He tutored Alexander, catalogued the living world, and wrote the rules of logic.
Aristotle (384–322 BC) was the Greek philosopher who built the first complete system of human knowledge — logic, ethics, politics, biology, physics and metaphysics — and whose authority over science and philosophy endured for nearly two thousand years after his death, from Baghdad to Paris.
Student of Plato, tutor of Alexander the Great and founder of the Lyceum school in Athens, he insisted that knowledge begins not in abstract ideals but in observation. His works — lecture notes compiled by his students — became the textbooks of the Islamic Golden Age, medieval Christianity and Renaissance science alike.
Born at Stagira in northern Greece in 384 BC, Aristotle joined Plato’s Academy in Athens at seventeen and stayed twenty years — first as the star pupil, then as a colleague who quietly disagreed with his master’s doctrine that true reality lies in abstract Forms. For Aristotle, reality was here, in the things you can touch and dissect.
In 343 BC King Philip II of Macedon hired him to tutor his thirteen-year-old son Alexander, the future conqueror of the known world. On returning to Athens Aristotle founded his own school, the Lyceum, where he walked the colonnades lecturing — his followers were called Peripatetics, “walkers.”
His surviving works — dense lecture notes, not polished books — run across every field: the Organon founded formal logic with the syllogism; the Nicomachean Ethics defined virtue as the mean between extremes; the Politics analyzed constitutions; his biological treatises classified some 500 animal species from direct observation and dissection.
He got plenty wrong — his physics held that heavy objects fall faster, his cosmology froze the Earth at the universe’s center — and his errors, frozen into doctrine, would delay science for centuries. But his method, observation before theory, became science’s permanent grammar.
After Rome fell, Aristotle survived in Arabic: scholars in Baghdad, then Avicenna and Averroes, preserved and extended him. Thomas Aquinas baptized him for Christian Europe — “The Philosopher,” Dante called him — and for five centuries no university lecture could contradict him.
The Scientific Revolution was in large part a rebellion against Aristotle — Galileo and Newton dismantled his physics piece by piece. Yet his logic still runs the world’s arguments, his ethics still anchors philosophy departments, and his biology earned him the title Darwin gave him: the first true biologist.
His afterlife in the Islamic world deserves its own chapter: in 9th-century Baghdad, the House of Wisdom translated his entire corpus into Arabic, and philosophers like Al-Farabi, Avicenna and Averroes built on him so thoroughly that when his works returned to Latin Europe in the 12th century, they arrived with Arabic commentaries attached — Aristotle mediated through Baghdad.
