Aristotle
Aristotle lived from 384 to 322 BC. He was a Greek philosopher who was a student of Plato and the tutor of Alexander the Great. Aristotle emphasized reason and observation of the natural world, and he is believed by many to be the greatest philosopher of all time.
Aristotle came to the Academy when he was seventeen and stayed there for twenty years until the death of Plato, although he was not believed to be implicated in this. Aristotle’s approach was the opposite of Plato: Aristotle thought experience was the key to knowledge, and embarked on the massive task of observing and compiling as much information as possible, although unfortunately this did not extend to counting the number of teeth in someone's mouth before making pronouncements on the subject. In contrast to Plato’s interest in physics and maths, Aristotle was fascinated by biology and classified over 500 animal species. He ultimately founded his own school, the Lyceum, and equipped it with specimens, libraries, maps and other accoutrements found in modern universities. Aristotle defended the usefulness of slavery.