Essays on Ancient Greek Philosophy

John Burnet's Early Greek Philosophy:
Chapter 9: Leucippus of Miletus

171. Leucippus and Democritus

We have seen (§§ 31, 122) that the school of Miletus did not come to an end with Anaximenes, and it is a striking fact that the man who gave the most complete answer to the question first asked by Thales was a Milesian. It is true that the very existence of Leucippus has been called in question. Epicurus is reported to have said there never was such a philosopher, and the same thing has been maintained in quite recent times. On the other hand, Aristotle and Theophrastus certainly made him the originator of the atomic theory, and they can hardly have been mistaken on such a point. Aristotle was specially interested in Democritus, and his native Stageirus is not very far from Abdera, the seat of the Atomist school.

The question is intimately bound up with that of the date of Democritus, who said that he himself was a young man in the old age of Anaxagoras, a statement which makes it unlikely that he founded his school at Abdera much before 420 B.C., the date given by Apollodorus for his floruit. Now Theophrastus stated that Diogenes of Apollonia borrowed some of his views from Anaxagoras and some from Leucippus, which must mean that there were traces of the atomic theory in his work. Further, Diogenes is parodied in the Clouds of Aristophanes, which was produced in 423 B.C., from which it follows that the work of Leucippus must have become known before that date. What that work was, Theophrastus also tells us. It was the Great Diacosmas usually attributed to Democritus. This means further that what were known later as the works of Democritus were really the writings of the school of Abdera, and included, as was natural, the works of its founder. They formed, in fact, a corpus like that which has come down to us under the name of Hippocrates, and it was no more possible to distinguish the authors of the different treatises in the one case than it is in the other.

Theophrastus found Leucippus described as an Eleate in some authorities, and, if we may trust analogy, that means he had settled at Elea. It is possible that his emigration was connected with the revolution at Miletus in 450-49 B.C, In any case, Theophrastus says distinctly that he had been a member of the school of Parmenides, and his words suggest that the founder of that school was then still at its head. He may quite well have been so, if we accept Plato's chronology. Theophrastus also appears to have said that Leucippus "heard" Zeno, which is very credible. We shall see, at any rate, that the influence of Zeno on his thinking is unmistakable.

The relations of Leucippus to Empedocles and Anaxagoras are more difficult to determine. It has become part of the case for the historical reality of Leucippus to say that there are traces of atomism in the systems of these men; but the case is strong enough without that assumption. The chief argument for the view that Leucippus influenced Empedocles is that drawn from the doctrine of "pores"; but we have seen that this originated with Alcmaeon, and it is therefore more probable that Leucippus derived it from Empedocles. Nor is it at all probable that Anaxagoras knew anything of the theory of Leucippus. It is true that he denied the existence of the void; but it does not follow that anyone had already maintained that doctrine in the atomist sense. The early Pythagoreans had spoken of a void too, though they had confused it with atmospheric air; and the experiments of Anaxagoras with the klepsydra and the inflated skins would only have had any point if they were directed against the Pythagorean theory. If he had really wished to refute Leucippus, he would have had to use arguments of a very different kind.

172. Theophrastus on the Atomic Theory

Theophrastus wrote of Leucippus as follows in the First Book of his Opinions:

Leucippus of Elea or Miletus (for both accounts are given of him) had associated with Parmenides in philosophy. He did not, however, follow the same path in his explanation of things as Parmenides and Xenophanes did, but, to all appearance, the very opposite (R. P. 185). They made the All one, immovable, uncreated, and finite, and did not even permit us to search for what is not; he assumed innumerable and ever-moving elements, namely, the atoms. And he made their forms infinite in number, since there was no reason why they should be of one kind rather than another, and because he saw that there was unceasing becoming and change in things. He held, further, that what is is no more real than what is not, and that both are alike causes of the things that come into being for he laid down that the substance of the atoms was compact and full, and he called them what is, while they moved in the void which he called what is not, but affirmed to be just as real as what is. R. P. 194.

173. Leucippus and the Eleatics

It will be observed that Theophrastus, while noting the affiliation of Leucippus to the Eleatic school, points out that his theory is, prima facie, just the opposite of that maintained by Parmenides. Some have been led by this to deny the Eleaticism of Leucippus altogether; but this denial is really based on the view that the system of Parmenides was "metaphysical," coupled with a great reluctance to admit that so scientific a hypothesis as the atomic theory can have had a "metaphysical" origin. This is merely a prejudice, and we must not suppose Theophrastus himself believed the two theories to be so far apart as they seem. As this is really the most important point in the history of early Greek philosophy, and as, rightly understood, it furnishes the key to the whole development, it is worth while to transcribe a passage of Aristotle which explains the historical connection in a way that leaves nothing to be desired.

Leucippus and Democritus have decided about all things practically by the same method and on the same theory, taking as their starting-point what naturally comes first. Some of the ancients had held that the real must necessarily be one and immovable; for, said they, empty space is not real, and motion would be impossible without empty space separated from matter; nor, further, could reality be a many, if there were nothing to separate things. And it makes no difference if any one holds that the All is not continuous, but discrete, with its parts in contact (the Pythagorean view), instead of holding that reality is many, not one, and that there is empty space. For, if it is divisible at every point there is no one, and therefore no many, and the Whole is empty (Zeno); while, if we say it is divisible in one place and not in another, this looks like an arbitrary fiction; for up to what point and for what reason will part of the Whole be in this state and be full, while the rest is discrete? And, on the same grounds, they further say that there can be no motion. In consequence of these reasonings, then, going beyond perception and overlooking it in the belief that we ought to follow the argument, they say that the All is one and immovable (Parmenides), and some of them that it is infinite (Melissus), for any limit would be bounded by empty space. This, then, is the opinion they expressed about the truth, and these are the reasons which led them to do so. Now, so far as arguments go, this conclusion does seem to follow; but, if we appeal to facts, to hold such a view looks like madness. No one who is mad is so far out of his senses that fire and ice appear to him to be one; it is only things that are right, and things that appear right from habit, in which madness makes some people see no difference.

Leucippus, however, thought he had a theory which was in harmony with sense, and did not do away with coming into being and passing away, nor motion, nor the multiplicity of things. He conceded this to experience, while he conceded, on the other hand, to those who invented the One that motion was impossible without the void, that the void was not real, and that nothing of what was real was not real. "For," said he, "that which is strictly speaking real is an absolute plenum; but the plenum is not one. On the contrary, there are an infinite number of them, and they are invisible owing to the smallness of their bulk. They move in the void (for there is a void); and by their coming together they effect coming into being; by their separation, passing away."

In this passage Zeno and Melissus are not named, but the reference to them is unmistakable. The argument of Zeno against the Pythagoreans is clearly given; and Melissus was the only Eleatic who made reality infinite, a point which is distinctly mentioned. We are therefore justified by Aristotle's words in explaining the genesis of Atomism and its relation to Eleaticism as follows. Zeno had shown that all pluralist systems yet known, and especially Pythagoreanism, were unable to stand before the arguments from infinite divisibility which he adduced. Melissus had used the same argument against Anaxagoras, and had added, as a reductio ad absurdum, that, if there were many things, each one of them must be such as the Eleatics held the One to be. To this Leucippus answers, "Why not?" He admitted the force of Zeno's arguments by setting a limit to divisibility, and to each of the "atoms" which he thus arrived at he ascribed all the predicates of the Eleatic One; for Parmenides had shown that if it is, it must have these predicates somehow. The same view is implied in a passage of Aristotle's Physics. "Some," we are there told, "surrendered to both arguments, to the first, the argument that all things are one, if the word is is used in one sense only (Parmenides), by affirming the reality of what is not; to the second, that based on dichotomy (Zeno), by introducing indivisible magnitudes." Finally, it is only by regarding the matter in this way that we can attach any meaning to another statement of Aristotle's that Leucippus and Democritus, as well as the Pythagoreans, virtually make all things out of numbers. Leucippus, in fact, gave the Pythagorean monads the character of the Parmenidean One.

174. Atoms

We must observe that the atom is not mathematically indivisible, for it has magnitude; it is, however, physically indivisible, because, like the One of Parmenides, it contains no empty space. Each atom has extension, and all atoms are exactly alike in substance." Therefore all differences in things must be accounted for either by the shape of the atoms or by their arrangement. It seems probable that the three ways in which differences arise, namely, shape, position, and arrangement, were already distinguished by Leucippus; for Aristotle mentions his name in connection with them. This explains, too, why the atoms are called "forms" or "figures," a way of speaking which is clearly of Pythagorean origin. That they are also called phusis is quite intelligible if we remember what was said of that word in the Introduction (§ VII). The differences in shape, order, and position just referred to account for the "opposites," the "elements" being regarded rather as aggregates of these (panspermiai), as by Anaxagoras.

175. The Void

Leucippus affirmed the existence both of the Full and the Empty, terms which he may have borrowed from Melissus. He had to assume empty space, which the Eleatics had denied, in order to make his explanation of the nature of body possible. Here again he is developing a Pythagorean view. The Pythagoreans had spoken of the void, which kept the units apart; but they had not distinguished it from atmospheric air (§ 53), which Empedocles had shown to be a corporeal substance (§ 107). Parmenides, indeed, had formed a clearer conception of space, but only to deny its reality. Leucippus started from this. He admitted, indeed, that space was not real, that is to say, corporeal; but he maintained that it existed all the same. He hardly, it is true, had words to express his discovery in; for the verb "to be" had hitherto been used by philosophers only of body. But he did his best to make his meaning clear by saying that "what is not" (in the old corporealist sense) "is" (in another sense) just as much as " what is." The void is as real as body.

176. Cosmology

It might seem a hopeless task to disentangle the cosmology of Leucippus from that of Democritus, with which it is generally identified; but that very fact affords a valuable clue. No one later than Theophrastus was able to distinguish their doctrines, and it follows that all definite statements about Leucippus in later writers must, in the long run, go back to him. If we follow this up, we shall be able to give a fairly clear account of the system, and we shall even come across some views which are peculiar to Leucippus and were not adopted by Democritus.

The fuller of the doxographies in Diogenes, which comes from an epitome of Theophrastus, is as follows:

He says that the All is infinite, and that it is part full, and part empty. These (the full and the empty), he says, are the elements. From them arise innumerable worlds and are resolved into them. The worlds come into being thus. There were borne along by "abscission from the infinite" many bodies of all sorts of figures "into a mighty void," and they being gathered together produce a single vortex. In it, as they came into collision with one another and were whirled round in all manner of ways, those which were alike were separated apart and came to their likes. But, as they were no longer able to revolve in equilibrium owing to their multitude, those of them that were fine went out to the external void, as if passed through a sieve; the rest stayed together, and becoming entangled with one another, ran down together, and made a first spherical structure. This was in substance like a membrane or skin containing in itself all kinds of bodies. And, as these bodies were borne round in a vortex, in virtue of the resistance of the middle, the surrounding membrane became thin, as the contiguous bodies kept flowing together from contact with the vortex. And in this way the earth came into being, those things which had been borne towards the middle abiding there. Moreover, the containing membrane was increased by the further separating out of bodies from outside; and, being itself carried round in a vortex, it further got possession of all with which it had come in contact. Some of these becoming entangled, produced a structure, which was at first moist and muddy; but, when they had been dried and were revolving along with the vortex of the whole, they were then ignited and produced the substance of the heavenly bodies. The circle of the sun is the outermost, that of the moon is nearest to the earth, and those of the others are between these. And all the heavenly bodies are ignited because of the swiftness of their motion; while the sun is also ignited by the stars. But the moon only receives a small portion of fire. The sun and the moon are eclipsed ... (And the obliquity of the zodiac is produced) by the earth being inclined towards the south; and the northern parts of it have constant snow and are cold and frozen. And the sun is eclipsed rarely, and the moon continually, because their circles are unequal. And just as there are comings into being of the world, so there are growths and decays and passings away in virtue of a certain necessity, of the nature of which he gives no clear account.

As it comes substantially from Theophrastus, this passage is good evidence for the cosmology of Leucippus, and it is confirmed by certain Epicurean extracts from the Great Diacosmas. These, however, give a specially Epicurean turn to some of the doctrines, and must therefore be used with caution.

177. Relation to Ionic Cosmology

The general impression we get from the cosmology of Leucippus is that he either ignored or had never heard of the great advance in the general view of the world which was due to the later Pythagoreans. He is as reactionary in his detailed cosmology as he was daring in his general physical theory. We seem to be reading once more of the speculations of Anaximenes or Anaximander, though there are traces of Empedocles and Anaxagoras too. The explanation is not hard to see. Leucippus would not learn a cosmology from his Eleatic teachers; and, even when he found it possible to construct one without giving up the Parmenidean view of reality, he was thrown back upon the older systems of Ionia. The result was unfortunate. The astronomy of Democritus was still of this childish character. He believed the earth was flat and rested on the air.

This is what gives plausibility to Gomperz's statement that Atomism was "the ripe fruit on the tree of the old Ionic doctrine of matter which had been tended by the Ionian physiologists." The detailed cosmology was certainly such a fruit, and it was possibly over-ripe; but the atomic theory proper, in which the real greatness of Leucippus comes out, was wholly Eleatic in its origin. Nevertheless, it will repay us to examine the cosmology too; for such an examination will serve to bring out the true nature of the historical development of which it was the outcome.

178. The Eternal Motion

Leucippus represented the atoms as having been always in motion. Aristotle puts this in his own way. The atomists, he says, "indolently" left it unexplained what was the source of motion, and did not say what sort of motion it was. In other words, they did not decide whether it was a "natural motion" or impressed on them "contrary to their nature." He even said that they made it "spontaneous," a remark which has given rise to the erroneous view that they held it was due to chance. Aristotle does not say that, however; but only that the atomists did not explain the motion of the atoms in any of the ways in Which he himself explained the motion of the elements. They neither ascribed to them a natural motion like the circular motion of the heavens and the rectilinear motion of the four elements in the sublunary region, nor did they give them a forced motion contrary to their own nature, like the upward motion that may be given to the heavy elements and the downward that may be given to the light. The only fragment of Leucippus which has survived is an express denial of chance. "Naught happens for nothing," he said, "but everything from a ground and of necessity."

Speaking historically, all this means that Leucippus did not, like Empedocles and Anaxagoras, find it necessary to assume a force to originate motion. He had no need of Love and Strife or Mind, and the reason is clear. Though Empedocles and Anaxagoras had tried to explain multiplicity and motion, they had not broken so radically as Leucippus with the Parmenidean One. Both started with a condition of matter in which the "roots" or "seeds" were mixed so as to be "all together," and they therefore required something to break up this unity. Leucippus, who started with an infinite number of Parmenidean "Ones," so to speak, required no external agency to separate them. What he had to do was just the opposite. He had to account for their coming together, and there was nothing so far to prevent his return to the old idea that motion does not require any explanation at all.

This, then, is what seems to follow from the criticisms of Aristotle and from the nature of the case; but it is not consistent with Zeller's opinion that the original motion of the atoms is a fall through infinite space, as in the system of Epicurus. This view depends, of course, on the further belief that the atoms have weight, and that weight is the tendency of bodies to fall, so we must now consider whether and in what sense weight is a property of the atoms.

179. The Weight of the Atoms

As is well known, Epicurus held that the atoms were naturally heavy, and therefore fell continually in the infinite void. The school tradition is, however, that the "natural weight" of the atoms was an addition made by Epicurus himself to the original atomic system. Democritus, we are told, assigned two properties to atoms, magnitude and form, to which Epicurus added a third, weight. On the other hand, Aristotle distinctly says that Democritus held the atoms were heavier "in proportion to their excess," and, this seems to be explained by the statement of Theophrastus that, according to him, weight depended on magnitude. Even so, however, it is not represented as a primary property of the atoms in the same sense as magnitude.

It is impossible to solve this apparent contradiction without referring briefly to the history of Greek ideas about weight. It is clear that lightness and weight would be among the very first properties of body to be distinctly recognized as such. The necessity of lifting burdens must very soon have led men to distinguish them, though no doubt in a crude form. Both weight and lightness would be thought of as things that were in bodies. Now it is a remarkable feature of early Greek philosophy that from the first it was able to shake itself free from this idea. Weight is never called a "thing" as, for instance, warmth and cold are; and, so far as we can see, not one of the thinkers we have studied hitherto thought it necessary to give any explanation of it at all, or even to say anything about it. The motions and resistances which popular theory ascribes to weight are all explained in some other way. Aristotle distinctly declares that none of his predecessors had said anything of absolute weight and lightness. They had only treated of the relatively light and heavy.

This way of regarding the notions of weight and lightness is clearly formulated for the first time in Plato's Timaeus. There is no such thing in the world, we are told there, as "up" or "down." The middle of the world is not "down" but "just in the middle," and there is no reason why any point in the circumference should be said to be "above" or "below" another. It is really the tendency of bodies towards their kin that makes us call a falling body heavy and the place to which it falls "below." Here Plato is really giving the view taken more or less consciously by his predecessors, and it is not till the time of Aristotle that it is questioned. For reasons which do not concern us here, Aristotle identified the circumference of the heavens with "up" and the middle of the world with "down," and equipped the elements with natural weight and lightness that they might perform their rectilinear motions between them. As, however, Aristotle believed there was only one world, and did not ascribe weight to the heavens proper, the effect of this reactionary theory on his cosmical system was not great; it was only when Epicurus tried to combine it with the infinite void that its true character emerged. It seems to me that the nightmare of Epicurean atomism can only be explained on the assumption that an Aristotelian doctrine was violently adapted to a theory which really excluded it. It is totally unlike anything we meet with in earlier days.

This suggests at once that it is only in the vortex that the atoms acquire weight and lightness, which are, after all, only popular names for facts which can be further analyzed. We are told that Leucippus held one effect of the vortex to be that like atoms were brought together with their likes. Here we seem to see the influence of Empedocles, though the "likeness" is of another kind. It is the finer atoms that are forced to the circumference, while the larger tend to the center. We may express that by saying that the larger are heavy and the smaller light, and this will amply account for everything Aristotle and Theophrastus say; for there is no passage where the atoms outside the vortex are distinctly said to be heavy or light.

There is a striking confirmation of this view in the atomist cosmology quoted above. We are told there that the separation of the larger and smaller atoms was due to the fact that they were "no longer able to revolve in equilibrium owing to their number," which implies that they had previously been in a state of "equilibrium" or "equipoise." Now the word isorropia has no necessary implication of weight in Greek. A ropê is a mere leaning or inclination in a certain direction, which is the cause rather than the effect of weight. The state of isorropia is therefore that in which the tendency in one direction is exactly equal to the tendency in any other, and such a state is more naturally described as the absence of weight than as the presence of opposite weights neutralizing one another.

Now, if we no longer regard the "eternal motion" of the premundane and extramundane atoms as due to their weight, there is no reason for describing it as a fall. None of our authorities do as a matter of fact so describe it, nor do they tell us in any way what it was. It is safest to say that it is simply a confused motion this way and that. It is possible that the comparison of the motion of the atoms of the soul to that of the motes in a sunbeam coming through a window, which Aristotle attributes to Democritus, is really intended as an illustration of the original motion of the atoms still surviving in the soul. The fact that it is also a Pythagorean comparison so far confirms this; for we have seen that there is a real connection between the Pythagorean monads and the atoms. It is also significant that the point of the comparison appears to have been the fact that the motes in the sunbeam move even when there is no wind, so that it would be a very apt illustration indeed of the motion inherent in the atoms apart from the secondary motions produced by impact and collision.

180. The Vortex

But what are we to say of the vortex itself which produces these effects? Gomperz observes that they seem to be "the precise contrary of what they should have been by the laws of physics"; for, "as every centrifugal machine would show, it is the heaviest substances which are hurled to the greatest distance." Are we to suppose that Leucippus was ignorant of this fact, which was known to Empedocles and Anaxagoras? We know from Aristotle that all those who accounted for the earth being in the center of the world by means of a vortex appealed to the analogy of eddies in wind or water and Gomperz supposes that the whole theory was an erroneous generalization of this observation. If we look at the matter more closely, we can see, I think, that there is no error at all.

We must remember that all the parts of the vortex are in contact, and that it is just this contact (epipsausis) by which the motion of the outermost parts is communicated to those within them. The larger bodies are more able to resist this communicated motion than the smaller, and in this way they make their way to the center where the motion is least, and force the smaller bodies out. This resistance is surely just the antereisis tou mesou which is mentioned in the doxography of Leucippus, and it is quite in accordance with this that, on the atomist theory, the nearer a heavenly body is to the center, the slower is its revolutions That is just the point which, as we have seen, Anaximander would seem not to have observed. There is no question of "centrifugal force" at all, and the analogy of eddies in air and water is in reality quite satisfactory.

181. The Earth and the Heavenly Bodies

When we come to details, the reactionary character of the atomist cosmology is very manifest. The earth was shaped like a tambourine, and floated on the air. It was inclined towards the south because the heat of that region made the air thinner, while the ice and cold of the north made it denser and more able to support the earth. This accounts for the obliquity of the zodiac. Like Anaximander (§ 19), Leucippus held that the sun was farther away than the stars, though he also held that these were farther away than the moon. By this time the occultation of the planets by the moon must have been observed. There seems to be no very clear distinction between the planets and the fixed stars. Leucippus appears to have known the theory of eclipses as given by Anaxagoras. Such other pieces of information as have come down to us are mainly of interest as showing that, in some important respects, the doctrine of Leucippus was not the same as that taught afterwards by Democritus.

182. Perception

Aetius expressly attributes to Leucippus the doctrine that the objects of sense-perception exist "by law" and not by nature. This must come from Theophrastus; for, as we have seen, all later writers quote Democritus only. A further proof of the correctness of the statement is that we also find it attributed to Diogenes of Apollonia, who, as Theophrastus tells us, derived some of his views from Leucippus. There is nothing surprising in this. Parmenides had already declared the senses to be deceitful, and said that color and the like were only "names," and Empedocles had also spoken of coming into being and passing away as only a name. It is not likely that Leucippus went much further than this. It would probably be wrong to credit him with Democritus's clear distinction between "true-born" and "bastard" knowledge, or that between the primary and secondary qualities of matter. These distinctions imply a definite theory of knowledge, and all we are entitled to say is that the germs of it were already to be found in the writings of Leucippus and his predecessors. Of course, these do not make Leucippus a sceptic any more than Empedocles or Anaxagoras, whose remark on this subject (fr. 21a) Democritus is said to have quoted with approval.

There appear to be sufficient grounds for ascribing the theory of perception by means of simulacra or eidôla, which played such a part in the systems of Democritus and Epicurus, to Leucippus. It is a natural development of the Empedoclean theory of "effluences" (§ 118). It hardly seems likely, however, that he went into detail on the subject, and it is safer to credit Democritus with the elaboration of the theory.

183. Importance of Leucippus

We have seen incidentally that there is a wide divergence of opinion among recent writers as to the place of Atomism in Greek thought. The question at issue is really whether Leucippus reached his theory on what are called "metaphysical grounds," that is, from a consideration of the Eleatic theory of reality, or whether, on the contrary, it was a pure development of Ionian science. The foregoing exposition will suggest the true answer. So far as his general theory of the physical constitution of the world is concerned, it has been shown, I think, that it was derived entirely from Eleatic and Pythagorean sources, while the detailed cosmology was in the main a more or less successful attempt to make the older Ionian beliefs fit into this new physical theory. In any case, his greatness consisted in his having been the first to see how body must be regarded if we take it to be ultimate reality. The old Milesian theory had found its most adequate expression in the system of Anaximenes (§ 31), but of course rarefaction and condensation cannot be clearly represented except on the hypothesis of molecules or atoms coming closer together or going farther apart in space. Parmenides had seen that very clearly (fr. 2), and it was the Eleatic criticism which forced Leucippus to formulate his system as he did. Even Anaxagoras took account of Zeno's arguments about divisibility (§ 128), but his system of qualitatively different "seeds," though in some respects it goes deeper, lacks that simplicity which has always been the chief attraction of atomism.