Democritus (Greek: Δημόκριτος, Dēmokritos, "chosen of the people") (ca. 460 BC – ca. 370 BC) was an Ancient Greek philosopher born in Abdera, Thrace, Greece. He was an influential pre-Socratic philosopher and pupil of Leucippus, who formulated an atomic theory for the cosmos.
His exact contributions are difficult to disentangle from his mentor Leucippus, as they are often mentioned together in texts. Their speculation on atoms, taken from Leucippus, bears a passing and partial resemblance to the nineteenth-century understanding of atomic structure that has led some to regard Democritus as more of a scientist than other Greek philosophers; nevertheless their ideas rested on very different bases. Largely ignored in Athens, Democritus was nevertheless well-known to his fellow northern-born philosopher Aristotle. Plato is said to have disliked him so much that he wished all his books burned. Many consider Democritus to be the "father of modern science".
Democritus was born in the city of Abdera in Thrace, an Ionian colony of Teos, although some called him a Milesian. He was born in the 80th Olympiad (460–457 BC) according to Apollodorus, and although Thrasyllus placed his birth in 470 BC, the later date is probably more likely. John Burnet has argued that the date of 460 is "too early", since according to Diogenes Laertius ix.41, Democritus said that he was a "young man (neos)" during Anaxagoras' old age (circa 440–428). It was said that Democritus' father was so wealthy that he received Xerxes on his march through Abdera. Democritus spent the inheritance which his father left him on travels into distant countries, to satisfy his thirst for knowledge. He travelled to Asia, and was even said to have reached India and Ethiopia. We know that he wrote on Babylon and Meroe; he must also have visited Egypt, and Diodorus Siculus states that he lived there for five years. He himself declared that among his contemporaries none had made greater journeys, seen more countries, and met more scholars than himself. He particularly mentions the Egyptian mathematicians, whose knowledge he praises. Theophrastus, too, spoke of him as a man who had seen many countries. During his travels, according to Diogenes Laertius, he became acquainted with the Chaldean magi. A certain "Ostanes", one of the magi accompanying Xerxes was also said to have taught him.
After returning to his native land he occupied himself with natural philosophy. He traveled throughout Greece to acquire a knowledge of its culture. He mentions many Greek philosophers in his writings, and his wealth enabled him to purchase their writings. Leucippus, the founder of the atomism, was the greatest influence upon him. He also praises Anaxagoras. Diogenes Laertius says that he was friends with Hippocrates. He may have been acquainted with Socrates, but Plato does not mention him and Democritus himself is quoted as saying, "I came to Athens and no one knew me." Aristotle placed him among the pre-Socratic natural philosophers.
The many anecdotes about Democritus, especially in Diogenes Laertius, attest to his disinterestedness, modesty, and simplicity, and show that he lived exclusively for his studies. One story has him deliberately blinding himself in order to be less disturbed in his pursuits; it may well be true that he lost his sight in old age. He was cheerful, and was always ready to see the comical side of life, which later writers took to mean that he always laughed at the foolishness of people.
He was highly esteemed by his fellow-citizens, "because," as Diogenes Laertius says, "he had foretold them some things which events proved to be true," which may refer to his knowledge of natural phenomena. According to Diodorus Siculus, Democritus died at the age of 90, which would put his death around 370 BC, but other writers have him living to 104, or even 109.
Popularly known as the Laughing Philosopher (for laughing at human follies), the terms Abderitan laughter, which means scoffing, incessant laughter, and Abderite, which means a scoffer, are derived from Democritus. To his fellow citizens he was also known as "The Mocker".
Philosophy and science
Democritus followed in the tradition of Leucippus, who seems to have come from Miletus, and he carried on the scientific rationalist philosophy associated with that city. They were both strict determinists and thorough materialists, believing everything to be the result of natural laws, and they will have nothing to do with chance or randomness. Unlike Aristotle or Plato, the atomists attempted to explain the world without reasoning to purpose, prime mover, or final cause. For the atomists questions should be answered with a mechanistic explanation ("What earlier circumstances caused this event?"), while their opponents search for explanations which, in addition to the material and mechanistic, also included the formal and teleological ("What purpose did this event serve?"). Modern science has focused on mechanistic questions, which have led to scientific knowledge, especially in physics, while teleological question can be useful in biology, in adaptationist reasoning at providing proximate explanations, though the deeper evolutionary explanations are often held to be thoroughly mechanistic. The atomists looked exclusively for mechanistic questions, and only admitted mechanistic answers. Their successors until the Renaissance became occupied with the teleological question, which arguably hindered progress.
The theory of Democritus and Leucippus held that everything is composed of "atoms", which are physically, but not geometrically, indivisible; that between atoms lies empty space; that atoms are indestructible; have always been, and always will be, in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape, and size. Of the mass of atoms, Democritus said "The more any indivisible exceeds, the heavier it is." But their exact position on weight of atoms is disputed.
Leucippus is widely credited with being the first to develop the theory of atomism, although Isaac Newton preferred to credit the obscure Moschus the Phoenician (whom he believed to be the biblical Moses) as the inventor of the idea. The Stanford Encyclopedia of Philosophy notes, "This theologically motivated view does not seem to claim much historical evidence, however."
Democritus, along with Leucippus and Epicurus, proposed the earliest views on the shapes and connectivity of atoms. They reasoned that the solidness of the material corresponded to the shape of the atoms involved. Thus, iron atoms are solid and strong with hooks that lock them into a solid; water atoms are smooth and slippery; salt atoms, because of their taste, are sharp and pointed; and air atoms are light and whirling, pervading all other materials. Democritus was the main proponent of this view. Using analogies from our sense experiences, he gave a picture or an image of an atom that distinguished them from each other by their shape, their size, and the arrangement of their parts. Moreover, connections were explained by material links in which single atoms were supplied with attachments: some with hooks and eyes others with balls and sockets. The Democritean atom is an inert solid (merely excluding other bodies from its volume) that interacts with other atoms mechanically. In contrast, modern, quantum-mechanical atoms interact via electric and magnetic force fields and are far from inert.
The theory of the atomists appears to be more nearly aligned with that of modern science than any other theory of antiquity. However, the similarity with modern concepts of science can be confusing when trying to understand where the hypothesis came from. It is obvious that classical atomists would never have had a solid empirical basis for our modern concepts of atoms and molecules. Russell  states that they just hit on a lucky hypothesis, only recently confirmed by evidence.
However Lucretius, describing atomism in his de rerum natura gives very clear and compelling empirical arguments for the original atomist theory. He observes that any material is subject to irreversible decay. Through time, even hard rocks are slowly worn down by drops of water. Things have the tendency to get mixed up: mix water with soil and you get mud, that will usually not un-mix by itself. Wood decays. However, we see in nature and technology that there are mechanisms to recreate 'pure' materials like water, air, metals. The seed of an oak will grow out into an oak tree, made of similar wood as historical oak trees, the wood of which has already decayed. The conclusion is that many properties of materials must derive from something inside, that will itself never decay, something that stores for eternity the same inherent, indivisible properties. The basic question is: why has everything in the world not yet decayed, and how can the exact same materials, plants, animals be recreated again and again? One obvious solution to explain how indivisible properties can be conveyed in a way not easily visible to human senses, is to hypothesise the existence of 'atoms'. These classical 'atoms' are nearer to our modern concept of 'molecule' than to the atoms of modern science. The other big point of classical atomism is that there must be a lot of open space between these 'atoms': the void. Lucretius gives reasonable arguments that the void is absolutely necessary to explain how gasses and fluids can change shape, flow, while metals can be molded, without changing the basic material properties.
The atomistic void hypothesis was a response to the paradoxes of Parmenides and Zeno, the founders of metaphysical logic, who put forth difficult to answer arguments in favor of the idea that there can be no movement. They held that any movement would require a void-which is nothing-but a nothing cannot exist. The Parmenidean position was "You say there is a void; therefore the void is not nothing; therefore there is not the void." The position of Parmenides appeared validated by the observation that where there seems to be nothing there is air, and indeed even where there is not matter there is something, for instance light waves.
The atomists agreed that motion required a void, but simply ignored the argument of Parmenides on the grounds that motion was an observable fact. Therefore, they asserted, there must be a void. This idea survived in a refined version as Newton's theory of absolute space, which met the logical requirements of attributing reality to not-being. Einstein's theory of relativity provided a new answer to Parmenides and Zeno, with the insight that space by itself is relative and cannot be separated from time as part of a generally curved space-time manifold. Consequently, Newton's refinement is now considered superfluous.
The knowledge of truth according to Democritus is difficult, since the perception through the senses is subjective. As from the same senses derive different impressions for each individual, then through the sense-impressions we cannot judge the truth. We can only interpret the sense data through the intellect and grasp the truth, because the truth (aletheia) is at the bottom (en bythoe).
"And again, many of the other animals receive impressions contrary to ours; and even to the senses of each individual, things do not always seem the same. Which then, of these impressions are true and which are false is not obvious; for the one set is no more true than the other, but both are alike. And this is why Democritus, at any rate, says that either there is no truth or to us at least it is not evident."
"Democritus says: By convention hot, by convention cold, but in reality atoms and void, and also in reality we know nothing, since the truth is at bottom."
There are two kinds of knowing, the one he calls "legitimate" (gnesie: genuine) and the other "bastard" (skotie: obscure). The "bastard" knowledge is concerned with the perception through the senses, therefore it is insufficient and subjective. The reason is that the sense-perception is due to the effluences of the atoms (aporroai) from the objects to the senses. When these different shapes of atoms come to us, they stimulate our senses according to their shape, and our sense-impressions arise from those stimulations.
The second sort of knowledge, the "legitimate" one, can be achieved through the intellect, in other words, all the sense-data from the "bastard" must be elaborated through reasoning. In this way one can get away from the false perception of the "bastard" knowledge and grasp the truth through the inductive reasoning. After taking into account the sense-impressions, one can examine the causes of the appearances, draw conclusions about the laws that govern the appearances, and discover the causality (aetiologia) by which they are related. This is the procedure of thought from the parts to the whole or else from the apparent to non-apparent (inductive reasoning). This is one example of why Democritus is considered to be an early scientific thinker. The process is reminiscent of that by which science gathers its conclusions.
"But in the Canons Democritus says there are two kinds of knowing, one through the senses and the other through the intellect. Of these he calls the one through the intellect ‘legitimate’ attesting its trustworthiness for the judgement of truth, and through the senses he names ‘bastard’ denying its inerrancy in the discrimination of what is true. To quote his actual words: Of knowledge there are two forms, one legitimate, one bastard. To the bastard belong all this group: sight, hearing, smell, taste, touch. The other is legitimate and separate from that. Then, preferring the legitimate to the bastard, he continues: When the bastard can no longer see any smaller, or hear, or smell, or taste, or perceive by touch, but finer matters have to be examined, then comes the legitimate, since it has a finer organ of perception."
"In the Confirmations ... he says: But we in actuality grasp nothing for certain, but what shifts in accordance with the condition of the body and of the things (atoms) which enter it and press upon it."
"Democritus used to say that 'he prefers to discover a causality rather than become a king of Persia'."
Ethics and politics
The ethics and politics of Democritus come to us mostly in the form of maxims. He says that "Equality is everywhere noble," but he is not encompassing enough to include women or slaves in this sentiment. Poverty in a democracy is better than prosperity under tyrants, for the same reason one is to prefer liberty over slavery. Those in power should "take it upon themselves to lend to the poor and to aid them and to favor them, then is there pity and no isolation but companionship and mutual defense and concord among the citizens and other good things too many to catalogue." Money when used with sense leads to generosity and charity, while money used in folly leads to a common expense for the whole society- excessive hoarding of money for one's children is avarice. While making money is not useless, he says, doing so as a result of wrong-doing is the "worst of all things." He is on the whole ambivalent towards wealth, and values it much less than self-sufficiency. He disliked violence but was not a pacifist: he urged cities to be prepared for war, and believed that a society had the right to execute a criminal or enemy so long as this did not violate some law, treaty, or oath.
Goodness, he believed, came more from practice and discipline than from innate human nature. He believed that one should distance oneself from the wicked, stating that such association increases disposition to vice. Anger, while difficult to control, must be mastered in order for one to be rational. Those who take pleasure from the disasters of their neighbors fail to understand that their fortunes are tied to the society in which they live, and they rob themselves of any joy of their own. He advocated a life of contentment with as little grief as possible, which he said could not be achieved through either idleness or preoccupation with worldly pleasures. Contentment would be gained, he said, through moderation and a measured life; to be content one must set their judgment on the possible and be satisfied with what one has-giving little thought to envy or admiration. Democritus approved of extravagance on occasion, as he held that feasts and celebrations were necessary for joy and relaxation. He considers education to be the noblest of pursuits, but cautioned that learning without sense leads to error.
Democritus was also a pioneer of mathematics and geometry in particular. We only know this through citations of his works (titled On Numbers, On Geometrics, On Tangencies, On Mapping, and On Irrationals) in other writings, since most of Democritus' body of work did not survive the Middle Ages. Democritus was among the first to observe that a cone or pyramid has one-third the volume of a cylinder or prism respectively with the same base and height. Also, a cone divided in a plane parallel to its base produces two surfaces. He pointed out that if the two surfaces are commensurate with each other, then the shape of the body would appear to be a cylinder, as it is composed of equal rather than unequal circles. However, if the surfaces are not commensurate, then the side of a cone is not smooth but jagged like a series of steps.
Anthropology, biology, and cosmology
His work on nature is known through citations of his books on the subjects, On the Nature of Man, On Flesh (two books), On Mind, On the Senses, On Flavors, On Colors, Causes concerned with Seeds and Plants and Fruits, and Causes concerned with Animals (three books). He spent much of his life experimenting with and examining plants and minerals, and wrote at length on many scientific topics. Democritus thought that the first humans lived an anarchic and animal sort of life, going out to forage individually and living off the most palatable herbs and the fruit which grew wild on the trees. They were driven together into societies for fear of wild animals, he said. He believed that these early people had no language, but that they gradually began to articulate their expressions, establishing symbols for every sort of object, and in this manner came to understand each other. He says that the earliest men lived laboriously, having none of the utilities of life; clothing, houses, fire, domestication, and farming were unknown to them. Democritus presents the early period of mankind as one of learning by trial and error, and says that each step slowly lead to more discoveries; they took refuge in the caves in winter, stored fruits that could be preserved, and through reason and keenness of mind came to build upon each new idea.
Democritus held that the Earth was round, and stated that originally the universe was composed of nothing but tiny atoms churning in chaos, until they collided together to form larger units-including the earth and everything on it. He surmised that there are many worlds, some growing, some decaying; some with no sun or moon, some with several. He held that every world has a beginning and an end, and that a world could be destroyed by collision with another world. His cosmology can be summarized with assistance from Shelley: Worlds rolling over worlds; From creation to decay; Like the bubbles on a river; Sparkling, bursting, borne away.
（Δημόκριτος). A celebrated philosopher, born at Abdera, about B.C. 494 or 490, but according to some, B.C. 470 or 460. His father was a man of noble family and of great wealth, and contributed largely towards the entertainment of the army of Xerxes on his return to Asia. As a reward for this service the Persian monarch made him and the other Abderites rich presents and left among them several Chaldaean Magi. Democritus, according to Diogenes Laertius, was instructed by these in astronomy and theology. After the death of his father he determined to travel in search of wisdom, and devoted to this purpose the portion which fell to him, amounting to one hundred talents. He is said to have visited Egypt and Ethiopia, the Persian Magi, and, according to some, even the Gymnosophists of India. Whether, in the course of his travels, he visited Athens or studied under Anaxagoras is uncertain. There can be little doubt, however, that during some part of his life he was instructed in the Pythagorean tenets, and particularly that he was a disciple of Leucippus (q.v.). After a long course of years thus spent in travelling, Democritus returned to Abdera, richly stored with the treasures of philosophy, but destitute even of the necessary means of subsistence. His brother Damosis, however, received him kindly and liberally supplied all his wants. According to the law of Abdera, whoever should waste his patrimony should be deprived of the rites of burial. Democritus, desiring to avoid this disgrace, gave public lectures to the people, chiefly from his larger Διάκοσμος, the most valuable of his writings; in return he received from his hearers many valuable presents and otlrer testimonies of respect, which relieved him from all apprehension of suffering public censure as a spendthrift.
Democritus, by his learning and wisdom, and especially by his acquaintance with natural phenomena, acquired great fame and excited much admiration among the ignorant Abderites. By giving previous notices of unexpected changes in the weather, and by other artifices, he had the address to make them believe that he possessed a power of predicting future events; and they not only looked upon him as something more than mortal, but even proposed to invest him with the direction of their public affairs. From inclination and habit, however, he preferred a contemplative to an active life, and therefore declined these public honours and passed the remainder of his days in solitude. It is said that from this time he spent his days and nights in caverns and sepulchres; and some even relate that, in order to be more perfectly master of his intellectual faculties, he blinded himself by means of a burning-glass. The story, however, is utterly incredible, since the writers who mention it affirm that Democritus employed his leisure in writing books and in dissecting the bodies of animals, neither of which could well have been effected without eyes. Nor is greater credit due to the tale that Democritus spent his leisure hours in chemical researches after the philosopher's stone-the dream of a later age; or to the story of his conversation with Hippocrates, grounded upon letters which are said to have passed between the father of medicine and the people of Abdera on the supposed madness of Democritus, but which are evidently spurious. The only reasonable conclusion that can be drawn from these and other tales is that Democritus was a man of lofty genius and penetrating judgment, who, by a long course of study and observation, became an eminent master of speculative and physical science; the natural consequence of which was that, like Roger Bacon in a later period, he astonished and imposed upon his ignorant and credulous countrymen. Petronius relates that he was perfectly acquainted with the virtues of herbs, plants, and stones, and that he spent his life in making experiments upon natural bodies.
Democritus has been commonly known under the appellation of "The Laughing Philosopher,"
and it is gravely related by Seneca (De Ira, ii. 10; De Tranq. 15) that he never appeared in public without expressing his contempt of the follies of mankind by laughter. Thus much, in fact, may be easily believed: that a man so superior to the generality of his contemporaries, and whose lot it was to live among a race of men who were stupid to a proverb, might frequently treat their follies with ridicule and contempt. Accordingly, we find that among his fellow-citizens he had the name of Γελασῖνος, or "the mocker" (cf. Juv. x. 33, 34).
Democritus appears to have been in his morals chaste and temperate, and his sobriety was repaid by a healthy old age. He lived and enjoyed the use of his faculties to the term of a hundred years, and at last died through mere decay.
Democritus expanded the atomic theory of his master Leucippus (q.v.), to support the truth of which he maintained the impossibility of division ad infinitum; and, from the difficulty of assigning a commencement of time, he argued the eternity of existing nature, of void space, and of motion. He supposed the atoms, originally similar, to be endowed with certain properties, such as impenetrability and a density proportionate to their volume. He referred every active and passive affection to motion, caused by impact, limited by the principle he assumed, that like can only act on like. He drew a distinction between primary motion and secondary; impulse and reaction; from a combination of which he produced rotary motion. Herein consists the law of necessity, by which all things in nature are ruled. From the endless multiplicity of falling atoms have resulted the worlds which we behold, with all the properties of immensity, resemblance, and dissimilitude which belong to them. The soul consists (such is his doctrine) of globular atoms of fire, which impart movement to the body. Maintaining his atomic theory throughout, Democritus introduced the hypothesis of images (εἴδωλα), a species of emanation from external objects, which make an impression on our senses, and from the influence of which he deduced sensation (αἴσθησις) and thought (νόησις). He distinguished between a rude, imperfect, and therefore false perception and a true one. In the same manner, consistently with his theory, he accounted for the popular notions of the Deity; partly through our incapacity to understand fully the phenomena of which we are witnesses, and partly from the impressions communicated by certain beings (εἴδωλα) of enormous stature and resembling the human figure which inhabit the air. To these he ascribed dreams and the causes of divination. He carried his theory into practical philosophy also, laying down that happiness consisted in an equability of temperament (εὐθυμία), whence he deduced his moral principles and prudential maxims. It was from Democritus that Epicurus (q.v.) borrowed the principal features of his philosophy. The fragments of Democritus have been collected and published by Mullach (Berlin, 1843), with notes. See Ueber weg, History of Philosophy (Eng. trans., N. Y. 1872), vol. i. pp. 67-71; and the dissertation by E. Johnson, Der Sensualismus des Demokrit (Plauen, 1868).