[The author is the Delta Kappa Epsilon Distinguished Professor of Philosophy at the University of North Carolina.]

I am about to introduce you to one of the handful of really great thinkers the world has produced -- Heraclitus of Ephesos, and, in a lesser way, to three of his predecessors -- Thales, Anaximander, and Anaximenes, all of whom hailed from Miletus, which, like Ephesos, is on the Ionian coast of Asia Minor.

Together these Ionian thinkers of the sixth and late fifth centuries brought about one of the most significant revolutions we know of, one that set the civilized world on a path that -- with minor and not so minor deviations -- it has followed ever since. What they did, to put it boldly and over simply, was to invent critical rationality; for the theories they advanced, whether on the nature and origins of the cosmos or on ethics and politics, were not offered as gospels to be accepted on divine or human authority or, like Hesiod’s cosmology, on the authority of the Muses but as rational products to be accepted or rejected on the basis of evidence and argument. Every university and college, every intellectual discipline and scientific advance, every step towards freedom and away from ignorance, superstition, and enslavement to repressive dogma is eloquent testimony to the power of their invention. If they had not existed, our world would not exist.

Of these thinkers Thales of Miletus on the Ionian coast of Asia Minor was the first. His reputation in antiquity was immense. He was one of the fabled Seven Sages (Solon was another). He is credited with being able to predict solar eclipses and with determining the height of the pyramids by measuring the length of their shadows. Whether he wrote anything is unknown. If he did, no genuine fragment of it has survived. But despite the fact that we possess none of Thales’ original words, we do know that he held that everything is water (or something to that effect).

The first thing to notice about this claim is that it is monistic. It says that there is really only one thing -- water -- and that everything else is in some way made up of or built out of it. We do not know precisely why Thales assigned such a fundamental role to water, but the following suggestions (among others) have been made: (1) he noticed that water is essential in various ways to the existence of living things (Aristotle, Metaphysics 983b22-7); (2) he noticed that water alone exists naturally as a solid, liquid, and gas, which suggested that it might be the fundamental stuff. Now if Thales did indeed take either of these routes to his watery monism, then his doctrine is a lovely prototype of many fundamental scientific doctrines. It is based (no doubt somewhat loosely) on evidence and argument and it suggests that a single thing underlies and explains the apparent diversity of phenomena. Modern scientists who claim that everything is mass-energy or that space-time is the only real thing are heirs to Thales.

Two ancient stories about Thales are worth repeating because of the somewhat different light they cast on early philosophy. The first is recounted in Plato’s Theaetetus:

• Thales was studying the stars and gazing aloft when he fell into a well; a witty and amusing Thracian servant-girl made fun of him because, she said, he was wild to know about what was up in the sky but failed to see what was in front of him and under his feet. The same joke applies to all who spend their life in philosophy. (174a).

The second story might be thought of as Thales’ response to the servant-girl. It is found in Aristotle’s Politics:

• The story goes that some people reproached Thales for being poor, on the grounds that it showed his philosophy was useless. But because of his knowledge of the stars, he realized there would be a bumper crop of olives in the following year. So, while it was still winter, he raised a little money and used it to secure all the olive presses in Miletus and Chios for future lease. He got them at a low rate because no one bid against him. When the olive season came, and the demand for olive presses was suddenly very heavy, he was able to sub-lease them at whatever rate he chose. He made a lot of money, thereby showing that philosophers could easily become wealthy if they wished, but that this is not something they care much about. (I.11 1259a)

The moral of the story is that apparently arcane knowledge can have important practical uses, that philosophy can help us to live well, and that we neglect it at our peril (see Plato, Republic 487d ff.).

Anaximander, a younger contemporary of Thales, is the first Greek whom we know to have produced a written account concerned with the natural world. Only a few words of it have survived, but ancient writers who possessed more of it give us a vivid idea of its astonishing scope. It contained a cosmogony or account of the origins of the cosmos; an account of the origins of life; astronomical, meteorological, and biological speculations; and a map of the known world. Our primary interest is in Anaximander’s most general explanatory doctrine, but a brief glimpse at two other views he espoused reveal something of his depth and range.

The first of these concerns the origin of human beings:

• [Anaximander] also declares that in the beginning humans were born from other kinds of animals, since other animals quickly manage on their own, and humans alone require lengthy nursing. For this reason, if they had been like this in the beginning, they would not have survived. (pseudo-Plutarch Stromata 2 = DK 12A10)

Here an observation coupled with an insightful piece of argument leads to a daring hypothesis: Human beings were not made by gods they came from other animals.

The second piece of Anaximandrian speculation noteworthy for its originality concerns the ancient question of what holds up the earth. Thales seems to have held that the earth is foating on water -- "as if the same question did not arise . . . for the water supporting the earth" (Aristotle, De Caelo 294a32-3). Perhaps aware of this defect in Thales’ answer and in other similar ones, Anaximander proposed a different kind of answer altogether:

• Some, like Anaximander . . . declare that the earth is at rest on account of its similarity. For it is no more fitting for what is established at the center an equally related to the extremes to move up rather than down or sideways. And it is impossible for it to make a move simultaneously in opposite directions. Therefore, it is at rest of necessity. (Aristotle, De Caelo 2.13 295b11-13 = DK 12A26)

The earth is not held up by something else. It does not move because there is nothing to cause it to move in one way rather than another. The cleverness of this answer is obvious, since it heads off the kind of criticism that Aristotle is able to bring against Thales.

I turn now to Anaximander’s fundamental doctrine, to his claim about everything:

• Of those who declare that the principle (archê) is one, moving, and unlimited (apeiron), Anaximander . . . said that the unlimited was the first principle and element of the things that are . . . He says that the principle is neither water nor any other of the things called elements, but some other nature which is unlimited, out of which come to be all the heavens and the worlds in them. This is eternal and ageless and surrounds all the worlds.

The fundamental stuff out of which everything else is made or comes to be isn’t any of the four recognized elements -- earth, water, fire, and air (or dry, wet, hot, and cold) -- but a fifth thing, the unlimited. Why? According to Aristotle (Physics 3.1 204b22-9 = DK 12A16) Anaximander argued as follows: If everything is water, then everything must have the properties of water. But not only do some things lack these properties, some even have properties that are opposite to those possessed by water. Earth is not only not wet, it is dry. Since nothing can be both wet and dry, how can dry earth just be some form of wet water? how can what just is wet water become dry? This is a powerful argument for thinking that if there is a single stuff of which all things (including the elements) are made, it cannot have any definite characteristics of its own.

More significantly, this Anaximandrian argument is a telling criticism of his predecessor, Thales. Hence it is a good example of the critical rationality I praised the Greek philosophers for inventing. Anaximander did not accept Thales’ doctrines on his authority or -- as we are asked to accept Hesiod’s cosmogony -- on the authority of the Muses, rather he submitted them to rational scrutiny, modifying those that failed to pass muster and accepting only those that did. In the Nicomachean Ethics, as he is about to criticize the doctrines of his own teacher Plato, Aristotle recommends this as the appropriate attitude for a philosopher to take to his forebears:

• It presumably seems better, indeed only right, to destroy even what is close to us if that is the way to preserve the truth. And we must especially do this when we are philosophers, [lovers of wisdom]; for though we love both the truth and our friends, piety requires us to honour the truth first. (I.6 1096a)

Paradoxically, then, it is by destroying Thales’ doctrines rather than by accepting them unquestioningly that Anaximander reveals himself as Thales’ true heir.

In addition to criticizing Thales’ doctrines, Anaximander made an important suggestion about what causes the elements to interact, and so to give rise to the things we see around us:

• The things that are perish into the things out of which they come to be, according to necessity, for they penalty and retribution to each other for their injustice in accordance with the ordering of time, as [Anaximander] says in rather poetical language. (Simplicius, Commentary on Aristotle’s Physics 24.18-21 = DK12B1 = A9)

His idea seems to be that elements, conceived of as opposite powers (dry, wet, hot, and cold) struggle with one another, sometimes one gaining the upper hand, sometimes another. When this happens the balance or equilibrium of the cosmos is disturbed: One opposite has gained "unjustly" at the expense of another and must of necessity -- or because of the laws governing the cosmos -- pay reparation to it in due course, so that equilibrium is restored once more. No doubt this is, as Simplicius says, "rather poetical," but it certainly shouldn’t be written off on that account, for it contains the fundamentally important notion that the natural world is governed by necessity (by law) not by the arbitrary whim of the gods, and is therefore intelligible and potentially explicable and manageable.

Anaximander’s follower, Anaximenes, developed Anaximander’s account of the elements and introduced significant economies into it. In Anaximander’s cosmology, there are four elements (earth, water, fire, and air) as well as the somewhat mysterious unlimited, whose relation to them is not fully explained. Thus Anaximander has five fundamental things in his ontology (on his list of what there really is). Anaximenes seems to have realized that the unlimited was unnecessary baggage, that one of the elements could play its role. He claimed that air is the fundamental principle of everything, and that earth, water, and fire are simply air which is to different degrees either rarified or condensed. Earth is very dense air; fire is very rarified air:

• The form of air is the following: when it is most even, it is invisible, but it is revealed by the cold and the hot and the wet, and movement. . . . For when it is dissolved into what is finer, it comes to be fire, and on the other hand air comes to be winds when it becomes condensed. Cloud results from air through felting [i.e. through becoming denser], and water when this happens to a greater degree. When condensed still more it becomes earth and when it reaches the absolutely densest stage it becomes stones. (Hippolytus, Refutation 1.7.1-3 = DK 13A7)

Thus Anaximenes’ theory is at once simpler and more complete than Anaximander’s. It needs only one thing -- air -- where Anaximander’s needs five, and it explains in a straightforward way, what Anaximander leaves mysterious, namely, how the one fundamental stuff can give rise to the other elements that appear in the world. This makes it a better theory and makes its development another good example of critical rationality -- or of a critically rational tradition -- in operation.

The next step in this line of argument was taken by Heraclitus of Ephesus (also on the Ionian coast of Asia Minor) -- a consummate thinker and writer, if a rather difficult one. In the following fragments, he speaks of the birth of one element as the death of another.

• It is . . . death to water to become earth, but from earth comes water and from water soul. (McK 10.74 = DK B36)

  Fire lives the death of earth and air lives the death of fire, water lives the death of air, earth that of water. (McK 10.76* = DK 76)

If we set out the claims they make in a table, we can see that they describe the same series of transformations familiar from Anaximenes:
 

DEATH OF	=	BIRTH OF
Fire		Air	B76
Air		Water	B76
Water		Earth	B36
Earth		Water	B36

Notice that the transformations are cyclical:

• Road A: fire Þ air Þ water Þ earth

  Road B: earth Þ water Þ air Þ fire

Thus when the entire cycle is complete what started as fire ends up being fire again.

Two questions naturally arise about this cycle of transformations: What causes it to occur? And what happens to fire (say) when it is caused to become air? Anaximander’s answer to the first question, couched in appropriate terms, is that strife between the opposites causes the transformations on Road A (the "downward" road), and that justice causes the transformations on Road B (the "upward" road). Heraclitus adopts this answer but sees that it can be simplified without loss of explanatory power. He sees that because the transformations are cyclical, we do not need two forces -- strife and justice -- to drive it, but only one. Hence he tells us that "justice is strife" (McK 10.83 = DK B80), that "the road up and the road down are one and the same" (McK 10.63 = DK 60), and that "the beginning and end are common on the circumference of a circle" (McK 10.67 = DK 103). Thus the force which transforms fire into air also transforms air back into fire. (This Heraclitean criticism of Anaximander is a model of critical scientific rationality at work. Physicists such as Steven Weinberg or Murray Gell-Mann who look for Grand Unified Theories in which gravitational, electromagnetic, and weak and strong forces are unified are heirs to Heraclitus.)

To see how Heraclitus answered the question about what happens to fire when strife causes it to become air, we must begin, as he surely did with Anaximenes. On Anaximenes’ view elements change into one another by becoming more rarified or more condensed. But this account is uneconomical because it introduces a new primitive notion -- rarefaction/ condensation -- over and above the original four elements. Heraclitus seems to have noticed this defect in Anaximenes’ theory and tried to rectify it. On his view all that happens when fire is transformed into air is that it dies down. Thus Road A (the "downward" road) is the progressive dying down of fire and Road B is its progressive re-kindling. Thus only fire "being kindled in measures and being extinguished in measures" (McK 10.77 = DK B30) is needed to explain how strife (justice) causes the elements to be transformed into one another, so that their cyclical transformations are simply "the turnings of fire" (McK 10.75 = DK B31).

But why does Heraclitus assign such a fundamental role to fire rather than to air or one of the other elements? Why does he identify the cosmos with "ever-living fire" (McK 10.77 = DK B30) rather than with ever-living air or ever-living water? Why is Road A the progressive dying down of fire rather than the progressive drying of the wet? To see a possible answer, we need to return to the first question we raised: What causes the elements to be transformed into one another? Anaximander’s answer was: Strife and justice. Heraclitus simplifies this to a single causal agent: Strife. But Anaximander does not tell us why the elements strive with one another in the first place. Strife enters the Alexandrian cosmos, as it were, from the outside; it is something extrinsic to, or over and above, the unlimited and the four elements. Strife, however, is intrinsic to a cosmos of fire. For fire is "want and satiety" (McK 10.85 = DK B65): it exists only when striving with what it is trying to burn; it simultaneously wants or needs fuel and is becoming hungry through consuming it. It is this dynamic feature, possessed by none of the other opposites, that most likely led Heraclitus to assign priority to it. It enables him to "reduce" strife to fire (since if fire exists so must strife) just as he has already reduced justice to strife.

One final theoretical advantage of fire deserves to be mentioned. Fire exists through striving with its fuel, but its striving is law governed or measured:

• Earth is poured out from sea, and is measured according to the same ratio it was before becoming sea. (McK 10.75 = DK B31)

After all, the size or heat of fire is proportional to the amount of fuel being consumed. Thus if fire is the fundamentally real thing, this offers an explanation of the order observed in such things as the seasons and the rising and setting of the sun.

There is no doubt that the monism that results from these reductions, is vastly more successful than any of the incipient monisms of his predecessors It is also fundamentally different in kind. Heraclitus does not tell us that the cosmos and all its contents are fundamentally fire, he tells us that they are fire "being kindled in measures and being extinguished in measures" (McK 10.77 = DK B30). This emphasizes the fact that what is fundamentally real for Heraclitus is not a static stuff to which change and activity are extrinsic, but a law-governed process or activity. Heraclitus thus differs from his predecessors, not simply in choosing fire rather than water, air, or the unlimited as his primary stuff, but in choosing law-governed change over static stability as being more fundamentally real. In the worlds of Thales, Anaximander, and Anaximenes change depends on stability; in Heraclitus’ world stability depends on change: "By Changing it is at rest" (McK 10.78 = DK B 84a).

Heraclitus’ powerful vision of the world will exert enormous influence over his successors, who will try in various ways to destroy, criticize, modify, and augment it. But it is not his theory so much as the spirit in which he offers it, that we have wanted to emphasize. He wasn’t the first to theorize in that spirit, he was part of a tradition of critical rationality that already existed. But he was the first to give explicit voice to that spirit:

• Listening not to me but to the logos (argument or account) it is wise to agree that all things are one. (McK 10.47 = DK B50)

This is the injunction that all the subsequent Greek philosophers you will meet follow. As students of Greek philosophy, it is an injunction we must strive to follow ourselves. If we do, we will be becoming what so many Greek philosophers thought was the best thing to be, critically rational human beings.

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