The investigation of the truth is in one way hard, in another easy. An indication of this is found in the fact that no one is able to attain the truth adequately, while, on the other hand, no one fails entirely, but everyone says something true about the nature of things, and while individually they contribute little or nothing to the truth, by the union of all a considerable amount is amassed.


On his long journey home from Troy to his wife, Penelope, in Ithaca, Odysseus, the hero of Homer’s Odyssey, was swept from his ship through the fury of Poseidon, the god of earthquakes and the sea, who had turned against him. Luckily, the goddess Leukothea, who lived in the depths of the sea, took pity on him and offered him a magic scarf that, when bound around him, would protect him, while the goddess Athena calmed the waves so that he could swim towards the shores of the land of the Phaeacians. In this crisis Odysseus still had to make his own decisions, in the short term at what moment he should leave the timbers of his ship and strike for shore. A massive wave sent by Poseidon made the decision for him, and he found himself swimming without any support. The coast came into view, but it was rugged. Is it better, Odysseus wondered, to land where he can and risk being crushed against the cliffs by a wave, or continue onwards in his exhaustion in the hopes of finding a sandy bay?

Odysseus’ ordeal ended happily. He was washed ashore and rescued by the beautiful Nausicaa, daughter of the Phaeacian king. He was saved by two goddesses who successfully challenged another god, Poseidon. So here is a man at the mercy of divine forces who nevertheless retained the power to think rationally and who saw rational thought as a means of bettering his chances. One can hardly say this is a revolutionary step; archaeological evidence from South African caves shows that individuals were able to provide “rational” adaptations to their changing environment (in the sense of adapting their tools) as long as 70,000 years ago. What is important is that Homer distinguishes rational thought, even at this primitive, almost instinctive level, as a mental activity, independent of the whim of the gods.2

This is the mental landscape of Greece in the eighth century or earlier—the Odyssey took its final form about 725 B.C. from much older oral traditions—but it is a world that is passing. Odysseus is an aristocrat, a king in his land of Ithaca, where he has palaces and cattle. His wife, Penelope, though vulnerable without him, has her own status. When they are finally reunited, they enjoy each other’s conversation as equals before they make together for the royal bed. Emerging is the world of the Greek city state, where, from the eighth century, one finds communities making focused settlements, typically with their own sacred spaces and public arenas. There is a shift, probably as a result of population increase, from the “aristocratic” extravagance of cattle farming to more intensive cultivation, of olives, cereals and vines. A peasant economy emerges based on a free citizenry relying on slaves for extra labour. Women are now segregated, the aristocratic palace replaced by the enclosed home, which, unlike Penelope’s palace in Ithaca, contains no allotted space in which women can appear before strangers. Fighting is no longer between aristocratic heroes meeting in single combat but between massed phalanxes of hoplites (the word comes from hoplon, a shield), made up of the peasantry, who fight side by side with each other and overwhelm their opponents by sheer weight and determination.3

Population increase and political infighting encouraged settlement overseas, and the city state, or polis as it was known in Greek, proved eminently exportable throughout the Mediterranean. One finds the same structure, domestic areas, public meeting places and a demarcated area, the temenos, for temples and sacrificial altars, in most Greek cities. Remarkably, despite the fragmentation and extent of settlement, there remained a common sense of Greek culture, sustained by religious festivals, many of them with games, oracles and centres of pilgrimage, at which Greeks from across the Mediterranean gathered.

The number and frequency of such festivals reflects the intensely spiritual nature of the ancient Greeks. They had a powerful sense of the sacred, often personified in gods and goddesses, elaborated in myth and celebrated at an enormous number of shrines, some natural such as caves and springs, others opulent temple complexes. Their gods remained close to them, traditionally portrayed in human form and displaying behaviour which was often all too human in its fits of jealousy and anger. Among the twelve Olympian gods the full spectrum of human life was represented, from the wild excess of emotion (Dionysus) to the calm exercise of reason (Apollo), from the lustful enjoyment of sex (Aphrodite) to virgin modesty (Artemis). Each god or goddess played a number of roles, accumulated from different traditions both inside and outside Greece. So Zeus, the father of the gods, could act as lord of the skies, as a bringer of victory, a symbol of sexual potency, the upholder of rulers and the god of thunder and lightning. Alongside the Olympian gods there was a mass of lesser deities, such as Pan, the god of shepherds, and local heroes with a range of roles. Ancient Greece vibrated with spiritual presences.4

Mediation with the gods took place through prayer and sacrifice. The sacrifice was the central point of almost every ritual. An animal—an ox, sheep, goat or pig—would be presented to the gods and then killed, burnt and eaten by the community. Sacrifices were not an aberrant or cruel activity—they were a sophisticated way of dealing with the necessity of killing animals in order to eat. In fact, the rituals surrounding sacrifice suggest that the Greeks felt some unease about killing animals they had reared themselves. So the illusion was created that an animal went to its death willingly, and before the killing all present threw a handful of barley at it, as if the community as a whole was accepting responsibility for the death. At the moment of the slaughter women would utter impassioned cries, again a recognition of the seriousness of what was being done in taking life. This was a common theme in ritual, also found in Greek tragic drama, an awareness that any transition involved a loss that had to be recognized within the ritual itself. There was also a strong belief that through the maintaining of the round of rituals the city had been protected. As one Athenian citizen put it in a public debate:

Our ancestors by sacrificing in accordance with the tablets of Solon [laws instituted in the early sixth century] have handed down to us a city superior in greatness and prosperity to any other in Greece so that it behooves us to perform the same sacrifices as they did if for no other reason than that of the success which has resulted from these rites. 5

So, Greek religion acted as mediator of political and social tensions. Transitions could be effected through the use of ritual and difficult decisions made with the help of oracles. Even so, political life was not easy, and in the seventh and sixth centuries in particular there were continual clashes between the old aristocratic elites and the newly wealthy, who had made their money through trade, and the rising peasant classes, increasingly conscious of their own cohesion and power. At the very worst a city would explode into civil war. Thucydides describes one case in 427 in Corfu, which saw a vicious spiral of terror and counter-terror between the ruling classes and “democrats.” In the resultant complete breakdown of order, where, as Thucydides puts it, “fanatical enthusiasm was the mark of a ‘real man,’ ” fathers killed sons, temples were violated by the massacre of those sheltering in them and many committed suicide rather than wait to be killed. “As for the citizens who held moderate views, they were destroyed by both the extreme parties, either for not taking part in the struggle or in envy at the possibility that they might survive.”6 The most sophisticated resolution of conflicts such as these was to be made in fifth-century Athens, where all male citizens came to share in government equally, in the Assembly, as jurors in the law courts and, for those aged over thirty, as administrators. Athenian democracy lasted some 140 years and, despite its exclusion of women and slaves, remains a remarkable political innovation.

It was in this resolution of internal conflicts that a remarkable intellectual development took place. It seems to have been based in an optimistic belief that there were forces that tended to good order.7 One finds such a feeling in the early sixth century B.C. in the verses of the Athenian statesman Solon, who had been charged with resolving a political crisis caused by the economic and social exploitation of a debt-ridden peasantry by the landed aristocracy. He proved to be a pragmatic statesman— it is human beings themselves, not the gods, who must bring peace and good order (the Greek word used is eunomie) to their cities. However, eunomie (who is personified as a daughter of Zeus) is seen as a force in her own right, even if one who works alongside mankind. In Solon’s own words:

Eunomie makes all things well ordered and fitted

and often puts chains on the unjust;

she smooths the rough, puts an end to excess, blinds insolence,

withers the flowers of unrighteousness,

straightens crooked judgements and softens deeds of arrogance,

puts an end to works of faction

and to the anger of painful strife, under her

all men’s actions are fitting and wise.8

In other words, the political world tends towards stability under the auspices of divine forces. The work of the politician lies in shifting the city’s affairs into their natural groove of harmony, and he will be sustained by eunomie in achieving this (“under her all men’s actions are fitting and wise”). However, remarkably and apparently uniquely to the Greek world, a further intellectual leap appears to have taken place; it was appreciated that if the city tended to good order, perhaps the universe, the cosmos, did as well. The natural world was seen to change according to rhythms, of the seasons but also of the movements of the stars, rhythms that appeared to persist in spite of the fragmented and unpredictable nature of everyday life. Only a few years later than Solon, in 585 B.C. in the Ionian city of Miletus on the coast of Asia Minor, the philosopher-scientist Thales is said to have predicted an eclipse of the sun (the eclipse did indeed take place and was independently recorded by the historian Herodotus). For Aristotle, writing some 200 years later, this was truly the moment when Greek philosophy began. An underlying order to the cosmos had been observed, and its movements were assumed to be so regular that future events could be predicted from empirical observations gathered over time.

This single instance was not revolutionary in itself—after all, the Egyptians had been able to work out a calendar based on the regular phases of the moon as early as 2800 B.C. Where Thales and his associates in Miletus went further was to speculate on why the world was as it was. They began to ask major questions. What was the cosmos made of, and why did it move in the way it did? Thales himself suggested that the world may have originated in a single substance, water, and that it rested on a base of water. He was challenged by another Milesian, Anaximander. What then did the water rest on? Anaximander suggested that the apparent stability of the world arose because it was at the centre of equally powerful forces—the Boundless, he called them—that surrounded the world on all sides and from which it had been formed. Just as a city would tend towards harmony, so would the cosmos be held in balance by these surrounding forces. Another Milesian, Anaximenes, suggested that everything came from air. If steam could be condensed into water and water could be frozen into ice, it followed that a single substance could change form dramatically, and perhaps air could be condensed into solid forms. These speculations were bound to be primitive, but they did represent a new way of thinking and, moreover, one in which each thinker was able to use observation and reason to challenge his rivals. So within 150 years of Odysseus’ swim to Phaeacia, rational decision-making had been transformed into something much more sophisticated and universal, what we might call science. Thinking about how the predictable rhythms of the natural world related to the observed chaos of the actual world presented, of course, a daunting challenge. But it was faced as early as 500 B.C. The brilliant Heraclitus (from the city of Ephesus, close to Miletus) believed that the underlying order (the word he used was logos, which will reappear many times in this book) was sustained by continual tensions between different forces. The harmonious city, said Heraclitus, is not one in which everyone lives in peace but one among whose citizens there is constant activity and debate. “Justice,” said Heraclitus, “is strife.” 9

Heraclitus’ insight that reasoned thought is born within the tensions of the city state is supported by modern research. Geoffrey Lloyd, who has carried out intensive explorations of the background to Greek scientific thinking, traces the origins of a systematic use of reason (without which empirical observations cannot be related to each other) to the intense political debates that raged within the Greek cities. If two factions wished to find a “just” solution to a problem without tearing apart their own city, then at some point there was likely to be a consideration of what was meant by “justice.” There was an incentive to go back to first principles and attempt to define an agreed basis, some kind of axiomatic statement, from which to begin the arguments that could only take place according to rational principles if agreement was to be maintained between the opposing parties. Lloyd argues that this process can be discerned within the fragments of political debate that survive, and, crucially, it was also applied to the study of the natural world. The terminology used supports this. Lloyd shows how a word such as “witness,” as used in the law courts, was the root of the word for “evidence” in scientific discourse, and how the term used for cross-examination of witnesses was adopted to describe the testing of an idea or hypothesis. He also argues that within the city the ability to argue persuasively conferred status, and that this status could be transferred into other areas of intellectual activity.10

So began the great adventure of the Greek speculative tradition. It was not a coherent process. Martin West writes:

Early Greek philosophy was not a single vessel which a succession of pilots briefly commanded and tried to steer towards an agreed destination, one tacking one way, the next altering course in the light of its own perceptions. It was more like a flotilla of small craft whose navigators did not start from the same point or at the same time, nor all aim for the same goal; some went in groups, some were influenced by the movements of others, some travelled out of sight of each other.11

One important development was the distinguishing and segregation of the process of reasoning itself. The earliest surviving sustained piece of Greek philosophical reasoning comes from the first half of the fifth century, from one Parmenides from the Greek city of Elea in southern Italy. Parmenides attempts to grasp the nature of the cosmos through the use of rational thought alone (in other words, without any reliance on empirical observation). He realizes that no argument can begin unless some initial assumptions are made. His “It is and it is impossible for it not to be” is the assumption with which he starts. As Parmenides, through a goddess who is given the role of developing the argument, works towards his conclusion that all material is a single undifferentiated and unchanging mass, many controversies arise, not least because of the problems in using verbs such as “to be” in a completely new context, that of philosophical reasoning. But what Parmenides did achieve was to show that once basic assumptions and axioms have been agreed upon, reason can make its independent way to a conclusion. However, his conclusion, that it is rationally impossible to conceive of materials undergoing change, seems absurd, and it raises for the first time the question of what happens when observation and reason contradict each other.

A follower of Parmenides, Zeno (who also came from Elea), highlighted this issue in his famous paradoxes. An arrow which has been shot cannot move, says Zeno. How can this possibly be? Because, answers Zeno, it is always at a place equal to itself, and if so it must be at rest in that place. So, as it is always at a place equal to itself, it must always be at rest. In Zeno’s most famous paradox, Achilles, the fastest man on foot, will never catch up with a tortoise, because when he has reached the place where the tortoise was, the tortoise will have moved on, and when he has reached the place to which the tortoise has progressed, it will have moved on yet further. While reason can suggest that Achilles will never catch the tortoise, experience tells us that he will and that he will soon outstrip it. Observation and reason may be in conflict, and the result is a conundrum. The fact that the Greeks recognized such problems yet were not daunted by them is a measure of their growing intellectual confidence.

The next step, then, in this parade of intellectual innovation is to try to isolate the circumstances in which rational argument can be used to achieve certainty without being challenged by what is actually observed by our senses. Here the achievement of Aristotle was outstanding. One of Aristotle’s many contributions to the definition of certainty was the introduction of the syllogism, a means by which the validity of a logical argument can be assessed.12 A syllogism is, in Aristotle’s own words, “an argument in which certain things being assumed [the premises], something different from the things assumed [the conclusion] follows from necessity by the fact that they hold.” What kinds of things can be “assumed”? The famous examples, although not used by Aristotle himself, are “All men are mortal” and “Socrates is a man.” Both premises seem fully tenable. No one has come up with an example of a man who has not died; it is part of the condition of being human. Similarly, anyone who met Socrates would have agreed that he was a man. From these two assumptions could be drawn the conclusion: “Therefore Socrates is mortal.” Aristotle went further, replacing the subjects of the assumptions with letters, so that it follows if all As are B, and C is an A, then C is B. One can substitute any suitable premises to create a valid conclusion. Aristotle goes on to explore the cases where the logic does not work. “A dog has four feet” and “A cat has four feet” are both reasonable assumptions to make from one’s experience of dogs and cats in everyday life, but it does not follow that a cat is a dog, and the student in logic has to work out why this is so. “All fish are silver; a goldfish is a fish; therefore a goldfish is silver” cannot be sustained because the example of a living goldfish would itself show that the premise that “All fish are silver” is not true.

Aristotle’s syllogisms can take us only so far; their premises have to be empirically correct and relate to each other in such a way that a conclusion can be drawn from their comparison. They provide the basis for deductive argument, an argument in which a specific piece of knowledge can be drawn from knowledge already given. The development of the use of deductive proof was perhaps the greatest of the Greeks’ intellectual achievements. Deductive argument had, in fact, already been used in mathematics by the Greeks before Aristotle systematized it. In an astonishing breach of conventional thinking, the Greeks conceived of abstract geometrical models from which theorems could be drawn. While the Babylonians knew that in any actual right-angled triangle the square of the hypotenuse equals the sum of the squares of the other two sides, Pythagoras’ theorem generalizes to show that this must be true in any conceivable right-angled triangle, a major development both mathematically and philosophically. A deductive proof in geometry needs to begin with some incontrovertible statements, or postulates as the mathematician Euclid (writing c. 300 B.C.) named them. Euclid’s postulates included the assertion that it is possible to draw a straight line from any point to any other point and that all right angles are equal to each other. His famous fifth postulate stipulated the conditions under which two straight lines will meet at some indefinite point. (It was the only one recognized as unprovable even in his own day and eventually succumbed to the analysis of mathematicians in the nineteenth century.) Euclid also recognized what he termed “common notions,” truths that are applicable to all sciences, not merely mathematics, such as “If equals be added to equals, the wholes are equal.” These postulates and “common notions” might seem self-evident, but in his Elements, one of the outstanding textbooks in history, Euclid was able to draw no less than 467 proofs from ten of them, while a later mathematician, Apollonius of Perga, was to show 487 in his Conic Sections. As Robert Osserman has put it in his Poetry of the Universe:

In a world full of irrational beliefs and shaky speculations, the statements found in The Elements were proven true beyond a shadow of a doubt . . . The astonishing fact is that after two thousand years, nobody has ever found an actual “mistake” in The Elements— that is to say a statement that did not follow logically from the given assumptions.13

Later mathematicians, such as the great Archimedes (see below, p. 43), were to develop new branches and areas of mathematics from these foundations.

Dealing with the natural world is a much more complex business. It seems to be in a constant state of change—the weather changes, plants grow, wars happen, men die. As Heraclitus had observed, all is in a process of flux. Yet if an underlying order can be assumed and isolated, then some progress can be made. Such progress assumes that the gods do not disturb the workings of the world on pure whim (as they do, for instance, in prescientific thinking—if the gods can intervene to change the course of the stars or the boiling point of water at random, for instance, then nothing is predictable). The next task is to isolate cause and effect, the forces that cause things to happen in a predictable way. One finds an excellent example of this process in the Histories of Herodotus (probably written in the 430s B.C.). Herodotus starts his famous survey of Egypt (book 2) with speculation on the causes of the annual Nile floods. He considers three explanations which, he tells us, others have put forward. One is that the summer winds force back the natural flow of the water, and as they die down a larger volume of water is released in compensation. This cannot be true, he notes, because the floods occur even in years when the winds do not blow. Moreover, no other rivers show this phenomenon. The second explanation is that the Nile flows from an ocean that surrounds the earth. This is not a rational explanation, says Herodotus; it can only be legend. Probably Homer or some other poet (he says somewhat scornfully) introduced the idea. The third explanation is that it is melting snows that cause the floods, but surely, says Herodotus, the further south you go the hotter it gets, as the black skins of the “natives” suggest. Snow would never fall in such regions. He goes on to provide an elaborate explanation of his own, based on the sun causing the Nile to evaporate just at a time when rainfall is low, so creating an artificially low volume of water in comparison to which the normal flow is a “flood.” He misses the true cause, the heavy summer rains that run down from the mountains of Ethiopia, but even if he reaches the wrong answer, Herodotus is aware of and consciously rejects mythological explanations. He uses observation and reason to discard some explanations and formulate others. Here is the process of “scientific” thinking at work.14

One of the most famous early “scientific” texts relates to epilepsy. Epilepsy had traditionally been known as “the sacred disease,” because its sudden onset and violent nature suggested an act of the gods, yet in a text attributed to Hippocrates, probably from the early fourth century B.C., the writer states:

I do not believe that the so-called “Sacred Disease” is any more divine or sacred than any other diseases. It has its own specific nature and cause; but because it is completely different from other diseases men through their inexperience and wonder at its peculiar symptoms have believed it to be of divine origin . . . [yet] it has the same nature as other diseases and a similar cause. It is also no less curable than other diseases unless by long lapse of time it is so ingrained that it is more powerful than the drugs that are applied. Like other diseases it is hereditary . . . The brain is the cause of the condition as it is of other most serious diseases...15

Here we have not only the specific rejection of the divine as a cause but a sophisticated attempt based on observation to say something about the real nature of epilepsy, its causes and its cures. It should be stressed, however, that the rejection of divine intervention did not mean a rejection of the gods themselves. The famous Hippocratic oath, which probably dates from the beginning of the fourth century, requires the physician to swear by the gods Apollo, Asclepius and Asclepius’ two daughters, Hygeia and Panacea. It was rather that the sphere of activity of the gods was diminished and there was greater reluctance, at least among intellectuals, to see natural events as caused by them. Alternatively, they could be seen as the forces that set in motion the regularity with which the natural world operates.

In dealing with the natural world, whether it be the universe, material objects such as earth and water, plants, animals or human beings themselves, the Greeks assumed, as a starting point, that there was an underlying order to all things. Their self-imposed task was to find out what this was for each discipline. In astronomy the Greeks made three assumptions: that the earth was at the centre of the universe, that the stars moved around it in a regular way, and that their movement was circular. In medicine the Greeks admitted that it was difficult to find a fundamental principle behind the working of so complex an organism as the human body, but they nevertheless began from the premise that the body (like the ideal city) tended towards eunomie—in this context, good health—and so illness suggested some aberration in the normal working of things. (The greatest physician of all, Galen, did attempt to base medical knowledge on incontrovertible, geometrical-style proofs but understandably ran into philosophical difficulties.) 16 These assumptions were only a starting point. There had then to be the gathering of empirical evidence, observations of the stars or the working of the body, so that explanations could be made. There were immense difficulties in this. Herodotus could never have reached the source of the Nile. In astronomy one had only the naked eye with which to observe the universe and rudimentary methods of preserving accurate recordings over time, although matters were helped when the findings from many centuries of observation by the Babylonians reached the Greek world in the third century B.C. Similarly in medicine, much could not be observed because a living body’s internal organs could not be seen functioning.

What is remarkable is how much the Greeks did achieve. In astronomy, for instance, of their three assumptions about the universe, one was false (that the sun revolves around the earth), but they were right in seeing a predictable pattern of behaviour in the stars, which for the planets at least was circular. Observations of the shadow of the earth on the moon convinced the Greeks that it was a sphere,17 and their assumption that the earth was at the centre of the universe was not based on ignorance or lazy thinking but was established after serious examination of the alternatives. If the earth was moving around the sun (as Aristarchus hypothesized early in the third century B.C.), then surely its relationship with the stars would change more radically over time. (The Greeks could not conceive that the stars were as far from the earth as they really are.) If the earth spun on its axis (as Heracleides of Pontus proposed in the fourth century), why were the clouds, which could be assumed to be stationary in relationship to the moving earth, not seen to be “left behind” as it spun round? Both reason and experience seemed to confirm the Greek view of an earth-centred universe. In time, of course, science would challenge this “common sense” perception of things.

Perhaps the most impressive feature of Greek astronomy is its ingenuity. It was clear that some stars did not appear to follow a regular course. They were termed planetes, the wanderers. Sophisticated attempts were made to give them regular movements that comprehended their observed wanderings in line with the assumption that their movement was circular. One hypothesis was that each planet moved around the circumference of a circle whose own centre was moving in a circle around the earth. As more records were made, such hypotheses became more and more elaborate, the most sophisticated being those of Ptolemy in the second century A.D. They were, of course, erroneous because the original assumption that the planets revolve around the earth was wrong. However, had the Greek intellectual tradition survived, it is easy to imagine that someone in ancient times might have taken the mass of observations, applied them to Aristarchus’ hypothesis that the sun was the centre of the solar system and the conclusion—that the earth and the planets revolve around the sun—would have fallen elegantly into place, as it did for Copernicus many centuries later. The very elegance of the solution would have, to the Greeks, confirmed that it was likely to be correct. In line with much of Greek thinking, the view that the earth was the centre of the universe remained an assumption, not an article of faith.

Greek astronomy was not confined to the observation of the planets and their motions. It was the combination of these observations with sophisticated mathematical calculation that was truly impressive. One of the most remarkable achievements of Greek astronomy was Hipparchus’ definition of the precession of the equinoxes in the second half of the second century B.C. As the earth is not an exact sphere its axes oscillate slightly. This oscillation causes a consistent shift in its position as a viewing platform, but the shift is so slight that it takes nearly 26,000 years, at a rate of roughly a degree every seventy years, for the earth to complete a circuit back to its original position. Using the naked eye, earlier observations from Babylonia and his own instruments for marking the position of the stars, Hipparchus noted the tiny shift, and his calculation of it as a degree every hundred years was remarkably accurate considering the primitive nature of his technology. Aristarchus calculated the relative sizes and distances of the sun and the moon by observing the full and half moons in relation to the sun, and Eratosthenes’ calculation of the circumference of the earth was possibly within 200 miles (320 kilometres) of the true figure. In all these cases mathematics, including for the first time trigonometry, was being put to practical use by being combined with meticulous observation. 18

Astronomy provides only one example of the Greeks’ search for “the truth.” Their concerns spread to every aspect of knowledge. It is in the nature of man, according to Aristotle, to be curious. Aristotle (384–322 B.C.) arrived in Athens from the northern Aegean (his father had been court physician to the king of Macedon and legend records that he himself was later tutor to Alexander “the Great”). His Macedonian connections made him vulnerable in Athens (for reasons which will become clear in chapter 4), and he travelled widely. He is found probing into every area of intellectual activity, exploring the ultimate nature of things, the ends of human life, the best form of government, the variety of animal life, the importance of tragedy, the nature of rhetoric, the problems of logic. His method was to master what had been said on any subject before, freely criticizing ideas he found inadequate and isolating the questions that needed to be answered. He would move forward himself only after accumulating as much empirical evidence as he could. So his work on zoology included studies of animal life that ranged from the European bison to the mite and from octopuses to oysters. When he was working out his views on the best form of government, he assembled details of 158 Greek constitutions. He speculated more profoundly than anyone before him on the nature of living organisms, exploring their essence, the essential features which made each distinct from other species, and the purpose of each species, which, in Aristotle’s philosophy, was central to its identity. 19

While Aristotle believed that an underlying unity would be found to all knowledge, he accepted that in the present state of knowledge much must remain provisional and unsure. Take, for example, a difficult question in the natural world, how to differentiate between “plants” and “animals.” A dogmatic scientist might have drawn up some arbitrary rules and simply classified each organism as one or the other. Aristotle realized that this was to avoid the real issue. He took some examples from the marine world, the sponge, the jellyfish, sea anemones, razor shells. He noted that when a sponge was pulled from a rock to which it was attached, it reacted by clinging to the rock. So perhaps it was some kind of animal. Yet it could not live detached from a rock, as an animal would. Jellyfish, on the other hand, lived as detached organisms but did not, so far as Aristotle could see, have any perception. They are like plants but, unlike other plants, do not stay attached to a base. Should one create a separate category, “plants which are detached,” or does one accept that it is possible to be an animal without having perception? Aristotle’s genius lay in realizing that these issues had to be worked out undogmatically, that observation had to continue and that sometimes the boundaries between categories would have to be redrawn as a result. In the natural world one could seldom, perhaps never, talk with absolute certainty in the face of the mass of living organisms that had to be categorized. It was this openness to the provisional nature of knowledge that helps make Aristotle one of the truly great philosophers.20

Aristotle also firmly believed that knowledge would be cumulative from generation to generation, and this process was supported by the competitive nature of Greek science. Take, for example, the idea of spontaneous generation. Aristotle first posited the concept after he had tried in vain to find out how eels spawned. He could find elvers, young eels, but no sign of what they grew from. The answer was straightforward if remarkable—eels spawned in the Bermudas and the young swam back to Europe—but, of course, this was well beyond any possibility of discovery in the fourth century B.C. The act of spawning was not observed for the first time until the 1920s. So the idea of spontaneous generation, from mud in the case of eels, was one possibility. Aristotle’s successor Theophrastus took the matter further. He examined many different cases of apparent spontaneous generation in plants and showed that, in fact, there were often tiny seeds from which plants grew. He noted too that spontaneous generation seemed to take place when earth was warmed. Even though he could not grasp the importance of this as we can today, he still recorded it as part of his investigation. He concluded by leaving the issue open: “More accurate investigation must be made of the subject and the matter in which spontaneous generation takes place be thoroughly inquired into . . . This is why an experienced person is needed to gather it [the evidence], who has the ability to observe the proper season and recognise the seed itself.” For Theophrastus it remained a possibility that every form of apparently spontaneous generation would one day be explained, although he insisted that the concept remain in place until it was actually disproved by empirical observation. He was also insistent on the importance of professional expertise, another important development in the history of science.21

Crucially, Theophrastus was not prepared to accept the views of even such a great scientist as Aristotle (who also happened to be an associate of his) uncritically. He actively sought out explanations (the tiny seeds) that might undermine Aristotle’s suggestion. This was fundamental to the nature of Greek science. It was essentially competitive, with each scientist not only building on earlier observations but seeking to outdo his predecessors. Geoffrey Lloyd sums up its distinctive nature:

The extant remains of Egyptian and Babylonian medicine, mathematics and astronomy can be combed in vain for a single example of a text where an individual author explicitly distances himself from, and criticises, the received tradition in order to claim originality for himself, whereas our Greek sources repeatedly do that.22

Lloyd gives a wide range of examples from medical treatises where an author explains what he believes, the observations on which the belief is based and why it differs from what has been believed before. Anyone, even an Aristotle, could be challenged by anyone who comes after. There can be certainty, in mathematics for instance, but this is based on postulates on which all agree. For the most part, and so far as the natural world is concerned, knowledge is always provisional, not restricted to an elite, and it grows as a result of “democratic” collaboration (see the quotation from Aristotle at the beginning of the chapter) and competition.23 This was the mainstream of Greek intellectual tradition. One had to distinguish between what could be known for certain and what could not be and develop tests or methods of argument that could be universally accepted. The Greeks had recognized that science is as much concerned with proving things false as with proving them true. Overall, this was a staggering achievement. In isolating and systematizing rational thought, the Greeks had founded science and mathematics in the form they are still followed today without implying that rational thought was the only path to truth. None of this would have been possible without an atmosphere of intellectual tolerance.

When the Greeks wrote about science, mathematics or any kind of systematic enquiry, including history or geography, they called their text a logos, or reasoned account. Logoi were typically written in prose, and their language reflected the nature of the task.24 The word logos itself, one of the most complex in Greek philosophy, came to take on other meanings, including “reasoned thought” itself. It was to re-emerge in a Christian context as “the Word” of God, although the relationship between God’s Word and reason itself was to prove problematic. The Greeks contrasted logos with muthos, an account in which reason plays no part. An obvious use of muthos is in telling a story about the gods (hence “myth”) or relating a narrative poem, and, in contrast to logoi, myths were normally related in verse. The important point to make is that myths were not devalued by the emergence of logoi. The Greeks realized that telling a story has its own uses far beyond entertainment and fulfills important emotional needs. Many cities focused their identity on foundation myths, which they used to foster the pride of their citizens.25 Myths were also used to underpin rituals at times of individual transition, from virginity to marriage, for instance. Perhaps the most sophisticated way in which the Greeks used myths was through tragic drama. Here a dilemma, based on the story lines of ancient myths, was presented in a play and acted through so that the consequences of the characters choosing one solution rather than another could be assessed by an audience, a truly democratic way of airing ethical issues. In his Poetics Aristotle argued that the purpose of tragic drama was to arouse pity and fear in the audience to give them some form of emotional catharsis, an experience which would make them more complete human beings.26

Aristotle’s support for the use of myth for human ends emphasizes that there is no necessary conflict between logos and muthos. Each has its value in its own context and neither threatens the other. One should not search for any form of absolute truth, in the sense of a belief whose certainty could be justified, in muthoi. Similarly, one should not use the word logos of truths that could not be defended by reasoned argument. Such a relaxed attitude to myth meant that the Greeks were tolerant and open about developing new stories about the gods and were able to speculate about their powers and attributes, even their very nature, without any sense of impropriety. Could the nature of the gods be grasped at all, asked Protagoras in the fifth century, in view “of the difficulty of the subject and the brevity of men’s lives”? Why should humans give the gods human form? asked the poet and natural philosopher Xenophanes; on this analogy horses would see their gods as horses. It is just as likely, Xenophanes went on, that there were gods, or even a single supreme divine figure, of a totally different nature from humanity. For Aristotle, reason suggested that there is a supreme “unmoved mover.” “Since motion must always exist and must not cease, there must necessarily be something eternal, either one thing or many, that first initiates motion, and this first mover must be unmoved.” Others suggested there were no gods at all. The world is totally material, argued the Atomists, with all matter being made up of tiny particles, atoms, literally “that which cannot be cut.” These more extreme forms of atheism did arouse concern. There remained a residual fear, certainly found among the population of Athens, for instance, that if the gods were rejected outright they might retaliate by withdrawing their patronage of the city. Sometimes this fear would erupt into intolerance, as in the case of Socrates, who was executed in Athens in 399 B.C. For the most part, however, Greek religion was undogmatic, its theology ever in flux. Myths and rituals were so interwoven into everyday life that no need was felt for an institutional hierarchy to defend them.27 Arguments over the divine were never restrained by doctrinal orthodoxy.

Although the achievement of the Greeks in establishing an atmosphere of tolerance in which considerable intellectual progress proved possible was remarkable, one should not idealize. We have already noted the difficulties in gathering empirical evidence and the way in which this limited what it was possible to know. Interpretation of empirical evidence also takes place within an ideological context. It was easy to rationalize from the observations of the human body that men were the active sex and women the passive, and the Hippocratic texts which concentrate on the diseases of women show how they were classified as “other” and how their organs, their “soft” flesh and their need to menstruate were explored within the context of male superiority. In her Hippocrates’ Woman: Reading the Female Body in Ancient Greece, Helen King shows how these attitudes persisted in the field of gynaecology (in the sense of a male profession telling women how they should regulate their bodies) well into modern times.28 Similarly, Aristotle links a hot climate to indolence and goes on to argue that those born in such regions are naturally slaves, available to the more active peoples, such as the Greeks, who have grown up in a relatively temperate environment. And it has to be remembered that even this level of “rational” thought was alien to most Greeks, who, it can be assumed, were oblivious to the sophisticated discussions of their educated peers. Irrationality flourished in the Greek world, much as it does, alongside scientific thinking, in ours.

The expanding use of rational thought can be seen as a symbol of the self-confidence of the Greeks, yet it was also fully accepted that human self-confidence had to be set within limits—no man should pretend he was a god. One reason, argues Herodotus, why the Persian king Xerxes was defeated when he invaded Greece in 480 was that his attempt to build a bridge across the Hellespont and to cut through a peninsula was an arrogant defiance of the natural order. He deserved his humiliation at the hands of the Greeks. Haughty behaviour (ate) or the deliberate humiliation of others ( hubris) were taboo. Such behaviour deserved the greatest humiliation of all, expulsion from the perpetrator’s native city, in addition to divine condemnation.

In his play Antigone, Sophocles summed it up:

Wonders are many and none more wonderful than man . . .

In the meshes of his woven nets, cunning of mind, ingenious man . . .

He snares the lighthearted birds and the tribes of savage beasts, and the creatures of the deep seas . . .

He puts the halter round the horse’s neck

And rings the nostrils of the angry bull.

He has devised himself a shelter

against the rigours of frost and the pelting rains.

Speech and science he has taught himself, and artfully formed laws for harmonious civic life . . .

Only against death he fights in vain.

But clear intelligence—a force beyond measure— moves to work both good and ill . . .

When he obeys the laws and honors justice, the city stands proud . . .

But man swerves from side to side, and when the laws are broken, and set at naught, he is like a person without a city, beyond human boundary, a horror, a pollution to be avoided.29

The closing lines of this famous speech are a reminder that the great achievements of the Greeks in the use of rational thought have to be set within the wider context of their views of just government and correct moral behaviour. How the Greek philosophers tackled this problem is the subject of the next chapter.

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