Anaxagoras of Clazomenae

c. 500-c. 428 b.c.

Greek Philosopher and Astronomer

The first professional philosopher to teach in Athens, Anaxagoras introduced Ionian physical speculation to mainland Greece. He correctly explained the phases of the Moon as well as the eclipses of both the Sun and Moon. He was also the first to clearly distinguish between mind and matter.

According to the most commonly adopted chronology of his life, Anaxagoras was born in Clazomenae around 500 b.c. This Greek colony in Asia Minor was 75 miles (121 km) north of Miletus—home of Thales (c. 625-c. 547 b.c.) and Anaximander (c. 610-c. 546 b.c.). Born to a wealthy family, Anaxagoras devoted himself to the study of natural philosophy. In either 480 or 456 b.c. he settled in Athens and established a school. He was a member of the enlightened and skeptical circle that gathered around Pericles (d. 429 b.c.). He was later prosecuted for impiety by enemies of Pericles and exiled to Lampsacus on the Hellespont. There, he founded another school shortly before his death.

Anaxagoras accepted the Parmenidean dictum that nothing comes into being and nothing perishes. However, unlike Parmenides (b. c. 515 b.c.), he rejected the idea that reality is a unity and motion impossible. Anaxagoras affirmed as real the multiplicity of forms and change we perceive about us and sought to reconcile this with Parmenidean logic. To this end, he postulated a plurality of primary elements. Infinite in number, these were understood to be ungenerated and indestructible.

Empedocles (c. 492-c. 432 b.c.) argued that the characteristics of different substances were determined by the relative mixtures of four primary elements—earth, air, water, and fire. Thus, a gold cup consisted of the four elements mixed in the appropriate proportions. Anaxagoras took exception to this because it seemed to contradict Parmenidean logic; specifically, it appeared to require something, in this case gold, coming into existence. As an alternative, Anaxagoras formulated his principle of homoemereity, which states that all perceptible bodies or natural substances are composed of an infinite number of infinitely divisible smaller parts. Furthermore, each part retains its characteristic features upon division. Thus, unlike Empedocles, he argued that a gold cup is composed of smaller parts, each of which is made of gold and nothing else.

Interpreting the principle of homoemereity satisfactorily has been confounded by Anaxagoras's further statement that "there is a portion of everything in everything." This would imply that every part of a gold cup contains a mixture of everything else, including flesh, wood, wine, etc. On the face of it, this contradicts his claim that the parts of the cup are composed solely of gold. Various suggestions have been put forward to resolve the conflict. One solution has it that Anaxagoras simply meant that gold predominates in each part. An objection leveled against this interpretation is that at some point in the process of subdivision there will be parts no longer dominated by gold. However, if the principle of homoemereity is only applied to the predominant ingredient, then inconsistency can be avoided. This may have been what Anaxagoras had in mind.

Anaxagoras taught that noûs, or mind, rules the world and brings order to it. He maintained that the universe originated as a homogenous, motionless mixture that noûs operated on by initiating a vortex. This gradually caused the dense, cold, and wet matter to concentrate at the center of the mixture and form into a disk-like Earth. The rare, hot, and dry matter floated free and supported Earth. The Sun, Moon, planets, and stars were torn from Earth by the continued vortical action and ignited by friction. In this cosmology, noûs is conceived of as distinct from that which is moved. Anaxagoras thus made the first clear distinction between mind and matter.

STEPHEN D. NORTON