Aristotle

Aristotle was born in Stagira on the Macedonian frontier; his father was physician to the Macedonian king. At seventeen he entered Plato's Academy and stayed twenty years. After Plato's death he left Athens, studied marine life in Asia Minor, and was hired to tutor Alexander. In 335 BCE he returned to found the Lyceum, whose members walked as they talked and so were called Peripatetics.

His surviving works are mostly lecture notes covering logic, physics, astronomy, biology, psychology, ethics, politics, rhetoric and poetics. He invented the syllogism, separating the form of reasoning from its content for the first time. Rejecting Plato's separate Forms, he insisted that form exists only in particular things, explained change through the four causes, and becoming through potentiality and actuality.

The Nicomachean Ethics holds that happiness is the soul's activity in accordance with virtue, and that virtue is a mean between extremes. The Politics says the human being is by nature a political animal. When Alexander died and Athens turned against Macedon, he fled to Euboea, saying he would not let the Athenians sin against philosophy twice, and died the next year. His works returned to Europe through the Arabic world and became the textbooks of the medieval universities.