Aristotle

• 1. The First Teacher

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  Ancient Greek scholars gave Aristotle a name reserved for one man: among medieval Muslim scholars he was "The First Teacher", and to Christians like Thomas Aquinas he was simply "The Philosopher". He lived from 384 to 322 BC, and according to the philosopher Bryan Magee, "it is doubtful whether any human being has ever known as much as he did". His writings span natural science, philosophy, linguistics, economics, politics, psychology, and the arts. Yet for a man this celebrated, the basic facts of his life sit on thin ground. The ancient biographies are speculative, and historians agree on only a handful of points. What survives is not the polished work he wrote for the public. Only around a third of his original output remains, and none of it was meant to be published. So how did a doctor's son from a small northern town become the figure Jonathan Barnes said could fill "a history of European thought"? What did he actually see when he cut open a fertilized hen's egg, and why did his physics of falling bodies last almost two thousand years before anyone overturned it? The chapters ahead follow his logic, his study of living things, his account of the soul, his ideas about cities and money, and the long afterlife of texts that were nearly lost for good.

• 2. From Stagira To The Lyceum

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  Stagira, in Chalcidice, sat about 55 kilometres east of modern-day Thessaloniki, and there Aristotle was born to a physician's family. His father Nicomachus served as personal physician to King Amyntas of Macedon and belonged to the medical guild of the Asclepiadae. That family trade likely seeded his early interest in biology and medicine. Both his parents died when he was young, and a man named Proxenus of Atarneus became his guardian.

  At seventeen or eighteen, Aristotle moved to Athens to study at Plato's Academy. He stayed nearly twenty years and became known as a researcher and lecturer, earning from Plato the nickname "mind of the school". He left in 348/47 BC after Plato died, reportedly disappointed when control of the Academy passed to Plato's nephew Speusippus. Anti-Macedonian feeling in Athens may also have pushed him out.

  Assos, in Asia Minor, took him next, at the invitation of his former fellow student Hermias of Atarneus. There he married Pythias, Hermias's adoptive daughter and niece, and they had a daughter they also named Pythias. With his colleague Theophrastus he did extensive work in botany and marine biology, continuing it on the nearby island of Lesbos.

  In 343/42 BC, Philip II of Macedon called him to Pella to tutor his thirteen-year-old son, Alexander. Aristotle taught the boy at the private school of Mieza, in the gardens of the Nymphs. He gave Alexander an annotated copy of the Iliad, said to have become one of the prince's most prized possessions. He also counselled Alexander to be "a leader to the Greeks and a despot to the barbarians".

  A year after Philip's assassination in 336 BC, Aristotle returned to Athens for the last time. As a metic he could not own property, so he rented a building near the sacred grove of Apollo Lykeios, which gave the place its name: the Lyceum. Its colonnade, the peripatos, gave his school its name, the Peripatetic. He ran courses and research there for twelve years and built a library of manuscripts, maps, and museum objects. His wife Pythias died, and he became involved with Herpyllis of Stagira, with whom he had a son named after his father, Nicomachus.

  In 322 BC, accused of impiety, he fled to his mother's family estate in Chalcis, Euboea. He reportedly said he would not let the Athenians "sin twice against philosophy", a nod to the trial and execution of Socrates. He died there of natural causes that same year, leaving a will asking to be buried beside his wife.

• 3. The Grammar Of Reasoning

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  The Prior Analytics gave the Western world its earliest systematic study of logic, and Aristotle's version dominated until 19th-century advances in mathematical logic. Immanuel Kant, in the Critique of Pure Reason, said that with Aristotle logic had reached its completion. His influence on the subject ran well into the 1800s.

  Six books make up what later editors called the Organon, compiled around 40 BC by Andronicus of Rhodes or his followers. They run from the Categories, which analyses simple terms, through On Interpretation, the two Analytics, the Topics, and On Sophistical Refutations. The arrangement moves from basic terms to propositions to the more complex forms of syllogism and demonstration.

  The syllogism is the engine of all this. From "all men are mortal" and "all Greeks are men", the conclusion follows that all Greeks are mortal. Aristotle would not have called this "logic" at all; he reserved that word for dialectics and labelled his own method "analytics".

  His Posterior Analytics holds his account of demonstration, or demonstrative knowledge, which today reads closer to epistemology than logic. For Aristotle, knowledge is that which is necessarily the case, tied closely to the study of causes. The mathematician George Boole would later fully accept this logic, then push beyond it with the algebraic system of his 1854 book The Laws of Thought.

• 4. Matter, Form, And The Four Causes

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  "Metaphysics" was never Aristotle's word. It comes from the title of a collection of his works, supplied by a later compiler; he called the subject "first philosophy" or theology, the study of being qua being. In Book VII of the Metaphysics he examines substance and essence, concluding that a particular substance combines both matter and form, a theory called hylomorphism. The matter of a house is its bricks, stones, and timbers; the form is the actual house, the covering for bodies and goods.

  Universals divided him from his teacher. Plato held that forms exist separately from the things that imitate them. Aristotle countered that the form of apple exists within each apple, not in a separate world of forms, and that universals are encountered only when instantiated in a particular substance.

  Change drives his Physics and On Generation and Corruption. He separates coming-to-be from growth, locomotion, and alteration, and introduces potentiality and actuality. The seed of a plant in the soil is potentially a plant; left unprevented, it will become one. As he put it, "animals do not see in order that they may have sight, but they have sight that they may see".

  Why anything exists or changes, he answered with four causes. The material cause is the wood of a table. The formal cause is its design. The efficient cause is the primary source, like the first domino knocking over the second. The final cause, the telos, is its purpose, which for living things implies adaptation to a particular way of life. These four explanations still echo in Niko Tinbergen's four questions for analysing animal behaviour.

• 5. Elements And Falling Bodies

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  Earth, water, air, and fire were the four elements Empedocles had proposed, and in On Generation and Corruption Aristotle tied each to two of four sensible qualities: hot, cold, wet, and dry. To this scheme he added a fifth, the heavenly aether, the divine substance of the spheres, stars, and planets. Earth and water move down, air and fire move up, and aether moves in a circle around the heavens.

  Motion came in two kinds. "Violent" motion, like a thrown stone, stops as soon as the agent stops causing it, because Aristotle treated rest as the natural state and never addressed friction. "Natural" motion, like a falling object, depends on the element involved. In the Physics he held that a falling body's speed is proportional to its weight and inversely proportional to the density of the fluid it falls through. From this he reasoned that in a vacuum the speed of fall would be infinite, an absurdity, so he concluded that a vacuum is impossible.

  Archimedes corrected him, showing that floating depends on mass and volume, not on a thing's elementary composition, so a metal boat can float by displacing enough water. John Philoponus and later Galileo are said to have shown by experiment that a heavier object does not fall faster than a lighter one. Galileo proposed that all bodies fall at the same speed whatever their weight.

  Not everyone agrees Aristotle was simply wrong. Carlo Rovelli argues his physics of motion holds within its domain, that of objects in Earth's gravitational field immersed in a fluid such as air. In that setting heavy bodies in steady fall do travel faster, and they fall more slowly in a denser medium. His writings on motion stayed influential into the early modern period, and his idea that the agent's effect stops the instant it ceases acting helped produce the medieval theory of impetus.

• 6. The Naturalist Of Lesbos

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  Two years on Lesbos, observing and describing the zoology of the island and its seas, made Aristotle the first person to study biology systematically. He worked especially at the Pyrrha lagoon in the island's centre. His data in History of Animals and his other zoological books came from his own observation, from knowledgeable people like beekeepers and fishermen, and from travellers' accounts.

  Sea life filled his notebooks. He described the catfish, the electric ray, the frogfish, and cephalopods such as the octopus and paper nautilus. His account of the hectocotyl arm of cephalopods, used in reproduction, was widely disbelieved until the 19th century. He gave accurate descriptions of the four-chambered stomachs of ruminants and of the embryological development of the hound shark.

  Form followed function in his eye. The heron has a long neck, long legs, and a sharp spear-like beak, while ducks have short legs and webbed feet. Charles Darwin noticed such differences too, but, unlike Aristotle, used them to build a theory of evolution. Aristotle treated mutations and hybrids as rare accidents, ridiculed the idea that accidents could yield orderly results, and never said one kind could change into another or that kinds could become extinct.

  Experiment in the modern sense was not his method, but in Generation of Animals he opens a fertilized hen's egg to watch the embryo's heart beating inside. He gathered data, found patterns across whole groups, and inferred causes. From live-bearing tetrapods he correctly predicted that brood size decreases with body mass, that lifespan increases with gestation period and body mass, and that fecundity decreases with lifespan.

  About 500 animal species he distinguished, arranging them on a graded scale of perfection with man at the top. He grouped vertebrates as "animals with blood" and invertebrates as "animals without blood", and noted exceptions, such as sharks having a placenta. Darwin called him the most important contributor to biology, writing in 1882 that next to "old Aristotle" his own scientific gods were "mere schoolboys".

• 7. Soul, Memory, And Dreams

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  Three kinds of soul appear in On the Soul: the vegetative, the sensitive, and the rational, and humans have all three. The vegetative soul governs growth and nourishment, the sensitive soul handles sensation and movement, and the uniquely human rational soul receives the forms of things and compares them using the nous, intellect, and logos, reason. For Aristotle the soul is the form of a living being, and, against most earlier thinkers but in accordance with the Egyptians, he placed the rational soul in the heart.

  Memory, he argued, is the ability to hold a perceived experience in the mind and to tell the inner appearance apart from a past occurrence. A memory is a mental picture, a phantasm, left as an impression on a semi-fluid bodily organ. Memory is of the past, prediction of the future, and sensation of the present. Recollection works by chains, where one memory stimulates the next through similarity, contrast, and contiguity, the relationships he set out in his laws of association. Only humans can remember impressions of intellectual activity such as numbers and words.

  Sleep, described in On Sleep and Wakefulness, he saw as a result of overusing the senses or of digestion, and as vital to the body. During sleep, thinking, sensing, and recalling do not function, yet the day's impressions, free of fresh distraction, surface as dreams. One claim broke with older belief: dreams are not foretelling and not sent by a divine being. When a dream seems to match a future event, Aristotle reasoned, it is simply coincidence. In De Anima he credits the faculty of imagination, phantasia, with the power to create, store, and recall images.

• 8. Cities, Money, And Lost Manuscripts

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  "Man is by nature a political animal," Aristotle wrote in the Politics, and he treated the city as a natural community, prior in importance to the family and the individual, "for the whole must of necessity be prior to the part". He conceived the city as an organism, a collection of parts none of which can exist without the others, and is considered one of the first to think of it this way. The aim of the city, he held, is not merely to avoid injustice or secure economic stability, but to let at least some citizens live a good life and perform noble actions.

  Ethics, for him, was practical rather than theoretical, aimed at becoming good rather than knowing for its own sake. In the Nicomachean Ethics he taught that virtue lies in a thing's proper function, its ergon, and that the human function is an activity of the soul in accordance with reason. He named the aim of all deliberate action eudaimonia, usually translated "happiness" or "well-being", reached through the virtuous mean between vices of excess and deficiency, such as courage between cowardice and rashness.

  Money drew some of his earliest economic thinking. In the Politics he offers an account of its origin: people grew dependent on one another, importing what they needed and exporting their surplus, and agreed to deal in something intrinsically useful like iron or silver. He distrusted retail trade and interest as unnatural, since interest makes a gain out of money itself rather than its use. He also saw money as a single universal standard that makes different goods commensurable, and a store of value for future exchange.

  His Rhetoric proposed three appeals: ethos to the speaker's character, pathos to the audience's emotion, and logos to logical reasoning. His Poetics held that arts like tragedy, comedy, and dance are all forms of mimesis, imitation, and taught that tragedy arouses pity and fear to effect a catharsis of those emotions. Only the portion on tragedy survives; the book on comedy is lost.

  Those surviving works almost did not reach us. Aristotle left his writings to Theophrastus, his successor as head of the Lyceum, who passed them to Neleus of Scepsis in Asia Minor, where they lay hidden for protection until the collector Apellicon bought them. More than 2300 years after his death, his name still marks the heavens. The Aristotle Mountains in Antarctica honour the continent he was the first to conjecture, the crater Aristoteles sits on the Moon, and the asteroid (6123) Aristoteles circles the main belt.