icosaedron: platonic solids
Necessitas et libertas sont unum, unde non est formidandum quod, cum agat necessitate naturae, non libere agat : sed potius immo omnino non libere ageret, aliter agendo, quam necessitas et natura, imo naturae necessitas requirit.

Giordano BRUNO

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The Atomists: logos and necessity
translated by Alison Quayle (original in French)

For many, the reference to the atomists comes from the epigraph in Jacques Monod's book, Chance and Necessity. Curiously enough, almost no one noted that this epigraph was apocryphal. The Greek philosophy of the time of the atomists did not consider chance as an authentic character of reality, which could be autonomous (move by itself) but was not intrinsically free from any chain of causes.

The world as described by the various schools of philosophy does seem more or less impossible to understand, at least if we want to explain it in detail. Some, like Heraclitus, insisted that there was constant change; others, like Parmenides, explained that the totality of Being was whole, continuous and permanent. Except perhaps for the Milesians, who produced real models of the world, they all insisted on a hidden law which, despite appearances, gave the world its order. It was the quest for an accurate description of the world that led to the discovery of the atomists' models. Their philosophical heritage draws on the wealth of descriptions developed by their predecessors, and dates from around 430 BCE at Abdera, with the teaching of Leucippus. Very little is known of this philosopher from the north of Eastern Greece, but his place in history was guaranteed when he put forward a description of the Universe in terms of a void and of indivisible, unchangeable microscopic Parminedean worlds; in other words, atoms. 

Leucippus was certainly very familiar with the reasoning of Zeno and Melissus, and especially with the contradictions arising from the continuous/discontinuous duality. The main objective of the atomist theory attributed to him was to resolve the problems of emergence (of forms) on the one hand, and of the way things change on the other. A convincing explanation was also needed to link the notions of time and space, which were so difficult to clarify. The first thing Leucippus did was to abandon altogether one of the consequences of Parmenidean reasoning, introducing a logical counterpart to one of the qualities of Being: Non-Being, the attributes of which were the Fullness and the Void. The One was still unique, but because the Void existed, it could divide itself into a multitude of fragments with infinitely varied forms. Time made an entrance here, setting these indivisible and vanishingly small "atoms" in perpetual motion.

The Greek atomists have been famous down through the ages, thanks to the materialist models referred to in Lucretius' De Rerum Natura. A few scattered phrases have entered almost unnoticed into French cultural consciousness. The everyday expression avoir des atomes crochus, literally “to have hooked atoms”, and meaning to have a lot in common with someone, is one example. The eminent biologist and writer Jacques Monod was someone whose family background would have made him familiar with the work of the atomists, and when he wanted to ascribe to human beings (as a biological life-form) a unique place in the Universe, he thought he remembered a phrase from Democritus that suited his purpose admirably:

Everything existing in the Universe is the fruit 
of chance and necessity(1)
He named his famous book after it: Chance and Necessity. However, chance is not a Greek notion, and necessity is not to be understood in its everyday meaning of what is required in order to achieve an end, but as something closer to inevitability, or that which cannot be any other way. Even if we do not agree with the view (very strongly held in Camus' day, for instance) that human life stands apart within the Universe, it is still legitimate to wonder about the origin of this quotation.  It is not to be found in Democritus, even if his thought is similar in some ways to what is attributed to him here. But among the surviving fragments by Leucippus there is one worth quoting, since it is superficially very similar, yet in deep meaning so distinct from the apocryphal epigraph that made Monod's book so successful:
οὐδεν χρῆμα ματην γίνεται ἀλλα παντα ἐκ λόγου τε και υπ᾽᾽ανάγκης gr_flag
Nothing happens in vain, but everything from reason (λόγος gr-flag),
and by necessity
This quotation from Leucippus is certainly nearer to Greek thought at the time, which could not be content with chance, an essentially unscientific notion. The two closest ideas in Greek are represented by the words τυχἠ gr-flag  (tukè, meaning something that cannot be understood or foreseen) αὐτόματον  gr-flag (automaton, meaning "acting by itself”), and rather express the idea of contingency, or of a process that occurs automatically, but is governed by laws, although we do not know them. So we should ask ourselves what mistranslation could have introduced anachronistic notion of chance, with no intrinsic cause.

What Leucippus was saying, and Democritus was to say later, was that there existed a Law (λόγος not νόμος  gr-flag) responsible for shaping matter into forms, but that this law could be no more than the result of a “construction principle”, and not the revelation of a pre-existing form with an intrinsic autonomy and its own life. One of the central ideas I will be developing in this text is precisely that the ways in which the forms of living things can be combined are the result of a great many organised constraints. If Life is not really “improbable”, this is because the material objects that make up living things, and their possible combinations, are not produced by random jumbling. There are basic laws, and basic shapes (mostly constrained by the limited range of primitive building blocks available), and it should be possible to find signs of them in present life forms.

Democritus was probably a pupil of Leucippus, and he certainly knew the philosophies of his contemporaries, especially the reasoning of the Eleatic school. In his description of the natural world he tried to resolve the two major conflicts between permanence and change, and between the continuous and the discontinuous. Resolving these apparent contradictions would give an extraordinarily powerful hold on the world, because it would be possible to accommodate measurement without irremediably destroying the infinitely smooth and continuous nature of reality. The gradual emergence of forms would then be due to the infinite combinatorial possibilities of the basic atoms. Categorised according to the way they move and their liability to interact, these atoms were driven by the inertia principle: they would continue along their initial path so long as they did not meet any other atom. When they did meet, they could either “bounce off”, each taking a new route, or they could hook up, cluster together and form a vortex.

Of course the image of the four elements that made up matter was the basis of atoms. The atoms of fire were the smoothest, and could only bump against each other, and in moving through matter made up of other atoms they could do no more than change the local activity, consequently altering the possibilities for interaction. They were true Parmenidean spheres. In complete contrast, atoms of Earth were much less mobile, and very likely to combine with each other, as could easily be seen with geological forms in nature. The vortices (δινἠ  gr-flag) formed gradually and grouped themselves together, producing the forms found in the earth and the heavens. The endlessly repeated interactions were the source of endless change, and forms appeared as a result of this experimentation without final cause (but not without efficient cause), joined together rather as a builder making a dry stone wall tries out various stones until one fits. Necessity imposed certain paths and certain interactions, so that although there was an infinite variety of forms, they were never just merely random. 

Democritus believed that we are able to learn about the world because we too are made up of atoms, and thus able to interact with the atoms that move in the void. Light was made of smooth atoms that entered our eyes and struck those of which we were made, causing us to react and to know the world directly. The role of the senses was therefore essential to the way knowledge is organised. It was the uniqueness of the nature of things that allowed us to have access to reality, despite our entirely relative position in the world.

The world had had no beginning and would have no end, and there was not even anything to prove that there was only a single world. Movement was a first principle of the Universe, and it was produced "automatically", by sheer "necessity". Of course the void was a necessary condition for movement to occur. The worlds — the Earth, Sun, and planets — were formed by the association of atoms that were attracted to each other by a natural affinity — "like attracts like" — after a tumult in which atoms of all shapes and sizes jostled together, bouncing off each other or hooking together. According to Diogenes Laertius, this is how Leucippus imagined the creation of the world:

that all things were infinite (ἄπειρα gr-flag), 
and were interchanged with one another; 
and that the universe was a vacuum (κενόν gr-flag), 
and full of bodies; also that the worlds were 
produced by bodies falling into the vacuum, 
and becoming entangled with one another; 
and that the nature of the stars originated in motion, 
according to their increase; 
also, that the sun is borne round in a greater circle around the moon;
that the earth is carried on revolving round the centre:
and that its figure resembles a drum (...)

the universe is infinite, as I have already mentioned;
that of it, one part is a plenum, and the other a vacuum.
He also says that the elements, 
and the worlds which are derived from them, are infinite, and are dissolved again into them; and that the worlds are produced in this manner: That many bodies, of various kinds and shapes, are borne by amputation from the infinite, into a vast vacuum; and then, they being collected together, produce one vortex (δινήν gr-flag); according to which they, dashing against one another, and whirling about in every direction, are separated in such a way that like attaches itself to like. But as they are all of equal weight, when by reason of their number they are no longer able to whirl about, the thin ones depart into the outer vacuum, as if they bounded through, and the others remain behind, and becoming entangled with one another, run together, and produce a sort of spherical shaped figure. This subsists as a kind of membrane (ὑμένα gr-flag); containing within itself bodies of every kind; and as these are whirled about so as to revolve according to the resistance of the centre, the circumambient membrane becomes thin, since bodies are without ceasing, uniting according to the impulse given by the vortex; and in this way the earth is produced, since these bodies which have once been brought to the centre remain there. On the other side, there is produced another enveloping membrane, which increases incessantly by the accretion of exterior bodies; and which, as it is itself animated by a circular movement, drags with it, and adds to itself, everything it meets with; some of these bodies thus enveloped re-unite again and form compounds, which are at first moist and clayey, but soon becoming dry, and being drawn on in the universal movement of the circular vortex, they catch fire, and constitute the substance of the stars. All the stars are set on fire by the rapidity of their own motion; and the sun is set on fire by the stars; (...) Leucippus admits also, that the production of worlds, their increase, their diminution, and their destruction, depend on a certain necessity, the character of which he does not precisely explain. (...)
Quite apart from the extraordinary evocativeness of this cosmic fresco, the themes it evokes are strikingly relevant even to modern cosmology. Any science-fiction writer would be delighted to be able to write such an accurate description of how the world will look 2500 years from now. But the atomists also created a philosophy of causality and an epistemology which we will look at again later. The fact that they introduced movement as a first principle is a clear prelude to Newton's philosophy in his much later Principia Mathematica.

Together with the idea of the void, this first principle made it possible to conceive a theory of the generation of objects from simple matter, in which the essential cause was the “necessity” of movement, which made countless atoms meet and create forms through trial and error (as in Empedocles), of which the most stable survived. So the fundamental criterion of form was just a criterion of stability, and not the immanence of an archetype that existed in another world. Similarly, the famous “potentialities” problem that haunted Aristotle and the Lyceum, and remained an important issue throughout the middle ages, did not arise: forms were created as the result of atoms or more complex forms meeting, and their potentiality depended on the likelihood of that meeting. Everything that had actually been produced was possible, but what had not yet been produced was only a potentiality to the extent that the meeting would actually occur in a foreseeable time and place (foreseeable on the basis of the data of the moment and place in question). It was important to understand that the world takes its course once only, and that no cause or force had been required to start atoms moving in the first place, because their movement was eternal, both in the past and in the future. For the atomists, contingency did not imply a chance that was intrinsically unpredictable, hence the expression “a necessary chance” found in some writers commenting on atomist thinking (2). It was the necessity of the meetings that was fundamental, and because movement continued for all eternity, the strictest causality could be both unpredictable to us, and “automatic” (αὐτόματον gr-flag). This gave rise to the interpretation of later commentators in terms of chance, and the misunderstanding in Jacques Monod's epigraph.

The reasons why strict atomist thought is hard to accept spontaneously will recur again and again. The first to spring to mind is always a certain finalism, found even in Monod himself in his concept of “teleonomy”. And usually, there are only two possibilities: either things happen at random, in which case they are the result of chance, or they have a certain regularity, which indicates that there is a motive force guiding them. At first, it is very difficult to imagine without thinking about it long and hard, that there could be a constant, aimless force that directs the construction of the world, or the way things happen, but this is the force that the atomists called necessity. It did not in any way imply the existence of Chance, or Indeterminism in itself. And if chance has become associated with atomist thought, it is only in the texts of their commentators or critics, especially of Aristotle (commentators rather than Aristotle himself, since as I said, Chance is not a Greek notion). The fact was that Aristotle could only accept things in terms of their final cause. So he could not accept the blind necessity of the vortex movement of atoms, without cause and without origin.

For him, there were only two possibilities: irregularity indicated “gratuitous” contingency, while any sign of regularity was proof of a final cause. This left no room for the atomists¡ third way, which evoked a permanent but aimless force they called necessity.

The atomists thought a great deal about how to explain the origin of things, and, well before Kant, they noticed a fundamental contradiction, which Aristotle recorded:

But they do not say well nor do they assign a necessary
cause who say simply that "it always happens so", 
and imagine that this is a first principle in these cases. 
Thus Democritus of Abdera says that «there is no beginning of the infinite; 
now the cause is a beginning, and the eternal is infinite; 
in consequence, to ask the cause of anything of this kind 
is to seek for a beginning of the infinite. 
Yet according to this argument, which forbids us to seek the cause, 
there will be no proof of any eternal truth whatever 
(Generation of Animals 742b17) (3)
The atomists thus rediscovered the Ionian principle of the unlimited as an original element, and this led them to accept movement as a first principle.

Finally, the atomists are known for their advanced theory of human and animal sense perception. Their vision of the world was particularly modern, because it unified their description of the nature of things by bringing into the picture the particular characteristics of the way human beings learnt about the world. It was atoms that were the link between objects and mankind. Leucippus said:

Every change produced by or impressed on things takes place
by virtue of a contact; all our perceptions are tactile,
and all our senses are varieties of touch.
Consequently, since our mind does not proceed from within  us 
to sally forth and touch external objects, 
it is necessary for these objects to come and touch our mind by passing 
through our senses. 
Now we do not actually see the objects coming nearer to us 
when we perceived them, therefore, they must send to our soul «something¡ 
which represents them, some image, eidola, some kind of shadow 
or some material... which envelops bodies, quivers on the surface, and can detach itself from them in order to bring to our soul the shape, the colors, and all the other qualities of the bodies from which they emanate.(4)
The underlying idea was that vision required physical contact between the observer and something given off by the object observed. It was the same for the other senses: each object perceived gave off particular atoms, which entered through special “pores” in the observer, of an appropriate shape for the object (5). The passage through these pores selected those constituents specific to the nature of the object, and these were responsible both for the sensation, and for its faithfulness to the object.

Unfortunately, very little writing from this period has survived, but the fertility of the atomists' thought led to continuing debates over more than a thousand years, on all sorts of issues that are right at the heart of our knowledge. The dominance of dualist, finalist thought meant that for a long time these debates were not very profound, and it certainly delayed a number of revolutionary changes. But some milestones remain, to show us how atomist thought has endured and been enriched, and that is what I intend to look at next.

1. As cited in the English translation of Chance and Necessity by Austryn Wainhouse (back to text)

2. For instance, the British commentator WKC Guthrie, in his remarkable History of Greek Philosophy, Cambridge University Press (Reed, 1978). But I must point out that for the mathematician René Thom, for example, this is an oxymoron! (back to text)

3. Translation by Arthur Platt, from On the Generation of Animals (back to text)

4. Translation from Revolting Ideas. An Introduction to the History of Science (back to text)

5. Need I point out how similar this is to the concept of the “receptor” on the surface of a cell? (back to text)