(Ἀναξαγόρας), a Greek philosopher, was born at Clazomenae in Ionia about the year B. C. 499. His father, Hegesibulus, left him in the possession of considerable property, but as he intended to devote his life to higher ends, he gave it up to his relatives as something which ought not to engage his attention. He is said to have gone to Athens at the age of twenty, during the contest of the Greeks with Persia, and to have lived and taught in that city for a period of thirty years. He became here the intimate friend and teacher of the most eminent men of the time, such as Euripides and Pericles; but while he thus gained the friendship and admiration of the most enlightened Athenians, the majority, uneasy at being disturbed in their hereditary superstitions, soon found reasons for complaint. The principal cause of hostility towards him must, however, be looked for in the following circumstance. As he was a friend of Pericles, the party which was dissatisfied with his administration seized upon the disposition of the people towards the philosopher as a favourable opportunity for striking a blow at the great statesman. Anaxagoras, therefore, was accused of impiety. His trial and its results are matters of the greatest uncertainty on account of the different statements of the ancients themselves. (D. L. 2.12, &c.; Plut. Per. 32, Nicias, 23.) It seems probable, however, that Anaxagoras was accused twice, once on the ground of impiety, and a second time on that of partiality to Persia. In the first case it was only owing to the influence and eloquence of Pericles that he was not put to death; but he was sentenced to pay a fine of five talents and to quit Athens. The philosopher now went to Lampsacus, and it seems to have been during his absence that the second charge of μηδισμὸς was brought against him, in consequence of which he was condemned to death. He is said to have received the intelligence of his sentence with a smile, and to have died at Lampsacus at the age of seventy-two. The inhabitants of this place honoured Anaxagoras not only during his lifetime, but after his death also. (D. L. 2.100.3; Dict. of Ant. s. v. Ἀναξαγόρεια.)

Diogenes Laertius, Cicero, and other writers, call Anaxagoras a disciple of Anaximenes; but this statement is not only connected with some chronological difficulties, but is not quite in accordance with the accounts of other writers. Thus much, however, is certain, that Anaxagoras struck into a new path, and was dissatisfied with the systems of his predecessors, the Ionic philosophers. It is he who laid the foundation of the Attic philosophy, and who stated the problem which his successors laboured to solve. The Ionic philosophers had endeavoured to explain nature and its various phenomena by regarding matter in its different forms and modifications as the cause of all things. Anaxagoras, on the other hand, conceived the necessity of seeking a higher cause, independent of matter, and this cause he considered to be νοῦς, that is, mind, thought, or intelligence. This νοῦς, however, is not the creator of the world, but merely that which originally arranged the world and gave motion to it; for, according to the axiom that out of nothing nothing can come, he supposed the existence of matter from all eternity, though, before the νοῦς was exercised upon it, it was in a chaotic confusion. In this original chaos there was an infinite number of homogeneous parts (ὁμοιομερῆ) as well as heterogeneous ones. The nou=s united the former and separated from them what was heterogeneous, and out of this process arose the things we see in this world. This union and separation, however, were made in such a manner, that each thing contains in itself parts of other things or heterogeneous elements, and is what it is, only on account of the preponderance of certain homogeneous parts which constitute its character. The νοῦς, which thus regulated and formed the material world, is itself also cognoscent, and consequently the principle of all cognition : it alone can see truth and the essence of things, while our senses are imperfect and often lead us into error.