Anaxagoras

Anaxagoras was born around 500 BCE in Klazomenai, an Ionian Greek city on the coast of Asia Minor, near modern Izmir in Turkey ^[1]. Ancient sources report that his father, Hegesibulus, belonged to a wealthy family, which gave the young man both leisure and the means to pursue inquiry rather than commerce or politics ^[2].

The Ionia of his childhood was a region in turmoil. Klazomenai took part in the Ionian Revolt against Persian rule, and the Persian reconquest of the coast shaped the world he grew up in. It was also the region that had produced Thales, Anaximander, and Anaximenes of nearby Miletus, the first Greek thinkers to seek natural rather than mythological explanations for the world ^[3]. Anaxagoras inherited that tradition directly, and later writers counted him among the last and most rigorous of the Ionian natural philosophers.

According to a story preserved by Diogenes Laertius, Anaxagoras eventually gave up his inheritance to relatives so that he could devote himself entirely to the study of nature. When asked whether he had no concern for his homeland, he is said to have pointed to the sky and answered that his homeland concerned him greatly ^[2]. Whatever the reliability of such anecdotes, they capture how antiquity remembered him: a man who valued understanding the heavens above property and civic ambition.

At some point in the first half of the fifth century BCE, Anaxagoras moved to Athens, becoming, so far as the record shows, the first philosopher to settle and teach there ^[1]. The exact date is disputed. Some ancient chronologies place his arrival around 480 BCE, roughly coinciding with the Persian invasion under Xerxes, while modern scholars debate whether he came earlier or later and how long his residence lasted ^[4]. Most accounts agree that he spent about thirty years in the city.

His timing was fortunate. Athens after the Persian Wars was growing into the political and cultural center of the Greek world, and its leading citizens sought out the new learning from Ionia. Anaxagoras became a close associate and teacher of Pericles, the statesman who dominated Athenian politics for decades. Plutarch, in his life of Pericles, credits Anaxagoras with shaping the statesman's gravity of manner and his elevated style of speech ^[5]. The tragedian Euripides was also reported to have studied with him, and traces of Anaxagorean cosmology have been detected in his plays ^[2].

Anaxagoras wrote a single book, a prose treatise on nature, of which only fragments survive through quotations by later authors such as Simplicius ^[3]. Socrates, in Plato's Phaedo, recalls that the book could be bought cheaply in the Athenian marketplace, a detail that suggests how widely his ideas circulated. For anyone asking who was Anaxagoras in the eyes of his contemporaries, the answer was clear: the resident scientist of Periclean Athens, admired by some and viewed with suspicion by others.

Any account of Anaxagoras achievements has to begin with the heavens. He taught that the sun is not a god but a mass of fiery metal or red-hot stone larger than the Peloponnese, and that the moon is an earthy body that shines by reflected sunlight and has plains, mountains, and ravines ^[1]. From these premises he gave what is generally regarded as the first correct explanation of eclipses: a solar eclipse occurs when the moon passes between the earth and the sun, and a lunar eclipse when the earth's shadow falls on the moon ^[4]. Ancient writers also connected him with the great meteorite that fell at Aegospotami around 467 BCE, claiming he had predicted that stones could fall from the sky; the fall itself is historical, and the association shows how firmly his name was linked to celestial matters ^[2].

His physics rested on a distinctive answer to the problem posed by Parmenides, who had argued that nothing can come to be from what is not. Anaxagoras proposed that nothing truly comes into being or perishes; instead, all change is the mixture and separation of ingredients that have always existed. His famous principle held that there is a portion of everything in everything, so that bread can nourish flesh and bone because flesh and bone are already present in it in minute amounts ^[3]. Things are named after whatever predominates in the mixture. This theory of infinitely divisible ingredients set him apart from the atomists, who insisted on indivisible particles moving in a void.

His most celebrated idea was Nous, or Mind. In the surviving fragments he describes Mind as unlimited, self-ruled, and mixed with nothing, the finest and purest of all things, which set the original mixture rotating and thereby began the separation of the cosmos into its present order ^[3]. Aristotle wrote that Anaxagoras seemed like a sober man compared with the random talkers who preceded him, because he made intelligence the cause of order in the world. Yet both Plato and Aristotle also complained that, having introduced Mind, Anaxagoras rarely used it in his detailed explanations, falling back instead on mechanical causes ^[6]. That tension, between a cosmic intelligence and a mechanistic physics, made him a lasting reference point in ancient philosophy.

His interests ran wider still. Later sources credit him with work on the causes of the Nile flood, which he attributed to melting snow in the south, with explanations of meteors, rainbows, and the Milky Way, and even, according to Plutarch, with an attempt at squaring the circle while in prison ^[2]. Whatever the details, his contemporaries saw in him a mind determined to bring the whole natural world under rational explanation.

Little is recorded about Anaxagoras as a private man, and almost nothing about a wife or children; the tradition presents him instead as wholly absorbed in inquiry ^[2]. Diogenes Laertius preserves a cluster of anecdotes to that effect. Asked why anyone should choose to be born rather than not, he reportedly answered: to study the heavens and the order of the whole cosmos. Told of the death of his son, he is said to have replied that he had known he fathered a mortal. Such stories are moralizing set pieces rather than verified biography, but they defined his ancient reputation for detachment and composure ^[2].

His nickname captured the same image. Later writers say he was called Nous, Mind, after the principle at the center of his philosophy, a label that could be worn as praise or mockery depending on the speaker ^[1]. In Athens his closest documented relationship was with Pericles, who by several accounts protected him, supported him, and revered him as a teacher. Plutarch relates that when Anaxagoras, neglected in old age, wrapped himself up and resolved to starve, Pericles hurried to him and pleaded with him to live, and the philosopher answered that those who need a lamp pour oil into it ^[5]. The anecdote, whatever its accuracy, reflects how the two men were remembered together.

Anaxagoras's Athenian career ended in a courtroom. He was prosecuted for impiety, with his claim that the sun is a fiery stone rather than a divinity cited as the offense; some sources add a charge of sympathizing with Persia ^[1]. The ancient accounts of the trial disagree on nearly every detail, including its date, the prosecutor, and the penalty. Many modern scholars connect it with a decree attributed to the seer Diopeithes against those who taught doctrines about the heavens, and read the whole affair as an indirect attack on Pericles through his friend ^[4]. Estimates of the date range from the 450s BCE to around 430 BCE.

What the sources agree on is the outcome: Anaxagoras left Athens. Plutarch says Pericles intervened to save him, and one tradition holds that the statesman personally escorted him from the city ^[5]. He withdrew across the Aegean to Lampsacus, a Greek city on the Hellespont in the territory of Persian-influenced Asia Minor, where he continued to teach and was received with honor rather than suspicion ^[2].

He died at Lampsacus in 428 BCE, at about seventy two years of age ^[1]. Diogenes Laertius reports that when the city's magistrates asked what they could do for him, he requested that the children be given a holiday from school each year in the month of his death, and that the custom was still kept generations later. The Lampsacenes buried him with public honors and, according to the same tradition, set up an altar inscribed to Mind and Truth ^[2].

The influence of Anaxagoras ran through the whole later course of Greek thought. Socrates, as Plato tells it in the Phaedo, was thrilled to hear that a thinker had made Mind the cause of all things, and then disappointed to find the book full of airs and waters and ethers instead; that disappointment helped push Socratic philosophy toward questions of purpose and value ^[6]. Aristotle engaged with Anaxagoras repeatedly in the Physics and Metaphysics, praising the introduction of intelligence into cosmology while criticizing its inconsistent use. Through these debates his ideas entered the permanent bloodstream of Western philosophy ^[3].

His trial acquired a symbolic weight of its own. Standing decades before the execution of Socrates, it became the earliest well-attested case of a Greek thinker prosecuted for teaching about nature, and later writers from antiquity to the modern era cited it in arguments about the freedom of inquiry ^[4]. In the history of science he is remembered for the eclipse explanation, the recognition that the moon shines by borrowed light, and the insistence that celestial bodies are physical objects governed by the same principles as things on earth. A crater on the moon carries his name, a quiet acknowledgment from the discipline he helped begin ^[7].

For readers of any Anaxagoras biography today, the basic Anaxagoras facts still impress: a provincial Ionian who reshaped the intellectual life of Athens, a theorist who dared to demote the sun from god to stone, and the first philosopher to make cosmic intelligence a subject of rational argument. The fragments of his book, barely a few pages of Greek, remain among the most studied texts of early philosophy, edited and analyzed continuously since the nineteenth century ^[3].