Anaxagoras (Greek: Ἀναξαγόρας, c. 500 BC – 428 BC) was a Pre-Socratic Greek philosopher famous for introducing the cosmological concept of Nous (mind), the ordering force.
In early manhood (c. 464-461 BC) he went to Athens, which was rapidly becoming the centre of Greek culture. There he is said to have remained for thirty years. Pericles learned to love and admire him, and the poet Euripides derived from him an enthusiasm for science and humanity.
Anaxagoras brought philosophy and the spirit of scientific inquiry from Ionia to Athens. His observations of the celestial bodies and the fall of meteorites led him to form new theories of the universal order. He attempted to give a scientific account of eclipses, meteors, rainbows and the sun, which he described as a mass of blazing metal, larger than the Peloponnese. The heavenly bodies, he asserted, were masses of stone torn from the earth and ignited by rapid rotation. However, these theories brought him into collision with the popular faith; Anaxagoras' views on such things as heavenly bodies were considered "dangerous."
About 450 Anaxagoras was arrested by Pericles' political opponents on a charge of contravening the established religion (some say the charge was one of Medism). It took Pericles' power of persuasion to secure his release. Even so he was forced to retire from Athens to Lampsacus in Ionia (c. 434-433 BC). He died there in around the year 428 BC. Citizens of Lampsacus erected an altar to Mind and Truth in his memory, and observed the anniversary of his death for many years.
Anaxagoras wrote a book of philosophy, but only fragments of the first part of this have survived, through preservation in work of Simplicius of Cilicia in the sixth century AD.
Mind causes motion. It rotated the primitive mixture, starting in one corner or point, and gradually extended until it gave distinctness and reality to the aggregates of like parts, working something like a centrifuge, and eventually creating the known cosmos. But even after it had done its best, the original intermixture of things was not wholly overcome. No one thing in the world is ever abruptly separated, as by the blow of an axe, from the rest of things.
It is noteworthy that Aristotle accuses Anaxagoras of failing to differentiate between nous and psyche, while Socrates (Plato, Phaedo, 98 B) objects that his nous is merely a deus ex machina to which he refuses to attribute design and knowledge.
Anaxagoras proceeded to give some account of the stages in the process from original chaos to present arrangements. The division into cold mist and warm ether first broke the spell of confusion. With increasing cold, the former gave rise to water, earth and stones. The seeds of life which continued floating in the air were carried down with the rains and produced vegetation. Animals, including man, sprang from the warm and moist clay. If these things be so, then the evidence of the senses must be held in slight esteem. We seem to see things coming into being and passing from it; but reflection tells us that decease and growth only mean a new aggregation (sugkrisis) and disruption (diakrisis). Thus Anaxagoras distrusted the senses, and gave the preference to the conclusions of reflection. Thus he maintained that there must be blackness as well as whiteness in snow; how otherwise could it be turned into dark water?
Anaxagoras marked a turning-point in the history of philosophy. With him speculation passes from the colonies of Greece to settle at Athens. By the theory of minute constituents of things, and his emphasis on mechanical processes in the formation of order, he paved the way for the atomic theory. However, his enunciation of the order that comes from an intelligent mind suggested the theory that nature is the work of design.