Anaxagoras was an ancient Greek philosopher born in 500 BC in Clazomenae in Asia Minor (what is now Turkey). He is known at the first philosopher to bring Ionian philosophy (the attempt to understand the world according to fundamental principles which originated in Miletus “the birthplace of philosophy”) to the city of Athens. He was a natural philosopher (i.e. scientist) best known for his understanding of the world as being made up of an infinite number of things and his belief that there is a guiding principle resonsible for the creation of the world (cosmogony) and how things work (cosmology) that he called Mind (nous). Like Empedocles, Anaxagoras was a pluralist philosopher, meaning that he tried to reconcile several different philosophical traditions in his own thought.

Anaxagoras came from wealth, but abandoned it to pursue the search for knowledge. He is seen as a classic example of a philosopher who was not concerned about the things going on around him (like politics or world events), but instead was exclusively focused on coming to a better understanding of the world (i.e. science). He left his hometown for Athens, the current center of Greek culture, where he was befriended by the great statesmen Pericles for his naturalistic understanding of the world. He also gained the admiration of the playwrights Euripides, Sophocles, and Aristophanes. He is credited as the first philosopher to correctly understand the cause of eclipses, as well as for having successfully predicted the fall of a meteorite. His understanding that the heavenly bodies are made up of fiery rock instead of being Gods was a major break with the traditional Greek mythological understanding of the world.

Anaxagoras, like his contemporary Empedocles, wrote in response to the philosopher Parmenides. Parmenides believed that change was not possible since the world is in truth only One eternal thing. Like Empedocles, Anaxagoras tries to show that change is possible. Empedocles accounted for change by understanding the world as being made up of the four primary elements: earth, water, wind and fire, which are constantly being mixed together to form new combinations through the principles of Love and Strife. Anaxagoras will instead put forth the notion that the world is created of an infinite number of things which are mixed together and separated by one fundamental principle which he calls Mind (nous).

Anaxagoras recognized the food animals and humans eat becomes hair, bones and flesh. He believed this happened because the food contained invisible pieces of hair, bone and flesh. Nourishment was the process by which the body absorbed these invisible ingredients. This understanding was based on the belief that everything can be divided into infinitely smaller things, and that every thing contains a certain amount of every other thing in the world. This allowed for him to understand how change was possible, while at the same time acknowledging Parmenides’ belief that something can’t come from nothing.

Anaxagoras believed things are what they are because they contain the most of a certain thing. For example, gold is gold because, even though it has a certain amount of every thing else, it mostly has gold. In this way, he understood snow to have some amount of blackness. The senses are helpful to understand things, but there is a limit to how much can be known through the senses alone. Anaxagoras’ theory is the opposite of what will become known as the atomistic theory. The atomistic theory will state that things cannot be divided infinitely, but are ultimately composed of small building blocks (atoms), and these building blocks contain only one type of substance.

Anaxagoras uses his understanding of the world (cosmology) to put forth his own account of the way the world came to be (cosmogony). Initially, everything was mixed together. Then, the principle Mind (nous) caused an initial rotation which resulted in things being separated out. Anaxagoras does not explain why this initial rotation happened, which is seen as a violation of the Principle of Sufficient Reason (i.e. that there should be a good reason to believe something, and if not then you shouldn’t). The Mind is the “finest of all things” which controls the way everything else moves. In this way, Anaxagoras distinguishes the “mover” from the “moved.” Plato will criticize this concept of Mind, saying that Anaxagoras uses it because he can’t explain why things are the way they are otherwise, and therefore calling it a deux ex machina (“the hand of God”).

Anaxagoras’ Mind is everywhere in the world and controls all events. It is the rational governing principle of the world that allows humans to understand why things happen. As such, it is a clear break with the traditional Greek mythological understanding of events as being the result of the whims of the Gods. For this reason, later philosophers such as Socrates and Aristotle will admire his concept of Mind. At the same time, they will want the world to be governed by more than just a mechanistic principle, (“this does that”) but also one that has a specific goal in mind (teleology).

In addition to making scientific observations, for example that the moon reflects the sun’s light, he also develops an understanding of how humans are able to sense and perceive things. For Anaximander, sensation and perception are the result of opposites interacting with one another. For example, heat is experienced when a cold hand touches something hot. For the same reason, a dark object won’t be seen in a dark room. It is because of difference that we can see and experience things. In contrast, Empedocles believed that we can perceive something because we have the same type of substance already in ourselves (“like by like”).

Anaxagoras also discusses biology. He believed humans are more intelligent than other animals because we have hands, since this allows us to create and use objects as instruments. He also suggested that an infant will be born male if the sperm comes from the right testicle, and female if it comes from the left. His focus on science (natural philosophy), and the attempt to understand things rationally, would create a foundation for scientific and philosophical thought in Athens.