Aristotle was born in Stagira in northern Greece in 384 b.c.e. His father was a doctor at the court of Amyntas III of Macedon, father of Philip II of Macedon and grandfather of Alexander the Great. In 367, Aristotle moved to Athens to study at Plato’s Academy, where he stayed for twenty years. Aristotle left the Academy in 347, the year Plato died, and some have speculated that he felt snubbed that Plato did not choose him as his successor. The more likely explanation, however, is that anti-Macedonian sentiment was on the rise in Athens, causing Aristotle to fear being persecuted for his associations with King Philip’s court.

Over the next four years, Aristotle traveled about the eastern Aegean, studying and teaching. During this time, he conducted a remarkable array of experiments and observations in the biological sciences. In 343, he was summoned back north to Macedonia to be the personal tutor to King Philip’s son, the young Alexander the Great. We do not know the precise relationship between Aristotle and Alexander, though their relationship has been the subject of much speculation and mythmaking over the centuries.

As the Macedonians came to dominate Greece, Aristotle returned to Athens and set up his own philosophical school at the Lyceum, where he taught from 335 until 323. What we have of Aristotle’s writings are mostly lectures he gave at the Lyceum in these years. Their dry style and uneven structure is due partly to the fact that they were lecture notes never intended for publication and partly to the fact that they were patched together into their present form by editors many centuries after Aristotle’s death. Aristotle published many popular works admired for their lively style, but none of these have survived.

Historically, Aristotle lived in the twilight years of the Greek city-state. Ancient Greece consisted of a number of independent city-states, of which Athens was the most significant. Though the city-states relied on slave labor and the disenfranchisement of women, the male citizens established one of the earliest forms of democracy, and in the span of less than two hundred years they managed to establish what the Western world still looks to as the basis of its political institutions, philosophy, mathematics, drama, art, and architecture. Because slaves and noncitizen workers performed the bulk of the city’s labor, male citizens enjoyed a great deal of leisure time. This leisure provided the opportunity for open inquiry into the nature of the world, and teachers like Aristotle were not uncommon.

Aristotle’s writings show that he was well versed in Platonic philosophy. The centerpiece of Plato’s philosophy is his Theory of Forms, according to which the objects of experience are just shadows of a higher world of Forms that lie beyond sensory experience. For example, the various things we see in this world that we call beautiful have beauty because they participate in the Form of Beauty, which is itself immaterial and eternal. In Plato’s view, the purpose of philosophy is to train the intellect to see beyond appearances and to grasp the higher world of Forms.

Counterbalancing the idealism of Plato’s philosophy is Aristotle’s background as the son of a doctor. Aristotle was probably brought up to pursue a medical career, and his writings on biology show a very sharp understanding of anatomy. Throughout his writings, Aristotle refers to biology as a paradigm for making sense of the world, much as Plato refers to mathematics. This emphasis on biology leads Aristotle to favor close observation of natural phenomena and careful classification as the keys to making sense of things. As a result, his philosophy is much more empirically oriented than Plato’s, and Aristotle rejects the idea that we can only make sense of this world by appealing to invisible entities beyond it.

Aristotle’s influence on subsequent generations is immense. Only Plato can compare in importance. Though Aristotle’s works were lost to the West for many centuries, they were preserved by Arab scholars and transmitted back to Europe in the Middle Ages. Thanks mostly to the work of St. Thomas Aquinas, Aristotle’s writings carried an authority in the late Middle Ages that was second only to the Bible. His work in logic and biology was not significantly improved upon until the nineteenth century. Though modern science and philosophy found their legs by rejecting or disproving many of Aristotle’s results, his methods continue to have a deep influence on philosophical and scientific thought.

Aristotle’s published writings were all lost or destroyed in the centuries after his death, and what we have are lectures, or notes on lectures, that Aristotle gave at the Lyceum. These works were first collected two centuries after Aristotle’s death by Andronicus of Rhodes. As a result, not only do we not know the chronology of Aristotle’s writings, but we are also unsure if Andronicus arranged them in the order that Aristotle had intended, or if all the works collected by Andronicus were written by Aristotle. We can also be quite confident that what Andronicus collected constitutes less than one-third of all of Aristotle’s writings. Even this small portion is impressive: Aristotle’s works are as vast as they are challenging.