(Δημόκριτος), was a native of Abdera in Thrace, an Ionian colony of Teos. (Aristot. Cael. 3.4, Meteor. 2.7, with Ideler's note.) Some called him a Milesian, and the name of his father too is stated differently. (D. L. 9.34, &c.) His birth year was fixed hy Apollodorus in Ol. 80. 1, or B. C. 460, while Thrasyllus had referred it to Ol. 77. 3. (Diog. Laert. l.c. § 41, with Menage's note; Gellius, 17.21 ; Clinton, F. H. ad ann. 460.) Democritus had called himself forty years younger than Anaxagoras. His father, Hegesistratus,--or as others called him Damasippus or Athenocritus,--was possessed of so large a property, that he was able to receive and treat Xerxes on his march through Abdera. Democritus spent the inheritance, which his father left him, on travels into distant countries, which he undertook to satisfy his extraordinary thirst for knowledge. He travelled over a great part of Asia, and, as some state, he even reached India and Aethiopia. (Cic. de Fin. 5.19; Strabo, xvi. p 703; A. H. C. Geffers, Quaestiones Democrit. p. 15, &c.) We know that he wrote on Babylon and Meroe; he must also have visited Egypt, and Diodorus Siculus (1.98) even states, that he lived there for a period of five years. He himself declared (Clem. Al. Strom. i. p. 304), that among his contemporaries none had made greater journeys, seen more countries, and made the acquaintance of more men distinguished in every kind of science than himself. Among the last he mentions in particular the Egyptian mathematicians (ἀρπεδόναπ-ται ; comp. Sturz, de Dialect. Maced. p. 98), whose knowledge he praises, without, however, regarding himself inferior to them. Theophrastus, too, spoke of him as a man who had seen many countries. (Aelian, Ael. VH 4.20; D. L. 9.35.) It was his desire to acquire an extensive knowledge of nature that led him into distant countries at a time when travelling was the principal means of acquiring an intellectual and scientific culture ; and after returning to his native land he occupied himself only with philosophical investigations, especially such as related to natural history. In Greece itself, too, he endeavoured by means of travelling and residing in the principal cities to acquire a knowledge of Hellenic culture and civilization. He mentioned many Greek philosophers in his writings, and his wealth enabled him to purchase the works they had written. He thus succeeded in excelling, in the extent of his knowledge, all the earlier Greek philosophers, among whom Leucippus, the founder of the atomistic theory, is said to have exercised the greatest influence upon his philosophical studies. The opinion that he was a disciple of Anaxagoras or of the Pythagoreans (Diog Laert. 9.38), perhaps arose merely from the fact, that he mentioned them in his writings. The account of his hostility towards Anaxagoras, is contradicted by several passages in which he speaks of him in terms of high praise. (D. L. 2.14; Sext. Empir. ad v. Math. 7.140.) It is further said, that he was on terms of friendship with Hippocrates, and some writers even speak of a correspondence between Democritus and Hippocrates; but this statement does not seem to be deserving of credit. (D. L. 9.42; Brandis, Handbuch der Griech. u. Röm. Philos. p. 300.) As he was a contemporary of Plato, it may be that he was acquainted with Socrates, perhaps even with Plato, who, however, does not mention Democritus anywhere. (Hermann, System der Platon. Philos.i. p. 284.) Aristotle describes him and his views as belonging to the ante-Socratic period (Arist. Metaph. 13.4 ; Phys. 2.2, de Partib. Anim. 1.1); but modern scholars, such as the learned Dutchman Groen van Prinsterer (Prosopograph. Platon. p.41, &c., comp. Brandis, l.c. p. 292, &c.), assert, that there are symptoms in Plato which shew a connexion with Democritus, and the same scholar pretends to discover in Plato's language and style an imitation of Democritus. (Persop. Plat. p. 42.) The many anecdotes about Democritus which are preserved, especially in Diogenes Laertius, shew that he was a man of a most sterling and honourable character. His diligence was incredible: he lived exclusively for his studies, and his disinterestedness, modesty, and simplicity are attested by many features which are related of him. Notwithstanding his great property, he seems to have died in poverty, though highly esteemed by his fellow-citizens, not so much on account of his philosophy, as "because," as Diogenes says, " he had foretold them some things which the event proved to be true." This had probably reference to his knowledge of natural phaenomena. His fellow-citizens honoured him with presents in money and bronze statues. Even the scoffer Timon, who in his silli spared no one, speaks of Democritus only in terms of praise. He died at an advanced age (some say that he was 109 years old), and even the manner in which he died is characteristic of his medical knowledge, which, combined as it was with his knowledge of nature, caused a report, which was believed by some persons, that he was a sorcerer and a magician. (Plin. Nat. 24.17, 30.1.) His death is placed in Ol. 105. 4, or B. C. 357, in which year Hippocrates also is said to have died. (Clinton, F. H. ad ann. 357.) We cannot leave unnoticed the tradition that Democritus deprived himself of his sight, in order to be less disturbed in his pursuits. (Cic. de Fin. 5.29; Gellius, 10.17; D. L. 9.36; Cic. Tusc. 5.39; Menage, ad Dioy. Laert. 9.43.) But this tradition is one of the inventions of a later age, which was fond of piquant anecdotes. It is more probable that he may have lost his sight by too severe application to study. (Brandis, l.c. p. 298.) This loss, however, did not disturb the cheerful disposition of his mind and his views of human life, which prompted him everywhere to look at the cheerful and comical side of things, which later writers took to mean, that he always laughed at the follies of men. (Senec. de Ira, 2.10; Aelian, Ael. VH 4.20.)

Of the extent of his knowledge, which embraced not only natural sciences, mathematics, mechanics (Brandis, in the iii. p. 134, &c.), grammar, music, and philosophy, but various other useful arts, we may form some notion from the list of his numerous works which is given by Diogenes Laertius (9.46-49), and which, as Diogenes expressly states, contains only his genuine works. The grammarian Thrasyllus, a contemporary of the emperor Tiberius, arranged them, like the works of Plato, into tetralogies. The importance which was attached to the researches of Democritus is evident from the fact, that Aristotle is reported to have written a work in two books on the problems of Democritus. (D. L. 5.26.) His works were composed in the Ionic dialect, though not without some admixture of the local peculiarities of Abdera. (Philopon. in Aristot. de gener. et corrupt. fol. 7, a.; Simplic. ad Aristot. de Coelo, fol. 150, a.; Suid. s. v. ρνσμός.) They are nevertheless much praised by Cicero on account of the poetical beauties and the liveliness of their style, and are in this respect compared even with the works of Plato. (Groen van Prinsterer, l.c.; Cic. de Div. 2.64, de Orat. 1.11, Orat. 20; Dionys. de Compos. verb. 24; Plut. Sympos. 5.7, p. 683.) Pyrrhon is said to have imitated his style (Euseb. Praep. Evang. 14.6), and even Timon praises it, and calls it περίφρονα καὶ ἀμφίνοον λέσχην. (D. L. 9.40.) Unfortunately, not one of his works has come down to us, and the treatise which we possess under his name is considered spurious. Callimachus wrote glosses upon his works and made a list of them (Suid. s. v.); but they must have been lost at an early time, since even Simplicius does not appear to have read them (Papencordt, de Atomicorum doctrina, p. 22), and since comparatively few fragments have come down to us, and these fragments refer more to ethics than to physical matters. There is a very good collection of these fragments by F. G. A. Mullach, " Democriti Abderitae operum fragments," Berlin, 1843, 8vo. Besides this work, which contains also elaborate dissertations on the life and writings of Democritus, the student may consult-- 1. Burchardt, Comment. crit. de Democriti de sensibus philosophia, in two programs, Minden, 1830 and 1839, 4to.2. Burchardt, Fragmente der Moral des Demokrit, Minden, 1834, 4to.3. Heimsöth, Democriti de anima doctrina, Bonn, 1835, 8vo.4. H. Stephanus, Poesis Philos. p. 156, &c.5. Orelli, Opusc. Graec. Sent. i. p. 91, &c. Concerning the spurious works and letters of Democritus, see Fabric. Bibl. Gr. i. p. 683, &c., ii. pp. 641, 639, iv. p. 333, &c.

The philosophy of Democritus has, in modern times been the subject of much investigation. Hegel (Vorlesung. üb. Gesch. d. Philos. i. p. 379, &c.) treats it very briefly, and does not attach much importance to it. The most minute investigations concerning it are those of Ritter (Gesch. d. Philos. i. p. 559), Brandis (Rhein. Mus. iii. p. 133, &c., and Gesch. der Griech. u. Röm. Philos. i. p. 294, &c.), Petersen (Histor. Philog. Studien. i. p. 22, &c.), Papencordt (Atomicorum doctrina), and Mullach (l.c. pp. 373-419).

It was Democritus who, in his numerous writings, carried out Leucippus's theory of atoms, and especially in his observations on nature. These atomists undertook the task of proving that the quantitative relations of matter were its original characteristics, and that its qualitative relations were something secondary and derivative, and of thus doing away with the distinction between matter and mind or power. (Brandis, l.c. p. 294.) In order to avoid the difficulties connected with the supposition of primitive matter with definite qualities, without admitting the coming into existence and annihilation as realities, and without giving up, as the Eleatic philosophers did, the reality of variety and its changes, the atomists derived all definiteness of phaenomena, both physical and mental, from elementary particles, the infinite number of which were homogeneous in quality, but heterogeneous in form. This made it necessary for them to establish the reality of a vacuum or space, and of motion. (Brandis, l.c. p. 303, &c.) Motion, they said, is the eternal and necessary consequence of the original variety of atoms in the vacuum or space. All phaenomena arise from the infinite variety of the form, order, and position of the atoms in forming combinations. It is impossible, they add, to derive this supposition from any higher principle, for a beginning of the infinite is inconceivable. (Aristot. de Generat. Anim. 2.6, p. 742b. 20, ed. Bekker; Brandis, l.c. p. 309, &c.c.) The atoms are impenetrable, and therefore offer resistance to one another. This creates a swinging, world-producing, and whirling motion. (This reminds us of the joke in the Clouds of Aristophanes about the god Δῖνος !) Now as similars attract one another, there arise in that motion real things and beings, that is, combinations of distinct atoms, which still continue to be separated from one another by the vacuum. The first cause of all existence is necessity, that is, the necessary predestination and necessary succession of cause and effect. This they called chance, in opposition to the νοῦς of Anaxagoras. But it does the highest honour to the mind of Democritus, that he made the discovery of causes the highest object of scientific investigations. He once said, that he preferred the discovery of a true cause to the possesssion of the kingdom of Persia. (Dionys. Alex. apud Euseb. Praep. Evang. 14.27.) We must not, therefore, take the word chance (τυχή) in its vulgar acceptation. (Brandis, l.c. p. 319.) Aristotle understood Democritus rightly in this respect (Phys. Auscult. 2.4, p. 196. 11; Simplic. fol. 74), as he generally valued him highly, and often says of him, that he had thought on all subjects, searched after the first causes of phenomena, and endeavoured to find definitions. (De Generat. et Corrupt. 1.2, 8, Metaph. M. 4, Phys. 2.2, p. 194, 20, de Part. Anim. i. p. 642, 26.) The only thing for which he censures him, is a disregard for teleological relations, and the want of a comprehensive system of induction. (De Respir. 4, de Generat. Anim. 5.8.) Democritus himself called the common notion of chance a cover of human ignorance (πρόφα-σιν ἰδίης ἀνοίης), and an invention of those who were too idle to think. (Dionys. apud Euseb. Praep. Evang. 14.27; Stob. Eclog. Eth. p. 344.)

Besides the infinite number of atoms existing in infinite space, Democritus also supposed the existence of an infinite number of worlds, some of which resembled one another, while others differed from one another, and each of these worlds was kept together as one thing by a sort of shell or skin. He derived the four elements from the form of the atoms predominating in each, from their quality, and their relations of magnitude. In deriving individual things from atoms, he mainly considered the qualities of warm and cold. The warm or firelike he took to be a combination of fine, spheric, and very movable atoms, as opposed to the cold and moist. His mode of proceeding, however, was, first carefully to observe and describe the phaenomena themselves, and then to attempt his atomistic explanation, whereby he essentially advanced the knowledge of nature. (Papencordt, l.c. p. 45, &c.; Brandis, l.c. p. 327.) He derived the soul, the origin of life, consciousness, and thought, from the finest fire-atoms (Aristot. de An. 1.2, ed. Trendelenburg); and in connexion with this theory he made very profound physiological investigations. It was for this reason that, according to him, the soul while in the body acquires perceptions and knowledge by corporeal contact, and that it is affected by heat and cold. The sensuous perceptions themselves were to him affections of the organ or of the subject perceiving, dependent on the changes of bodily condition, on the difference of the organs and their quality, on air and light. Hence the differences, e. g., of taste, colour, and temperature, are only conventional (Sext. Empir. ad v. Math. 7.135), the real cause of those differences being in the atoms.

It was very natural, therefore, that Democritus described even the knowledge obtained by sensuous perception as obscure (σκοτίην κρίσιν). A clear and pure knowledge is only that which has reference to the true principles or the true nature of things, that is, to the atoms and space. But knowledge derived from reason was, in his opinion, not specifically different from that acquired through the senses; for conception and reflection were to him only effects of impressions made upon the senses; and Aristotle, therefore, expressly states, that Democritus did not consider mind as something peculiar, or as a power distinct from the soul or sensuous perception, but that he considered knowledge derived from reason to be sensuous perceptions. (De Anim. 1.2. p. 404, 27.) A purer and higher knowledge which he opposed to the obscure knowledge obtained through the medium of the senses, must therefore have been to him a kind of sensation, that is, a direct perception of the atoms and of space. For this reason he assumed the three criteria (κριτήρια) : a. Phaenomena as criteria for discovering that which is hidden : b. Thought as a criterion of investigation : and c. Assertions as criteria of desires. (Sext. Emp. ad v. Math. 7.140; Brandis, l.c. p. 334.) Now as Democritus acknowledged the uncertainty of perceptions, and as he was unable to establish a higher and purely spiritual source of knowledge as distinct from perceptions, we often find him complaining that all human knowledge is uncertain, that in general either nothing is absolutely true, or at least not clear to us (ἄδηλον, Aristot. Metaph. Γ. 5), that our senses grope about in the dark (sensus tenebricosi, Cic. Ac. 4.10, 23), and that all our views and opinions are subjective, and come to us only like something epidemic, as it were, with the air which we breathe. (Sext. Emp. ad v. Math. 7.136, 137, 8.327, Hypotyp. 1.213 ; D. L. 9.72, ἐτεῇ δʼ οὐδὲν ἴδμεν, ἐν βυθῷ γὰρ ἡ ἀλ́ηεια, which Cicero translates in profundo veritatem esse.)

In his ethical philosophy Democritus considered the acquisition of peace of mind (εὐθυμία) as the end and ultimate object of our actions. (D. L. 9.45; Cic. de Fin. 5.29.) This peace, this tranquillity of the mind, and freedom front fear (φόβος and δεισδαιμονία) and passion, is the last and fairest fruit of philosophical inquiry. Many of his ethical writings had reference to this idea and its establishment, and the fragments relating to this question are full of the most genuine practical wisdom. Abstinence from too many occupations, a steady consideration of one's own powers, which prevents our attempting that which we cannot accomplish, moderation in prosperity and misfortune, were to him the principal means of acquiring the εὐθυμία. The noblest and purest ethical tendency, lastly, is manifest in his views on virtue and on good. Truly pious and beloved by the gods, he says, are only those who hate that which is wrong (ὅσοις ἐχθρὸν τὸ αδικεῖν). The purest joy and the truest happiness are only the fruit of the higher mental activity exerted in the endeavour to understand the nature of things, of the peace of mind arising from good actions, and of a clear conscience. (Brandis, l.c. p. 337.)