Aristotle was the most important student of Plato. He was born in 384 B.C. in Stagira (Halkidiki). He joined the Academy at the age of seventeen until the death of his teacher. He was not elected a headmaster of the Academy, and, after spending some years in Lesvos, Asia Minor, and the court of Macedonia as the teacher of young Alexander, he returned to Athens, where he founded the Lyceum. Aristotle died in Chalkida in 322 B.C.
The works that Aristotle published during his lifetime are all lost. His unpublished course books, however, have survived. Those were published, in the form they have today, by Andronicus of Rhodes in the 1st c. B.C. Aristotle made a decisive contribution in every discipline. In philosophy, he pursued the successful combination of the platonic philosophy with the natural philosophy of the Presocratics; moreover, he established the branch of Logic. With regards to the sciences, Aristotle laid the grounds for physics, chemistry, and meteorology, while he also brought forward the importance of biology. His practical philosophy, although appropriated to the criteria of the Greek city-state, is still topical. Finally, he systematized rhetoric, and established the theory of literature ("Poetics"). In fine, the Aristotelian textbooks represent the encyclopaedia of knowledge of the 4th century B.C.
Aristotle proposes a threefold classification of knowledge: human knowledge is distinguished in "poetical", "practical", and "theoretical". Theoretical philosophy, which comprises physics, mathematics, and the "first philosophy" (i.e., metaphysics) is considered the highest human knowledge. In his metaphysics, Aristotle rules out the autonomous existence of the Forms. On the contrary, he ascertains that the only existing beings (the Aristotelian "substances") are the particular sensible beings, which have matter and form. Nevertheless, even though human knowledge begins with perception, it concludes in the knowledge of the universal forms that exists innately in the perceptible beings.
Aristotle owns his great reputation mostly in his theories about nature; they were accepted by all future thinkers until the 17th c. (Byzantines, Arabs, and Medieval Europeans). The Aristotelian universe is unborn and perennial; it is subject to eternal motion, but at the same time permeated by order; it functions teleologically, for every being moves toward the attainment of its predetermined form.