Aristotle was born in 384 B.C. in a small town called Stagira. His parents died when he was still young, and he was raised as an orphan. Though little is known about Aristotle's early years, the occupation of his father, Nicomachus, did have a significant influence on his development. Nicomachus was a physician, and this probably accounted for Aristotle's especially strong interest in biology, a science that had long been considered inferior to other disciplines.
At the age of eighteen, Aristotle entered Plato's Academy and soon became the undisputed top student. He spent about twenty years there. Though Aristotle criticized many of Plato's theories, he was always careful to acknowledge his debt to his former master and stress the common ground that they shared. As much as he did depart from Plato's thought, the teacher's presence always bore some mark on the student's work.
When Plato died in 347 B.C., Aristotle left Athens and spent some years traveling, taking part in various intellectual circles at Assos and Lesbos. At Lesbos he began conducting his biological research, while his prior work had been concerned primarily with metaphysics and politics, in the form of responses to or even expositions of Plato's ideas. In 343 B.C. he was asked to tutor Philip's son, the future Alexander the Great. He spent three years with Alexander teaching primarily the standard subjects, such as rhetoric and poetry. He also encouraged Alexander's ambitions to conquer Persia, reinforcing the belief that non-Greeks were barbarians. Aristotle's xenophobic beliefs would never soften, and as Alexander's attitude toward the Persians changed, tension increased between the two men.
Soon after Philip's death in 336 B.C., Aristotle returned to Athens, where he founded the Lyceum. It was here that he undertook his most important work, and many of his surviving writings were based on lectures prepared for the school. Much of his work has not been dated precisely, and he was constantly revising much of it. Moreover, we know little about his life apart from this work, and hence this biography is organized around the works themselves. His greatest achievement is generally considered to be the syllogism, which helped to launch the field of logic–a field that Aristotle essentially created single-handedly. Logic was the fundamental tool that made all understanding and learning possible, for it helped one to recognize when proof was necessary and how to evaluate such proof.
After logic, Aristotle's contributions to biology are among his most significant. He identified 495 different animal species and classified them shrewdly. The care he showed in his collection of data, along with the insight he provided into his research, afforded his work great longevity. In contrast to his work in the natural sciences, his biological achievements would remain unsurpassed for centuries.
He also wrote major works on Ethics, Politics, Poetics, and Rhetoric. With the exception of Aristotle's Rhetoric, all of these works continue to be studied in colleges today, not only for historical reasons but as the groundwork of its field. The definition of tragedy provided in the Poetics remains fundamentally relevant to literary criticism, while the Ethics and Politics provide appropriate starting points for moral and political philosophy.
Aristotle died in 322 B.C., having contributed more to Western knowledge than any other individual ever had before or has had since.