Plato is known today as one of the greatest philosophers
of all time. He was born about 429 BC, close
to the time when Pericles died,
and he died in 347 BC, just after the birth of Alexander
the Great. Plato was born in Athens, to a very rich and powerful
family. Many of his relatives were involved with Athenian politics,
though Plato himself was not.
When Plato was a young man, he went to listen to Socrates, and learned a lot from Socrates about how to think, and what sort of questions to think about. When Socrates was killed in 399 BC, Plato was very upset (He was 30 years old when Socrates died) . Plato began to write down some of the conversations he had heard Socrates have. Practically everything we know about Socrates comes from what Plato wrote down.
After a while, though, Plato began to write down his own ideas about philosophy instead of just writing down Socrates' ideas. One of his earlier works is the Republic, which describes what Plato thought would be a better form of government than the government of Athens. Plato thought that most people were pretty stupid, and so they should not be voting about what to do. Instead, the best people should be chosen to be the Guardians of the rest. (Remember Plato was from a rich aristocratic family so he probably considered himself among the best people!).
Plato also thought a lot about the natural world and how it works. He thought that everything had a sort of ideal form, like the idea of a chair, and then an actual chair was a sort of poor imitation of the ideal chair that exists only in your mind. One of the ways Plato tried to explain his ideas was with the famous metaphor of the cave. He said, Suppose there is a cave, and inside the cave there are some men chained up to a wall, so that they can only see the back wall of the cave and nothing else. These men can't see anything outside of the cave, or even see each other clearly, but they can see shadows of what is going on outside the cave. Wouldn't these prisoners come to think that the shadows were real, and that was what things really looked like?
Suppose now that one of the men escaped, and got out of the cave, and saw what real people looked like, and real trees and grass. If he went back to the cave and told the other men what he had seen, would they believe him, or would they think he was crazy?
A video about Plato's Cave
Plato says that we are like those men sitting in the cave: we think we understand the real world, but because we are trapped in our bodies we can see only the shadows on the wall. One of his goals is to help us understand the real world better, by finding ways to predict or understand the real world even without being able to see it.
It's possible that Plato's ideas about the difference between reality and the illusion we perceive are related to Hindu and Buddhist ideas about nirvana, which were forming in India about the same time.
To find out more about Plato, check out these books from Amazon or from your local library:
Socratic Dialogues (Penguin Classics), by Plato, translated by Trevor
Saunders (1987). This is, according to Plato, what Socrates said.
The Republic (Dover Thrift Editions), by Plato. Translated by Benjamin Jowett. A very very cheap edition of Plato's Republic, in his own words (translated into English).
Philosophy and Science in Ancient Greece: The Pursuit of Knowledge, by Don Nardo (2004). For teenagers. Don Nardo has written many books for young people about the ancient Greeks.
The Cambridge Companion to Greek and Roman Philosophy, edited by David Sedley (1997).