The Atomists represent the last phase of Ionian speculation concerning
nature. They accept the dualistic ideas which characterize the Later
Ionian philosophy, but by their substitution of necessity for
intelligent force they abandon all that dualistic philosophy had to
bequeath to them, and fall lower than the level which the early
hylozoists had reached.
It was at Miletus that the Ionian philosophy first appeared, and it was
Miletus that produced Leucippus, the founder of Atomism, who virtually
brings the first period of Greek philosophy to a close. So little is
known of Leucippus that his very existence has been questioned. His
opinions, too, have been so imperfectly transmitted to us that it is
usual to speak of the tenets of the Atomists without distinguishing
how much we owe to Leucippus, who by Aristotle and Theophrastus is
regarded as the founder of the system, and how much we owe to
Democritus, who was the ablest and best-known expounder of atomistic
 Cf. Burnet, op. cit., p. 350.
Life. Democritus of Abdera was born about the year 460 B.C. It is
said -- though it is by no means certain -- that he received instruction
from the Magi and other Oriental teachers. It is undoubtedly true that,
at a later time, he was regarded as a sorcerer and magician, -- a
fact which may account for the legend of his early training. He was
probably a disciple of Leucippus. There is no historical foundation for
the widespread belief that he laughed at everything.
 Cf. Zeller, Pre-Socratic Phil., II, 213, n.
Sources. If, as is probable, Leucippus committed his doctrines
to writing, no trustworthy fragment of his works has reached us. From
the titles and
the fragments of the works of Democritus it is evident that the latter
covered in his written treatises a large variety of subjects. The most
celebrated of these treatises was entitled megas diakosmos. Mullach
(Fragmenta, I, 340 ff.) publishes fragments of this and other
Aristotle in the Metaphysics and elsewhere gives an adequate
account of the doctrines of Leucippus and Democritus.
General Standpoint. One of the reasons which led the Eleatics to
deny plurality and Becoming was that these are inconceivable without
void, and void is unthinkable. Now, the Atomists concede that without
void there is no motion, but they maintain that void exists, and that
in it exists an infinite number of indivisible bodies (atomoi)
which constitute the plenum. Aristotle is therefore justified in
saying  that according to Leucippus and Democritus the elements are
the full (plÍres) and the void (kenon). The full
corresponds to Eleatic Being and the void to not-Being. But the latter
is as real as the former.  On the combination and separation of atoms
depend Becoming and decay.
 Met., I, 4, 985 b, 4.
 Cf. Arist., Phys., IV, 6, 213 a, 31, for arguments by
which the Atomists proved the existence of the void.
The Atoms. The atoms, infinite in number and indivisible, differ
in shape, order, and position.  They differ, moreover, in quantity, or
magnitude,  for they are not mere mathematical points, their
indivisibility being due to the fact that they contain no void. They
have, as we would say, the same specific gravity, but because of their
different sizes they differ in weight. 
 Arist., Met., I, 4, 985 b, 14.
 Arist., Phys., III, 4, 203 a, 33.
 Arist., De Generatione et Corruptione, I, 8, 324 b and 325
The Motion by which the atoms are brought together is not caused
by a vital principle inherent in them (hylozoism),
nor by love and hatred, nor by any incorporeal agency, but by
natural necessity, by virtue of which atoms of equal weight come
together. It is, therefore, incorrect to say that the Atomists
explained the motion of the atoms by attributing it to chance.
Aristotle gave occasion to this misunderstanding by identifying
automaton and tuchÍ though it is Cicero  who is
accountable for giving the misapprehension the wide circulation which
 De Nat. Deorum, I, 24, 66.
The atomistic explanation was, therefore, that atoms of different
weights fell with unequal velocities in the primitive void. The heavier
atoms, consequently, impinged on the lighter ones, imparting to them a
whirling motion (dinÍ). The Atomists, as Aristotle
remarks,  did not advert to the fact that in vacuo all bodies
fall with equal velocity. Nowhere in the cosmological scheme of the
Atomists is there place for mind or design; it is utter materialism and
casualism, if by casualism is meant the exclusion of intelligent
 Phys., IV, 8, 225 a.
Anthropology. Plants and animals sprang from moist earth.
Democritus, according to our authorities, devoted special attention to
the study of Man, who, he believes, is, even on account of his bodily
structure alone, deserving of admiration. He not only describes as
minutely as he can the bodily organization of man, but, departing from
his mechanical concept of nature, takes pains to show the utility and
adaptation of every part of the human body. But over all and permeating
all is the soul. Now the soul, for the Atomists, could be
nothing but corporeal. It is composed of the finest atoms, perfectly
smooth and round, like the atoms of fire.  Democritus, accordingly,
does not deny a distinction between soul and body. He teaches that the
soul is the noblest part of man; man's crowning glory is moral
excellence. He is said to have reckoned the human soul among the
divinities.  And yet, for Democritus, as for every
materialist, the soul is but a finer kind of matter. Indeed, according
to Aristotle,  the Atomists identified soul-atoms with the atoms of
fire which are floating in the air.
 Arist., De An., I, 2, 403 b, 28.
 Cf. Zeller, op. cit., II, p. 262.
 De Respiratione, 4, 472 a, 30.
The Atomists' theory of cognition was, of course, determined by
their view of the nature of the soul. They were obliged to start out
with the postulate that all cognitive processes are corporeal
processes, and since the action of body upon body is conditioned by
contact, they were obliged to conclude that all the senses are mere
modifications of the sense of touch. 
 Arist., Met., IV, 5, 1009 b, and De Sensu, 4, 442 a,
The contact which is a necessary condition of all sense-knowledge is
effected by means of emanations (aporroai, -- the term is
Aristotle's), or images (eidŰla, deikela). These
are material casts, or shells, given off from the surface of the
object; they produce in the medium the impressions which enter the
pores of the senses. They are practically the same as the Epicurean
effluxes, which Lucretius describes:
Quae, quasi membranae, summo de corpore rerum
Dereptae, volitant ultro citroque per auras.
Thought cannot differ essentially from sense-knowledge. They are
both changes (heteroiŰseis) of the soul-substance
occasioned by material impressions. Logically, therefore, Democritus
should have attached the same value to thought as to sense-knowledge,
and since sense-knowledge is obscure (skotiÍ), he should have
concluded that no knowledge is satisfactory. He saves himself, however,
from absolute Scepticism, although at the expense of logical
consistency; for he maintains that thought, by revealing the existence
of invisible atoms, shows us the true nature of things. The doctrine
which Aristotle  attributes to Democritus is his opinion as to what
Democritus should have taught, rather than an account of what he
actually did teach. 
 Met., IV, 5, 1009 a, 38.
 Cf. Zeller, op. cit., II, 272.
Ethics. Although most of the extant fragments which contain
Democritus' ethical teachings are merely isolated axioms without any
scientific connection, yet our secondary authorities attribute to him a
theory of happiness which is really the beginning of the science
of ethics among the Greeks. From what Democritus says of the
superiority of the soul over the body, of thought over sense, it is
natural to expect that he should place man's supreme happiness in a
right disposition of mind and not in the goods of the external world.
"Happiness," he says,  "and unhappiness do not dwell in herds nor in
gold; the soul is the abode of the Divinity." Happiness is in no
external thing, but in "cheerfulness and well-being, a right
disposition and unalterable peace of mind." The word which is here
rendered cheerfulness (euthumia) is interpreted by Seneca
and other Stoics as tranquillity. Democritus, however, was more
akin to the Epicureans than to the Stoics, and it is probable that by
euthumia he meant "delight" or "good cheer."  There is in the
moral maxims of Democritus a note of pessimism. Happiness, he believes,
is difficult of attainment, while misery seeks man unsought.
 Frag. 1.
 Cf. Sidgwick, Hist. of Ethics, p. 15.
Historical Position. The atomistic movement is recognized as an
attempt to reconcile the conclusions of the Eleatics with the facts of
experience. It is not easy, however, to determine with accuracy how far
the Atomists were influenced by their predecessors and contemporaries.
Even if the dates of Heraclitus, Anaxagoras, Empedocles, and Leucippus
were known more definitely than they are, it would still be a matter of
no small difficulty to show in what degree each philosopher depended on
and in turn influenced the thought and writings of the others. One
thing is certain: it was Atomism which more than any of the other
pre-Socratic systems prepared the way for Sophism and the consequent
contempt of all knowledge.
In the first place, atomistic philosophy was materialistic, and
"Materialism ends where the highest problems of philosophy begin."
Moreover, the armor of the Atomist offered several vulnerable points to
the shafts of Sophism. He fallaciously concluded that atoms are
uncaused because they are eternal; and, what is worse, he
inconsistently maintained the difference in value between
sense-knowledge and thought. The Sophists might well argue, as indeed
some of them did argue, that if the senses are not to be trusted,
reason also is untrustworthy, for the soul, according to the Atomists,
is, like the senses, corporeal. Thus did atomistic philosophy prepare
the way for Sophism.