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date: 03 March 2021


, of Abdera
  • David John Furley
  •  and C. C. W. Taylor

In Thrace, b. 460–57 bce (Apollod. in Diog. Laert. 9. 41), 40 years after Anaxagoras according to his own statement quoted by Diogenes (6). He travelled widely, according to various later accounts, and lived to a great age. In later times he became known as ‘the laughing philosopher’, probably because he held that ‘cheerfulness’ (euthymiē) was a goal to be pursued in life. There is a story that he visited Athens—‘but no one knew me’ (Diog. Laert. 9. 36); this may be a reflection of the undoubted fact that Plato (1), although he must have known his work, never mentioned him by name.


Diogenes Laertius 9. 46–9 mentions 70 titles, arranged in tetralogies by Thrasyllus like the works of Plato, and classified as follows: Ethics, Physics, Unclassified, Mathematics, Music (which includes philological and literary criticism), Technical, and Notes. None of these works survives. Of his physical theories, on which his fame rests, only meagre quotations and summaries remain; the majority of texts that have come down to us under his name are brief and undistinguished moral maxims.

From the time of Aristotle, Democritus and Leucippus (3) are jointly credited with the creation of the atomic theory of the universe (see atomism); it is now impossible to distinguish the contribution of each. Aristotle's account of the origin of the theory (gen. corr. 1. 8) rightly relates it to the Eleatics (see Eleatic school). Parmenides argued that what is real is one and motionless, since empty space is not a real existent; motion is impossible without empty space, and plurality is impossible without something to separate the units. Division of what is real into units in contact, i.e. with no separating spaces, is ruled out because (a) infinite divisibility would mean there are no real units at all, and (b) finite divisibility is physically inexplicable. Against these arguments, says Aristotle, Leucippus proposed to rescue the sensible world of plurality and motion by asserting that empty space, ‘the non-existent’, may nevertheless serve to separate parts of what exists from each other. So the universe has two ingredients: Being, which satisfies the Eleatic criteria by being ‘full’, unchanging, and homogeneous, and Non-being or empty space. The pieces of real Being, since it is their characteristic to be absolutely indivisible units, are called ‘atoms’ (i.e. ‘uncuttables’). They are said to be solid, invisibly small, and undifferentiated in material; they differ from each other in shape and size only (perhaps also in weight), and the only change they undergo is in their relative and absolute position, through movement in space.

By their changes of position the atoms produce the compounds of the changing sensible world. Compounds differ in quality according to the shape and arrangement of the component atoms, their congruence or otherwise (i.e. their tendency to latch together because of their shape), and the amount of space between them. It is a matter of controversy whether the atoms have a natural downward motion due to weight (as later in Epicurean theory: see Epicurus, Doctrines)) or move randomly in the void until their motion is somehow directed by collisions with other atoms. In the course of time, groups of atoms form ‘whirls’ or vortexes, which have the effect of sorting out the atoms by size and shape, like to like. Some of these are sorted in such a way as to produce distinct masses having the appearance of earth, water, air, and fire: thus worlds are formed—not one single world, as in most Greek cosmologies, but an indeterminate number scattered thoughout the infinite void, each liable to perish through random atomic motions, as they were originally formed. Leucippus and Democritus produced an account of the evolution within worlds of progressively more complex stages of organization, including human cultures (traces in Diod. Sic. 1. 7–8 and see Lucr. bk. 5).

The soul, which is the cause of life and sensation, is made of fine round atoms, and is a compound as perishable as the body. Perception takes place through the impact of eidōla (thin atomic films shed from the surfaces of sensible objects) upon the soul-atoms through the sense organs. Perceptible qualities are the product of the atoms of the sensible object and those of the perceiving soul. (A relatively full account is preserved in Theophr. Sens. 49–82.) They therefore have a different mode of existence from atoms and void—‘by convention’ as opposed to ‘in reality’. See atomism.

Little is known about Democritus' mathematics, although mathematical writings appear in the lists of his works; he must have been a diligent biologist, for Aristotle quotes him often.

Many surviving fragments deal with ethics, but they are mostly short maxims, hard to fit together into a consistent and comprehensive doctrine (see Havelock (in bibliog. below), ch. 6 for a bold effort). His positions, as reported, are close to those of Epicurus, and it is hard to know whether this is historically genuine or a prejudice of the doxographers. His ethical ideal seems to include the idea that the soul-atoms should be protected from violent upheavals; well-being which leads to ‘cheerfulness’ (euthymiē) is a matter of moderation and wisdom (B 191). It is important not to let the fear of death spoil life, and to recognize the limits to which man is necessarily confined (B 199, 203). Pleasure is in some sense the criterion of right action, but there must be moderation in choosing pleasures (B 189, 207, 224, 231). In social ethics, Democritus was apparently prepared to link his view of contemporary society with his theory of the evolution of human communities; he saw that a system of law is by nature necessary for the preservation of society.

Democritus is a figure of great importance who has suffered intolerably from the triumph of his opponents, Plato, Aristotle, and the Stoics (see Stoicism). He defended the infinite universe, plural and perishable worlds, efficient, non-teleological causes, and the atomic theory of matter, as opposed to the single, finite, and eternal cosmos of Aristotle, teleology, and the continuous theory of matter. The best brains preferred his opponents' arguments, and Epicurus and Lucretius were his only influential followers until the post-Renaissance scientific revolution—by which time his books were lost. See alchemy.


Ancient sources
  • H. Diels and W. Kranz, Fragmente der Vorsokratiker, 6th edn. (1952), no. 68.
  • S. Luria, Democritea (1970) (Greek and Latin texts with comm. in Russian;. (Italian trans., ed. G. Girgenti [2007]).
  • C. C. W. Taylor, The Atomists: Leucippus and Democritus. Fragments (1999).
Modern literature
    (1) General
    • K. Lasswitz, Geschichte der Atomistik (1890).
    • H. Cherniss, Aristotle's Criticism of Presocratic Philosophy (1935).
    • S. Sambursky, The Physical World of the Greeks (1956).
    • W. K. C. Guthrie, History of Greek Philosophy (1965–1981), 2.
    • J. Barnes, The Presocratic Philosophers (1979).
    • D. Furley, The Greek Cosmologists 1 (1987).
    (2) Collections
    • F. Romano (ed.), Democrito e l'atomismo antico (1980).
    • L. G. Benakis (ed.), Proceedings of the First International Congress on Democritus (1984).
    (3) Special
    • C. Bailey, The Greek Atomists and Epicurus (1928. repr. 1964).
    • S. Luria, ‘Die infinitesimallehre der antiken Atomisten,’ Quellen und Studien zur Geschichte der Mathematik B 2 (1933).
    • K. Von Fritz, Philosophie und sprachlicher Ausdruck bei Demokrit, Platon, und Aristoteles (1938).
    • G. Vlastos, Philosophical Review 1945.
    • G. Vlastos, Philosophical Review 1946.
    • V. E. Alfieri, Atomos Idea (1953).
    • E. Havelock, The Liberal Temper in Greek Politics (1957).
    • D. J. Furley, Two Studies in the Greek Atomists (1967).
    • T. Cole, Democritus and the Sources of Greek Anthropology (1967).
    • R. Löbl, Demokrits Atome (1976).
    • A. Stuckelberger, Antike Atomphysik (1979).
    • D. O'brien, Theories of Weight in the Ancient World 1: Democritus on Weight and Size (1981).
    • D. Sedley, Phronesis 1982.
    • E. L. Hussey, in P. Cartledge and F. D. Harvey (eds.), CRUX (1985), 118 ff.
    • H. Baltussen, Theophrastus on Theories of Perception (1993), with extensive bibliogs.