No one seems to have noticed yet, but 2021 marks a pretty important anniversary in the history of Western science and civilization. 2,500 years ago this year a philosopher named Anaxagoras arrived in Athens, Greece.
No one held any celebration at that time. However, it was an important historical and intellectual milestone. Before Anaxagoras, ancient Greek science (or to be less anachronistic, natural philosophy) had not been practiced much in Greece itself. Natural philosophy originated in the early 6th century BC. in the Greek settlement of Miletus in Ionia, the western coast of present-day Turkey. A second branch of primordial Greek science soon took root in southern Italy after an Ionian, a fanatic of mathematics named Pythagoras, moved there.
Anaxagoras, born in the Ionian city of Clazomenae, was the first natural philosopher to reside in Athens and promote the Ionic philosophical vision there. As science historian George Sarton wrote, Anaxagoras "introduced the scientific spirit to Athens." Shortly afterwards, Athens became the center of philosophical research in the Western world, as the triumvirate of Socrates, Plato, and later Aristotle established philosophy as an essential component of civilized intellectual discourse.
To be honest, there is some doubt about the exact date of Anaxagoras' transfer to Athens. But the biographer of the philosophers Diogenes Laercius wrote that Anaxagoras began to do philosophy in Athens at the age of 20 and says he was 20 when the Persian king Xerxes attacked Greece – and that was 480 BC, 2,500 years ago. (You may think 2021 would have done that 2,501 years ago, but only if you forgot there was no year 0, then you have to subtract one year from the calculation.)
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It is possible that during his time in Athens, Anaxagoras met the young Socrates, but the direct link with Socrates and his philosophical descendants was through the philosopher Archelaus. Anaxagoras "was the first to encourage Archelaus the Athenian to practice philosophy," wrote the famous physician Galen. And Archelaus was the master of Socrates, who taught Plato, who taught Aristotle, whose influence dominated science for two millennia.
Anaxagoras emerged about a century after the first Ionic philosophers, Tales of Miletus and his younger contemporary Milesian anaximander. Together with a third Milesian, Anaximenes, they had established a new way of seeing the natural world. They sought explanations for phenomena in natural causes, rather than attributing them to the behavior of mythological gods invented by poets to explain cosmic history. The lightning was no longer a sign of an angry Zeus, Anaximander declared, but blinked when the clouds were disturbed by the wind.
Although the original Milesians disagreed on all issues, they insisted that natural philosophy should be based on an underlying foundation (called arche or arkhé), a principle from which all reality could be derived. “The notions of beginning, origin, principle of government, and cause were closely united in the one word arche,” wrote the philosopher-historian William Guthrie.
Thales thought that the fundamental principle was water; Anaximenes said air. Anaximander thought that everything arose from a mysterious material called apeiron, which means something like the unlimited or the unlimited. In Italy, the Pythagoreans promoted the idea that the underlying foundation of everything was number.
For Anaxagoras, the arche was nous or "mind" (sometimes translated as "intellect" or "intelligence"). His approach extended the scientific ideas of his Ionic predecessors to address questions posed by the Italian philosopher Parmenides. Everything had to always be as it is, Parmenides reasoned, because nothing could become nothing: non-existence could not produce existence, because non-existence does not exist, by definition of existence. Parmenides concluded that reality consisted of an immovable and ever-present mass of undifferentiated equality that filled all space. Therefore, there was no room for any movement or change: the world perceived by the senses was false, an illusion that hid the true nature of reality. The senses offered a "way of looking"; the only reason provided the "path of truth."
Although it sounds to modern ears, in those days it was a difficult argument to refute. But Anaxagoras had a sophisticated and subtle mind; in responding to Parmenides, he introduced a completely new idea of fundamental reality, claiming that all the different types of matter are already present in any piece of matter. There is no need to "emerge" anything new, because there are already all possible things to begin and continue to exist in everything, even in quantities too small for the senses to detect. A supposedly pure piece of gold, for example, also contains small “seeds” of any other type of matter. Our senses are too coarse to notice the seeds. (On the other hand, the seeds also contained smaller amounts of everything. Anaxagoras had conceived the notion of infinite divisibility, another novel thought).
Any piece of matter could change for something else by virtue of changes in the relative amounts of its seeds. Eating vegetables, for example, could produce flesh and bone in the body because the digestive process concentrated imperceptibly diffuse flesh and bone seeds into the original food.
Initially, all matter was a large static mass. At some point in the past, nous or mind, we fix that mass in a rotating motion, concentrating heavy things (like the earth) in the middle, creating the Earth. Pieces of earth spinning outward became stars and the sun and moon.
Anaxagoras walnuts were the only distinctive ingredient in his system. Other things mingled with everything else. But the mind was his. “The mind is something infinite and independent and does not mix with anything,” he wrote. But the mind (while maintaining its purity) is present in many things, including all people, called by Anaxagoras "the wisest of animals." (Guthrie recounts that when asked why some people do not seem so wise, "it is said that Anaxagoras commented that although all men have intellect, they do not always use it").
Despite his own considerable intellect, Anaxagoras' theory of matter was erroneous. But his reputation rests on many other contributions to scientific thought. A century ago, Thomas Heath, the eminent scholar of Greek science and mathematics, declared that Anaxagoras was "a great man of science" who "enriched astronomy with a discovery of time": that the light of the moon is not its own, but a reflection of sunlight. (Some scholars say he received the idea from Parmenides, but in any case, it is still very deserving that a crater near the north pole of the moon is called Anaxagoras.)
Anaxagoras wrote a treatise covering many other scientific topics, including meteorology and geology. He supposedly predicted that a rock could fall to Earth from the sky; in any case, he obtained credit for such a prediction when a meteorite fell on Thrace (now Turkey) in 467 BC. He argued that the Earth was flat. And that he was propped up in space by the air beneath her, echoing his Ionic predecessor Anaximenes.
The scientific importance of Anaxagoras is not based, however, on the accuracy of his theories but on the insight of his attitude. He expressed a scientific attitude by renouncing the supernatural more clearly than his predecessors. Even Thales felt that "there were gods in all things," Aristotle and Thales had written, and others had attributed souls to celestial bodies. From his known writings there is no sign that Anaxagoras' nous was in any way religious: it was a natural component of the cosmos, giving it direction, just as the human mind induces a human body to move its limbs. “He nowhere in the existing material identifies the mind with a divine principle or god,” as one scholar observed.
Even more profoundly, Anaxagoras identified a key issue that has baffled science professionals ever since: the relationship between reason and the senses. It was the absolute devotion to reason — and the utter disrespect for the senses — that led Parmenides to declare reason the path of truth and sensible phenomena as illusory.
Anaxagoras fully agreed that the senses could deceive, calling them "weak" and unable to "distinguish what is true." The human senses are simply not sharp enough to perceive reality clearly in high definition. Reality has more than we can see. But – the key point – with senses complemented by the intellect, we can infer a lot about the deeper and invisible reality of what we see, Anaxagoras realized. "Appearances are visions of things that are invisible," he wrote, or in another translation, "phenomena are a vision of the invisible." Reality is richer than it immediately appears, but the human mind is still able to explore it and discover much about it. And with that realization, progress was made possible in the scientific understanding of reality.
Of course, Anaxagoras' emphasis on natural explanations and his contempt for the gods put him in trouble. Athenian officials accused him of impiety, convicted him and sentenced him, on some counts, to death, by others only to prison. His friend the Athenian politician Pericles intervened to organize the exile, and Anaxagoras spent his last years in Lampsacus, a city in what is now northwestern Turkey, where he was revered as a defender of the mind and truth.