## 1. Life and Works



According to ancient reports, Democritus was born about 460 BCE (thus,
he was a younger contemporary of Socrates) and was a citizen of
Abdera, although some reports mention Miletus. As well as his
associate or teacher Leucippus, Democritus is said to have known
Anaxagoras, and to have been forty years younger than the latter (DK
68A1). A number of anecdotes concern his life, but their authenticity
is uncertain.



The work of Democritus has survived only in secondhand reports,
sometimes unreliable or conflicting: the reasoning behind the
positions taken often needs to be reconstructed. Much of the best
evidence is that reported by Aristotle, who regarded him as an
important rival in natural philosophy. Aristotle wrote a monograph on
Democritus, of which only a few passages quoted in other sources have
survived. Democritus seems to have taken over and systematized the
views of Leucippus, of whom little is known. Although it is possible
to distinguish some contributions as those of Leucippus, the
overwhelming majority of reports refer either to both figures, or to
Democritus alone; the developed atomist system is often regarded as
essentially Democritus'.



Diogenes Laertius lists a large number of works by Democritus on many
fields, including ethics, physics, mathematics, music and cosmology.
Two works, the *Great World System* and the *Little World
System* (see the entry on
 doxography of ancient philosophy),
 are sometimes ascribed to Democritus, although Theophrastus reports
that the former is by Leucippus (DK 68A33). There is more uncertainty
concerning the authenticity of the reports of Democritus' ethical
sayings. Two collections of sayings are recorded in the fifth-century
anthology of Stobaeus, one ascribed to Democritus and another ascribed
to an otherwise unknown philosopher 'Democrates'. DK
accepts both as relating to Democritus, but the authenticity of
sayings in both collections is a matter of scholarly discussion, as is
the relationship between Democritus' atomism and his ethics.


## 2. Atomist Doctrine



Ancient sources describe atomism as one of a number of attempts by
early Greek natural philosophers to respond to the challenge offered
by Parmenides. Despite occasional challenges (Osborne 2004), this is
how its motivation is generally interpreted by scholars today.
Although the exact interpretation of Parmenides is disputed, he was
taken to have argued that change is merely illusory because of some
absurdities inherent in the idea of 'what is not'. In
response, Leucippus and Democritus, along with other Presocratic
pluralists such as Empedocles and Anaxagoras, developed systems that
clarified how change does not require that something should come to be
from nothing. These responses to Parmenides suppose that there are
multiple unchanging material principles, which persist and merely
rearrange themselves to form the changing world of appearances. In the
atomist version, these unchanging material principles are indivisible
particles, the atoms. The idea that there is a lower limit to
divisibility is sometimes taken as an answer to Zeno's paradoxes about
the impossibility of traversing infinitely divisible magnitudes
(Hasper 2006). Reconstructions offered by Wardy (1988) and Sedley
(2008) argue, instead, that atomism was developed as a response to
Parmenidean arguments.



The atomists held that there are two fundamentally different kinds of
realities composing the natural world, atoms and void. Atoms, from the
Greek adjective *atomos* or *atomon*,
'indivisible,' are infinite in number and various in size
and shape, and perfectly solid, with no internal gaps. They move about
in an infinite void, repelling one another when they collide or
combining into clusters by means of tiny hooks and barbs on their
surfaces, which become entangled. Other than changing place, they are
unchangeable, ungenerated and indestructible. All changes in the
visible objects of the world of appearance are brought about by
relocations of these atoms: in Aristotelian terms, the atomists reduce
all change to change of place. Macroscopic objects in the world that
we experience are really clusters of these atoms; changes in the
objects we see--qualitative changes or growth, say--are
caused by rearrangements or additions to the atoms composing them.
While the atoms are eternal, the objects compounded out of them are
not. Clusters of atoms moving in the infinite void come to form
*kosmoi* or worlds as a result of a circular motion that
gathers atoms up into a whirl, creating clusters within it (DK
68B167); these *kosmoi* are impermanent. Our world and the
species within it have arisen from the collision of atoms moving about
in such a whirl, and will likewise disintegrate in time.



In supposing that void exists, the atomists deliberately embraced an
apparent contradiction, claiming that 'what is not'
exists. Apparently addressing an argument by Melissus, a follower of
Parmenides, the atomists paired the term for 'nothing'
with what it negates, 'thing,' and claimed that--in a
phrase typical of the atomists--the one 'no more'
exists than the other (DK 67A6). Schofield (2002) argues that this
particular phrase originated with Democritus and not his teacher
Leucippus. By putting the full (or solid) and the void ontologically
on a par, the atomists were apparently denying the impossibility of
void. Void they considered to be a necessary condition for local
motion: if there were no unoccupied places, where could bodies move
into? Melissus had argued from the impossibility of void to the
impossibility of motion; the atomists apparently reasoned in reverse,
arguing from the fact that motion exists to the necessity for void
space to exist (DK 67A7). It has been suggested that Democritus'
conception of void is that of the (temporarily) unfilled regions
between atoms rather than a concept of absolute space (Sedley 1982).
Void does not impede the motion of atoms because its essential quality
is that of 'yielding,' in contrast to the mutual
resistance of atoms. Later atomist accounts attest that this
'yielding' explains the tendency of bodies to drift into
emptier spaces, driven out by collision from more densely packed
regions (Lucretius *DRN* 6.906-1089).



Some controversy surrounds the properties of the atoms. They vary in
size: one report--which some scholars question--suggests
that atoms could, in principle, be as large as a cosmos, although at
least in this cosmos they all seem to be too small to perceive (DK
68A47). They can take on an infinite variety of shapes: there are
reports of an argument that there is 'no more' reason for
the atoms to be one shape than another. Many kinds of atoms can
interlock with one another because of their irregular shapes and hooks
at their surface, accounting for the cohesiveness of some compounds.
It is not clear whether the early atomists regarded atoms as
conceptually indivisible or merely physically indivisible (Furley
1967). The idea that there is a smallest possible magnitude seems to
suggest that this is the lower limit of size for atoms, although
notions like being in contact or having shape seem to entail that even
the smallest atoms have parts in some sense, if only mathematically or
conceptually.



There are conflicting reports on whether atoms move in a particular
direction as a result of their weight: a number of scholars have tried
to reconcile these by supposing that weight is not intrinsic to the
atoms, but is a result of the centripetal tendencies set up in the
cosmic whirl (cf. O'Brien 1981; Furley 1989, pp. 91-102). Atoms
may have an inherent tendency to a kind of vibratory motion, although
the evidence for this is uncertain (McDiarmid 1958). However, their
primary movement seems to result from collision with other atoms,
wherein their mutual resistance or *antitupia* causes them to
move away from one another when struck. Democritus is criticized by
Aristotle for supposing that the sequence of colliding atoms has no
beginning, and thus for not offering an explanation of the existence
of atomic motion *per se*, even though the prior collision with
another atom can account for the direction of each individual atomic
motion (see O'Keefe 1996). Although the ancient atomists are often
compared to modern 'mechanistic' theories, Balme warned of
the danger of assuming that the atomists share modern ideas about the
nature of atomic motion, particularly the idea that motion is inertial
(Balme 1941).



According to different reports, Democritus ascribed the causes of
things to necessity, and also to chance. Probably the latter term
should be understood as 'absence of purpose' rather than a
denial of necessity (Barnes 1982, pp. 423-6). Democritus
apparently recognized a need to account for the fact that the
disorderly motion of individual distinct atoms could produce an
orderly cosmos in which atoms are not just randomly scattered, but
cluster to form masses of distinct types. He is reported to have
relied on a tendency of 'like to like' which exists in
nature: just as animals of a kind cluster together, so atoms of
similar kinds cluster by size and shape. He compares this to the
winnowing of grains in a sieve, or the sorting of pebbles riffled by
the tide: it is *as if* there were a kind of attraction of like
to like (DK 68B164). Although this claim has been interpreted
differently (e.g. Taylor 1999b p. 188), it seems to be an attempt to
show how an apparently ordered arrangement can arise automatically, as
a byproduct of the random collisions of bodies in motion (Furley 1989,
p. 79). No attractive forces or purposes need be introduced to explain
the sorting by the tide or in the sieve: it is probable that this is
an attempt to show how apparently orderly effects can be produced
without goal-directioned forces or purpose.



Democritus regards the properties of atoms in combination as
sufficient to account for the multitude of differences among the
objects in the world that appears to us. Aristotle cites an analogy to
the letters of the alphabet, which can produce a multitude of
different words from a few elements in combinations; the differences
all stem from the shape (*schema*) of the letters, as A
differs from N; by their arrangement (*taxis*), as AN differs
from NA; and by their positional orientation (*thesis*), as N
differs from Z (DK 67A6). These terms are Aristotle's interpretation
of Democritus' own terminology, which has a more dynamic sense
(Mourelatos 2004). This passage omits differences of size, perhaps
because it is focused on the analogy to letters of the alphabet: it is
quite clear from other texts that Democritus thinks that atoms also
differ in size.



He famously denies that perceptible qualities other than shape and
size (and, perhaps, weight) really exist in the atoms themselves: one
direct quotation surviving from Democritus claims that 'by
convention sweet and by convention bitter, by convention hot, by
convention cold, by convention color; but in reality atoms and
void' (DK 68B9, trans. Taylor 1999a). There are different
accounts of this distinction. Furley argues that the translation
'convention' should not be taken to suggest that there is
anything *arbitrary* about the perception of certain colors,
say: the same configuration of atoms may be regularly associated with
a given color (Furley 1993; cf. Barnes 1982, pp. 370-7). What
Democritus rejects with the label 'merely conventional'
is, perhaps, the imputation of the qualities in question to the atoms,
or perhaps even to macroscopic bodies. Mourelatos (2005) draws
the contrast as that between intrinsic and relational properties.



While several reports of Democritus' view, apparently direct
quotations, mention exclusively sensible qualities as being unreal, a
report of Plutarch includes in the list of things that exist only by
convention the notion of 'combination' or
*sunkrisis*. If this report is genuinely Democritean, it would
broaden the scope of the claim considerably: the idea that any
combination--by which he presumably means any cluster of
atoms--is 'unreal' or merely
'conventional' suggests that Democritus is drawing a more
radical distinction than that between sensible and nonsensible
qualities. The implication would be that anything perceived, because
it is a perception of combinations of atoms and not atoms themselves,
would be suspect, not merely the *qualia* experienced by means
of individual sense organs. One report indeed attributes to Democritus
a denial that two things could become one, or vice versa (DK 68A42),
thus suggesting that combinations are regarded as conventional.



Commentators differ as to the authenticity of Plutarch's report. As
the word *sunkrisis* does not occur in other reports, Furley
(following Sandbach) suggests that it is most likely an error for
*pikron*, 'bitter' which occurs instead in another
report. However, Furley concedes that *Plutarch* at least
understands the earliest atomists to be committed to the view that all
combinations of atoms, as much as sensible qualities, should be
understood as conventional rather than real (Furley 1993 pp.
76-7n7). This would suggest that everything at the macroscopic
level--or, strictly, everything available to perception--is
regarded as unreal. The ontological status of arrangement or
combination of atoms for Democritus is a vexed question, that affects
our understanding of his metaphysics, his historical relationship to
Melissus, and the similarity of his views to the modern
primary-secondary quality distinction (Wardy 1988; Curd 1998; Lee
2005; Mourelatos 2005; Pasnau 2007). If we take the
'conventionality' thesis to be restricted to sensible
qualities, there is still an open question about Democritus' reason
for denying their 'reality' (Wardy 1988; O'Keefe 1997;
Ganson 1999).


## 3. Theory of Perception



Democritus' theory of perception depends on the claim that
*eidola* or images, thin layers of atoms, are constantly
sloughed off from the surfaces of macroscopic bodies and carried
through the air. Later atomists cite as evidence for this the gradual
erosion of bodies over time. These films of atoms shrink and expand;
only those that shrink sufficiently can enter the eye. It is the
impact of these on our sense organs that enables us to perceive.
Visible properties of macroscopic objects, like their size and shape,
are conveyed to us by these films, which tend to be distorted as they
pass through greater distances in the air, since they are subject to
more collisions with air atoms. A different or complementary account
claims that the object seen impresses the air by the
*eidola*, and the compacted air thus conveys the image to
the eye (DK 68A135; Baldes 1975). The properties perceived by other
senses are also conveyed by contact of some kind. Democritus' theory
of taste, for example, shows how different taste sensations are
regularly produced by contact with different shapes of atoms.



Theophrastus, who gives us the most thorough report of Democritus'
theory, criticizes it for raising the expectation that the same kinds
of atoms would always cause similar appearances. However, it may be
that most explanations are directed towards the *normal* case
of a typical observer, and that a different account is given as to the
perceptions of a *nontypical* observer, such as someone who is
ill. Democritus' account why honey sometimes tastes bitter to people
who are ill depends on two factors, neither of which undercut the
notion that certain atomic shapes regularly affect us in a given way.
One is that a given substance like honey is not quite homogeneous, but
contains atoms of different shapes. While it takes its normal
character from the predominant type of atom present, there are other
atom-types present within. The other is that our sense-organs need to
be suitably harmonized to admit a given atom-type, and the disposition
of our passageways can be affected by illness or other conditions.
Thus someone who is ill may become unusually receptive to an atom-type
that is only a small part of honey's overall constitution.



Other observed effects, however, require a theory whereby the same
atoms can produce different effects without supposing that the
observer has changed. The change must then occur in the object seen.
The explanation of color seems to be of this variety: Aristotle
reports that things acquire their color by 'turning,'
*trope* (*GC* 1.2, 315b34). This is the
Democritean term that Aristotle had translated as
'position,' *thesis*, i.e. one of the three
fundamental ways in which atoms can alter and thus appear differently
to us. Aristotle gives this as the reason why color is not ascribed to
the atoms themselves. Lucretius' account of why color cannot belong to
atoms may help clarify the point here. We are told that if the sea's
atoms were really blue, they could not undergo some change and look
white (*DRN* 2.774-5), as when we observe the sea's
surface changing from blue to white. This seems to assume that, while
an appearance of a property P can be produced by something that is
neither P nor not-P, nonetheless something P cannot appear not-P.
Since atoms do not change their intrinsic properties, it seems that
change in a relational property, such as the relative position of
atoms, is most likely to be the cause of differing perceptions. In the
shifting surface of the sea or the flutter of the pigeon with its
irridescent neck, it is evident that the parts of the object are
moving and shifting in their positional relations.



By ascribing the causes of sensible qualities to relational properties
of atoms, Democritus forfeits the *prima facie* plausibility of
claiming that things *seem* P because they *are* P. Much
of Theophrastus' report seems to focus on the need to make it
plausible that a composite can produce an appearance of properties it
does not intrinsically possess. Democritus is flying in the face of at
least one strand of commonsense when he claims that textures produce
the appearance of hot or cold, impacts cause colour sensations. The
lists of examples offered, drawing on commonsense associations or
anecdotal experience, are attempts to make such claims persuasive.
Heat is said to be caused by spherical atoms, because these move
freely: the commonsense association of quick movement with heating may
be employed here. Betegh (2020) suggests that larger void spaces are
directly associated with heating, rather than that rarefaction
indirectly causes heat by allowing freer and more frequent atomic
motion.



Aristotle sometimes criticizes Democritus for claiming that visible,
audible, olfactory and gustatory sensations are all caused by touch
(DK 68A119). Quite how this affects the account of perception is not
clear, as the sources tells us little about how touch is thought to
work. Democritus does not, however, seem to distinguish between touch
and contact, and may take it to be unproblematic that bodies
communicate their size, shape and surface texture by physical
impact.


## 4. The Soul and the Nature of Living Things



In common with other early ancient theories of living things,
Democritus seems to have used the term *psyche* to refer
to that distinctive feature of living things that accounts for their
ability to perform their life-functions. According to Aristotle,
Democritus regarded the soul as composed of one kind of atom, in
particular fire atoms. This seems to have been because of the
association of life with heat, and because spherical fire atoms are
readily mobile, and the soul is regarded as causing motion. Democritus
seems to have considered thought to be caused by physical movements of
atoms also. This is sometimes taken as evidence that Democritus denied
the survival of a personal soul after death, although the reports are
not univocal on this.



One difficulty faced by materialist theories of living things is to
account for the existence and regular reproduction of functionally
adapted forms in the natural world. Although the atomists have
considerable success in making it plausible that a simple ontology of
atoms and void, with the minimal properties of the former, can account
for a wide variety of differences in the objects in the perceptible
world, and also that a number of apparently orderly effects can be
produced as a byproduct of disorderly atomic collisions, the kind of
functional organization found in organisms is much harder to
explain.



Democritus seems to have developed a view of reproduction according to
which all parts of the body contribute to the seed from which the new
animal grows, and that both parents contribute seed (DK 68A141; 143).
The theory seems to presuppose that the presence of some material from
each organ in the seed accounts for the development of that organ in
the new organism. Parental characteristics are inherited when the
contribution of one or other parent predominates in supplying the
appropriate part. The offspring is male or female according to which
of the two seeds predominates in contributing material from the
genitals. In an atomist cosmos, the existence of particular species is
not considered to be eternal. Like some other early materialist
accounts, Democritus held that human beings arose from the earth (DK
68A139), although the reports give little detail.


## 5. Theory of Knowledge



One report credits Democritus and Leucippus with the view that thought
as well as sensation are caused by images impinging on the body from
outside, and that thought as much as perception depends on images (DK
67A30). Thought as well as perception are described as changes in the
body. Democritus apparently recognized that his view gives rise to an
epistemological problem: it takes our knowledge of the world to be
derived from our sense experience, but the senses themselves not to be
in direct contact with the nature of things, thus leaving room for
omission or error. A famous fragment may be responding to such a
skeptical line of thought by accusing the mind of overthrowing the
senses, though those are its only access to the truth (DK68B125).
Other passages talk of a gap between what we can perceive and what
really exists (DK 68B6-10; 117). But the fact that atoms are not
perceptible means that our knowledge of their properties is always
based on analogy from the things of the visible world. Moreover, the
senses report properties that the atoms don't really possess, like
colors and tastes. Thus the potential for doubt about our knowledge of
the external world looms large.



Later philosophers adapted a Democritean phrase *ou mallon* or
'no more' in the argument that something that seems both P
and not-P is 'no more' P than not-P. Arguments of this
form were used for sceptical purposes, citing the conflicting evidence
of the senses in order to raise concern about our knowledge of the
world (de Lacy 1958). Democritus does not seem to be pursuing a
consistently skeptical program, although he does express concern about
the basis for our knowledge.



The idea that our knowledge is based on the reception of images from
outside us is employed in Democritus' discussion of the gods, wherein
it is clear that our knowledge of the gods comes from
*eidola* or giant films of atoms with the characteristics
we attribute to the gods, although Democritus denies that they are
immortal. Some scholars take this to be a deflationary attack on
traditional theology as based on mere images (Barnes 1982, pp.
456-61), but others suppose that the theory posits that these
*eidola* are really living beings (Taylor 1999a, pp.
211-6). Although atomism is often identified as an atheist
doctrine in later times, it is not clear whether this is really
Democritus' view.


## 6. Indivisibility and Mathematics



The reasons for supposing that there are indivisible magnitudes
apparently stem from Zeno of Elea's account of paradoxes that arise if
extension is understood to be infinitely divisible, i.e. composed of
an infinite number of parts. The atomists may have sought to avoid
these paradoxes by supposing that there is a limit to
divisibility.



It is not clear, however, in what sense the atoms are said to be
indivisible, and how the need for smallest magnitudes is related to
the claim that atoms are indivisible. Furley suggests that the
atomists may not have distinguished between physical and theoretical
indivisibility of the atoms (Furley 1967, p. 94). The physical
indivisibility of the atoms seems to be independent of the argument
for indivisible magnitudes, since the solidity of atoms--the fact
that there is no void within them--is said to be the reason why
they cannot be split. The existence of void space *between*
atoms is cited as the reason why they can be separated: one late
source, Philoponus, even suggests that atoms could never actually
touch, lest they fuse (DK 67A7). Whether or not Democritus himself saw
this consequence, it seems that atoms are taken to be indivisible
whatever their size. Presumably, though, there is a smallest size of
atom, and this is thought to be enough to avoid the paradoxes of
infinite divisibility.



A *reductio ad absurdum* argument reported by Aristotle
suggests that the atomists argued from the assumption that, if a
magnitude is infinitely divisible, nothing prevents it actually having
been divided at every point. The atomist then asks what would remain:
if the answer is some extended particles, such as dust, then the
hypothesized division has not yet been completed. If the answer is
nothing or points, then the question is how an extended magnitude
could be composed from what does not have extension (DK 68A48b,
123). 



Democritus is also said to have contributed to mathematics, and to
have posed a problem about the nature of the cone. He argues that if a
cone is sliced anywhere parallel to its base, the two faces thus
produced must either be the same in size or different. If they are the
same, however, the cone would seem to be a cylinder; but if they are
different, the cone would turn out to have step-like rather than
continuous sides. Although it is not clear from Plutarch's report how
(or if) Democritus solved the problem, it does seem that he was
conscious of questions about the relationship between atomism as a
physical theory and the nature of mathematical objects.


## 7. Ethics



The reports concerning Democritus' ethical views pose a number of
interpretative problems, including the difficulty of deciding which
fragments are genuinely Democritean (see above, section 1). In
contrast to the evidence for his physical theories, many of the
ethical fragments are lists of sayings quoted without context, rather
than critical philosophical discussions of atomist views. Many seem
like commonsense platitudes that would be consistent with quite
different philosophical positions. Thus, despite the large number of
ethical sayings, it is difficult to construct a coherent account of
his ethical views. Annas notes the Socratic character of a number of
the sayings, and thinks there is a consistent theme about the role of
one's own intellect in happiness (Annas 2002). The sayings contain
elements that can be seen as anticipating the more developed ethical
views of Epicurus (Warren 2002).



It is also a matter of controversy whether any conceptual link can be
found between atomist physics and the ethical commitments attributed
to Democritus. Vlastos argued that a number of features of Democritus'
naturalistic ethics can be traced to his materialist account of the
soul and his rejection of a supernatural grounding for ethics (Vlastos
1975). Taylor is more sceptical about the closeness of the connection
between Democritus' ethical views and his atomist physics (Taylor
1999a, pp. 232-4).



The reports indicate that Democritus was committed to a kind of
enlightened hedonism, in which the good was held to be an internal
state of mind rather than something external to it (see Hasper 2014).
The good is given many names, amongst them *euthymia* or
cheerfulness, as well as privative terms, e.g. for the absence of
fear. Some fragments suggest that moderation and mindfulness in one's
pursuit of pleasures is beneficial; others focus on the need to free
oneself from dependence on fortune by moderating desire. Several
passages focus on the human ability to act on nature by means of
teaching and art, and on a notion of balance and moderation that
suggests that ethics is conceived as an art of caring for the soul
analogous to medicine's care for the body (Vlastos 1975, pp.
386-94). Others discuss political community, suggesting that
there is a natural tendency to form communities.


## 8. Anthropology



Although the evidence is not certain, Democritus may be the originator
of an ancient theory about the historical development of human
communities. In contrast to the Hesiodic view that the human past
included a golden age from which the present day is a decline, an
alternative tradition that may derive from Democritus suggests that
human life was originally like that of animals; it describes the
gradual development of human communities for purposes of mutual aid,
the origin of language, crafts and agriculture. Although the text in
question does not mention Democritus by name, he is the most plausible
source (Cole 1967; Cartledge 1997).



If Democritus is the source for this theory, it suggests that he took
seriously the need to account for the origin of all aspects of the
world of our experience. Human institutions could not be assumed to be
permanent features or divine gifts. The explanations offered suggest
that human culture developed as a response to necessity and the
hardships of our environment. It has been suggested that the sheer
infinite size of the atomist universe and thus the number of possible
combinations and arrangements that would occur by chance alone are
important in the development of an account that can show how human
institutions arise without assuming teleological or theological
origins (Cole 1967). Although here, as on other questions, the
evidence is less than certain, it is plausible that Democritus
developed a powerful and consistent explanation of much of the natural
world from a very few fundamentals.



For the reception and subsequent history of Democritean atomism, see
the related entry on ancient atomism.