitutive of all possible substances. But the portions in this primitive mixture are so exceedingly small that none of them can reveal any of its specific properties. Aristotle called them homoiomerê Their various motions give rise to the different material beings of the universe. The specific properties of a body appear when that body is composed principally of particles corresponding to those properties, but it never possesses such particles to the exclusion of the other sorts. "There are parts of all in all things," and hence the possibility of the mutual transformation of bodies generally.

The significance of Anaxagoras in philosophy does not lie so much in his having felt and proclaimed the necessity of an intellectual being in the universe -- Anaximenes had already done this -- but in having so clearly asserted the irreducibility of the material and the immaterial. His philosophy marks the final stage in the evolution of cosmological speculations in Greece anterior to Socrates. It is wholly physical; yet, the study of a directive intelligence suggests considerations of a psychological nature. Anaxagoras may be accordingly regarded as closing the period of formation and leading up to the Sophists and Socrates.