Aristotle classified animals. He classified governments. He classified arguments, virtues, categories of being, types of causation, literary genres, and rhetorical strategies. He wrote about physics, metaphysics, ethics, politics, biology, psychology, logic, and poetry. He invented formal logic. He was wrong about the number of teeth women have because he never bothered to count them, which tells you something important about the gap between systematic thinking and actually checking your work. He was the tutor of Alexander the Great, the student of Plato, and the single most influential intellectual in Western history. He was also, in many specific claims, demonstrably incorrect. Both of these things are true at the same time.

He Invented the Way We Think About Thinking

Before Aristotle, arguments were won by whoever was more persuasive. After Aristotle, arguments could be evaluated by whether they were logically valid. His system of syllogistic logic, laid out in the Prior Analytics, formalized deductive reasoning into a structure that held for over two thousand years. If all men are mortal, and Socrates is a man, then Socrates is mortal. The conclusion follows necessarily from the premises. Logicians at the University of Oxford have traced the influence of Aristotelian logic through medieval Islamic and European philosophy and into the foundations of modern formal logic. Gottlob Frege and Bertrand Russell eventually replaced his system with predicate logic in the late 19th century, but for two millennia, Aristotle's logic was logic. There was no alternative. He had not merely described how people reason. He had created the framework within which reasoning itself was understood. What strikes me about this is not the achievement but the audacity. He was a human being who decided to catalog the rules by which all human thought operates, and he got close enough that nobody improved on his work for twenty-three centuries.

The Biology Was Ambitious and Sometimes Hilarious

Aristotle dissected over fifty species of animals. He described the anatomy of sea urchins, octopuses, and cuttlefish with a precision that marine biologists at the University of Cambridge have verified as remarkably accurate. He correctly identified that dolphins are mammals, not fish. He noted that hyenas have unusual reproductive anatomy. He observed that the chameleon changes color. He also believed that women have fewer teeth than men, that eels generate spontaneously from mud, and that the brain's function is to cool the blood. He got the big picture astonishingly right and the specific facts occasionally spectacularly wrong, and the pattern tells you something about how systematic observation works. You see more clearly when you have a framework, but the framework also makes you confident about things you should have checked. Researchers at the Max Planck Institute for the History of Science have studied Aristotle's biological methodology and concluded that his observational technique was genuinely empirical for his era. He looked at things. He dissected things. He just also extrapolated from insufficient data with the confidence of a man who believed the universe was fundamentally rational and therefore deducible.

He Thought Slavery Was Natural and He Was Wrong

This needs to be said without qualification. Aristotle argued in the Politics that some people are natural slaves, suited by nature to serve others. He believed this was as natural as the relationship between soul and body. He was wrong, and the wrongness is not a minor detail. It is a fundamental moral failure embedded in one of the most influential political philosophies in history. Scholars at Princeton's Department of Classics have documented how Aristotle's defense of slavery was used for centuries to justify the institution, from Roman law through American slaveholders who cited his authority. The man who invented logic used it to argue for the permanent subjugation of human beings. That is not a paradox. It is a lesson about the limits of intelligence without empathy. I think about Aristotle when I think about the relationship between brilliance and moral clarity. They are not the same thing. A person can catalog the entire structure of human knowledge and still fail to recognize the humanity of the person standing next to them. Aristotle's legacy is both the framework and the failure, and ignoring either one is a mistake.