Anaxagoras

Anaxagoras of Clazomenae (c. 500 – 428 BCE) brought Ionian natural philosophy to Athens, where he lived for some thirty years and taught, among others, Pericles. He was eventually tried for impiety, the charge resting on his claim that the sun was not a god but a red-hot mass of stone larger than the Peloponnese. He withdrew to Lampsacus, where he was honoured until his death.

Everything in everything

Anaxagoras accepted the Eleatic rule that nothing comes to be from what is not, and drew an unusual conclusion from it. If hair cannot come from what is not hair, and flesh from what is not flesh, then the bread we eat must already contain hair and flesh in some proportion. Every portion of matter, however small, contains a share of every kind of stuff; a thing is called gold or bone according to which ingredient predominates in it. There is no smallest part, because division never reaches a pure element.

Mind as the mover

What set this mixture in motion, and continues to order it, he called Nous, Mind. Mind is unmixed with anything else, knows all things, and began a rotation at one point in the original mass that spread outward and is still spreading. The rotation separated the dense from the rare, the cold from the hot, and threw the heavy bodies toward the centre while the fiery ones were flung to the periphery.

All things were together; then Mind came and set them in order.

Socrates, in Plato's account, says he was delighted to read this and then disappointed: having named Mind, Anaxagoras went on to explain each event by air, vortices and physical necessity, as though Mind had given the first push and retired. The complaint is fair, and it marks the point where later philosophy would try to do better.

Claims he is remembered for

• The moon shines by reflected sunlight and has plains and ravines.
• Eclipses are caused by the interposition of the moon or the earth, not by omens.
• A meteorite that fell at Aegospotami was, he said, evidence that the heavenly bodies are stone.
• The senses are too weak to judge the truth; a colour changed drop by drop is not seen to change.

Assessment

His physics is a compromise between Parmenides and the older Ionians: no coming-to-be, only rearrangement, but a rearrangement rich enough to produce the world. His Mind is the first cause in Greek thought that is explicitly intelligent and explicitly separate from what it moves.