The Cave and the Light: Plato Versus Aristotle, and the Struggle for the Soul of Western Civilization

by Arthur Herman

In addition, the Timaeus’s insistence that physical matter is simply inert material waiting for the imprint of nous, or reason, in order to have any significance or motion became a central theme of ancient and medieval science. Even Plato’s rival Aristotle will make it a starting point for his own work.27 Likewise, the idea of planetary motion as a harmonious system of circles or spheres (later called “the music of the spheres”), and of man as a microcosm of the universe with a body, mind, and soul in tune with the larger harmonies of creation, marks the start of long, influential chapters in Western thought. The sacred geometry of the Timaeus would reach across the Middle Ages to the Renaissance. It leaves its mystic imprint on the philosopher Nicholas of Cusa (one of whose disciples will be a Polish astronomer named Nicolaus Copernicus), on Leonardo da Vinci, and even on the Sistine Chapel ceiling. It is not for nothing that Raphael has Plato offer the Timaeus as his most representative work in The School of Athens or that Pythagoras himself appears in the painting sketching a diagram of the tetraktys, which Pythagoras proposed, and Plato accepted, as the symbol of the created eternal realm. Still later, Plato’s often expressed view that “God is always doing geometry” and “Where there is number there is order; where there is no number there is nothing but confusion, formlessness, and disorder” would decisively shape the scientific views of Copernicus, Kepler, and Galileo...

The sacred geometry of the Timaeus would reach across the Middle Ages to the Renaissance. It leaves its mystic imprint on the philosopher Nicholas of Cusa (one of whose disciples will be a Polish astronomer named Nicolaus Copernicus), on Leonardo da Vinci, and even on the Sistine Chapel ceiling. It is not for nothing that Raphael has Plato offer the Timaeus as his most representative work in The School of Athens or that Pythagoras himself appears in the painting sketching a diagram of the tetraktys, which Pythagoras proposed, and Plato accepted, as the symbol of the created eternal realm. Still later, Plato’s often expressed view that “God is always doing geometry” and “Where there is number there is order; where there is no number there is nothing but confusion, formlessness, and disorder” would decisively shape the scientific views of Copernicus, Kepler, and Galileo, not to mention Isaac Newton and Albert Einstein.b28

Following Aristotle’s example with animals, he turned to dissection to discover what was going on inside the human frame. His curiosity was insatiable. Some ancient sources claim he turned to human vivisection in his work, including experiments on criminals handed over to him by the Ptolemaic government.7 Are the stories true? Given the fact that a couple of centuries later Galen mentions testing new poisons on condemned criminals, and the fact that slaves were routinely tortured to extract information in legal cases, there is no reason to doubt them. Centuries later, the Christian critic Origen blamed Herophilus for carrying free scientific inquiry too far and called him “that butcher who cut up innumerable human beings so that he could study nature.” It was a first hint of the battles to come between religion and science over what we call medical ethics.8 It may be unfair to Herophilus to have Jack Kevorkian or Josef Mengele hovering over his reputation. Certainly the corpus of his anatomical writings might have been scientific Alexandria’s greatest gift to posterity, if it had not perished in the great fire that devastated large portions of the Great Library in 48 BCE.†9

Aristarchus’s heliocentric theory was an astonishing leap into the future. However, it found no buyers among other Hellenistic astronomers. They took a straightforward geometric, rather than dynamic, view of motion. As orthodox Aristotelians, they couldn’t understand the idea of force or acceleration except in terms of something pushing something else (it will take Galileo and Newton to set that issue straight). Nor could they understand why, if the earth really did rotate, everything not tied down or rooted in the ground did not eventually fly off in the opposite direction.10 It’s not known how Aristarchus answered what, given the assumptions of the time, were reasonable objections backed by the authority of Aristotle himself, or even if he did. In the end, Greek astronomers preferred to stick to Aristotle’s “celestial spheres” to explain the movement of the planets and the stars.‡ The earth remained the center of the universe for another two thousand years. Even so, the mathematical computations of Alexandrian astronomy remained at a very high level. The philosopher of mathematics Bertrand Russell has called them “works of astonishing genius.”11 This amazing—if ultimately misleading—work culminated in the treatises of the great Ptolemy (no relation to the ruling dynasty) in the first century CE. Ptolemaic astronomy was Alexandria’s last word on the geocentric view of the cosmos. It would remain Europe’s principal guide to astronomy until the Renaissance. Ptolemy’s greate...

The first was the geometer Euclid. We know almost nothing about his life. He may have been from Athens; he may even have studied at Plato’s Academy. We do know he was teaching mathematics in Alexandria about the time Strato arrived and that Ptolemy I once asked him if there wasn’t an easier way to study geometry than by taking Euclid’s classes. Euclid is supposed to have answered, “There is no royal road to geometry.” Anyone who has read his or her way through the Elements knows what he meant. As a textbook, Euclid’s Elements is peerless in its clarity and majesty of progression from first principles, or axioms, to particular demonstrations, or proofs. They move from the definition of line and point on the first pages to Pythagoras’s famous theorem and beyond. For more than two thousand years, they have been the model of a priori reasoning at its most dignified. The subtext of the Elements is also the principle Euclid may have absorbed from his teachers at the Academy: that mathematics and geometry are reason’s direct insight into the mind of the “supreme geometer,” God Himself. Indeed, Euclid’s principal works could almost have served as textbooks for Plato’s Rulers in the Republic. They were the Elements for arithmetic and geometry; the Conic Sections for the study of proportion and harmony; and his Phaenomena as a guide to astronomy, since it focuses on the theory of uniformly rotating spheres.13

When Archimedes returned to Syracuse, his interest in things aquatic did not stop. He continued his research in the principles of hydraulics and another field he largely invented, hydrostatics, or the study of fluids at rest. This is the origin of the most famous story about Archimedes. It tells how the king of Syracuse, Hiero II, once asked him to figure out the gold content of a certain sacrificial wreath or crown. Archimedes was pondering the problem as he eased himself into his morning bath, noticed the water spilling over the sides of the bath, and realized that by weighing the volume of water displaced by an object, he could determine how much gold or silver it contained. According to the story, he then leaped out and ran down the street stark naked, shouting: “I have found it! I have found it!” (Eureka! Eureka!)26 A charming story, which dates back at least to the Roman architect Vitruvius. Most modern scholars doubt it happened, which doesn’t mean it isn’t true. What is far more revealing is that Archimedes, in his own treatise on hydrostatics, never mentions it or tells us anything about how he discovered or researched any of his amazing works.

Taken together, they laid the future cornerstone of what comes to be called calculus, or the mathematics of infinity (Archimedes was the first mathematician to use the concept of infinity in his work). Without it, modern math and science as we know it would not exist. In one sense, the impetus to Archimedes’s math research was proving that Plato had been wrong: you can’t form a sphere out of a series of triangles or pentagons, as Plato claimed in the Timaeus, any more than you can form a circle out of a square. Archimedes showed this by demonstrating that you can’t measure the area of a circle or sphere or cylinder using any kind of straight line. However, you can measure it by slicing it into pieces that can be bounded by straight lines, then slicing that part left over into measurable pieces again and again, until finally there is nothing left unmeasured.28 This is what calculus, and the concept of infinity, enabled Archimedes to do. He discovered, for example, that the area of a sphere is four times the area of its greatest circle; and that the area of a parabola (like the one described by a stone flung from a catapult) is four-thirds the area of the triangle enclosed within it. Archimedes’s work was also establishing in passing another scientific landmark for the future. If you can’t measure something, then it probably doesn’t exist. It’s a notion that Aristotle would have rejected at once. It was, however, another logical outgrowth of his own scientific method.b Archi...

Archimedes tied a series of pulleys to a dry-docked three-masted ship loaded with cargo and passengers, and then, to the crowd’s stunned amazement, he lifted it into the harbor by himself. This led Hiero to declare, “From this day forward, Archimedes is believed no matter what he says,” which led Archimedes to reply in the full flush of triumph, “Give me a lever and a place to stand, and I shall move the earth.”30

Shortly after Archimedes’s masterful show in Syracuse harbor, however, the city faced the deadliest threat of all. There was a new regional power in the central Mediterranean basin, the imperial republic to the north: Rome. Breaking Syracuse to its will was the key to Rome’s hegemony over Sicily and the rest of Italy, and in 214 BCE an enormous Roman fleet and army gathered at the entrance to the harbor. Syracuse went to battle stations, and its most famous citizen, now in his seventies, sprang into action. The best description of what happened next is by the Greek historian Polybius. He wrote it not long after the siege of Syracuse, when some of the participants may still have been alive. He tells us how the Syracusans put Archimedes in charge of constructing their defenses and how he laid them out so that “they would have everything ready to hand, and could respond to any attack by the enemy with a countermove.”31 The Romans were hardly amateurs when it came to besieging cities. Their plan was a simultaneous land and sea assault, with boats equipped with massive mobile siege towers rowing up to storm Syracuse’s walls. However, as Polybius relates, “Archimedes had constructed artillery which could cover a whole variety of ranges, so that while the attacking ships were still at a distance he scored so many hits with his catapults and stone-throwers” that the Roman general Marcus Claudius Marcellus had to call off the attack before his men reached the walls. On the landward...

fell back to count their losses, Archimedes’s machines continued to harass their retreat.

Most people know the quotation from the Confessions “O God, make me good, but not yet!” But few realize the tension and despair underlying that famous bon mot. Like Aristotle, Augustine believed that the quality of life we lead depends on the choices we make. The tragedy is that left to our own devices—and contrary to Aristotle—most of those choices will be wrong. There can be no true morality without faith and no faith without the presence of God.

Boethius is the first Christian thinker to realize that Plato and Aristotle were still indispensable to Western civilization. They still provided an essential and rational framework for dealing with the real world—and also dying in it. Philosophy as “a preparation for death” was no moot point for Boethius. Soon after he finished the Consolation, his guards led him away. He was forced to kneel on the stone floor, and a cord was tied around his temple and across his eyes. On Theodoric’s order, the executioner wound the cord tighter and tighter until the Roman’s eyes popped loose from their sockets. Then, in unbearable agony, he was bludgeoned to death with iron rods. Back in his cell sat the abandoned manuscript. It read: Happy the man whose eyes once could Perceive the shining fount of good: Happy he whose unchecked mind Could leave the chains of earth behind.5

The evidence of the senses further corroborates the fact that the earth is round. How else would eclipses of the moon show segments shaped as we see them? In eclipses the outline is always curved; and since it is the interposition of the earth that makes the eclipse, the form of this line will be caused by the form of the earth’s surface, which is therefore spherical.… The text was in Arabic, but the author was a Greek.2 The man’s name, Gerard noted, was Aristotle. He read on. “Again, our observations make it evident, not only that the earth is circular, but also that it is of no great size.”

Their names should be better known than they are. Adelard of Bath risked starvation and death to travel to Sicily and Antioch, where he translated the works of Euclid and various Arab writers on astronomy and mathematics and wrote his own treatise on the astrolabe. Around 1150, James of Venice put together the first Latin translation of Aristotle’s Metaphysics and On the Soul.

The most dedicated and most important, however, was Gerard of Cremona. Until his death in 1187, he translated no fewer than eighty-seven books from the Arabic, including Ptolemy and Euclid, and a precious hoard of texts by Aristotle. These included the Posterior Analytics, which completed the West’s knowledge of Aristotle’s works on logic.* Gerard also turned out Latin versions of Aristotle’s pathbreaking scientific treatises, not only On the Heavens but the Physics, On Generation and Corruption, and Meteorology, as well as Arab commentaries on the Metaphysics and On the Soul—the key texts of Aristotle’s entire philosophy. Aristotle’s Politics, Nicomachean Ethics, and Rhetoric had to wait a few more years to find a suitable translator.

For the fact remains that without Arab help, western Europe would never have recovered its knowledge of Greek science and mathematics—still the foundations of modern science today—or understood how to interpret it.7 Arabs supplied Europe with a new scientific vocabulary, with words like algebra, zero, cipher, almanac, and alchemy; and a new system of recording numbers that we still call Arabic numerals. Arab tables of astronomic observation and mathematical calculation, as well as manuals on medicine, introduced the Western mind to the great discoveries of the Greeks—as did the works of Arab commentators on Aristotle.

Aquinas was no Averroist. His life’s work would be an implicit repudiation of Averroës’s idea that reason has a higher claim to truth than faith does.12 Instead, Thomas Aquinas’s reading of Aristotle led him in a different direction. He would conclude that faith and reason are actually two sides of the same coin. His writings would try to persuade his age that men are part of both a divine and a human order, and both have valid standing in their lives.

The work Aquinas did in the next sixteen years changed the face of Western Christianity and philosophy. He wrote commentaries on virtually everything Aristotle wrote; he wrote on the Book of Job, the Gospel of John, and Paul’s epistles; he wrote a seminal treatise on the nature of evil and another on building aqueducts and on military siege operations.21 Above all, he also wrote the two works that would earn him the title of Universal Doctor of the Catholic Church: the Summa Contra Gentiles and Summa Theologica.

Aquinas’s point is always that we humans are down here, while the ideas and celestial beings and the supreme eternal truths are all up there. Everything that Plato and Neoplatonists and Saint Augustine said were the most intelligible and true are also the most removed from our experience. Why? Maybe because the human mind tends to be dazzled and confused by too much divine wisdom.23 Maybe that’s why God decided to put us in the cave in the first place, Aquinas is hinting. He didn’t want us overwhelmed by too much light at once.

here Aristotle points the way. “As Aristotle himself shows,” Aquinas writes in the Summa Contra Gentiles, “man’s ultimate happiness consists of seeking the knowledge of truth” through reason.24 Then as we move forward, we discover that truths human and divine, the objects of reason and those of faith, actually reinforce each other. They don’t form parallel tracks, as Averroës claimed. They ultimately converge: not just in God their Supreme Creator, but in ourselves as human beings.

In prison his hands were tied behind his back, and he was then lifted to the ceiling by rope and pulley. At a command, he was dropped straight down until the rope stopped him with the jerk. The term for this torture was strappado. One drop was usually enough to loosen a prisoner’s tongue; four were enough to dislocate a person’s shoulders, perhaps permanently. Machiavelli endured six drops of the strappado but still refused to name names. Instead, he was left to rot in prison. “The walls were full of lice so big and fat they seemed like butterflies,” Machiavelli would remember later; the stench was almost unbearable. Day and night, he could hear the sound of clanking chains and the cries of other prisoners being tortured.31 Then, after twenty-two days of wondering whether he would live or die, Machiavelli was set free. He returned to his house and farm outside Florence, where every evening, as he told a friend in a letter, “at the door I take off the day’s clothing, covered with mud and dirt, and put on garments regal and courtly,” in order to read his favorite ancient authors, including Aristotle.32 His goal was to find out why freedom had failed.

History teaches us what human beings are like in reality rather than what we would like them to be.

Machiavelli’s fusion of Polybius and Aristotle yielded a future of gloom. The Romans had read Polybius to discover how a great empire would be doomed if it failed to keep Aristotle’s balance of monarchy, aristocracy, and democracy—the One, the Few, and the Many. Machiavelli’s reading was far more pessimistic. Not just Rome, but every free society is doomed from the start. Real republics exist in real time, not on some eternal plane like Plato’s literary version. “All human affairs are ever in a state of flux and cannot stand still,” the Discourses explains, meaning that every society will experience either constant improvement or decline.

When a republic organized around Aristotle’s principle of balance expands its power and place in the world, as it must, it becomes rich and powerful. But in the process, the balance is lost: a free society’s “basic principles will be subverted,” Machiavelli declared, and it will soon be faced with ruin.”35

To Machiavelli, the very things that give a free republic like ancient Rome or Athens or pre-Medici Florence verve and energy—prowess in war, a vigorous politics, the accumulation of riches from trade and empire—ultimately turn back on themselves. Prosperity and success turn men’s passions toward self-enrichment rather than service to the State. The battle of conflicting interests between rich and poor, which Machiavelli ...

Politics becomes a cycle of vendetta and payback.37 Meanwhile, the habits of wealth and luxury undermine the important virtues necessary to sustain free institutions, including honor and service in arms—even the passion for freedom itself. Men become soft and effeminate, like the bakers and tinkers of Machiavelli’s failed militia.38 People prefer the comfortable life to the stern sacrifices of their forefathers. New legislation on Plato’s model won’t help, either: “The modification of the laws did not suffice to keep men good.” On the contrary, Machiavelli declared, “the new laws are ineffectual, because the [society’s] institutions, which remain constant, are corrupt.”

Once a free people have reached this point, Machiavelli concluded, there is no hope left. Their empire may expand, as Rome’s did under the emperors. The wealth can continue to pour in. The arts may flourish; the political factionalism makes for dramatic entertainment, while people ignore the underlying rot. But such a society is doomed, unless a major crisis forces a change in its thinking.

This is where The Prince comes in. He is the instrument of last resort, the man who pulls a corrupt society out of its self-destructive rut and puts it back on the road to political health. However, he is no Platonic soul doctor; no high-minded Philosopher Ruler. As Machiavelli noted in the Discourses, such a man will not be greeted as a messiah.

“The first way to lose your State is to neglect the art of war.” He must learn from the example of both the lion and the fox, Machiavelli wrote, since at times he will be forced to act like a beast as well as a human being.

“It is better to be feared than loved if one cannot be both.”44 Yet such a man can still save the state, and preserve its liberty.

For Machiavelli had uncovered the final paradox of liberty on Aristotle’s model.

To the just belongs injustice. All the same, Machiavelli knew there was no guarantee that people will put up with the measures that are meant to save them from themselves.

Constantinople, the largest city in the world and capital of the Byzantine Roman Empire (Rum to Arabs and Turks), had fallen. Europe’s last surviving link to the age of the Caesars would be remade as a Muslim city and renamed Istanbul. It would remain the headquarters of the sultan’s descendants for the next 460 years. The greatest church in the world would become a mosque and its magnificent mosaics of biblical scenes and images of the saints would be whitewashed into oblivion, where they remain to this day.

It’s a metaphor Plato himself would have appreciated.4 The Middle Ages had known Plato’s Timaeus in various versions; its cosmology was unimaginable without it. The rest of his works, however, were a closed book for nearly five hundred years. In the 1100s, Arab libraries yielded up a sprinkling of Platonic dialogues, which found Latin translators. Leonardo Bruni himself did several, including the Phaedo and the Laws, which were widely admired.5 But none of this was enough to shake loose Aristotle’s iron grip on the Western mind. It was the influx of Greek scholars into Italy in the 1400s, both before and after the fall of Constantinople, that finally woke the West from its dogmatic scholastic slumbers.

Indeed, everyone in the ancient world, Ficino pointed out, from Greeks and Jews to early Christians and Zoroastrians, had recognized that Plato’s writings were divinely inspired.

This love that manages to rise above the merely carnal and physical to a higher spiritual level, Ficino termed “Platonic love.” The term has stuck ever since. Platonic love is supposed to be about far more than two friends not sleeping together. As the great Ficino scholar Paul Oskar Kristeller explained, “There can never be two friends only; there must always be three: two human beings and God.”13

Love’s ascent, in short, teaches us how to become creators like God Himself.16 Ficino’s Academy spread his Platonic

Most people wouldn’t think of the pagan goddess of love as a symbol of concord and balance. Certainly not the Romans, who saw only her frankly carnal nature, let alone Augustine or Neoplatonists of the Middle Ages. But in the 1400s, the poets and scholars at the Florentine Academy did—just as she and her allegorical entourage in Botticelli’s painting symbolized the concord between ancient and modern thought. What Ficino had proved (or at least seemed to prove) was that there was no real clash between Christian and pagan systems of theology. In the end, they arose from the same source: the soul’s love of beauty and perfection and its relentless aspiration for knowledge of God and therefore of ourselves.

The Sistine ceiling contains no direct references to Christianity or Christ. Michelangelo the Platonist didn’t feel the need for any, because his message is more universal. Instead all the scenes are from the Old Testament, which every Renaissance Platonist knew to be the ground zero of docta religio, the true religion shared by all peoples and faiths. In the same way, Michelangelo has paired each male biblical prophet with a female Roman pagan prophet, the sibyls who had prophesied the coming of a future Savior. This symbolizes the harmony of the religious revelation of the Hebrews not only with Christianity, but with the religion of the ancients.

Michelangelo’s ceiling was finished in 1512. The next year a church council officially endorsed Ficino’s doctrine of the immortality of the soul. The world seemed on the verge of a final reconciliation of ancient philosophy and Christian theology, exactly what Raphael had made visible in his frescos in the Stanze.

The holy relic that drew the young monk most was Pilate’s Staircase, the Scala Santa. It stood in a small chapel near Saint John Lateran. It consisted of twenty-eight white marble steps and was supposed to have been trod by Jesus when he was brought before Pontius Pilate. Constantine’s mother, Saint Helen, had brought the staircase from Jerusalem to Rome in the fourth century. Legend had it that the dark stains in the marble were drops of Christ’s own blood. Penitents stood in a long line to crawl up the Scala Santa on their knees. They were supposed to kiss each step on the way up, then at the top utter a short prayer. The reward for this feat, according to a recent papal decree, was a plenary indulgence—in effect a Get Out of Purgatory Free card.

“It pains me to the heart,” Luther wrote, “that this damnable arrogant pagan rascal has seduced and fooled so many of the best Christians with his misleading writings,” especially the Physics and Metaphysics and On the Soul. It was time to shove these works aside and start over with Holy Scripture, and Holy Scripture alone. Time to clean house, intellectually and spiritually. Gazing at the volumes on his shelf, “I cannot avoid believing,” Luther mused, “that it was Satan himself who introduced the study of Aristotle.”7

The man who discovered the power behind that authority was not Gutenberg or Caxton or even Luther. It was Erasmus of Rotterdam. Later, some would say Erasmus “laid the egg that Luther hatched.” This is not true. But Erasmus was the first to slay the scholastic giant—and he used the sword of Renaissance Platonism to do it.

What really focused Galileo’s attention on the heavens, however, was the sudden appearance of a supernova in the night sky in October 1604. Such a thing was not supposed to happen. According to Aristotle, no change should ever occur in the heavens. Everything existing in the celestial spheres, like the sky and the planets, was made from an immaculate and unalterable substance called the quintessence. The heavens were, as an Aristotelian philosopher says in one of Galileo’s later dialogues, “ingenerable, incorruptible, inalterable, invariant, eternal”—indeed, as perfect and definitive as Aristotle’s own works.21 Galileo’s regard for Aristotle was already fading, thanks to his work on motion. The appearance of the supernova only confirmed his suspicion that the more he saw of the workings of nature, the more slipshod Aristotle’s system seemed to be. He could recall the words of his father, Vincenzo, in a different context: “It appears to me that those who rely simply on the weight of authority to prove any assertion, without searching out the arguments to support it, act absurdly.”22 Now, Galileo decided, it was time to take the examination of nature to another level.

Galileo discovered that the moon was not a perfect unblemished geometric sphere, as Aristotle’s cosmology demanded. It was rutted with craters and studded with mountains. He then turned his attention to Venus. He found that it was illuminated in a series of phases like the moon, suggesting that Venus must revolve around the sun as a fixed source of light.

Aristotle had said that all celestial bodies were perfect. This meant they couldn’t have any flaws. Therefore the moon’s craters didn’t exist, any more than the moons of Jupiter (or, as Galileo soon discovered, the moons of Saturn).

Copernicus had come up with the notion that the earth must be going around the sun along with the other planets without making any new astronomical observations. He had simply found the idea in a book on the ancient Greek mathematician Aristarchus.§ Again, the chief reason Copernicus did not publish his theory during his lifetime was not that he feared the disapproval of the Church—he was worried it was so contrary to our everyday experience, it would be laughed off the stage.26 Nothing any astronomer had ever seen, not even Tycho Brahe’s meticulous observations from his island observatory outside Copenhagen, confirmed any aspect of it. Brahe himself felt perfectly comfortable sticking to the old geocentric theory.

The Vitruvian Man sprang from the same passion. Leonardo borrowed the Roman architect Vitruvius’s belief that the parts of the human body all exist in exact proportion to one another, in order to construct a visual allegory of man’s place in the cosmos. Leonardo’s man stands at the center of not one but two geometric figures, the square and the circle. Far from trying to combine the two, in other words “squaring the circle,” Leonardo was content to show that the ratios derived from the golden section place the human being at the center of both geometric figures,

Mathematical mechanics might even explain the workings of the human body—as the English physician William Harvey discovered when he realized that the circulation of the blood followed the laws of hydraulics and that the human heart was nothing more than a mechanical pump.

Bacon was entirely ignorant of mathematics. Descartes was steeped in it. Reducing the operations of the universe to a series of lines, circles, numbers, and equations suited his reclusive personality. His most famous saying, “I think, therefore I am” (cogito, ergo sum), could be stated less succinctly but more accurately as “Because we are the only beings who do math, we rule.”