Aristotle: The Greek Thinker Who Tried to Understand Everything

From Stagira to Plato's Academy

Aristotle was born in 384 BC in Stagira, a small town on the Chalcidice peninsula in northern Greece. His father, Nicomachus, was a physician at the court of Amyntas III, king of Macedon and grandfather of Alexander the Great. Growing up in a medical family may help explain one of Aristotle's lifelong habits: he looked closely at living things and wanted to know how their parts worked.

His father died while Aristotle was still a child, and a guardian named Proxenus took charge of his upbringing. At about seventeen, Aristotle travelled to Athens, then the intellectual capital of the Greek world, and joined the Academy, the school founded by the philosopher Plato. He stayed there for about twenty years, first as a student and later as a teacher and researcher. Plato reportedly called him "the mind of the school".

Aristotle admired his teacher but did not simply repeat him. Plato believed that the true reality of things lies in perfect, unchanging Forms that exist apart from the physical world. Aristotle came to think that form and matter cannot be separated: the "form" of a horse exists in actual horses, not in some other realm. This disagreement shaped everything he later wrote. A famous later Latin saying, Amicus Plato, sed magis amica veritas ("Plato is a friend, but truth is a greater friend"), grew out of a passage in his Nicomachean Ethics, where he explains that a philosopher must honour truth even above his friends.

Travels, a Royal Pupil and the Lyceum

After Plato died around 347 BC, Aristotle left Athens. He spent several years in Assos, on the coast of Asia Minor, at the court of a ruler named Hermias, and married Pythias, a relative of Hermias. He then moved to the island of Lesbos, where he and his friend Theophrastus studied the plants and sea creatures of the island's great lagoon. Many of the observations in his biological works probably come from this period.

In 343 BC King Philip II of Macedon invited Aristotle to tutor his son, Alexander, who was then thirteen years old. Lessons took place at Mieza, a quiet place away from the royal court. We know little about what was taught, but ancient writers say Aristotle introduced the prince to literature, especially Homer, as well as politics and ethics. Alexander later went on to conquer an empire stretching from Greece to India, though historians debate how much his famous teacher actually influenced him.

In 335 BC Aristotle returned to Athens and opened his own school in a public sports ground called the Lyceum. He built up a large library and organised research in which his students gathered information on many subjects. His followers became known as the Peripatetics, from the Greek word peripatos, a covered walkway at the school. A popular tradition says Aristotle liked to walk up and down while teaching, and the name later came to mean "those who walk around".

When Alexander died in 323 BC, a wave of hostility against Macedon swept through Athens, and Aristotle, with his Macedonian connections, was accused of impiety. According to ancient accounts, he left the city so that Athens would not "sin twice against philosophy", a reference to the execution of Socrates. He moved to Chalcis on the island of Euboea, where he died the following year, in 322 BC, at about 62. His friend Theophrastus took over the Lyceum.

What Survives: Lecture Notes, Not Polished Books

Aristotle wrote on an astonishing range of subjects: logic, physics, astronomy, weather, biology, psychology, ethics, politics, economics, rhetoric, poetry and more. Yet only around a third of his original output has survived. Ironically, the works he prepared for the general public, elegant dialogues that the Roman orator Cicero compared to a "river of gold", are almost entirely lost.

What we have instead are mostly treatises: dense, carefully argued texts that seem to be lecture notes or teaching materials used inside the school. That is why Aristotle can feel difficult to read. The sentences are compact, he often returns to a problem from several angles, and he assumes his listeners already know the background.

The story of how these texts reached us is itself remarkable. According to the ancient geographer Strabo, Aristotle's manuscripts passed to Theophrastus and then to his heirs, who hid them in a cellar, where they were damaged before being rediscovered and eventually taken to Rome. In the first century BC the scholar Andronicus of Rhodes arranged and edited them. Even the word metaphysics may come from this editorial work: the books on "first philosophy" were placed after the Physics, and in Greek meta ta physika simply means "after the physics". Today scholars still cite Aristotle using page numbers from an edition published in Berlin in 1831 by Immanuel Bekker.

Logic: A Toolkit for Thinking

Aristotle is regarded as the founder of formal logic, the study of what makes an argument valid. His logical writings were later grouped together under the name Organon, meaning "tool" or "instrument", because logic was seen as the tool needed for every other kind of study.

The syllogism

His central invention was the syllogism, an argument in which a conclusion follows necessarily from two premises. The classic textbook example runs:

• All humans are mortal.
• Socrates is a human.
• Therefore, Socrates is mortal.

If the two premises are true and the form is correct, the conclusion cannot be false. Aristotle went further than giving examples: he worked out systematically which combinations of statements such as "all", "some" and "no" produce valid conclusions and which do not. He also catalogued common tricks and errors in reasoning, many of which we still call fallacies.

His system was so complete that it dominated logic for more than two thousand years. In the late eighteenth century the German philosopher Immanuel Kant remarked that logic had not been able to take a single step forward since Aristotle. Only in the nineteenth century did mathematicians such as George Boole and Gottlob Frege build new forms of logic that went beyond it, work that eventually fed into the design of computers.

A Naturalist Before Biology Existed

For many modern scientists, Aristotle's most impressive achievement is in biology. He described hundreds of animal species, from insects and fish to elephants, and he dissected many of them. His works such as History of Animals, Parts of Animals and Generation of Animals are among the earliest systematic studies of living things.

Aristotle tried to group animals by their features. He divided them into animals "with blood" and "without blood", which corresponds surprisingly well to the modern division between vertebrates and invertebrates. He noticed that dolphins and whales breathe air, give birth to live young and feed them with milk, linking them to land mammals rather than to fish. He also arranged living things in a kind of ladder from simple to complex, an idea later called the scala naturae, or "ladder of nature".

Some of his observations were so unusual that later naturalists dismissed them, only to find out he was right. He described how male octopuses use a specially modified arm in reproduction, something not confirmed until the nineteenth century. He also wrote that the male of a certain river catfish guards the eggs for weeks, a claim confirmed in the nineteenth century by the naturalist Louis Agassiz, which is why the species is now called Silurus aristotelis. Charles Darwin, after reading a translation of Aristotle's biology, wrote that his own scientific heroes, Linnaeus and Cuvier, were "mere school-boys to old Aristotle".

Physics, the Cosmos and the Four Causes

Aristotle believed that to truly understand something, you must know why it is the way it is. He identified four kinds of "cause" or explanation, which can be illustrated with a bronze statue:

1. Material cause: what it is made of (the bronze).
2. Formal cause: its shape or structure (the design of the statue).
3. Efficient cause: what brought it into being (the sculptor at work).
4. Final cause: its purpose or goal (to honour a god or a person).

The idea of the final cause was especially important to him. He thought nature itself acts for ends: an acorn develops in order to become an oak, and teeth are shaped the way they are because they serve for biting and chewing. He also used the paired ideas of potentiality and actuality to explain change: the acorn is potentially an oak, and growth is the process of that potential becoming real.

In his picture of the universe, the Earth sat motionless at the centre. Everything below the Moon was made from four elements, earth, water, air and fire, each with a natural place it tends to move towards. The heavens, he argued, were made of a fifth, unchanging substance, later called the aether, and the stars and planets were carried around on nested spheres. At the very top he placed an "unmoved mover", an eternal source of all motion that itself does not move.

He also offered clear evidence that the Earth is a sphere. During a lunar eclipse, the shadow of the Earth on the Moon is always curved. And when travellers go north or south, different stars become visible above the horizon, which only makes sense on a round, and not very large, Earth.

Ethics: Happiness and the Golden Mean

Aristotle's Nicomachean Ethics, probably named after his son Nicomachus, asks a simple question: what is the best life for a human being? His answer is eudaimonia, usually translated as "happiness" or "flourishing". For Aristotle, this was not a passing feeling of pleasure but a whole life lived well, using our distinctively human capacity for reason.

To live well, he argued, we need virtues, good traits of character. Many virtues lie at a midpoint between two extremes, an idea often called the "golden mean". Courage, for example, lies between cowardice (too much fear) and recklessness (too little). Generosity lies between stinginess and wastefulness. The right point is not a mathematical average; it depends on the situation and must be found with practical wisdom, which he called phronesis.

Crucially, Aristotle believed that virtues are learned by practice. Just as people become builders by building and musicians by playing music, they become fair by doing fair actions and brave by doing brave ones. Good habits, formed from a young age, make good character. He also devoted two whole books of the Ethics to friendship, distinguishing friendships based on usefulness, on pleasure and, the most lasting kind, on admiring each other's good character.

Politics, Rhetoric and Poetry

In his Politics, Aristotle described humans as "political animals": beings who naturally live together in communities and can only fully flourish as citizens of a city-state. His students gathered information on the constitutions of more than 150 Greek states. Most of these studies are lost, but the Constitution of the Athenians was rediscovered on an Egyptian papyrus and published in 1891.

He classified governments by asking who rules and in whose interest. Rule by one person could be a good monarchy or a bad tyranny; rule by a few could be aristocracy or oligarchy; rule by the many could be a well-balanced "polity" or what he called a disorderly democracy. The good forms serve the common good, while the bad forms serve only the rulers. He favoured a mixed system with a strong middle class, which he believed made a state more stable.

In the Rhetoric, he analysed persuasion and named three ways a speaker convinces an audience: through ethos (the speaker's character and trustworthiness), pathos (the emotions of the listeners) and logos (the argument itself). These terms are still taught in schools and used in debate, law and advertising.

His Poetics is the earliest surviving work of literary theory. He described tragedy as an imitation of an action that, through pity and fear, brings about catharsis, often understood as a kind of emotional cleansing or release. He insisted that plot is the most important element of a drama and that a good story needs a beginning, a middle and an end. A second book of the Poetics, believed to have dealt with comedy, has been lost.

Where Aristotle Got It Wrong

Aristotle relied heavily on observation, but he did not carry out controlled experiments in the modern sense, and some of his conclusions turned out to be mistaken:

• He taught that heavier objects fall faster than lighter ones. Galileo challenged this in the late sixteenth and early seventeenth centuries, and it was eventually overturned.
• He thought the heart, not the brain, was the centre of thought and feeling, and that the brain mainly served to cool the blood.
• He believed some small creatures, such as certain insects, arise spontaneously from mud or decaying matter.
• His Earth-centred universe was replaced by the Sun-centred model of Copernicus, Kepler and Galileo.

His social views also reflected the prejudices of his time. He defended slavery, arguing that some people were slaves "by nature", and he regarded women as inferior to men. Modern readers reject these ideas, and they show that even the greatest thinkers can be limited by the society around them. Part of what made his errors so long-lasting was his immense authority: for centuries, scholars often quoted Aristotle rather than testing his claims.

Two Thousand Years of Influence

After the fall of the Western Roman Empire, most of Aristotle's works were lost to Western Europe for centuries, but they were preserved and studied in the Byzantine Empire and translated into Arabic. Philosophers of the Islamic world, such as Avicenna (Ibn Sina) and Averroes (Ibn Rushd), wrote influential commentaries on them; Averroes became known in Europe simply as "the Commentator". The Jewish philosopher Maimonides also drew deeply on Aristotle.

In the twelfth and thirteenth centuries, Latin translations spread through Europe's new universities. The theologian Thomas Aquinas combined Aristotle's philosophy with Christian teaching so successfully that medieval writers often referred to Aristotle simply as "the Philosopher". The Italian poet Dante called him "the master of those who know". In Raphael's famous Renaissance fresco The School of Athens, Aristotle stands at the centre beside Plato: Plato points up to the heavens, while Aristotle holds his hand out flat towards the earth, a gesture often read as a sign of his focus on the observable world.

Even after the Scientific Revolution overturned his physics and astronomy, Aristotle's influence did not disappear. His logic remained a core subject for centuries, his biological observations still impress zoologists, and his ideas about virtue have returned in modern philosophy under the name "virtue ethics". Words we use every day, such as energy, category and metaphysics, carry traces of his vocabulary. The opening line of his Metaphysics, "All men by nature desire to know", sums up the spirit of a thinker who believed that curiosity is part of what makes us human.