Leucippus and Democritus believed that the world was populated by nothing but atoms
floating in void. Why did they think that atoms could not move without void? How did their
view explain phenomena like density? Why did their contemporaries (i.e. the pre-Socratics
and their successors) reject the idea of void unfilled by matter? Aristotle’s theory of motion
(understood as “change of place”) is, by contrast, unable to account for the possibility of
regions of void. Explain Aristotle’s theory of motion, and outline some of the ways it breaks
down/becomes complicated when we try to account for motion through a pocket of void. Is
Newton’s theory able to make sense of void? How so? it has to be 2-3 paragraphs long so about 1 page double spaced

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Almost nothing is known of Leucippus, who was the founding theorist of
atomism. Epicurus, a post-Aristotelian philosopher who adopted certain
aspects of Presocratic atomism is even said to have denied that Leucippus
existed. Leucippus’ birthplace is variously given as Miletus, Abdera, and
Elea (Miletus and Elea could represent the Milesian and Eleatic influences
on his work, and Democritus, his pupil and associate was from Abdera). It
is likely that Leucippus proposed the atomic system sometime around 440
to 430 BCE, thus he is contemporary with the other post-Eleatic thinkers
Anaxagoras and Empedocles as well as Melissus. Two books are attributed to
Leucippus: On Mind and The Great World System (Makrokosmos).
Democritus himself says that he was young when Anaxagoras was an
old man; his birth date is usually placed at about 460; he lived well into the
fourth century (tradition says he lived to be about 100 years old), and so was
a contemporary of Socrates, Plato, and perhaps even the young Aristotle.
Democritus was born in Abdera, in Thrace, a birthplace he shares with the
sophist Protagoras, but he traveled widely throughout the ancient world
(later sources say he went to India, but this is doubtful). Ancient sources
list about seventy titles of books by Democritus on all sorts of subjects, both
philosophical (on natural philosophy, ethics, mathematics, literature, and
grammar) as well as on other perhaps more popular topics: He apparently
wrote books on his travels; there are also reports of treatises on medicine,
farming, military science, and painting. One of his books was called The
Little World System (Mikrokosmos), in obvious homage to his teacher and
associate Leucippus.
The selections included here concentrate on atomism, the scientific and
metaphysical theory begun by Leucippus and continued by Democritus.
Unfortunately, very few passages from Leucippus and Democritus on
atomism survive; most of the evidence we have about the view comes from
Aristotle and the Aristotelian commentators.1 We must keep in mind that
these reports will also involve interpretation; atomism, which is a mechanistic
theory, was the major competitor to the teleological systems of both Plato
and Aristotle. The word atomos in Greek means “uncuttable,” and so atoms
are things that cannot be cut, split, or actually divided. The atomists claim
that there is an indefinite number of these atoms, each of which is uniform,
not subject to coming-to-be or passing-away, and unchangeable in any other
way, except position, an external change that does not affect the inner core of
atomic being. Atoms thus satisfy the Parmenidean requirements for reality.
Individual atoms are imperceptible: most of them are very small, though
Democritus may have said that there could be an atom as large as the cosmos.
All atomic stuff is the same; atoms differ from one another only in shape and
size (there is controversy about whether pre-Platonic atomists considered
weight as a property of atoms).
The second player in the atomic system is “the empty” (void). Void is where
the atoms are not, and atoms are able to move into the empty. The atomists
explicitly call the void “the nothing” or the “what is not,” whereas atoms
are called “the something” or the “what is.” Hence they explicitly challenge
Parmenides’ proscription against what-is-not; yet there is good evidence that
they insisted that the void is real in its own right, and not simply the negation
of what-is. Void separates atoms, which allows them to move and come
close to one another without melding into each other. The mixing together
and separating of the different types of atoms into different arrangements
is responsible for all the aspects of the sensible world, and so what looks
like coming-to-be and passing-away is merely rearrangement of the basic
entities—atoms and void. All else is, as Democritus says, “by convention.”
Democritus offered complex accounts of the structure of physical objects (i.e.,
arrangements of atoms) and of perception, thought, and knowledge, as well
as of many other aspects of human life. There are many fragments on ethical
matters attributed to him, but the authenticity of these is unclear.
1. (67B2) No thing happens at random but all things as a result of a
reason and by necessity.2
(Aëtius 1.25.4)
1. Aristotle wrote a multivolume work on Democritus; only fragments survive,
thanks to Simplicius, who quotes some passages (see selection 5, below).
2. This is one of the few fragments that can be assigned to Leucippus with
some confidence. Leucippus’ DK number is 67, while Democritus’ is 68.
2. (67A1) Leucippus’ opinion is this: All things are unlimited and
they all turn around one another; the all [the universe] is both the
empty [void] and the full. The worlds come to be when the atoms
fall into the void and are entangled with one another. The nature
of the stars comes to be from their motion, and from their increase
[in entanglements]. The sun is carried around in a larger circle
around the moon; and whirled around the center, the earth rides
steady; its shape is drumlike. He was the first to make the atoms
first principles.
(Diogenes Laertius, Lives of the Philosophers 9.30; tpc)
3. (67A6) Leucippus and his associate Democritus declare the full and
the empty [void] to be the elements, calling the former “what-is” (to
on) and the other “what-is-not” (to mē on). Of these, the one, “whatis,” is full and solid, the other, “what-is-not,” is empty [void] and
rare. (This is why they say that what-is is no more than what-is-not,
because the void is no less than body is.) These are the material
causes of existing things. . . . They declare that the differences
are the causes of the rest. Moreover, they say that
the differences are three: shape, arrangement, and position. For
they say that what-is differs only in “rhythm,” “touching,” and
“turning”—and of these “rhythm” is shape, “touching” is arrangement, and “turning” is position. For A differs from N in shape, AN
from NA in arrangement, and Z from N in position. Concerning
the origin and manner of motion in existing things, these men too,
like the rest, lazily neglected to give an account.
(Aristotle, Metaphysics 1.4 985b4–20)
4. (67A9) After establishing the shapes, Democritus and Leucippus
base their account of alteration and coming-to-be on them: coming-to-be and perishing by means of separation and combination,
alteration by means of arrangement and position. Since they held
that the truth is in the appearance, and appearances are opposite
and infinite, they made the shapes infinite, so that by reason of
changes of the composite, the same thing seems opposite to different people, and it shifts position when a small additional amount is
mixed in, and it appears completely different when a single thing
shifts position. For tragedy and comedy come to be out of the same
(Aristotle, On Generation and Corruption 1.1 315b6–15)
5. (68A37) Democritus believes that the nature of the eternal things
is small substances (ousiai) 3 infinite in number. As a place for
these he hypothesizes something else, infinite in size, and he
calls their place by the names “the void,” “not-hing” (ouden) and
“the unlimited” [or, “infinite”] and he calls each of the substances
“hing” (den) and “the compact” and “what-is.” He holds that the
substances are so small that they escape our senses. They have all
kinds of forms and shapes and differences in size. Out of these as
elements he generates and forms visible and perceptible bodies.
are at odds with one another and move in
the void because of their dissimilarity and the other differences I
have mentioned, and as they move they strike against one another
and become entangled in a way that makes them be in contact
and close to one another but does not make any thing out of them
that is truly one, for it is quite foolish that two or more
things could ever come to be one. The grounds he gives for why
the substances stay together up to a point are that the bodies fit
together and hold each other fast. For some of them are rough,
some are hooked, others concave, and others convex, while yet
others have innumerable other differences. So he thinks that they
cling to each other and stay together until some stronger necessity
comes along from the environment and shakes them and scatters
them apart. He describes the generation and its contrary, separation, not only for animals but also for plants, kosmoi, and altogether
for all perceptible bodies.
(Aristotle, On Democritus, quoted by Simplicius,
Commentary on Aristotle’s On the Heavens 295.1–22)
6. (67A8, 68A38) Leucippus . . . did not follow the same route as
Parmenides and Xenophanes concerning things that are, but
seemingly the opposite one. For while they made the universe one,
immovable, ungenerated, and limited, and did not even permit the
investigation of what-is-not, he posited the atoms as infinite and
ever-moving elements, with an infinite number of shapes, on the
grounds that they are no more like this than like that and because
he observed that coming-to-be and change are unceasing among
the things that are. Further, he posited that what-is is no more
3. Translator’s note: Ousia, “substance,” is a noun derived from the verb einai,
“to be.” There is a connection in language and meaning between ousia and on.
than what-is-not, and both are equally causes of things that come
to be. For supposing the substance of the atoms to be compact and
full, he said it is what-is and that it moves in the void, which he
called “what-is-not” and which he declares is no less than what-is.
His associate, Democritus of Abdera, likewise posited the full and
the void as principles, of which he calls the former “what-is” and
the latter “what-is-not.” For positing the atoms as matter for the
things that are, they generate the rest by means of their differences.
These are three: rhythm, turning, and touching, that is, shape,
position, and arrangement. For by nature like is moved by like,
and things of the same kind move toward one another, and each
of the shapes produces a different condition when arranged in a
different combination. Thus, since the principles are infinite, they
reasonably promised to account for all attributes and substances—
how and through what cause anything comes to be. This is why
they say that only those who make the elements infinite account
for everything reasonably. They say that the number of the shapes
among the atoms is infinite on the grounds that they are no more
like this than like that. For they themselves assign this as a cause
of the infiniteness.
(Simplicius, Commentary on Aristotle’s Physics 28.4–26)
7. (67A7) Leucippus and Democritus have accounted for all things
very systematically and in a single theory, taking the natural starting point as their own. For some of the early philosophers held
that what-is is necessarily one and immovable. For the void is not,
and motion is impossible without a separate void, nor can there
be many things without something to keep them apart. . . . But
Leucippus thought he had arguments that assert what is generally granted to perception, not abolishing coming-to-be, perishing,
motion, or plurality. Agreeing on these matters with the phenomena and agreeing with those who support the one [that is, the
Eleatics] that there could be no motion without void, he asserts that
void is what-is-not and that nothing of what-is is not, since what
strictly is is completely full. But this kind of thing is not one thing
but things that are infinite in number and invisible because of the
minuteness of their size. These move in the void (for there is void),
and they produce coming-to-be by combining and perishing by
coming apart, and they act and are acted upon wherever they happen to come into contact (for in this way they are not one), and they
generate by becoming combined and entangled. A
plurality could not come to be from what is in reality one, nor one
from what is really many, but this is impossible.
(Aristotle, On Generation and Corruption 1.8 324b35–325a36)
8. (67A19) They declare that their [atoms’] nature is but one, as if each
one were a separate piece of gold.
(Aristotle, On the Heavens 1.7 275b32–276a1)
9. (68A59) Plato and Democritus supposed that only the intelligible
things are true (or, “real”); Democritus because
there is by nature no perceptible substrate, since the atoms, which
combine to form all things, have a nature deprived of every perceptible quality.
(Sextus Empiricus, Against the Mathematicians 8.6)
10. (68A47) Democritus specified two : size
and shape; and Epicurus added weight as a third.
(Aëtius 1.3.18)
11. (67A15) Since the bodies differ in shape, and the shapes are infinite, they declare the simple bodies to be infinite too. But they did
not determine further what is the shape of each of the elements,
beyond assigning a spherical shape to fire. They distinguished air
and water and the others by largeness and smallness.
(Aristotle, On the Heavens 3.4 303a11–15)
12. (67A14) These men [Leucippus, Democritus, and Epicurus] said
that the principles are infinite in multitude, and they believed
them to be atoms and indivisible and incapable of being affected
because they are compact and have no share of void. (For they
claimed that division occurs where there is void in bodies.)
(Simplicius, Commentary on Aristotle’s On the Heavens 242.18–21)
13. (67A13) Those who abandoned division to infinity on the grounds
that we cannot divide to infinity and as a result cannot guarantee
that the division cannot end, declared that bodies are composed
of indivisible things and are divided into indivisibles. Except that
Leucippus and Democritus hold that the cause of the primary
bodies’ indivisibility is not only their inability to be affected but
also their minute size and lack of parts.
(Simplicius, Commentary on Aristotle’s Physics 925.10–15)
14. (68A48b) Democritus would appear to have been persuaded by
arguments that are appropriate to the science of nature. The point
will be clear as we proceed. For there is a difficulty in supposing
that there is a body, a magnitude, that is everywhere divisible and
that this [the complete division] is possible. For what will there be
that escapes the division? . . . Now since such a body is everywhere
divisible, let it be divided. What, then, will be left? A magnitude?
But that cannot be. For there will be something that has not been
divided, whereas we supposed that it was everywhere divisible.
But if there is no body or magnitude left and yet the division will
take place, either will consist of points and
its components will be without magnitude, or it will be nothing
at all so that even if it were to come to be out of nothing and be
composed of nothing, the whole thing would then be nothing but
an appearance. Likewise, if it is composed of points it will not be
a quantity. For when they were in contact and there was a single
magnitude and they coincided, they made the whole thing no
larger. For when it is divided into two or more, the whole is no
smaller or larger than before. And so even if all the points are put
together they will not make any magnitude. . . . These problems
result from supposing that any body whatever of any size is everywhere divisible. . . . And so, since magnitudes cannot be composed
of contacts or points, it is necessary for there to be indivisible bodies and magnitudes.
(Aristotle, On Generation and Corruption 1.2 316a13–b16)
15. (67A7) When Democritus said that the atoms are in contact with
each other, he did not mean contact, strictly speaking, which occurs
when the surfaces of the things in contact fit perfectly with one
another, but the condition in which the atoms are near one another
and not far apart is what he called contact. For no matter what,
they are separated by void.
(Philoponus, Commentary on Aristotle’s On
Generation and Corruption 158.27–159.3)
16. (68B156) [When Democritus declares that] There is no more reason
for the “hing” {Greek: den} to be than the nothing {Greek: mēden,
not-hing}, [he is calling thing body and nothing void, and declaring that this too (void) has some nature and existence of its own.]
(Plutarch, Against Colotes 1108F; tpc)
17. (67A19) By “void” people mean an interval in which there is no
perceptible body. Since they believe that everything that is is body,
they say that void is that in which there is nothing at all. . . . So it
is necessary to prove4 . . . that there is no interval different from
bodies . . . which breaks up the totality of body so that it is not
continuous, as Democritus, Leucippus, and many other natural
philosophers say, or that there is anything outside the totality of
body, supposing that it is continuous. . . . They say that (1) there
would be no change in place (that is, motion and growth), since
it does not seem that there would be motion unless there were
void, since what is full cannot admit anything else. . . . (2) Some
things are seen to contract and be compressed; for example, they
say that the jars hold the wine along with the wineskins, since
the compressed body contracts into the empty places that are in
it. Further, (3) all believe that growth takes place through void,
since the nourishment is a body and two bodies cannot coincide.
(4) They also use as evidence what happens with ash: it takes no
less water to fill a jar that contains ashes than it does to fill the
same jar when it is empty.
(Aristotle, Physics 4.6 213a27–b22)
18. (67A16) This is why Leucippus and Democritus, who say that the
primary bodies are always moving in the void (that is, the infinite)
must specify what motion they have and what is their natural
(Aristotle, On the Heavens 3.2 300b8–11)
4. Translator’s note: This passage forms part of Aristotle’s treatment of void,
in which he both presents the arguments offered in favor of the thesis that void
exists and shows why they fail. Aristotle here says that he needs to refute the
view that void exists.
19. (67A18) For they say that there is always motion. But why it is and
what motion it is, they do not state, nor do they give the cause of
its being of one sort rather than another.
(Aristotle, Metaphysics 12.6 1071b33–35)
20. (68A58) They say that motion occurs because of the void. For they,
too, say that nature5 undergoes motion in respect of place.
(Aristotle, Physics 8.9 265b24–25)
21. (67A16) Leucippus and Democritus said that their primary bodies,
the atoms, are always moving in the infinite void by compulsion.
(Simplicius, Commentary on Aristotle’s On the Heavens 583.18–20)
22. (68A47) Democritus, saying that the atoms are by nature motionless, declares that they move “by a blow.”
(Simplicius, Commentary on Aristotle’s Physics 42.10–11)
23. (68A47) Democritus says that the primary bodies (these are the
compact things) do not possess weight but move by striking
against one another in the infinite, and there can be an atom the
size of a kosmos.
(Aëtius 1.12.6)
24. (67A6) These men [Leucippus and Democritus] say that the atoms
move by hitting and striking against each other, but they do not
specify the source of their natural motion. For the motion of striking each other is compelled and not natural, and …
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