books burnt. Heath esteems him highly as a mathematician. â€
The fundamental ideas of the common philosophy of Leucippus and Democritus were due to the former, but as regards the working out it is hardly possible to disentangle them, nor is it, for our purposes, important to make the attempt. Leucippus, if not Democritus, was led to atomism in the attempt to mediate between monism and pluralism, as represented by Parmenides and Empedocles respectively. Their point of view was remarkably like that of modern science, and avoided most of the faults to which Greek speculation was prone. They believed that everything is composed of atoms, which are physically, but not geometrically, indivisible; that between the atoms there is empty space; that atoms are indestructible; that they always have been, and always will be, in motion; that there are an infinite number of atoms, and even of kinds of atoms, the differences being as regards shape and size. Aristotle ‡ asserts that, according to the atomists, atoms also differ as regards heat, the spherical atoms, which compose fire, being the hottest; and as regards weight, he quotes Democritus as saying «The more any indivisible exceeds, the heavier it is.» But the question whether atoms are originally possessed of weight in the theories of the atomists is a controversial one.
The atoms were always in motion, but there is disagreement among commentators as to the character of the original motion. Some, especially Zeller, hold that the atoms were thought to be always falling, and that the heavier ones fell faster; they thus caught up the lighter. ones, there were impacts, and the atoms were deflected like billiard
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* From Thales to Plato, p. 193.
€ Greek Mathematics, Vol. I, p. 176.
â
€ On Generation and Corruption, 326 . ¡
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balls. This was certainly the view of Epicurus, who in most respects based his theories on those of Democritus, while trying, rather unintelligently, to take account of Aristotle’s criticisms. But there is considerable reason to think that weight was not an original property of the atoms of Leucippus and Democritus. It seems more probable that, on their view, atoms were originally moving at random, as in the modern kinetic theory of gases. Democritus said there was neither up nor down in the infinite void, and compared the movement of atoms in the soul to that of motes in a sunbeam when there is no wind. This is a much more intelligent view than that of
Epicurus, and I think we may assume it to have been that of Leucippus and Democritus. *
As a result of collisions, collections of atoms came to form vortices. The rest proceeded much as in Anaxagoras, but it was an advance to explain the vortices mechanically rather than as due to the action of mind.
It was common in antiquity to reproach the atomists with attributing everything to chance. They were, on the contrary, strict determinists, who believed that everything happens in accordance with natural laws. Democritus explicitly denied that anything can happen by chance. †Leucippus, though his existence is questioned, is known to have said one thing: «Naught happens for nothing, but everything from a ground and of necessity.» It is true that he gave no reason why the world should originally have been as it was; this, perhaps, might have been attributed to chance. But when once the world existed, its further development was unalterably fixed by mechanical principles. Aristotle and others reproached him and Democritus for not accounting for the original motion of the atoms, but in this the atomists were more scientific than their critics. Causation must start from something, and wherever it starts no cause can be assigned for the initial datum. The world may be attributed to a Creator, but even then the Creator Himself is unaccounted for. The theory of the atomists, in fact, was more nearly that of modern science than any other theory propounded in antiquity.
The atomists, unlike Socrates, Plato, and Aristotle, sought to ex-
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* This interpretation is adopted by Burnet, and also, at least as regards Leucippus, by Bailey (op. cit. p. 83).
€ See Bailey, op. cit., p. 121, on the determinism of Democritus.
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plain the world without introducing the notion of purpose or final cause. The «final cause» of an occurrence is an event in the future for the sake of which the occurrence takes place. In human affairs, this conception is applicable. Why does the baker make bread? Because people will be hungry. Why are railways built? Because people will wish to travel. In such cases, things are explained by the purpose they serve. When we ask «why?» concerning an event, we may mean either of two things. We may mean: «What purpose did this event serve?» or we may mean: «What earlier circumstances caused this event?» The answer to the former question is a teleological explanation, or an explanation by final causes; the answer to the latter question is a mechanistic explanation. I do not see how it could have been known in advance which of these two questions science ought to ask, or whether it ought to ask both. But experience has shown that the mechanistic question leads to scientific knowledge, while the teleological question does not. The atomists asked the mechanistic question, and gave a mechanistic answer. Their successors, until the Renaissance, were more interested in the teleological question, and thus led science up a blind alley.
In regard to both questions alike, there is a limitation which is often ignored, both in popular thought and in philosophy. Neither question can be asked intelligibly about reality as a whole (including God), but only about parts of it. As regards the teleological explanation, it usually arrives, before long, at a Creator, or at least an Artificer, whose purposes are realized in the course of nature. But if a man is so obstinately teleological as to continue to ask what purpose is served by the Creator, it becomes obvious that his question is impious. It is, moreover, unmeaning, since, to make it significant, we should have to suppose the Creator created by some super-Creator whose purposes He served. The conception of purpose, therefore, is only applicable within reality, not to reality as a whole.
A not dissimilar argument applies to mechanistic explanations. One event is caused by another, the other by a third, and so on. But if we ask for a cause of the whole, we are driven again to the Creator, who must Himself be uncaused. All causal explanations, therefore, must have an arbitrary beginning. That is why it is no defect in the theory of the atomists to have left the original movements of the atoms unaccounted for.
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It must not be supposed that their reasons for their theories were wholly empirical. The atomic theory was revived in modern times to explain the facts of chemistry, but these facts were not known to the Greeks. There was no very sharp distinction, in ancient times, between empirical observation and logical argument. Parmenides, it is true, treated observed facts with contempt, but Empedocles and Anaxagoras would combine much of their metaphysics with observations on water-clocks and whirling buckets. Until the Sophists, no philosopher seems to have doubted that a complete metaphysic and cosmology could be established by a combination of much reasoning and some observation. By good luck, the atomists hit on a hypothesis for which, more than two thousand years later, some evidence was found, but their belief, in their day, was none
the less destitute of any solid foundation. *
Like the other philosophers of his time, Leucippus was concerned to find a way of reconciling
the arguments of Parmenides with the obvious fact of motion and change. As Aristotle says: â€
Although these opinions [those of Parmenides] appear to follow logically in a dialectical discussion, yet to believe them seems next door to madness when one considers the facts. For indeed no lunatic seems to be so far out of his senses as to suppose that fire and ice are «one»: it is only between what is right and what seems right from habit that some people are mad enough to see no difference.
Leucippus, however, thought he had a theory which harmonized with sense-perception and would not abolish either coming-to-be and passing-away or motion and the multiplicity of things. He made these concessions to the facts of perception: on the other hand, he conceded to the Monists that there could be no motion without a void. The result is a theory which he states as follows: «The void is a not-being, and no part of what is is a not-being; for what is in the strict sense of the term is an absolute plenum. This plenum, however, is not one; on the contrary, it is a many infinite in number and invisible owing to the minuteness of their bulk. The many move in the void (for there is a void): and by coming together they produce coming-to-be, while by separating they pro-
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* On the logical and mathematical grounds for the theories of the atomists, see Gaston Milhaud, Les Philosophes Géomètres de la Grèce, Ch. IV.
€ On Generation and Corruption, 325 a.
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duce passing-away. Moreover, they act and suffer action whenever they chance to be in contact (for there they are not one),
