Aristotle

Aristotle was a Greek philosopher and scientist who set out to study nearly everything, from logic and the heavens to animals, poetry and politics, and to put it all in order. He was born in 384 BCE at Stagira, a small town on the Chalcidice peninsula in the north of Greece, where his father Nicomachus was physician to Amyntas III, king of Macedon and grandfather of Alexander the Great. At seventeen he went to Athens and joined Plato's Academy, and he stayed twenty years, first as a student and then as a colleague, until Plato died in 347 BCE.

Passed over for the head of the Academy, which went to Plato's nephew Speusippus, he crossed to Assos on the coast of Asia Minor, ruled by Hermias, a former member of the Academy, and married Hermias's niece Pythias. There, and then on the island of Lesbos with his younger friend Theophrastus, he began the close study of living animals, many of them from the lagoon of Pyrrha. In 343 BCE Philip II of Macedon called him to teach his thirteen-year-old son Alexander, at a sanctuary of the Nymphs at Mieza; the lessons lasted perhaps three years.

In 335, with Alexander now king, Aristotle went back to Athens and opened his own school in the Lyceum, a gymnasium outside the city walls. His followers were called Peripatetics, after the covered walk where they talked; he built up a great library, gave lectures, some of them open to the public, and set his students to collect facts, among them the constitutions of 158 Greek states. When Alexander died in 323 and Athens turned against Macedon, he was threatened with a charge of impiety. Saying he would not let the city sin twice against philosophy, as it had with Socrates, he withdrew to his mother's town of Chalcis on Euboea, and died there the next year.

Perhaps two hundred works went under his name; about thirty survive, most of them lecture notes rather than finished books, edited in Rome around 60 BCE by Andronicus of Rhodes. In them he founded formal logic, with the syllogism; described more than five hundred kinds of animal; explained change by four causes; placed an unmoving, round earth at the centre of the universe; held that happiness comes only from a life of excellence and that man is by nature a political animal; and wrote the first theory of tragedy. He rejected Plato's theory of forms and trusted observation: when theory and the facts disagree, he said, believe the facts.

His influence is hard to overstate. Translated from Syriac and Greek into Arabic in ninth- and tenth-century Baghdad, he became 'the First Teacher' of Islamic philosophy, and the commentaries of Avicenna and of Averroes of Córdoba, 'the Commentator', carried him back to the Latin West in the twelfth century. There he was simply 'the Philosopher': Thomas Aquinas reconciled him with Christian theology, and his system framed Christian philosophy until Copernicus, Galileo and Descartes overturned his cosmos and his physics. His ethics, revived as virtue ethics since the 1950s, and his politics are still argued over as living philosophy.