Anaxagoras (born c. 500 bce, Clazomenae, Anatolia [now in Turkey]—died c. 428, Lampsacus) was a Greek philosopher of nature remembered for his cosmology and for his discovery of the true cause of eclipses. He was associated with the Athenian statesman Pericles.
About 480 Anaxagoras moved to Athens, then becoming the centre of Greek culture, and brought from Ionia the new practice of philosophy and the spirit of scientific inquiry. After 30 years’ residence in Athens, he was prosecuted on a charge of impiety for asserting that the Sun is an incandescent stone somewhat larger than the region of the Peloponnese. The attack on him was intended as an indirect blow at Pericles, and, although Pericles managed to save him, Anaxagoras was compelled to leave Athens. He spent his last years in retirement at Lampsacus.
Only a few fragments of Anaxagoras’s writings have been preserved, and several different interpretations of his work have been made. The basic features, however, are clear. His cosmology grows out of the efforts of earlier Greek thinkers who had tried to explain the physical universe by an assumption of a single fundamental element. Parmenides, however, asserted that such an assumption could not account for movement and change, and, whereas Empedocles sought to resolve this difficulty by positing four basic ingredients, Anaxagoras posited an infinite number. Unlike his predecessors, who had chosen such elements as heat or water as the basic substance, Anaxagoras included those found in living bodies, such as flesh, bone, bark, and leaf. Otherwise, he asked, how could flesh come from what is not flesh? He also accounted for biological changes, in which substances appear under new manifestations: as men eat and drink, flesh, bone, and hair grow. In order to explain the great amount and diversity of change, he said that “there is a portion of every thing, i.e., of every elemental stuff, in every thing,” but “each is and was most manifestly those things of which there is most in it.”
The most original aspect of Anaxagoras’s system was his doctrine of nous (“mind” or “reason”). The cosmos was formed by mind in two stages: first, by a revolving and mixing process that still continues; and, second, by the development of living things. In the first, all of “the dark” came together to form the night, “the fluid” came together to form the oceans, and so on with other elements. The same process of attraction of “like to like” occurred in the second stage, when flesh and other elements were brought together by mind in large amounts. This stage took place by means of animal and plant seeds inherent in the original mixture. The growth of living things, according to Anaxagoras, depends on the power of mind within the organisms that enables them to extract nourishment from surrounding substances. For this concept of mind, Anaxagoras was commended by Aristotle. Both Plato and Aristotle, however, objected that his notion of mind did not include a view that mind acts ethically—i.e., acts for the “best interests” of the universe.