K. Dickson
A Short History of Ancient Greek Science, Technology, and Medicine
published as "Science, Technology, and Health" in J. Kirby (ed.), World Eras: Ancient Greeks (Gale 2000)


Table of Contents
Introduction

Myths & Legends
Ancient Technology
First Philosophers
Importance of Early Greek Speculation
Pythagoreanism
The Problem of Change
Pluralism
Atomism
Greek Medicine
Plato
Astronomy
Aristotle
 

Introduction

Much of what these pages discuss may seem hardly like a history of science at all. This is the result of a number of important differences between modern science and science as it first emerged in ancient Greece.

To begin with, the word ‘science’ itself has no exact equivalent in the ancient Greek language. Instead, it generally used rather broad terms like philosophia ("love of wisdom") and epistêmê ("knowledge") to describe the investigation of nature. The sorts of things included in ancient ‘scientific’ research were equally broad, and crossed over into categories that the modern world usually does not consider part of true science at all.

Next, most of the things we now identify as essential for scientific activity are absent from the history of ancient thought. Relatively few examples can be found of Greek thinkers engaged in forming hypotheses, constructing experiments, conducting careful research guided by rigorous methods, keeping detailed records, proposing and testing and re-testing theories. With only occasional exceptions, much of what the Greeks did often seems to a modern reader like ‘(pure) speculation’ at best, unsupported by any real ‘scientific’ methods and procedures. Only in the work of Aristotle in the middle of the fourth century BCE, at the very end of the period this chapter covers, will Greek scientific activity begin to resemble what we now call ‘science’—and even then it will still fall short of our definition.

Though they lacked most of the tools, methodologies, and results we now consider to be genuinely scientific, however, the early Greeks nonetheless made lasting contributions to Western science. This is especially the case in their development of the habits of thinking and frames of mind that provide the necessary conditions for scientific research. Before valid investigative procedures can be established, before precise instruments can be made and experiments can be designed—before ‘science’ can happen, that is—certain specific types of questions must be asked. These are questions for which procedures, instruments, and experiments produce the right kinds of answers.

Different questions seek different answers, after all. For instance, certain questions—"Which god caused the earthquake?" and "Who put a magic curse on my cow and made it fall sick?"—are not the sorts of questions whose answers are likely to result in an objective and scientific understanding of disasters and disease. As long as the questions asked about events in the world assume divine or supernatural activities at work beneath the surface, the only acceptable answers will be the ones that include gods and magic. Until different, scientific questions are asked, then, truly scientific answers are impossible. As we will see, the Greeks formulated the first genuinely scientific questions. They also went a long way towards determining what rules should be used to judge the structure and validity of the answers.

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Myths & Legends

All cultures encode and transmit their values to later generations in the form of narratives. The ancient Greeks are certainly not exceptions to this rule. Before the development of rational thought and expression, they turned to traditional stories or myths for answers. Cosmogonic myths addressed broad questions about the source and nature of the world. How did the universe originate? How is it structured? Who controls its operation? Other myths addressed more specific questions about observable events. What causes storms? Why do crops grow from the earth? How do adult beings create new ones? Where does disease come from? What makes thunder? What exactly are those bright objects that move—some slowly, some rapidly—across the sky by day or night?

For the most part, the traditional answers to such questions involved the assumption that powerful, supernatural agents—gods, spirits, demons—were responsible for much of what happened beyond immediate human control. The great god Zeus, lord of the sky, sent rain to irrigate the ground and make plants grow. His bolts of lightning—powerful weapons manufactured by creatures known as Cyclopes—sometimes hit the earth, and wherever they struck, the Greeks erected temples to mark the sacred spot. Earthquakes, on the other hand, were traditionally said to be caused by the rough god Poseidon, master of horses and the sea. When angered, he would strike his trident against the walls of hollow caves deep below the ground, producing violent tremors at the surface. The development of Western science involved the discovery of different habits of thinking and a different language to express answers that did not involve the existence of gods.

Many ancient legends were also aetiological. That is to say, they aimed to explain the origin of familiar objects or practices. The Greeks had an especially rich assortment of stories about three specific technological issues: the wondrous technology enjoyed by the gods; the first inventors of various tools and ways of doing things; and the accomplishments of legendary technicians.

Among gods, it was the lame Hephaestus, god of forge-fire and the almost magical craft of metallurgy, who presided over most technology. He credited with such fantastic creations as automatic doors, robotic servants with the power of speech, and unbreakable nets so fine as to be invisible. The goddess Athena, daughter of Zeus, was also closely involved with technological activity. The bridle and ship were said to be her special inventions. She also controlled the crafts of pottery, weaving, and the manufacture of products from olives and olive wood, both sacred to her.

Other legends attributed the invention of all the basic technologies to the Titan Prometheus, who reportedly gave human beings not only fire, but also the full range of tools and practices essential for their survival.

On the Origin of Human Technology

Finally, a number of legends surround the famous craftsman Daedalus, along with his son Icarus and his nephew Perdix. The nephew is credited with having invented the first saw, using the backbone of a fish as his model. Daedalus himself constructed the mazelike structure or labyrinth on the island of Crete in which the monstrous Minotaur, half-bull and half-man, was imprisoned. Later, in his attempt to escape from Crete, Daedalus is said to have invented wings for himself and his son by attaching feathers to their arms with molten wax. Daedalus warned Icarus not to fly too close to the son, but the boy ignored him. The wax melted from his wings, and he plunged to his death in the sea far below. To this day Greeks call it the Icarian Sea to commemorate his tragic flight.

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Ancient Technology

The actual history of Greek technology is another matter. Here the early Greek contributions are fewer and much harder to determine. Most of the basic technological innovations enjoyed by the early Greeks came to them second-hand, from even older cultures in which they had evolved through long, unrecorded ages of trial and error. The fundamental Western methods and tools of agriculture, irrigation, viticulture (wine-making), animal husbandry, metallurgy, mining, transport, navigation, textile manufacture, pottery, and building all have histories that stretch far back into the third and fourth millennia BCE. They belong to discoveries and developments made in the far more ancient civilizations of Mesopotamia and ancient Egypt.

The Greeks of the time covered by this chapter—the Archaic and Classical Periods—were the beneficiaries of this development. They took up techniques that had passed anonymously down through other cultures and countless earlier generations. They used, adapted, extended, and refined them. And in most cases they just as anonymously handed them down to those who came after. The most noteworthy Greek innovations in technology—especially in mechanics and hydraulics —occurred only later, during the Hellenistic Period, from roughly the third through the first centuries BCE.

At the same time, of course, the ancient Greeks relied on a great variety of skills to make their world habitable. The construction of buildings—especially the temples whose remains still mark the modern Greek landscape—required sophisticated architectural design and a mastery of engineering techniques. Blocks of marble and other kinds of stone needed first to be mined and quarried, then cut to shape, transported long distances by both land and sea, and finally erected on site through the use of ramps, pulleys, cranes, and winches. A number of developments, all impossible to credit to a single individual, arose in the slow process of improving ancient techniques. By the mid fifth-century BCE, for instance, archaeology reveals that iron bars were used (apparently for the first time) to reinforce wood and stone structures.

The ancient Greek historian Herodotus (480-425 BCE) records a number of the technological marvels of his day. In the year 512 BCE, a Greek engineer named Mandrocles reportedly constructed a bridge of boats across the Bosphorus. This is the strait of water separating Europe from Asia near the modern city of Istanbul, Turkey. The bridge enabled the great Persian emperor, Darius, to cross his army into Europe and wage war against the Greeks.

Herodotus also mentions what he considered "three of the greatest engineering feats in the Greek world." The first was a tunnel, eight feet by eight feet and nearly one mile long, cut through a mountain on the island of Samos, in order to conduct water from one side of the island to the other. He credits this construction to the engineer Eupalinus. The second was an artificial harbor on the same island, enclosed by a breakwater running nearly one quarter of a mile into the sea. Third was the Samian temple to the goddess Hera, built around 500 BCE and the largest such structure in all of Greece.

Given how large a role the sea played in ancient Greek life, the construction of ships, both for transport and warfare, was likewise a central activity. The poet Homer’s epic poem, theOdyssey, takes place in a world in which Greeks and others regularly navigate the Aegean and Mediterranean Seas in ships of all different types. During Classical times, the state-of-the-art warship was the so-called trireme. It was developed during the sixth century, and set the standard for light, relatively fast attack ships. It was a narrow vessel roughly 120 feet in length and 20 feet wide, and manned by a crew of about 200 men. In open water it relied on a large, square sail. In battle, the mast was lowered and the the ship propelled instead by banks of rowers at an average speed of around five knots. The name trireme means "three-oared," and probably refers to the placement of the rowers in three separate tiers. The prow of the trireme was extended just below the waterline by a long, curved "beak" made of wood covered with bronze—making the ship an extremely effective weapon for ramming.

In certain respects, however, the ancient Greek world remained what can be called pretechnological. Practical innovations—the construction of machines, for instance—always lagged far behind abstract and conceptual ones. This was due first and in large part to the fact that ancient Greece was a slave society. It has been estimated that, in a representative city on the Greek mainland, as much as one-third to one-half of the total population consisted of slaves. They were mostly captives taken in war or the children bred from them, and their misery is often overlooked or forgotten when we think of the remarkable achievements of the Greeks. For Aristotle, in fact, a slave has the status of a "human tool," whose availability makes the need to develop other tools less pressing. Necessity is certainly the mother of invention. The abundant supply of cheap manual labor in the ancient world tended to reduce the need for technological innovations.

Another factor that retarded Greek technology was a cultural or ideological one. The minority of Greeks who were educated enough to be concerned with scientific and technological problems were generally less interested in practical issues than in abstract, theoretical ones. Practical solutions, like manual labor, were considered matters for the lower class.

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First Philosophers

The philosopher-scientists whom tradition cites as earliest were all sixth-century Milesians, residents of the prosperous city of Miletus on the southern coast of what is now modern Turkey. This may be one of the few things that can be said with any certainty, since our information about them is notoriously thin. With the exception of a single phrase quoted nearly a millennium after the fact, we have no direct access to their work. Our fragmentary reports of their theories in fact usually come from summaries written much later, and from authors who had their own motives for attributing one idea or another to a particular thinker. Here extreme caution is called for, both in presenting Milesian ideas and also in interpreting their meaning.

Our evidence indicates two main directions or aims of Milesian research. On the one hand, they were concerned with the investigation of specific natural phenomena, such as earthquakes, lightning, and the behavior of animals. Here they seem to have collected evidence and searched for the simplest and most comprehensive explanations of what those phenomena were and how they operated. On the other hand, they also had much broader, cosmological interest in the ultimate nature of reality: what the universe is made of, where it came from, and what processes seem to govern how it works. It is because of their abiding concern with physical reality that later generations of Greek thinkers referred to them as physiologoi or "natural scientists."

Thales (fl. 585 BCE), for instance, who is always cited as the earliest of the group, is said to have explained earthquakes by claiming that the flat disk of the earth floats on an ocean of water whose waves cause violent tremors on the land above. Although the story that he successfully predicted a solar eclipse in the year 585 BCE probably credits him with greater astronomical skill than he actually had, it does point to an early interest in what later Greeks called ta meteora ("the things above the air"). Some sources in fact mention a book by Thales entitled Nautical Astronomy—while others claim he wrote two books, On the Solstice and On the Equinox—but since nothing has survived from any of them, it is impossible to determine their content.

Theories about lightning and thunder are attributed to his younger contemporary, Anaximander (fl. 550 BCE), along with a theoretical model of what we call the solar system. A flat-topped, cylindrical earth in the middle is surrounded by three concentric rings of fire. These rings are hidden by mist that thins out in spots to make holes through which the fire becomes visible to observers on earth. The closest ring has the greatest number of perforations, and thus offers a glimpse of stars; the next, with only one hole, shows the moon; and the most remote is that of the sun. Eclipses are caused when the holes either narrow or else completely (though always temporarily) close. Anaximander also assigned specific widths to each ring, calculated in terms of the diameter of the earth: the ring of stars is nine times its diameter, while those of the moon and sun are 18 and 27 times as wide, respectively. This geometrical ratio is important, since it indicates an interest in the use of mathematics as a means of uncovering and measuring physical reality. This interest remained a strong one throughout the history of Greek science.

Anaximander’s Map

Anaximander is also said to have claimed that human beings first arose in a watery environment as fishlike creatures, and took on human shape only after a long period of gestation and development. Though this is hardly a theory of evolution, the account nonetheless suggests that Anaximander might have collected and fossils and observed different species of marine life. If nothing else, it points to the great variety and breadth of Milesian interests, encompassing what are now the distinct sciences of physics, geology, meteorology, astronomy, and biology.

It is for cosmology—the theory of the origin and fundamental nature of the world—that the Milesians are best known. Here, however, the greatest caution is needed, since our main source for Milesian cosmology is the philosopher Aristotle (384-322 BCE), who lived some two hundred years later. In the course of his research, Aristotle in fact provided what might be called the first history of Greek science and philosophy. Though he is an invaluable source of information that might otherwise have been lost to us, Aristotle also tended to present earlier Greek thinkers as the precursors of his own style of thinking, and this in turn often tended to misrepresent their true ideas and motives.

According to Aristotle, then, each of the Milesians proposed a different answer to the question of what ‘stuff’ things are made of—what he himself called the ‘material cause’ of the world. Thales allegedly said this stuff is "water"; Anaximander called it "the Limitless" (to apeiron); and a third Milesian thinker, Anaximenes (fl. 545 BCE), claimed it is "air." What exactly each thinker meant may be impossible to recover, but each was probably asking a different question from the one Aristotle later put in his mouth.

If Thales actually thought water was the elemental ‘stuff,’ in the sense of the primary substance out of which all things are made, no indication has survived as to how he explained the transformation of water into everything else in the world. How exactly, for example, did this desk ‘come from’ water? For that matter, would Thales really have said that water is what this desk is ‘made of’? Traditional myths of creation, including those told by the Greeks, usually claimed that the world had emerged from the sea, or else from a kind of watery, primordial soup. Thales himself may have had these traditions in mind in making his own claims. In any case, it may be more likely that he saw water as something that was temporally first in the order of creation, as the earliest source rather than the basic ingredient of things.

With Anaximander the situation is more abstract, since he proposed an indeterminate, limitless material as the origin of what is. Rather than a specific substance, like water or air, however, the apeiron is the indefinite and undifferentiated source of everything in the universe. All things naturally come into existence from it through separation, and also dissolve back into it again at regular intervals. The process by which things emerge and return, moreover, seems to have been bound by a kind of moral principle as well, since Anaximander is said to have written (in what may well be our first direct quote from a Greek thinker) that this happens "according to necessity, for they pay penalty and retribution to each other for their injustice according to the arrangement of time." If this line—from the pages of an author 1000 years later than Anaximander himself—is correct, it suggests a grand, cyclic process of generation and destruction that ultimately preserves balance and symmetry, as if a law of conservation were at work.

Our evidence provides no clue whether Thales or Anaximander answered the question of just exactly how the universe came into being from “water” or “the Limitless.” It is with the third of the Milesians, Anaximenes, that this issue was addressed. His claim that aêr (“air” or “mist”) is the primary stuff might at first seem like a step backward from Anaximander’s more abstract apeiron. However, it was a step that allowed the youngest Milesian to propose a mechanism for change. Later accounts report that, according to Anaximenes, the condensation and rarefaction of “air” bring the basic substances of the world into existence: “Made finer, air becomes fire; made thicker, it becomes wind, then cloud, then (when thickened still more) water, then earth, then stones. Everything else comes into being from these”—in the words of a late commentator.

With Anaximenes, then, we have what might be called the first account of the mechanics of creation. The creation of the universe, along with all perceptible changes within it, are here reduced to the operation of two simple, physical processes acting on an equally simple, physical ‘stuff.’ It is very likely that direct, empirical observation of such natural events as evaporation and freezing offered support for his theory, and might even have inspired it.


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Importance of Early Greek Speculation

Though exact details of Milesian speculation are often difficult to capture, its significance is clear and hard to overstate. It is especially important for the degree to which it embodies influential trends that later became more explicit in the history of Greek scientific thought.

First, the Milesians were the first to distinguish consistently between what is ‘natural’ and what is ‘supernatural,’ and also to exploit that distinction. These two categories might well be familiar to us now, but for thinkers in the sixth century BCE, the difference between them was revolutionary. The fact is that the theories of Thales, Anaximander, and Anaximenes are as remarkable for what they omit as for what they actually say. Against a background of mythical and religious accounts of the origin and nature of the world, they instead declared that valid explanations of events must be found in regular, rational patterns of natural causes and effects, instead of in the arbitrary will of supernatural forces. Of course, Thales’ claim that earthquakes happen because the earth rocks back and forth on choppy water is in reality no more true than the pious belief that they are caused by an angry god named Poseidon, waving his trident underground or at the bottom of the sea. By excluding gods and other supernatural causes from their explanations, however, Thales and the other Milesians created a new way of thinking and talking about the world. Rational claims could now challenge traditional beliefs.

Another scientific feature of their work is the fact that the Milesians seem to have focused their attention on studying types rather than particulars. That is to say, they sought explanations for ‘earthquake,’ for example, as a class of events instead of as a unique thing that happens now and then, here or there, as Poseidon wills it. Rational accounts should be as comprehensive as possible and, ideally, universally applicable, true for every instance they seek to explain.

Milesian speculation aimed, as Aristotle later put it, to "save the phenomena" (sôzein ta phainomena) by uncovering the universal truths they embody, the rational principles that underlie a multiplicity of singular events. "Saving" here chiefly means ‘rescuing’ phenomena by building explanatory frameworks in which the events can be understood; without such frameworks, they are simply ‘lost’ and unintelligible. True to this aim, early Greek speculation exhibited a strong tendency to generalize—often (and even absurdly) far beyond the available evidence—in order to include more and more things under a single explanation. The simpler and more inclusive the explanatory framework, after all, the greater its explanatory power and the stronger its claim to being genuine ‘science.’

The fact is that the Milesians might well even be said to have invented ‘nature’ itself, in the sense that their efforts helped to shape the very concept of a naturalistic, rational world. Their work created a new category of events—namely, events whose explanation is not to be found by searching the heavens for signs of divine, supernatural activity. Instead, this new category of ‘nature’ includes all those events whose explanations are (or potentially could be) rational. By doing so, the Milesians implicitly defined the object of all later Western science as a collection of regular causes and effects governed by lawlike principles. This is clearest in the case of Anaximenes, whose identification of condensation and rarefaction as the forces behind all change had the effect of defining the world as an orderly system of simple, physical processes.

Moreover, if nature is reasonable, it can be understood best by using human powers of reason. This may seem obvious, and even a little circular, but it nonetheless marks an important step in the development of scientific thinking. It is a question of which tool is appropriate for which job. If everything that happens in the world results from the behavior of supernatural beings, then events can be understood only in terms of personal decisions made by gods. Since personal decisions are generally influenced by emotions and feelings more than logic, the powers of reason are inadequate to explain and predict them. That is decidedly not the case if nature is instead regarded as "a collection of regular causes and effects governed by lawlike principles," as we said above. Then its hidden workings can be understood and expressed best by rational minds using regular, orderly, lawlike principles of reasoning. Hard critical thinking—not blind acceptance of authority, not pious emotion, not prayer—now opens the way to true knowledge about the world.

Just as important, this early speculation developed in a context of open debate. The freedom with which the Milesians rejected supernatural explanations already implies a kind of deliberate confrontation, a contest between ‘modern’ ideas and traditional lore. At the same time, the new thinkers also seem to have been engaged in vigorous, public competition with each other; this is indeed a feature of all Greek science, and perhaps of Greek culture as a whole. Anaximander’s proposal of "the Limitless" looks like an abstract challenge to the simple, material stuff claimed by Thales; and in the notion of contracting and expanding "air" there seems to be an attempt by Anaximenes to solve what was problematic or lacking in both earlier theories. Whether passion for debate reflected Greek political and social conditions—the Milesians lived during a time of political instability, amidst many competing forms of government—or whether it helped create them is a very good question. Whatever the answer, the critical climate encouraged these early thinkers to challenge ancient religious beliefs, to analyze claims and counter-claims carefully, to search for compelling evidence to support new theories, and eventually to create a language appropriate for rational, scientific discourse.

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Pythagoreanism

The life and views of Pythagoras (fl. 530 BCE) are hard to reconstruct, since the man himself inspired a cult and became quickly shrouded in legends spun by his disciples. According to Empedocles (492-435 BCE), who was strongly influenced by his thinking, Pythagoras "stretched his mind and easily saw each and every thing in ten or twenty generations." His followers were concentrated in the southern Italian town of Croton, and remained active as a group down through the fourth century BCE. In general, they tended to divide themselves into mystics on the one hand and mathematicians on the other. Here our main concern is with the latter group, though both shared the same premise that the essence of all things could be expressed in numbers.

The chief proof for this claim that reality is numerical was their observation of the simple ratios that underlie harmony in musical scales?that of the octave (1:2), for instance, in which a string divided in half vibrates twice as fast to produce the same note in a higher register. The fact that some phenomena exhibit a numerical orderliness suggested to the Pythagoreans that the universe as a whole might have a quantitative, mathematical basis. At its best, this marked an important shift away from how the Milesians approached nature, since their primary aim seems to have been to isolate the physical ‘stuff’ of the world. For this reason, the Milesians are generally identified as materialists. For the Pythagoreans, on the other hand, the search for truth pointed not in the direction of matter but instead of structure and form. Numbers and ratios expressed in numbers were the keys to understanding the essence of reality. The influence of this belief on both the direction and also the language of all later Western science is obvious.

At its worst, however, the same insights also tended to promote a kind of mystical speculation among the Pythagoreans. For some of them, especially those who belonged to the mystical group called the Akousmatikoi ("Listeners"), numbers had the status of quasi-divine objects of worship. The "Listeners," that is to say, went far beyond strict, mathematical research and sought to discover numbers beneath all aspects of experience. They assigned numerical values not just to objective relations but also to things and qualities. The number ‘3,’ for instance was identified as Male, ‘2’ as Female, and ‘5’ as Marriage; Justice, by contrast, was ‘4.’

The Pythagoreans generalized their discovery of ratios in music into a view of the whole universe itself as "a musical scale and a number." This is the source of the famous idea of the ‘music of the spheres,’ according to which the moon, sun, planets, and stars were believed to produce different musical notes as they spin through space. To the mind trained to hear them, these notes all blend together into perfect harmony. Here it is easy to see how the same point of departure could produce both pure mathematics and a kind of hazy, contemplative mysticism. Contemplation of the music of the spheres is simultaneously a scientific and a spiritual act.

Empirical investigation and experimentation among the Pythagoreans were more consistent than in the case of the Milesian physiologoi. A great deal of Pythagorean attention was in fact directed to astronomy, in attempts to calculate the relative distances and sizes of the heavenly bodies, and to provide accounts of both lunar and solar eclipses. The group was especially noted for its research on acoustics, through the measurement of lengths of vibrating strings and columns of air. They have been credited with classifying numbers into ‘odd’ and ‘even.’ Geometry, the science of ‘solid numbers,’ was also a central part of their work. The proof that bears their name—the so-called ‘Pythagorean theorem,’ namely that the square of the hypotenuse of a right triangle equals the sum of squares of the other two sides (a2 + b2 = c2)—seems to date from the late fourth century BCE. Its truth was in fact a very old one, known even to the ancient Babylonians as many as five hundred years earlier. What the Greeks did was to provide a conclusive demonstration.

The major and abiding contribution of the Pythagorean group is what could be called its ‘arithmetization’ of the world, its view of reality as somehow numerical. Even if it tended to become entangled in mystical beliefs, their basic insight—that the science of numbers is fundamental to every science of nature—had profound influence. Here we are far indeed from a view of phenomena as playthings and manifestations of willful gods. Reality is instead orderly, regular, mathematical, and easily accessible to rational minds. Nature indeed is number, at least in the sense that mathematics provides the most objective way of talking about natural events. At the same time, Pythagorean work on geometric problems also helped to further hone a scientific language of theorem, evidence, and proof.

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The Problem of Change

The early fifth century is a turning-point in the history of Greek science, since it was then that the problem of change first began to be raised in a systematic manner. The Milesians, we have seen, focused their attention mainly on identifying the basic ‘stuff’ of the world; and the Pythagoreans turned away from that material ‘stuff’ to look instead at the mathematical structure and form of the world. Neither group directly addressed a simple but crucial fact of everyday observation: things change.

Change is an obvious feature of all things, and is directly confirmed by our senses. But what exactly is it? And how does the fact that the world always changes impact on our ability to understand it scientifically? Consider Anaximenes, who more than any other earlier thinker seems to have speculated on how one thing can turn into another. He claimed that everything is "air," and proposed condensation and rarefaction as the two processes that account for how "air" changes into everything else in the world—fire, clouds, rain, rocks, and so forth. Now, this claim is circular. If water, for example, is nothing but condensed "air," and fire is "air" that has been rarefied even more, then "air" itself is not really a unique ‘stuff’ at all, but instead just another phase in an endless cycle. That is, it could just as easily be said that "air" is nothing but rarefied water or condensed fire. And if this is so, then what sense does it make to claim that "air"—and not water or fire or earth or wood or metal or anything else, for that matter—is the primordial reality?

The problem of change has two main aspects. The first has to do with what passes for an acceptable answer to the question, ‘What is real?’ The ancient Greeks implicitly believed that whatever the true nature of reality is, that true nature must always be true. Reality cannot be one thing now and another thing at some other time. After all, this is what motivated them to "save the phenomena" in the first place, by searching for something fixed and permanent beneath the constantly shifting things and events in the world. But if the answer (as in the case of Anaximenes) is that this fundamental ‘something’ is sometimes "air" and sometimes something else, have we really found what we are looking for? Does a changeable reality fit the definition of what ‘reality’ really should be?

The second aspect of the problem of change has to do with how we can know what is real. What evidence do we have for talking about reality? What basis do we have for judging whether our evidence is valid or not? How can we be sure that we know anything at all about reality? These and similar questions mark the beginning of Western epistemology, the study of the relation between the mind and the world. The Greek thinkers of the fifth century BCE put these questions in a more direct form, by contrasting the mind with the senses. The mind insists that reality be permanently true, but our five senses only present us with a picture of change; nothing we hear, see, taste, touch, or smell conforms to the idea of a permanent truth. Which is the true path to genuine knowledge of the world, then, reason or sensory experience?

The first response to these questions was that of Heraclitus of Ephesus (fl. 500 BCE) in Asia Minor. The surviving fragments of his book are written in a deliberately obscure and riddling style, making it hard to agree on how exactly to interpret many of his claims. On the one hand, Heraclitus apparently argued that change is indeed the essence of reality itself. He is said to have summed this up in the famous claim that "everything flows" (panta rhei): "We step and do not step into the same river," he wrote, "we are and we are not." According to Plutarch (45-120 CE), a later commentator:

For it is not possible to step twice into the same river, according to Heraclitus, nor to touch anything twice: due to the velocity of its change, the thing scatters and collects itself again—or rather, it does not come together and depart, approach and withdraw at one time and then at another, but instead does all this simultaneously. The constantly flowing water of a stream always makes it a different stream from the one into which we just stepped. For that matter, we ourselves also participate in change—our cells, for instance, are constantly dying and being regenerated—so that even the one who steps into the stream is different from the one who stepped there a moment ago. This would seem to make any notion of a fixed and permanent reality quite impossible.

At the same time, however, Heraclitus also insisted on a single unifying principle behind or beneath or within that constant flux. He called this the logos—a term that embraces a range of meanings, from "word" or "account" to "reason," "ratio," and "rationality"—and described it as a kind of balance that underlies and also controls all change. Although he identified the logos with the element fire, it is unlikely that Heraclitus thought of it as a material substance, like the "water" and "air" of the Milesians. Fire instead offered a brilliant metaphor for the constantly changing, constantly identical world: "The cosmos...was always and is and shall be an ever-living fire kindled in measures and extinguished in measures." The reference to "measures" once again points to an abiding Greek belief in the ultimate orderliness and measurability of the universe. Beneath or behind or within all change, the logos remains constant.

On the epistemological problem of knowledge—How exactly can we know what is real?—Heraclitus implied that the senses are untrustworthy witnesses that must be brought under the control of the rational mind. After all, how else except by reasoning can we discover the invisible logos concealed by the world’s apparent flux?

Far more radical, however, was the view of the next major thinker, Parmenides, born around 515 BCE in the southern Italian city of Elea. For Parmenides, pure logic alone pointed the way to a truth that completely contradicted every shred of evidence our senses can provide.

His main argument, rigorously abstract, is preserved in a poem called The Way of Truth. One of its chief aims is to deny that reality could ever be subject to change. The basic argument can be summarized in four points:

(1) Whatever is, is—and if it is, it is impossible for it not to be.

(2) There was never a time when it was not, because then it would have been non-existent, and ‘what is’ can never come from what is not, since by definition ‘what is not’ has no reality.

(3) Therefore, ‘what is’ must have always been.

(4) If this is true, nothing can ever come into being at all.
 
 

The upshot of these dense and knotty claims is that reality always was, is, and will forever be the same. Despite everything our senses report, it is actually static and eternal. There is no coming-to-be or passing-away. Change is an illusion, then: nothing is really born, grows, and dies. Parmenides went even further to claim that reality is perfectly homogeneous—that is, it has no parts, but is instead a single, uniform whole. This means that no distinct things exist at all, despite the fact that the evidence of our senses insists on quite the opposite.

Parmenides’ Way of Truth is a startling tour de force. It utterly rejects the senses and relies on reason aided only by the new science of logic. This argument marked both a starting-point and a challenge for all later fifth-century thought. Logic seemed to demand that his reasoning about the true nature of reality be accepted, or at least that all other claims about reality had to have the same logical structure. Fundamental reality must indeed be permanent and unchanging. But if this is the case, our five senses are not only untrustworthy but even deceptive, since they present us with a view of the world that, on Parmenides’ terms, is totally false. Each of the thinkers who came after him were forced to confront this problem and work out some way of solving it.

On the one hand, philosophers like Zeno of Elea (fl. 450 BCE) and Melissus of Samos (fl. 440 BCE)—collectively known as Eleatics—further refined the tools of logic to support Parmenides. Zeno in particular is famous for a series of logical paradoxes, all of which construct rigorously logical arguments to prove something that completely contradicts intuition and experience. Among the most famous and familiar is the paradox which denies that an arrow can traverse a given space, from A to B, because it would first need to cross an infinite number of fractions of that distance—halfway, one quarter, one eighth, one sixteenth...—in a finite amount of time. Zeno’s conclusion, of course, is that motion is logically absurd.

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Pluralism

On the other hand, attempts were made to save the evidence of the senses and counter the total denial of change. The so-called Pluralists, Empedocles and Anaxagoras, sought to do this by making an initial compromise. Each granted Parmenides’ claim that reality is indeed forever changeless, but then went on to assert that it is also fundamentally plural. That is, the universe is a composite of basic, indivisible substances that each enjoy the characteristics of the Eleatic ‘what is’—namely, each is eternal and unchanging. Since there are many such permanent and timeless entities, however, the world of the senses can be constructed by bringing them together into different combinations. Coming-to-be and passing-away are the results of their temporary mixtures.

For Empedocles (492-435 BCE), the "roots" (rhizomata) of reality are the elements earth, air, fire, and water. They are original substances in the sense that they are uncreated and ever-lasting, just as Parmenides had demanded reality should be. They are also originative, in that they are the constituents out of which everything that exists is made. He answered the question of how the unlimited number and variety of things in nature could be analyzed back into these four simple elements by claiming that they combine in fixed and definite proportions to create each distinct thing in the world. Bone, for example, is compounded from four parts fire, two parts water, two parts earth; blood is a composite of all four elements in equal proportions. He apparently made no effort to demonstrate these claims experimentally. Despite the brilliant idea of proportion, it would be wrong to see in his work a precursor of modern chemistry.

Empedocles’ system also included two forces that are responsible for the combination and separation of the elements. These are Love and Strife, which work together but in opposite ways to bring everything in the universe into existence. Strife makes each of the elements move apart from the others and gather together. When the power of Strife is supreme, the universe has the shape of four concentric rings of pure earth, water, air, and fire. When Love is dominant, on the contrary, the elements all mingle together to form a homogeneous sphere. The movement from Love to Strife and from Strife back to Love once more is cyclic and eternal, and the world as we experience it comes into being in the periods in between these two extremes of total unity (Love) and total separation (Strife). Over the course of numberless ages, the world is alternately created, dissolved, and then created all over again.

The position taken by Anaxagoras (born ca. 500 BCE) is superficially similar, in that he also regarded reality as plural and composite. Whereas Empedocles analyzed it into the four basic elements, however, Anaxagoras multiplied the number of fundamental entities to include both every natural substance—gold, iron, bone, wood, leaf, hair, flesh, etc.—and even such qualities as ‘hot’ and ‘cold.’ Each of these substances, according to Anaxagoras, is basic and elementary, and their presence accounts for the great variety of nature. His most famous claim is that "in everything there is a portion of everything." That is to say, any given thing—a piece of bread, for instance—contains a share of every other thing in the world. This peculiar theory might well have been an attempt to explain the transformative process of digestion, through which the food we ingest somehow becomes flesh, hair, blood, and bone. Tiny particles of bone, for instance, are present in whatever we might eat; when the food is digested, these particles separate out and go to add themselves to the bone that is already in our body.

As theories go, this is hardly economical, since it assumes a virtually unlimited number of primary substances. This of course duplicates on the infinitesimal level the variety of visible things whose origin the theory is supposed to explain. In keeping with the rationalism of Greek speculation, Anaxagoras attributed the coming-to-be and dissolution of things to the activity of a cosmic "Mind" (nous), which guides all natural processes from within nature itself by making the mixture of infinite primary elements slowly spin and separate out to form all the things of the known world.

Anaxagoras is also noteworthy as the first recorded victim of the conflict between science and traditional ideas that had begun with the Milesians some one hundred years earlier. While living in Athens, he is said to have been formally accused of impiety, on the ground that he claimed the sun is a fiery rock somewhat bigger than southern Greece, and not (as a majority of people believed) the great god Helios. Tried and convicted, he was exiled from Athens and spent the years until his death in 428 BCE in a remote corner of the Greek world. While his choice of political associates may have had something to do with the case, his fate also illustrates a genuine tension between ‘subversive’ new theories and conservative religious belief that was to surface on other occasions in the history of Greek culture.
 

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Atomism

Certainly the most original fifth-century contribution to the ongoing debate on the nature of change was that of Leucippus (Leukippos) of Miletus (fl. 430 BCE). Next to nothing is known about his life, except that he wrote two books (On Mind and The Great World System) and was the teacher of the far better known Democritus of Abdera (fl. 430 BCE). It is through his pupil that Leucippus’ revolutionary insights into the world of nature have mainly been preserved. In turn, the list of works attributed to Democritus runs to more than seventy titles, and includes studies on such diverse subjects as mathematics, farming, medicine, grammar, ethics, and literature. In what remains of his writings on physics or natural science, the atomic theory that Leucippus proposed and Democritus further developed marks a highpoint in ancient speculation.

The main features of this theory are, once again, direct responses to the demand for an eternally changeless reality offered by Parmenides; and like the answer of the Pluralists, the Atomists too adopted an Eleatic description of their fundamental substance. This was the ‘atom’—from the Greek word atomon, meaning "indivisible." Each atom is ungenerated, uniform, unalterable, and incapable of any further division. Note that this last characteristic distinguishes ancient Greek atoms from the splittable ones of modern physics.

Infinite in number, the atoms of Democritus differ from each other in three respects only: shape (as the letter ‘A’ differs from ‘N’), arrangement (as ‘AN’ differs from ‘NA’), and relative position (as ‘N’ is ‘Z’ turned on its side). Their different shapes are innumerable, ranging from the smooth, rounded atoms that compose water to the rough, jagged, and uneven ones out of which iron is made. The only other natural reality allowed by Leucippus and Democritus is an infinite void that separates each atom from the others and provides the empty space in which they all continuously move in all directions, often with a whirling motion, and bump into each other. Chance collisions among atoms account for the world of sense experience, since the couplings of hooked atoms or atoms whose shape in some way fits that of others gives rise to compound objects. In a fragment from his lost work on Democritus, Aristotle explains the theory as follows:

The atoms are carried about in the void...and as they are carried about, they collide and are bound together in a binding that makes them touch and get close to each other, but which does not actually produce any other single thing... He explains how these entities remain together by reference to how the atoms get entangled with and stuck to each other. For some of them are rough, some hooked, some concave, some convex, and others have countless other different aspects. He thinks they keep hold of one another and stay together until such time as a stronger force from outside touches them, shakes them, and scatters them apart. The apparent coming-to-be and passing-away of things is thus really a rearrangement—joining and separation—of invisible, infinite, and indestructible entities. Moreover, since atoms and void are both infinite, and since motion has always existed, Democritus believed that there must have always been an infinite number of worlds. Each is made of precisely the same unchangeable atoms in different configurations.

Both the breadth of Democritus’ interests and the rational consistency of his atomism are clear from how he applied his theory to explain sense perception, and so also to address the problem of knowledge. First, he believed that our experience of the world is ultimately sensual, the result of physical contact between atoms streaming from objects and entering our organs of perception. Waves of atoms thrown off the surface of this desk, for instance, make a kind of impression in the air which then passes as an image into my eye. Different shapes and arrangements of atoms are directly responsible for the variety of possible sensations. For example, the atoms of honey are generally round and smooth in shape, in contrast to the sharp, thin ones that pungent stuff like vinegar is made of.

The data provided by the five senses concern only the shape and arrangement of atoms, however, not the atoms themselves. Everything perceived by the senses is therefore "secondary" and, in a sense, unreal. The chance combinations of atoms do not "actually produce any other single thing," but instead only create the illusion of permanent objects. In actual fact, the atomic arrangements responsible for our sensations of sight, sound, taste, touch, and smell are really impermanent and illusory. The only things that truly exist are atoms per se and the void. Since the senses cannot provide direct access to atoms themselves, only to their shapes and configurations, the rational mind alone has claim to knowledge of reality.

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Greek Medicine

It is hard to give a precise epidemiology of the ancient Greek world—that is, a clear picture of the kinds of diseases and ailments that were common in the Mediterranean at that time. The preservation of a large body of fifth- and fourth-century Greek medical writings provides less help than might be expected. This is because the categories used by ancient doctors to diagnose their patients were often completely different from modern ones. Many of the symptoms and signs they considered important for identifying diseases are simply irrelevant in modern systems of classification. The same is true of their methods of investigation—the pulse, for instance, was not used as a diagnostic tool until the third century BCE—which often makes Greek accounts omit what for us is crucial information. Greek physicians neither envisioned nor discussed diseases in the modern language of germ-theory, now about one hundred and fifty years old. All this generally results in vague descriptions that are impossible to match with contemporary ones.

What little can be learned from the texts must be supplemented by the modern science of palaeopathology, which studies skeletal remains for information on diet and health. From these sources, it is likely that dysentery, typhoid and malarial fever, epilepsy, tuberculosis, diphtheria, rabies, and chicken pox were all common in ancient Greece. Various forms of conjunctivitis (a chronic inflammation of the eyes) seem to have been especially widespread. Evidence also exists for the presence of inheritable conditions, for example, certain strains of anemia. Beyond that, not much more can be said with any certainty. A devastating plague ravaged the city of Athens 430-427 BCE. Despite the fact that we possess contemporary written accounts of the epidemic, its actual nature is still a matter of debate—Was it bubonic plague? cholera? measles?—and may never be identified.

With Greek medicine we are in the unusual position of having direct and rather extensive evidence, instead of the second-hand fragments and quotations in which most of the other thinkers are preserved. Dating from roughly 420 to 350 BCE, a group of about sixty texts has survived under the name of the Hippocratic Corpus. The title is deceptive, since these texts represent neither the work of a single author—it is doubtful whether any was actually written by the legendary physician, Hippocrates of Cos (fl. 450 BCE)—nor even the position of a single medical school.

The writings themselves cover a broad range of topics, including anatomy, physiology, pharmacology, embryology, gynecology, epidemiology, surgery, and dietetics; they are obviously the product of a group (or groups) of very distinct individuals. Their styles also differ considerably. While some are clearly textbooks for professional physicians, others take the form of detailed, clinical case histories and even public lectures pitched to a non-specialist audience. These different styles, moreover, imply widely different contexts of use. A book such as the one titled On Airs, Waters, Places, for instance, was obviously written as a guide for itinerant doctors, allowing them to identify and treat diseases specific to particular regions and climates. A work like the Aphorisms, on the other hand, which contains practical advice condensed into short, pithy sentences and slogans, was probably meant as a teaching tool.

Their diversity offers a rare glimpse of the social context in which early medicine developed. It is important to recognize that doctors in ancient Greece had no formal, institutional status. No standardized course of training and examination authorized them to practice, no special licensing distinguished competent from quack, and no official control guaranteed the overall quality of care. Although some evidence exists of doctors hired at public expense to provide services for a particular community, by far the majority traveled from settlement to settlement like most other artisans, plying their trade alongside healers of all kinds—diviners, exorcists, priests, magicians, herbalists, midwives, athletic trainers, hawkers of ‘old family recipes’ and miracle cures. The kind of medicine represented by the Hippocratic Corpus was simply one among a number of therapeutic options. For that matter, in the fifth and fourth centuries, it was definitely newfangled and strange, and very much in need of advertising its benefits in order to attract a clientele. The polemical tones of many of the Hippocratic texts in fact confirm that they were written in direct and often hostile competition with traditional medical practitioners. Just as in the case of Greek natural philosophy, open criticism and public debate accompanied the growth of rational medicine.

In the middle of the fifth century BCE—and for many hundreds of years afterwards, for that matter—an average person’s first choice in illness was most probably not to consult a professional Hippocratic doctor at all. Instead, the patient would most likely have turned to any number of ‘folk’ remedies at hand. These would have brought her or him into contact with a variety of individuals and, consequently, a variety of different interpretations of disease and means of treatment.

On the one hand, there existed an ancient tradition of herbal and pharmacological lore, offering treatments for disease based on the medicinal properties of plants, minerals, and other natural stuff. This lore was the product of centuries of trial and error, and undoubtedly offered practical and in some cases very effective remedies, as it continues to do today in most parts of the world. On the other, popular belief generally explained disease by reference to some kind of supernatural agency. Sickness was caused by offended gods and angry demons, for instance, or else by the sinister workings of magical curses and spells. As a result, people sought remedies tailored to suit what they thought was the true cause of their affliction: prayers, incantations, sacrifices, cleansings, special dietary prescriptions and ritual behaviors. The author of the Hippocratic text called On the Sacred Disease refers with contempt to quasi-magical cures for epilepsy that included, among other things, prohibitions against wearing black and touching goats.

Throughout the ancient world, and alongside the achievements of rational medicine, belief in the healing powers of the great god Asclepius, son of Apollo, probably drew the most devout support among the general public. Hundreds of shrines to Asclepius have been identified across the Mediterranean, and the cult flourished from its official establishment in the fourth century BCE well into Roman and early Christian times. Central to Asclepiadic therapy was the so-called ‘dream cure.’ After ritual offerings and purifications, the pious patient would sleep in a special dormitory attached to the shrine, and there would be visited in dreams by the god himself. Asclepius would either prescribe a remedy for the patient to purchase later from priests who took care of the temple, or else he might even directly effect the cure.

The results, advertised on dozens of stone tablets displayed in the precinct of Asclepius’ main temple at Epidaurus, were often quite spectacular:

A man of Torone with leeches. In sleep he saw a dream. It seemed to him that the god cut open his chest with a knife and removed the leeches, which he put into his hands, and then he stitched up his chest again. At daybreak he departed, cured, with the leeches in his hands. Against such a background of tradition, magic, and religion, it was imperative for doctors both as individuals and as a group to distinguish themselves and establish their credibility. Despite ongoing theoretical disputes within the profession, they all consistently rejected supernatural cures as ‘superstitious’ and firmly endorsed the same rationalist framework that had motivated research since the time of the Milesians in the preceding century. Disease had natural causes, not supernatural ones, and treatment must be rational in order to be scientific and effective.

Earlier thinkers had in fact also concerned themselves with the human body and biological processes. Both Empedocles and Anaxagoras had speculated on the ultimate constituents of flesh and bone, and Alcmaeon of Croton (fl. 470 BCE) in southern Italy was credited with dissection of an eyeball and discovery of the optic nerve. Even more important was his definition of ‘health’ as the "equal balance" (isonomia) within the body of such basic qualities as moist and dry, cold and hot, bitter and sweet. The "dominance" of any one of them, on the other hand, caused illness.

Alcmaeon’s definition was highly influential and productive. While opinions differed widely over which theory of disease to endorse—and even over whether ‘theory’ was useful at all in a science that was supposed to cure sick individuals, not ‘sickness’ itself—the Corpus still shows a general agreement on basic issues. One of the most common ideas is that of illness as a kind of disequilibrium that needs to be corrected. Specifically, most Hippocratic writers seem to have viewed health as a balance in the relative quantities of certain natural fluids that were present in the human body. This is the basis of the well-known theory of the four "humors" (khumoi) or "juices": yellow bile, black bile, phlegm, and blood.

The existence of these fluids seemed to be a matter of simple observation. Blood—all too visible in the case of wounds, hemorrhages, and menstruation—was obviously crucial for life, and also played a central role in religious and magical medicine. It was believed that the quantity of blood in the body regularly reached its height during the spring, when venesection or blood-letting would be used to drain off any harmful excess. A vein would be cut, usually in the wrist or ankle, but in other parts of the body too, depending on where the physician felt the most blood had accumulated.

Forms of dysentery (an intestinal disorder), on the other hand, which were common in the dry, hot summer months, were often accompanied by high fever and vomiting of bile. This was interpreted as the body’s spontaneous attempt to purge an abnormal abundance of that fluid. Cold, damp winters, by contrast, seemed to favor over-production of the white, sticky phlegm that caused colds and respiratory ailments. The fourth humor, black bile (melan kholê), was the most mysterious of the group. It was thought to be observable in excrement and sometimes in the dark fluid of vomit, as well as in blackish, dried blood. Its seasonal peak occurred in the autumn months, dry and cold, when black bile brought on prolonged, chronic ailments that were especially difficult to cure, owing to the humor’s thick and malignant character.

Hippocratic Humoral System

This apparent link between humors and seasons was further generalized into an elaborate web of regional, climatic, and meteorological links. The Hippocratic text called On the Nature of Man presented the theory in its most systematic form; many other texts assumed it as a basis for their own theorizing. Here the four humors are associated not only with the seasons but also with the four parts of the known world—Europe, Africa, Asia, and Greece—and thus incidentally provided a justification for racial and ethnic stereotyping. The inhabitants of the far north, for instance, dwellers in perpetual winter, tend on the whole to be white, fat, lazy, and mentally slow, due to the abundance of phlegm in their bodies. By contrast, and due to the yellow bile in which their tissues are soaked, Egyptians and Libyans are usually dry and dark, thin and easily agitated southerners. It goes without saying that the Greeks themselves happen to live in by far the best climate and locale in the whole world, thanks to which their temperament is the most moderate, balanced, and healthiest!

These associations provided a structure for still other links. The author of On the Nature of Man assigned to each humor a set of qualities—blood (hot and wet), yellow bile (hot and dry), black bile (cold and dry), phlegm (cold and wet)—and in doing so brought them into line with the quartet of elements (fire, air, earth, and water) proposed by Empedocles as the "roots" of reality. Over the following centuries, this highly influential theory was further expanded to include four stages of life (childhood, adolescence, adulthood, old age), four times of day, four types of fever, four colors, four flavors, four food groups, and even four emotional ‘temperaments’ or personality types—sanguine, bilious, melancholy, and phlegmatic. In Christian times, the evangelists Matthew, Mark, Luke, and John were also inducted into the club.

Humoral theory was not just a diagnostic tool, but also provided a framework for therapy. With few exceptions, Hippocratic medicine used diet and regimen as its primary means of cure. Since disease was defined as humoral imbalance, both preventative care and restorative treatment generally took the form of allopathic remedies—that is, a cure by opposites. On the one hand, removal of excess humors was attempted by administering various purgative drugs, some of them unfortunately quite toxic. This was certainly true in the case of hellebore, a poisonous herb of the lily family, which was frequently used to induce vomiting. On the other, a careful categorization of foods and beverages in terms of what were believed to be their active qualities (hot/cold, wet/dry) offered a way of returning the patient to a balanced condition by prescribing diets to compensate for whichever humoral excess afflicted the body. Imbalances caused by an abnormal amount of black bile (cold and dry), for example, would be treated by a regimen of foods that generate heat and moisture.

It should be noted that "diet" (dieta) in ancient medicine had a far broader meaning than the modern term suggests, and meant not simply food and drink but instead an entire style of living. This included exercise, bathing, and fixed routines of sleep and waking, as well as the patient’s emotional state. The course of therapy, whether after the fact of disease or to prevent its occurrence, was seen as a way the doctor could assist the body’s own natural tendency towards equilibrium. Illness was not a supernatural affliction but instead a rational, physiological process that ran a foreseeable course. The expert physician was the one who could accurately predict its phases and prescribe correctly at each stage.

The theory of the four humors clearly embodies both the strength and also the weakness of Hippocratic speculation. In this respect it is an emblem of much of ancient science as a whole, for that matter. On the one hand, it is simple, elegant, and rigorously rational. On the basis of a very small number of assumptions it generated a complex, highly explanatory, and increasingly comprehensive system that put the human body at the center of a vast network of signs and events in nature. The churning humors, with their alternating cycles of hot and cold and wet and dry, were the microcosm of physical processes in the world at large, driven by the same fundamental laws that govern the production of rain, for instance, or the change from summer to fall. Time, place, climate, season, weather, temperament, age, diet, and habits were all indicators of health or disease, and also suggested the means for diagnosis and treatment. Rather than appealing to divine intervention to account for even the most bizarre and spectacular diseases—such as epilepsy, the subject of On the Sacred Disease, which attributes its cause not to God but to phlegm—the system rested on the rationalist foundation of early Greek physics.

At the same time, the humoral theory was obviously also sheer speculation with hardly any basis in empirical methods and real physiology. What is conspicuously lacking from a modern point of view are any signs of experimental rigor to match the rigor of theorizing. It is true that Hippocratic writers sometimes point to observable events to support their claims, as when one author refers to evidence gained from the autopsy of a goat as ‘proof’ that phlegm in the brain causes epileptic seizures. For the most part, however, humoral theory developed and existed in a highly rarefied atmosphere, as a closed system that was true on its own terms and so incapable of ever being disproved. Moreover, as a framework for understanding disease and a guide for its treatment, it continued in effect for at least two millennia, well into the seventeenth century of our own era, with results that often did far more harm than good to the patient. In reference to the practice of venesection to purge blood, for instance, which was still in common use not too much more than a century ago, one historian (Majno, The Healing Hand, p. 420) has remarked that "medicine has never produced a greater absurdity"—nor a more dangerous one, it might be added.

Not to minimize genuine Hippocratic contributions, however, the limits in which early Greek doctors worked must be kept in mind. Their fanciful understanding of physiology resulted from poor anatomical knowledge. This in turn was in large part due to strong religious prohibitions against opening the human body. The famous Hippocratic Oath in fact expressly forbids the practice of surgery. For the most part—and wisely, given the lack of sanitary conditions for treatment —invasive medical procedures were avoided.

Moreover, the Hippocratic Corpus does in fact also contain evidence of conscientious and detailed observation of facts. The importance of observation was especially emphasized because it provided material for the fine art of ‘prognosis.’ Here the physician, after examining a patient, would try to describe the prior course of the disease and also predict its outcome. This was meant partly to help identify the ailment and (where possible) project a plan for cure, but partly also as a public display to showcase the physician’s expertise—and so too the legitimacy of his profession—since "he will improve his reputation as a doctor and people will feel confident about putting themselves in his hands."

Therefore the authors of the books that go under the name of Epidemics provided careful, day-by-day descriptions of individual case-histories and the climatic conditions in which they arose, sometimes covering as much as four months of continuous medical history. The text named Prognosis is devoted to painstaking descriptions of the patient’s face, eyes, complexion, hands, feet, movements, and overall behavior—including sleep patterns, upright and recumbent posture ("how he lies in bed"), and types of breathing. These disciplined, rigorous empirical records gave rise to the so-called ‘Hippocratic faces,’ a collection of diagnostic signs to guide the physician in identifying diseases and anticipating what course they would run. The following is representative:

Nose sharp, eyes sunken, temples hollow, the ears cold and drawn back with their lobes twisted, the skin of the face hard, stretched, and dry, and its color pale or dusky. If this is the appearance of the face at the onset of the disease, and it is impossible to base a diagnosis on other signs, the patient should be asked if he has insomnia, severe diarrhea, or ravenous hunger. If he affirms any of these, the case should be considered less severe...since its crisis will be reached in a day and a night. But if he affirms none of them... For sheer accuracy of observation, such case-histories went unrivaled for at least two thousand years. Equally valuable insights and, on the whole, more successful styles of therapy—if often painful ones—are also found in a group of texts devoted to the diagnosis and treatment of fractures, dislocations, and head wounds.

A number of texts in the Corpus are gynecological—that is, they are concerned with female anatomy and physiology. This itself is very interesting, since it suggests communication between the (exclusively male) Hippocratics and the anonymous women who treated conditions specific to women and acted as midwives. We know next to nothing about female patients and female care-givers at this time, however, for ancient Greek culture was vigorously misogynist, denying women both a place and a voice in society.

The writings on ‘female problems’ tend to exhibit a mixture of keen observation and pure mythology, legitimate research and blind sexism. A male fetus grows on the right (‘stronger’) side of the womb, a female on the left. Male sperm contributes the essential substance of the future child; the mother merely provides a place for incubation, a kind of pot or oven where the embryo is ‘cooked’ for nine months. The uterus itself, for that matter, was believed to be an independent and highly mobile organ, which sometimes ‘wandered’ through the body in search of the vital moisture it craved. By squeezing or knocking against other organs in the course of its travels, it drove young women to fits of nervous anxiety, giddiness, delirium, spells of choking and fainting—in short, to what was called ‘hysteria,’ from the Greek word hustera,meaning ‘womb.’ In such cases most doctors prescribed marriage as a cure.

Medical theory intersected philosophical ideas in the case of embryology. The treatise On the Nature of the Child is remarkable as the first systematic observation on record of the development of an embryo, using hen’s eggs incubated over a period of twenty days. For the most part, however, such empirical work took second place to debate over the much broader issues of generation and growth. Here the main question was that of the nature of the plant or animal seed, and how a fully formed, fully differentiated being could grow from it. The answer proposed and generally accepted by physicians and philosophers alike was that the seed is composed of elements drawn and distilled from every part of the body, and therefore essentially contains each of its substances—tissue, bone, hair, blood, and so on.

The resemblance between this theory—known as pangenesis—and theories put forward by some of the Pluralists and Atomists is obvious. It emphasizes how interdependent all branches of what are now distinguished as separate disciplines—philosophy, physics, chemistry, biology, medicine—originally were. Many physicians were at the same time practicing philosophers, in fact, and quite a few physicists dabbled in medicine. It also points to the ongoing, open and (to borrow a modern term) ‘interdisciplinary’ nature of research in fifth- and fourth-century Greece.

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Plato

Plato (428-347 BCE) is now best known as the main representative of idealist philosophy in the West and the founder of the Academy, the first Western university. He is far less often recognized, however, as a mathematical philosopher (or philosophical mathematician), even though that is how he might have preferred to describe himself.

Of course, his ‘purely’ philosophical activity also influenced Greek scientific research, although that influence was certainly a mixed and not always encouraging one. Plato’s idealism on the whole tended to devalue the world of the senses as an unstable realm of continual ‘coming-to-be’ and ‘passing-away.’ It is but a pale shadow of the real world of the Forms. If the world we perceive is unreal, however, then research into natural phenomena is correspondingly of less value and importance than efforts to comprehend the ideal Forms on which things in our world are modeled. Truth is to be found not in the visible but instead in the intelligible world, and must be accessed by reason and not by sensory experience. Why waste time using the imperfect senses to learn more about a world that is ultimately an illusion?

In his epistemological position, Plato clearly owed much to Parmenides, who likewise rejected the senses in favor of pure, abstract logic. On these terms, Plato judged the value of a particular line of scientific research by how much it uncovered patterns in the natural world that pointed the mind towards the eternal, ideal realm of changeless Being. For the most part, only geometry and astronomy, both highly mathematical, seemed to live up to this high standard. The emphasis here on mathematics also reveals a Pythagorean influence on Plato.

Central to an understanding of Platonic science is the late dialogue known as the Timaeus. There, Plato gives what he calls a "plausible story"—the best that can be offered, given the fact that it aims to explain the dim world of the senses. Specifically, he provides an account of the arrangement of all things in the world by a divine artisan or Demiurge (demiourgos). Unlike the God of the Judeo-Christian and Islamic traditions, the Demiurge is not a creator in the strict sense of the word, since he works with pre-existent matter. Further, he is not even omnipotent or all-powerful, since matter itself can stubbornly resist his efforts to form it in one way or another. He is instead a god who shapes, and who does so by keeping one eye fixed on the eternal Forms, which provide him with patterns for the things in this world. From this starting-point, and in the form of a mythic tale that perhaps should not be not taken too literally, Plato goes on to construct an entire cosmology. He intends it to be as comprehensive as possible, combining mathematics, physics, biology, and physiology into a unique and complex system.

His debts to earlier Greek thinkers are fairly easy to identify. From Empedocles he borrowed the notion that all substances are compounded from the four basic "roots," earth, water, air, and fire. In a much more radical move, however, and certainly with Pythagorean inspiration, he identified each of these four with a solid geometrical form. Fire is a four-sided figure or tetrahedron, and resembles a pyramid. Earth is a cube, and thus has six sides. Air is an octahedron, or eight-sided polygon. The last and most complex element, finally, is the twenty-sided icosahedron of water. Greek geometry, whose exact details in the century before Plato are hazy at best, had already determined that these four shapes—plus a fifth, the dodecahedron (=12 sides)—are the only regular geometrical solids.

Plato then went on to analyze each of these shapes even further, namely into a combination of one or the other of two basic types of triangles: the right and the equilateral. Two right isosceles triangles, for instance, or else four equilateral ones, can be joined to form one face of a cube; the whole solid itself, then, would equal 6 x 4 or 24 triangles. The element air, identified with an octahedron, can be broken down into eight such triangles; water, the icosahedron, is made up of twenty.

Bizarre as this theory might seem to modern eyes, it makes sense and even has a number of recognizable strengths in its own right. To begin with, it marks an advance over Empedocles and the other Pluralists, since it reduces their four elements to a single, fundamental reality. Moreover, by analyzing fire, air, water, and earth into 4, 8, 20, and 24 triangles, respectively, it takes care of a major problem that the Empedoclean system leaves unresolved. According to Empedocles, each of the four "roots" is fundamental and basic, in the sense that it is incapable of any further analysis. Air, for instance, cannot be broken down into smaller, constituent parts, nor can it ever change into anything else—despite the fact that direct observation offers plenty of evidence that air indeed condenses into water, and water evaporates into air. How can these simple changes be explained if each of the four "roots" permanently keeps its own form?

Plato’s composite elements, by contrast, can be easily transformed into one another by the simple addition or subtraction of the triangles out of which they are made. Remove two triangles from earth, for instance, and the result will be fire. This results in a kind of ‘chemistry’ of combinations and proportions that is very similar to the one that Empedocles proposed, but which operates on a much more fundamental level. Further, Empedocles’ vague talk of "four parts fire, two parts water, two parts earth" as a recipe for the production of "bone," for example, could now be replaced by seemingly more precise, mathematical formulas, such as the one Plato offers to account for how (one icosahedron of) water changes in the process of boiling into (two octahedra of) air and (one tetrahedron of) fire: 20 = {2 x 8} + 4.

What is perhaps most important of all about the cosmological account in the Timaeus is the fact that it completes the project begun by the Pythagoreans. In their belief that number is the basic reality, the Pythagoreans had sought (both mystically and mathematically) to uncover the hidden numerical structure of the world. In this respect, they ‘mathematized’ nature. Plato’s own work in the Timaeus carries this process to its logical conclusion by identifying ultimate reality with geometrical forms. The earlier Greek thinkers were materialists: the fundamental ‘stuff’ of the world was always seen by them as precisely that—‘stuff’—that is, as a physical entity. Although Plato’s four elements (earth, air, fire, and water) are material, however, his system reduced them to the far more abstract, non-material shapes of the triangles. The physical world could now be constructed, broken down, and remade again by combining geometrical parts. Once this had been accomplished, the old questions of what reality is made of and how it undergoes all its innumerable changes seemed that much closer to being resolved. Moreover, the preferred language in which acceptable answers to these questions were to be cast was from then on decidedly the language of mathematics.

The Timaeus is not limited to this kind of mathematical cosmology, however. It also covers issues of astronomy, biology, and human physiology as well.

In Plato’s astronomical scheme, for instance, a spherical earth lies at the center of a greater sphere of the heavens, on whose inner surface the stars are embedded like bright nails. As the outer sphere turns, the stars are carried around the earth in a daily rotation. The sun, moon, and the other planets revolve at different speeds around what is known as the ecliptic. If the earth’s equator is extended outward to the sphere of the fixed stars, it forms a plane called the celestial equator. The ecliptic is an imaginary circular plane tilted about 23° to the celestial equator. The path of the sun along the ecliptic intersects the celestial equator at the fall and spring equinoxes, the two days each year when day and night have equal lengths. As far as it goes, this is a relatively accurate picture.

It was well known in the ancient world that the planets sometimes move erratically. At times they seem to change speed—to speed up or slow down—in their revolution "around the earth," and sometimes they even appear to move backwards. One of Plato’s most significant contributions to astronomy was his claim that these apparently irrational movements could be explained by supposing that each planet moved on not one but a number of circular tracks. He proposed that planetary motion should be thought of as a combination of orbits within orbits, in which the clockwise turns of one track, for instance, would cause the adjacent track move counter-clockwise, and so on. This, he felt, might result in the creation of a regular, geometrical model of what looked like highly irregular behavior. If successful, what better example could there be of discovering order behind disorder, and so of "saving the phenomena"? The impact of this notion on Greek and much of later western astronomy was to be profound.

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Astronomy

It is indeed in the science of astronomy that the ancient Greeks made their greatest and most influential advances. Here more than in any other field of research, mathematical and mechanical models were constructed, applied, analyzed, challenged, then further refined and applied again in an effort to "save the phenomena."

The fourth century BCE marks a turning-point in early astronomical work. Prior to this, we have already noted Anaximander’s sixth-century model. He had proposed a system in which sun, moon, and stars orbit a cylindrical earth on tracks whose diameters are respectively 27, 18, and 9 times earth’s diameter. His theory clearly owes more to love of symmetry than any empirical observation Anaximander ever could have made.

The Pythagoreans, too, had speculated about the nature and shape of the heavens. Philolaos, a member of the group who lived in the last half of the fifth century, surprisingly theorized that the earth is not located at the center of the universe, but instead orbits around a "central fire." He further theorized that another or ‘counter-earth’ orbited the fire at a point always precisely opposite the position of the earth, and was therefore never actually visible to us. He is said to have used its existence to explain why lunar eclipses happen more often than eclipses of the sun.

The observation of the heavens also had very practical value in the ancient world. To begin with, it was regularly carried out as part of such ‘non-theoretical’ business as farming and navigation. For Greeks no less than for the Babylonians long before them, constellations marked off cardinal points, provided means of keeping time, and also predicted seasonal change. A considerable body of oral, anonymous lore had developed on this basis, and was used both for reckoning at sea and also to determine cycles of planting and harvest.

The need for accurate civic and religious calendars likewise encouraged astronomical observation, since here precise counting was required to measure the terms of public offices and to establish the all-important dates of festivals in honor of the gods. This need was especially great given the fact that the ancient Greek world traditionally measured time on the basis of the phases of the moon. Such lunar calendars had months of roughly twenty-nine or thirty days, resulting in a twelve-month year about 348 days long (29 x 12 = 348). This lunar year had to be reconciled somehow with the somewhat greater number of days (365) that resulted when a year was measured by the course of the sun.

A certain Meton of Athens (ca. 432 BCE) is credited with accurately calculating how many additional or ‘intercalary’ days should be added to the lunar calendar over the course of a nineteen-year cycle in order to bring it into alignment with the solar calendar. One of his contemporaries, Euktemon, also measured the exact lengths of each of the four seasons, based on careful observations of the equinoxes and solstices. (The solstices, in June and December, are the two days on which the sun reaches its farthest northern and southern positions along the ecliptic.)

The primary aim of fourth-century Greek astronomy was the task set for it by Plato. In the Timaeus, he had proposed that it should be possible to construct a rational, geometric account of the motion of the stars, sun, moon, and the five known planets (Mercury, Venus, Mars, Jupiter, and Saturn). From the viewpoint of an observer on earth, as we said, their movements exhibit both orderliness and also strange, puzzling irregularities. Plato’s challenge was to design a model that would "save" those irregularities by making them regular and rational.

Whatever the model, it had to take several different motions into consideration, and then construct a geometric model that would precisely reproduce these movements:

    (1) On the one hand, there is the steady, daily revolution of all the celestial bodies around the earth from east to west?or so it seemed, assuming a geocentric universe, namely one in which the earth rests unmoving at the center while all the other heavenly bodies turn around it.

    (2) Over the course of many weeks and months of nights, the constellations also seem to follow a longer, slower orbital path from east to west. Some disappear from view at certain seasons, but then always reappear in roughly the same place in the sky at roughly the same time each year. Their imaginary track through the heavens forms the circle or ‘belt’ called the zodiac.

    (3) Further, the sun, moon, and planets themselves move in the opposite direction, from west to east, against the background of constellations. They all follow the same path—the tilted orbit known as the ecliptic—but they do so at varying speeds, ranging from a single month for the moon to nearly thirty years for the planet Saturn to make one zodiacal orbit.

    (4) Most problematic of all were the so-called ‘stations’ and ‘retrograde’ movements of the planets. The name ‘planet’ in fact derives from the Greek verb planasthai, which means "to wander." Unlike the sun, moon, and ‘fixed’ stars, the planets moved irregularly and therefore required a special explanation. When observed over the length of a year, planets such as Mars seem to stop in the course of their normal, easterly movement through the zodiac, and to hold still for a number of nights. They then appear to move backward (‘retrograde’), east to west, sometimes for as long as a month, before continuing on an easterly course again.

Plato’s challenge to the students in his Academy, to the astronomers of his own and later generations, was to produce a systematic account of this peculiar and seemingly unsystematic motion. Here it is important to note Plato’s underlying assumption—characteristically Greek, and at the same time also characteristically scientific—that these anomalies are not real but instead only apparent. Behind those visible oddities, Plato believed, are movements that are actually uniform, orderly, and mathematically expressible. This assumption still motivates modern astronomy, along with all the other sciences of the West. The actual search for a solution to the problem of planetary motion as Plato had posed it in fact occupied Western astronomers for the next two thousand years.

The challenge was taken up first by Plato’s own associate, the astronomer Eudoxus of Cnidus (ca. 408-355 BCE). He was indeed a gifted polymath, with a rather broad range of interests. The tradition credits him with research on mathematics, geography, medicine, and music along with astronomy. Precious little of his work survives, however, and his writings are on the whole patched together from quotations found in writers like Aristotle and the very much later Simplicius (sixth century CE).

Eudoxus’ solution to the problem of how celestial bodies move was to propose not one but a whole series of four simple, circular movements for each of the planets, and three each for the sun and moon. The result is a highly ingenious mechanical model. Spheres within spheres within spheres move in complex, contrary rotations, like cogs in a machine, all perfectly regular and orderly. The combined movements all together produce the illusion of irregular, ‘wandering’ planets.

In his solution, each of the four spheres assigned to a planet produces one element of its total movement. To understand how this works, imagine the earth surrounded by four concentric, turning spheres; these constitute the system of a single planet—Mars, for instance.

In this model, the planet itself rides along the equator of the smallest or innermost sphere (D), but its overall movement is also a result of the motions of each of the three increasingly larger ones (C, B, and A). Their motions are as follows:

The largest and outermost sphere (A) turns from east to west once every twenty-four hours on an axis that runs north to south. This accounts for how, to a terrestrial observer, Mars seems to orbit the earth at just that speed. Modern astronomy, of course, now correctly attributes this to our planet’s own rotation.

The next sphere (B) rotates far more slowly and in the opposite direction, west to east, against the backdrop of the constellations. It turns once every 22 months, since this is the actual time it takes Mars to complete one circuit through the zodiac. Rather than being perfectly north-south, the axis of this second sphere is tilted a little, at right angles to the ecliptic. This detail helps account for apparent changes in the speed and position of Mars at various times over the course of two years.

The motions of the two innermost spheres (C and D) are the most important ones. Eudoxus designed them to account for the bizarre ‘stations’ and ‘retrograde’ movements that drew so much scientific attention to the planets in the ancient world. After all, this is what had motivated Plato’s demand for a rational solution in the first place. By tilting the axes of these two spheres at certain specific angles to each other, and by making them rotate in opposite directions at equal speeds, Eudoxus produced the appearance of a curving movement called a hippopede or "horse-fetter."

The hippopede is a path shaped like a figure-8. As Mars moves back and forth along it, the planet makes a looping motion. This combines with its slow, easterly movement along the zodiacal track and the fast east-west spin of its daily rotation to create the illusion of a planet that periodically stops, stands still, goes back, and then moves again. From the fixed point of an astronomer on earth, the model Eudoxus proposed seemed to answer Plato’s challenge successfully.

The Eudoxan solution is a remarkably imaginative leap. It moves from erratic, irregular sensory data to a vision of the uniform and orderly events that can explain them. Moreover, it is a leap of the mind more than the eye, an astonishing stretch of the imagination, guided by rules of geometry. It is a feat of sheer mathematical theorizing, for in the absence of telescopes and other tools for measurement it completely lacked empirical support.

The model of course has many weaknesses. In particular, it could not account for changes in planetary brightness. From observation, any given planet regularly gets dimmer at certain times of year, then brighter again—a fact which modern astronomy explains in terms of its varying distance from earth. Nonetheless, the model designed by Eudoxus established the standard pattern for addressing the question of how planets move. Later astronomers tinkered with his geometry, adding or subtracting orbital paths in ever more ingenious and intricate combinations to produce the observed effect.

Eudoxus had proposed a total of twenty-seven spheres as the minimum number necessary to replicate the apparent movements of the planets. They were increased to thirty-four by Callippus of Cyzicus (fl. 330 BCE), a somewhat younger astronomer. Aristotle added an additional twenty-two spheres, to bring the total number up to fifty-six. Heraklides of Pontus (fl. 350 BCE) complicated the model even further by proposing a theory of ‘epicycles.’ According to this, the planets Venus and Mercury actually orbit the sun while the sun itself orbits the earth. He is also credited with the striking minority view that the earth itself rotates on an axis while the surrounding heavens stay at rest!

The strange movements of the planets remained a central problem for astronomy for nearly two millennia after Plato had first made it a scientific challenge. In fact, it was not until the seventeenth century that models in which the planets move around inside perfectly circular spheres were finally abandoned. They were then replaced by a model in which their orbits are instead elliptical. The one who proposed this new shape was none other than the great German scientist Johannes Kepler (1571-1630), one of the founders of modern astronomy. The various solutions to Plato’s problem indeed changed over time, and new tools—such as the telescope, first used some time after 1609—brought the heavens ever closer to the eye. What never changed, however was the demand that had first been expressed by the ancient Greeks. The observable phenomena far in the sky, above and around the earth, had to be "saved" by constructing mechanical models of the universe that conformed to laws of geometry. The orderliness of those far distant worlds was first dreamed of in the mathematical imagination of ancient Greeks.
 

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Aristotle

Born in 384 BCE, Aristotle grew up in an environment that offered him many rich opportunities to observe and think about the natural world. His father was court physician to Amyntas II, king of the territory of Macedonia in northern Greece. His later interest in biology has often be attributed to his father’s influence upon him. At the age of seventeen, Aristotle went to Athens to study under the famous Plato, with whom he stayed for the next twenty years. After Plato’s death in 348, Aristotle spent some years in the islands of the eastern Aegean, apparently studying and collecting specimens of plant and animal life. He was then invited back to the royal court of Macedon to serve as tutor to the young prince Alexander, known to later ages as Alexander the Great. In 335, Aristotle returned to Athens and there established an institute called the Lyceum, where he worked and taught until his death in 322.

In Aristotle we find a consistent pattern of deliberate, conscientious research on as broad a range of scientific fields as were recognized in antiquity, along with the creation of entirely new fields that had previously been unknown: logic, epistemology, cosmology, medicine, physiology, psychology, biology, zoology, botany, optics, acoustics, physics, dynamics, mathematics, astronomy, rhetoric, political science, ethics, and literary theory. Roughly thirty of his more than 150 books have survived. Given the vast scope of his work, the following pages can only touch lightly on some of their highlights. It should also be remembered that Aristotle was as deeply commited to teaching and cooperative work as he was to independent research. Just as important as his own writings, therefore, is the long tradition of scientific research that he set in motion, and that continued to operate through many later generations of researchers, teachers, and students at the Lyceum.

What is worth noting first is the remarkable degree of attention Aristotle gave to the language of science and the structure of scientific claims. This was partly his response to the epistemological problems Greek philosophers and scientists had faced for at least one hundred years. It will be remembered that in the early fifth century, Parmenides profoundly influenced the direction of Greek science and philosophy by using the new tool of logic to construct an argument that made rational sense but at the same time seemed to contradict everything the five senses suggested about the world, thereby setting rigorous logical criteria for proofs. Whether one supported or rejected Parmenides’ argument, all subsequent thinkers nonetheless at least had to conform to the same rules of logic he had used.

Aristotle’s concern with scientific language was partly also his own recognition that claims must meet rigorous criteria and standards in order to be true. If scientific knowledge (epistêmê) is genuine, after all, it must be based on valid proof (apodeixis). How, then, is it possible to recognize when a proof is valid or not? Are there rules that govern how valid proofs are put together? Are there logical steps that can be taken to test an argument for fallacies and inconsistencies? Are there clear, objective measures that can be applied to any given claim in order to refute it if it is false and confirm it if it is true?

In a group of books known collectively as the Organon, Aristotle carefully analyzed these and similar questions. The result of his efforts is a finely detailed and rigorously argued exposition nature of reasoning. Here, and for the first time in any consistent and comprehensive way, he established the structure of valid, logical demonstrations, and mapped out the shape of different kinds of premises—axioms, definitions, hypotheses—that provide the starting-points for scientific claims about the world. He categorized types of arguments, investigated their forms, distinguished between abstract and empirical claims, and spelled out the basic rules an argument must follow in order to be logical. He then went on to determine what degrees of certainty each different branch of science was capable of giving, based on the kinds of proofs it was able to offer for its claims. The Greek word organon means "utensil" or "implement," and in this painstaking work on the grammar of proofs, Aristotle indeed fashioned a tool that has shaped and continues to shape all later scientific discourse.

For Aristotle, epistêmê or scientific knowledge is knowledge of the essential "causes" (aitiai) of any given thing. These causes are four in number, and in the case of any given thing it is necessary for all four causes to be investigated and identified before true knowledge of that thing is possible. A valid, scientific account of something—whether it is inanimate (stone, water, spoon) or living (tree, animal, person), artificial (statue, table, machine) or natural (catfish, flower, embryo)—must fully explain:

(1) what it is made of
(2) what shape or form it has
(3) what made it what it is, and
(4) what purpose or function it serves.
These four criteria correspond to what are usually termed the (1) material cause, (2) formal cause, (3) efficient (or ‘moving’) cause, and (4) final (or ‘telic’) cause. They form the basis not only of Aristotelian physics, but also of his understanding of each and every thing and event in the world as a whole. They provide the basic answers to every question that can possibly be asked, from why a rock falls when dropped to what kind of life a human being ought to live.

A few examples will help to clarify his meaning. This chair I now sit on, for instance, mostly has wood as its ‘material’ cause; this is what it is made of. Its ‘formal’ cause is what makes this mass of wood a chair and not, say, a bookshelf or a coat-rack or a desk. In a word, the ‘formal’ cause accounts for its shape, which clearly does much to define what any given lump of matter is. This chair was made in a factory by a worker, who thus provided its ‘motive’ or efficient cause, namely, the series of acts by which this stuff took on this shape. Finally, this chair was made for a specific purpose—its ‘final’ or ‘telic’ cause—which is to support me comfortably as I sit at the computer.

Of course, the same holds for natural no less than artificial things. Take an acorn. Its material cause is the woody stuff it is made of. Its formal cause is identical with the shape it has, which distinguishes it as an acorn and not, for example, a pine cone or a coat-rack. Its efficient cause is the oak tree that produced it. Notice here that the efficient cause is not necessarily the same as a human agent; it does not matter that the tree was not conscious of producing the acorn. Last, its final cause is the goal towards which the acorn naturally tends, namely to grow into an adult oak itself.

Obviously, the idea of "cause" is somewhat narrower for us than it was for Aristotle. We generally mean by it the person or thing that directly produces a certain effect. That is to say, we tend to identify "cause" with what Aristotle calls the efficient cause. His idea of material and formal causes was meant as a direct response to Plato, whose philosophy of idealism made the ideal Form alone real and entirely detached from matter. For Aristotle, on the contrary, form and matter are inseparable. Although the word ‘dog’ can be defined in a universal way, so as to include all real dogs in its description, there is still no ideal ‘Dog’ apart from actual, living ones like Fido and Rex.

By far the most important of the causes for Aristotle, however, is the final or ‘telic’ one—from the Greek word telos, meaning "end" or "goal." Its sense is clear in the case of an artificial thing like a chair, since here the final cause is identical to the purpose or function for which the craftsman made it. Final causes also operate in the world of natural things, as in the case of the mature oak that is the ultimate goal of the acorn’s development. There is a major difference between the final cause of artificial and natural things, however. As far as the natural world goes, Aristotle firmly insists that no god exercises providential control over things, and that nature itself also has no deliberate, conscious aim. That is to say, there is no equivalent in nature to the craftsman in the realm of art and manufacturing.

The different ends towards which natural things grow—seeds into plants, for instance, or children into adults—are instead internal or immanent in the things themselves. Acorns naturally become oaks, not pine trees; penguins give birth to penguins, not mice. Democritus and the Atomists had claimed that all things in the world are the temporary result of purely random atomic collisions. Atoms bump into each other by chance and stick together to form certain objects, which break up when a stronger outside force splits them apart again. On the contrary, Aristotle claims that each and every natural thing exhibits a genuine purposiveness. Propelled by an inner drive—an immanent teleology—each moves steadily toward realizing its own specific kind of perfection. Each strives to actualize its innate potential.

The distinction between what is actual (energeia) and what is potential (dunamis), in fact, was the key to Aristotle’s approach to the old Parmenidean dilemma of change. The puzzle had already been occupying Greek thinkers for more than a century. How can something come into being? Not from nothing (‘what is not’), since ‘what is not’ does not exist. Not from something, for whatever already exists is already in existence, and therefore has no need to come into being at all. Aristotle’s concept of dunamis neatly cuts through that logical knot. An acorn, for example, indeed is an oak, at least in the sense that it has the potential to grow into one; while in another sense, it is of course not actually an oak at all. It has the dunamis to be something else, even if that other something has not yet been actualized in the world. The concept of potential thus lets something come into being from ‘nothing,’ namely from what does not really exist yet. Change—the movement from being potential to being actual—is logically possible after all. The evidence of the senses, which show us a world of constant change, is finally vindicated!

Aristotle applied his ideas of dunamis and immanent teleology most successfully in his works on biology and physiology. These account for the largest share of his extant writings, in fact, and include such important texts as History of Animals, Parts of Animals, Motion of Animals, Generation of Animals, and the group of essays known as the Short Natural Histories or Parva Naturalia. This was clearly the subject to which this doctor’s son gave most of his attention, and in which he probably achieved the best balance between theory and observation.

His research on plants and animals is indeed remarkable for its depth of detail and empirical rigor. As we saw, these qualities were generally lacking among the earlier Greek scientists, who tended to devote themselves more to theoretical speculation than to observation and experiment. Relying on specimens gathered widely throughout the known world, however, Aristotle himself distinguished more than 500 different species of animals, performed frequent dissections, and made precise records of anatomical descriptions. His discussion of unusual features of the placenta of a species of dogfish, for example—whose accuracy western biologists doubted for more than 2100 years—was finally verified in the middle of the nineteenth century. It should be remembered that all of this highly detailed work was accomplished without the aid of any of the modern instruments that biologists normally use—no magnifying glass or microscope, for instance, was available to Aristotle. The overall system of zoological classification (or taxonomy) he constructed remained in effect until the time of the great Swedish biologist Linnaeus (1707-1778). It would be easy to compile quite a long list of Aristotelian insights in biology that waited centuries to be confirmed by later researchers.

Aristotle’s Classification of Animals

Aristotle’s investigations in this field were not limited to anatomy and classification, however, but also ranged widely and deeply over physiology, nutrition and growth, locomotion, sensation, and reproduction. With reference to this last topic, Aristotle used rigorous logic to reject the idea of pangenesis. Most of the Hippocratic medical writers had believed that in both plants and animals, the seed draws its material from the parent’s whole body. Aristotle proposed instead the idea that the male parent supplies the formal and the efficient cause of the offspring, whereas the female contributes only the matter. This was consistent both with his theory of four causes and also, unfortunately, with his sexism as well.

Aristotle was also deeply interested in the variety of living creatures in nature and what accounted for the differences among them. In his History of Animals and especially in his work On the Soul, he identified the soul of a living creature with its formal cause, in the belief that form is what provides each thing with its true definition and essential characteristics. For Aristotle, the entire natural world is a vast hierarchy of different types of souls. Plants have what he termed a nutritive soul, which is the cause of their growth, nourishment, and reproduction.

Next in order are animals. These are superior to plants because, in addition to a nutritive soul, they also have a sensitive soul, which gives animals the ability to experience their surroundings. Among animals as a class, moreover, there is a hierarchy that runs from those that possess only one of the senses—clams, for instance—right up to the higher animals, which have all five. Aristotle also felt that the sensitive soul in animals that have all or at least most of the five senses also gives them the power of locomotion. Since they can fully sense the world, they can also move towards what is good and away from what harms them.

At the very top of the hierarchy of earthly creatures come human beings. Along with the capacities that the first two souls represent—growth, nourishment, reproduction, sensation, and locomotion—people also have the higher capacity of reason. According to Aristotle, this is made possible by their rational soul.

This graduated scale is indeed just one series of links in a much larger ‘Chain of Being,’ which stretches from the lowest to the very highest order of things, both inanimate and living. Here Aristotle used his theory of causes and his idea of immanent teleology as explanatory tools to connect all things in the universe into a single, systematic, comprehensive, and rational whole. At the same time, the hierarchical order of things in the world is reflected in a similar ordering of all the branches of science that study them.

At the very lowest link in the chain is pure matter. It is the stuff out of which everything is made, but lacks form and purpose. Next come the four elements (earth, air, fire, water) which Aristotle borrowed from Empedocles. It will be remembered that Plato did the same. But whereas Plato went on to analyze the elements into abstract geometric entities, Aristotle reduced them to combinations of sensible qualities (hot/cold, wet/dry).

Their character and behavior are completely determined by what Aristotle identified as their formal and final causes. It should come as no surprise that, even though they are inanimate, each of the four elements nonetheless still exhibits immanent teleology. Fire naturally moves up, for instance, away from the center of the world, while rocks move in the opposite direction. For Aristotle, this does not happen because the force of gravity. In fact, the true nature of gravity was not fully appreciated for more than 2000 years after Aristotle, until Sir Isaac Newton formulated his famous law of gravitation in the seventeenth century. Instead, Aristotle believed the behavior of a falling rock must be explained in terms of its natural tendency to move downwards. Because it is made of earth, it naturally moves towards the place where the greatest mass of earth is located.

In his Physics, Aristotle was the first to formulate and then explore such common Western scientific concepts as force, movement, speed, place, weight, mass, distance, and resistance. He used them to develop a theory to account for what he called "forced" or "unnatural motion" here on earth. "Natural motion" occurs when an object obeys its immanent tendency to move, as when a rock falls down. "Unnatural motion," on the other hand, is motion that is imparted to a body from the outside, as when a rock is thrown up in the air, against its nature. Aristotle’s Physics is the beginning of the science of dynamics.

The laws that govern the motion of celestial bodies are the subject of Meteorology, On the Heavens, and also the Metaphysics, in which science and philosophy together reach their highest point of speculation. Aristotle’s observation of the movements of the planets and stars led him to postulate the existence of an entirely new, fifth element. His reasoning was influenced greatly by his discoveries in the study of dynamics. The four terrestrial elements, inherited from Empedocles, naturally move either up or down. Moreover, they tend to move along linear vectors—that is, in straight lines—and they always stop once they have reached their natural destinations. The stars and planets, however, behave quite differently. On the one hand, they all move in regular and circular patterns, as Eudoxus had so elegantly shown. On the other, and even more remarkable, the stars and planets never stop. Their movement is perpetual and ceaseless, unlike anything that can be observed here in the earthly world. Aristotle reasoned that they must therefore be made of something non-terrestrial, something much more refined and perhaps even divine. This ‘something’ is aithêr—an eternal stuff in constant circular motion, unaffected by the impermanence that touches everything on earth.

On the basis of these five elements, then, and in keeping with his new laws of dynamics, Aristotle proceeded to construct a comprehensive picture of the entire universe. The picture would remain virtually the same for more than 1500 years, throughout Greek and Roman times in the ancient world, during the whole of the medieval period, and right up to the European Renaissance.

At the center of the cosmos is our dense planet. It is made of elemental earth (cold and dry) that has naturally collected here. The earth’s spherical shape is confirmed, among other things, by the shadow it casts on the moon during lunar eclipses. Ideally, if the four "lower" elements existed in an unmixed state, the earth would be surrounded by perfectly concentric rings of water, air, and fire. This is how the elements naturally tend to collect, with the heaviest at the center and the lightest at the outermost ring. However, most things in our world are in reality mixtures of earth, water, air, fire, and water, and each element is rarely found in an unadulterated condition.

In Aristotle’s cosmology, the orbit of the moon begins precisely where fire, the lightest terrestrial element, achieves its farthest reach. Everything above this point is made of aithêr, the fifth and purest element of all. Beginning with the moon, a system of ‘aitherial’ bodies extends out to the largest sphere of the universe. Next after the moon comes the sun, then the five known planets, and finally the "fixed" stars. The stars are "fixed" because they were believed to be embedded in the inner wall of the outermost sphere, and to turn along with its slow movement. Aristotle further refined the geometrical model that Eudoxus had designed, and his celestial bodies move along a total of fifty-six rotational tracks within tracks within tracks within tracks. In his system, moreover, each orbiting sphere touches both the sphere above and the sphere below it. In this way, celestial motion is communicated from heaven’s outermost circle down into our dense, sublunary region. The spheres turn in a complex pattern of rotations and counter-rotations, producing what we all observe when we turn our eyes upward to the nighttime sky.

They were meant to do much more than just produce an illusion, however. Aristotle connected all fifty-six spheres together, made each touch the next sphere in line, and made motion pass all the way down the line of spheres from beginning to end. This changed the Eudoxan model of the universe in a radical way. Eudoxus, after all, had proposed a geometrical model. It was an abstract, theoretical answer to an intriguing puzzle that Plato had said was in need of some solution. His concern was principally with calculating the minimum number of circular tracks that were necessary to imitate the observed movement of the sun, planets, and stars. As a result, his answer was more like a design hypothesis than an blueprint for a model that could actually work.

By physically linking each sphere to the next, Aristotle transformed this geometrical model into a dynamic and mechanical one. The fifty-six spheres in his system are like the cogs in a divine machine, and their turns and counter-turns are really meant to show how the heavenly bodies actually behave as they move through celestial space. Rather than being merely hypothetical, the spheres in his model obey the laws of both physics and dynamics, at least as Aristotle conceived them. The result is a working model, not simply an abstract sketch. This set the precedent for over two millennia of astronomical models built to reflect the real shape of the universe.

Aristotle’s theory of causes required that the eternal, perfectly circular movement of all the celestial bodies starting with the moon be natural, not forced. Forced motion, after all, is contrary to nature, and in the end it is always defeated by the tendency every object has to move in the way that is proper to it. That is why rocks always fall to earth, despite how much effort we might put into throwing them up in the air. The moon, sun, planets, and stars continue to move around and around for ever because this is in keeping with their immanent teleology.

But where does this motion come from? What causes it? A rock, for instance, falls because it is made of the element earth, because earth is the heaviest element, and because the heaviest always moves toward the center. Once a rock reaches the center, however, it stops moving. If we ask why a certain specific rock actually moves, then, the only answer can be that someone or something at some time removed it from its natural place at the center. The rock falls because it has been displaced, and it is attempting to return to its proper "home."

What about the celestial bodies, then, the ones that are all made of aithêr, the pure fifth element? They eternally move in a circle because this is their natural way; it expresses their immanent teleology. But where does their motion come from? What could have started it? Aristotle reasoned that the source of celestial motion must logically be something that does not itself move. Otherwise, any attempt to understand it gets stuck on an endless treadmill of what is called ‘infinite regress,’ where each answer only raises the same question all over again. If the source of celestial movement is something that also moves, then it must get its own motion from some other source, and then that source must itself be either moving or unmoved. If it is moved, then the question is thrown back yet another step. To avoid spinning our logical wheels forever, then, reason demands that the ultimate source of motion is something that is unmoved.

At the source of all movement, celestial and earthly, Aristotle theorized the existence of what he called a "Prime" or "Unmoved Mover." He identified it with God. This God is the most complete being imaginable. Unlike everything else in the universe, which naturally strives to fulfill its inner goal or immanent teleology, God is already fully actualized. That is to say, in God there is nothing potential—no dunamis at all—but only pure reality (energeia). Since God is complete, God has no need of anything else; this means that God is perfectly autonomous and self-sufficient. God is entirely separate from all other things.

What does God, the Unmoved Mover, do for all eternity? The only thing such a being could do, in keeping with its perfect reality, is to spend all of eternity contemplating itself. God cannot act, after all, since action would imply that God does not already have what it needs, or that God wants something else. This is impossible, however, since God is by definition perfect and complete. If God cannot act, then, God must think. And the universe offers no other object of thought worthy enough of God except for God himself.

How, then, does this most perfect being, entirely absorbed in thinking about itself, make the stars and planets move? It cannot do so in the way that an efficient (or ‘moving’) cause makes things happen. After all, it is not as if the Unmoved Mover turns some kind of heavenly crank, which turns the sphere of the stars, which turns the spheres of Saturn, which turn the spheres of Jupiter—and so on, down to the spheres of the moon. Instead, God makes things move in the way that a final or ‘telic’ cause works. God is a totally perfect being, fully actualized—in fact, the only such being in the entire universe. As a result, God embodies the desire that every natural thing has to realize its potential and thus achieve its own perfection. Since God represents what is ultimately real, God is the ultimate aim of immanent teleology. God is the goal that every existing thing—from rock to fire to seed to human soul to ‘wandering’ planet—naturally seeks to become. The whole universe turns out of desire for God.

Here obviously we pass from science to theology and religion, and thus well beyond the limits of material this chapter is supposed to cover. For Aristotle, however, these boundaries are not as definite as they are for us, since his world was far more interconnected than ours. No clear line separates ‘physics’ from ‘theology.’ The fact is that ‘theology’ is simply what every rational person should study after completing the study of ‘physics,’ for physics leads naturally to the study of God as the Unmoved Mover of the cosmos. Everything is bound together—biology, zoology, physics, astronomy, dynamics, theology... This is because the theory of the four causes offers a complete and comprehensive theory of every thing and action in the universe.

The very range of his theory has much to do with Aristotle’s profound influence on subsequent generations of philosophers and scientists, especially throughout the ancient world and from the thirteenth century up through the Renaissance. Three aspects of his work deserve to be mentioned by way of summarizing the reasons for his impact on Western thought.

First, his work addressed and offered answers to questions that had occupied Greek thought for upwards of three centuries: What is reality made of? How does its ‘stuff’ change into the variety of things that we experience through our senses? What causes this change? How is the universe structured? How can phenomena be "saved"? How can reality be apprehended? How do we know that we know? How can we prove it? How can our knowledge be communicated? Here Aristotle did not just propose grand, unified solutions to specific problems. He also analyzed the language itself in which scientific claims should be cast in order to be genuinely objective.

Next, Aristotle contributed greatly to the content and in some cases even the very definition of a variety of scientific disciplines. Any number of the different branches of research that make up the various departments in a modern university were either created by Aristotle or else given their first, clear definition by him. These branches are familiar to us now, but they were literally unknown or only vaguely distinguished in the early fourth century BCE. The sheer range and scope of Aristotle’s scientific attention have seldom ever been matched.

Moreover, in founding the Lycaeum, Aristotle created the first genuinely scientific research community in the West. He also gave it a genuinely scientific research agenda—into physics, mechanics, dynamics, medicine, geometry, astronomy, zoology, biology, botany, chemistry, and mineralogy, to name the most important fields. That agenda has driven western scientific investigation ever since. Along with the agenda, finally, Aristotle bequeathed a set of methodological procedures —especially those of logical argument and detailed, empirical observation—by which all science still continues to be guided.

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