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In all probability, credit for the fundamental ideas of the atomic theory—Greek speculation’s greatest achievement—should go to Leucippus of Miletus rather than to his pupil, Democritus. However, almost nothing is known of Leucippus.

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Rational speculation about the nature of the world began not earlier than the sixth century b.c.e. Four or five generations later it had progressed, in Democritus, to an essentially correct account of the nature of matter. This amazing fact has led to both exaggeration and underestimation of the Greek achievement. Some people conclude that science stood still until the revival of the atomic theory in the seventeenth century. However, scientists point out that modern atomic physics rests on evidence derived from careful quantitative experimentation of which the Greeks knew nothing; therefore, it is said, the ancient theory was merely a lucky guess—and the Greeks made all possible guesses. A brief review of the development of early Greek physics will show that while Democritus did not have English chemist and physicist John Dalton’s reasons for asserting that the world consists of atoms moving in the void, he nevertheless had some very good ones.

Early Assumptions

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The men of Miletus, especially Anaximander, who made the break with mythological world accounts in the early sixth century b.c.e., took over from previous creation myths two important assumptions. First, Milesians accepted the belief that there was a creation, or rather a development: The world was not always as it is now but had in the beginning been something simple and homogeneous, like the “chaos” of the myths. Differentiation, complexity, and organization have a history. Second, the Milesians accepted the theory that there exists an impersonal force making for order and “justice” in the universe at large. The Milesians were the first philosophers; they dispensed altogether with the “will of the gods” as an explanatory principle because they assumed that the natural forces that made the universe what it is were still operative. The problem, as they conceived it, was to identify the original simple world stuff out of which all things had come and to describe the process that had differentiated and organized it into the present world. Not “divine” inspiration but ordinary human reason, they thought, was capable of solving the problem. Because conclusions based on reasons invite criticism and modification, unlike revelations, which can be only accepted or rejected, the history of rational speculation was progressive.

In addition to the ideas of ultimate oneness, development, and “justice” inherited from religion, the earliest philosophers assumed with “common sense” that nothing can come out of nothing or be absolutely destroyed and that our senses reveal directly the constituents of the world, at least as it is now. We feel heat and cold; we taste sweetness and bitterness; we see red and green. Heat, cold, sweetness, bitterness, red, and green are therefore parts of the objective world; together they make it up. These are now regarded as qualities of matter, but early Greek thought does not make this distinction; “the hot,” “the cold,” “the wet,” “the dry,” and so on, in various combinations, are the stuff of things. One must simply find out the unity underlying this diversity. For example, Anaximenes, the third of the Milesian “physicists,” held that the fundamental stuff is mist. Everything is really mist; the things that do not appear to be mist are mist that has been thickened or thinned. Very thin mist is fire; mist somewhat thickened is water; thickened still more, mist is stone.

Parmenides’ Objections

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There is an inconsistency here that Parmenides (in effect) pointed out. No doubt the theory of Anaximenes squares with observation, for fire, when cooled and “thickened,” becomes smoke and smoke is easy to regard, at this stage of thought, as a kind of fog or mist. Condensed mist is water, and water thickened still more becomes ice, a solid, a kind of stone. However, is the theory compatible with logic? Fire is (identical with) “the hot and dry”; water is (identical with) “the cold and wet.” How, then, can the one be transformed into the other without violating the fundamental principle that nothing can come from nothing? Where did the cold come from? Where has the hot gone? If cold and hot are thought of as substances, it seems that there can be no satisfactory answer to this question. Something has come out of “nothing”; something has disappeared into “nothing.” Worse still, as Parmenides saw, if there is ultimately just one stuff, that stuff must be just the kind of stuff it is, so that it cannot logically be both hot and cold, both wet and dry. Therefore change is impossible. If things seem to change (as they do), this must be mere illusion, for logic pronounces it contradictory.

It is important to see that Parmenides was right, given his assumptions of monism, nothing from nothing, and identity of things and qualities. Parmenides had another argument (a fallacious one) to show that the kind of change called motion cannot really occur. Parmenides said that if a thing moves, there must be room for it to move into—that is, there must be empty space. However, there cannot be any empty space, for empty space would be just “nothing,” “that which is not,” and the assertion that there is empty space amounts to saying “That which is not, is,” a statement of contradiction.

Empedocles and Anaxagoras Respond

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The philosophers Empedocles and Anaxagoras tried to develop systems that would meet the logical objections of Parmenides without flying in the face of common sense. They argued that motion could occur without empty space if the moving thing displaced what was in front of it, as a fish swims in water. For the rest, they abandoned monism. Empedocles said that there are six basic stuffs, while Anaxagoras held that the number of stuff is infinite—that there are as many stuffs as there are sensible discriminations—and all things are made by the mixture and separation of these stuffs.

The philosophy of Anaxagoras successfully met Parmenides’ criticism, but at too high a price. Although it is hard to say precisely just what it is that we are asking for when we demand an explanation of something, at any rate it is clear that an explanation is not satisfactory unless in some sense the ideas used in the explanation are simpler, or more unified, than the thing to be explained. However, if one’s explanatory principles are as diverse as the things to be explained, the requirement cannot be met. “Flour is a mixture in which flour-stuff predominates, and water is a mixture in which water-stuff predominates, and the two make bread because when they are mixed and baked the bread-stuff in both of them comes to the fore.” This may be true, but it is too easy and it does not explain anything.

Leucippus and Democritus Respond

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Leucippus and Democritus discovered a better way of answering Parmenides. As to motion, Leucippus flatly declared that “nothing” does exist; Democritus more appropriately dismissed Parmenides’ quibble with another: “Hing’ exists no more than not-hing,’“ the point of the joke being that if “Nothing’ does not exist” is a truth of logic, elimination of the double negative must also produce a logical truth: “Hing’ does exist.” However, “hing,” so far from existing, is not even a word. (Greek for “nothing” is mden, of which m means “not,” while den has no meaning in isolation.)

There is, then, a void, and things that move in it. These things are atoms—”uncuttables.” Each separate atom is like the “reality” of Parmenides, uncreated, indestructible, unchanging. The matter in an atom is homogeneous, and nothing can happen to one internally; that is, each atom is infinitely hard. Atoms differ from one another in size and shape—that is all. They do not differ in color, for instance, but not because they are all the same color. They do so because they have no color at all (not even black or gray). Similarly for heat, moisture, taste, and odor. Atoms have always been (and always will be) in motion—”like the motes in a sunbeam.” They jostle one another, and in their jostlings, two kinds of processes occur that result in the “coming-into-being” of the large-scale aggregates with which we are familiar. One is vortex motion, the effect of which is to separate random aggregates according to likenesses, the heavier—that is, the bigger—atoms going to the center, the lighter ones to the periphery. The other process is the hooking on to each other by atoms of like configurations.

One atom can affect another only by colliding with it; and the outcome of a collision (hooking, or change of direction or speed) is determined by the sizes, shapes, and velocities of the atoms involved in the collision. However, the sizes and shapes are eternal, and the velocities in their turn are outcomes of previous collisions. Therefore, there is no such thing as “chance” in nature; “Nothing happens at random,” Leucippus pronounced in the one sentence of his that has survived, “but everything from a rationale and by necessity.” Ideally, explanation should consist in finding out the laws of motion and impact and using these to show how one atomic configuration came about from a previous one. Such a complex act is of course impossible; however, Democritus sought to apply the fundamental idea of mechanical causation to observable phenomena.

An ancient story illustrates Democritus’s method and highlights its difference from traditional concepts. Considerable interest had been aroused by the extraordinary death of a prominent man. When he was strolling along a beach, an eagle had dropped a turtle on his head. Why? It was recalled that an oracle had said that he would die of “a bolt from Zeus.” This had been thought to be a prediction of death by a stroke of lightning. However, someone pointed out that the eagle was a bird sacred to Zeus; thus, the oracle was fulfilled. This explanation satisfied most Greeks but not Democritus. He went to the beach and observed the habits of eagles. He found that they were fond of turtle meat. In order to get at it, an eagle would seize a turtle in his talons, fly into the air with it, and drop it on a rock to crack the shell. This observation, together with the fact that the deceased had been bald, provided an explanation that satisfied Democritus. The curious event was shown to be one item in a natural regularity or pattern. It was unnecessary to postulate the purposes of unseen beings to account for the fact. Aristotle complained, quite unjustifiably, that Democritus “reduced the explanation of nature to the statement, Thus it happened formerly also.’” Actually, Democritus understood the character of scientific explanation far better than did Aristotle.

In sum, Democritus’s reason for asserting that reality consists of atoms moving in the void is that this statement can be deduced from the premises: Nothing can come from nothing, change really occurs, and motion requires a void. That this explanation must be mechanistic also follows from these assumptions if it is further allowed that all interaction is impact. Democritus’s mechanism was also the culmination of the rejection of animistic and supernatural will or forces by all his philosophical predecessors.

Democritus’s atomism, and still more his mechanism, agree in principle with the fundamental tenets of modern physical science. What modern physicists have that Democritus lacked is a conception of controlled, quantitative experimentation, together with a technique of mathematical manipulation of the data. For this reason, Democritus, though he declared that he would “rather discover one causal explanation than gain the kingdom of the Persians,” failed utterly to add to detailed knowledge of nature. In fact, he was much behind his own times, still believing, for instance, that the earth is a flat disc, though the Pythagoreans had long understood its sphericity. In detailed explanations, Democritus could do no better than this: “Thunder is produced by an unstable mixture forcing the cloud enclosing it to move downward. Lightning is a clashing together of clouds by which the fire-producing atoms rubbing against each other are assembled through the porous mass into one place and pass out. And the thunderbolt occurs when the motion is forced by the very pure, very fine, very uniform and closely-packed’ fire-producing atoms, as he himself calls them.” (The foregoing is an ancient paraphrase, not a quotation from Democritus.) It must be admitted that this account of lightning is no worse than any other prior to that given by American Benjamin Franklin, and a considerable improvement over “Zeus is angry.”

Qualities and Sensations

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“By convention color, by convention sweet, by convention bitter; but in reality atoms and void.” Thus Democritus states his theory. The atoms alone are real, and their only inherent qualities (Democritus distinguished clearly between thing and quality) are size, shape, and solidity. Then what about color, sweet, bitter, and the rest? They are “by convention.” What does this mean? Democritus held that a person’s soul consists of particularly fine and spherical, hence mobile, atoms. When certain “images” from the external world—the images being, of course, themselves assemblages of atoms—impinge on the soul atoms, a sensation is produced. The sensation occurs only within the ensouled body; hence, it is not “out there” because the external world is colorless and odorless. This is a part of the meaning of “by convention,” a phrase that might be rendered as “subjective.” The sensations are also subjective in the sense that they lead us to suppose, falsely, that the world is colored and odorous.There are two forms of knowledge, one genuine, one obscure. Of the obscure sort are all these: sight, hearing, smell, taste, touch. The genuine is distinguished from this. . . . Whenever the obscure cannot sense any farther into the minute by seeing or hearing or smelling or tasting or touching, but [it is necessary to pursue the investigation] more finely, [then the genuine, which has a finer organ of knowing,] comes up.

The organ of “genuine knowledge” would seem to be the “Pure Reason” that led Democritus to deduce the atomic nature of matter. However, Democritus was worried, as well he might have been, about the “obscure.” He portrayed the senses speaking thus to the mind: “Wretched mind, getting from us your confidences you cast us down? That is your own downfall.’” For the information on which even the atomic theory is based is, after all, derived ultimately from observation through the senses.

If reality consists of matter with only its “primary qualities,” what kind of reality do sensation, thought, and consciousness in general have? This problem besets all forms of materialism and is often alleged to be fatal to it as a worldview. Democritus spent much effort in trying to account for sensations on atomic principles. Thus, he claimed that sour fluids consist of angular and twisted atoms, while honey is made of rounded, rather large ones. This was, of course, inconsistent with his claim that tastes are subjective effects. He could have patched up the account to some extent by considering not only the atomic constitution of the food but also that of the tongue that interacts with it; but there is no evidence that he did so. Perhaps it was despair at this problem that led him to exclaim, “In reality we know nothing. For truth is in a depth.”

Materialists should say that sensations are not things at all; but Democritus held that they are illusory things. This, at any rate, is the impression we get from ancient discussions of his theory of knowledge. It may be mistaken, for the accounts all come from hostile critics who may well have misunderstood or misrepresented Democritus.

Unlike most Greek philosophers, Democritus was a partisan of democracy. He said: “Poverty in a democracy is as much preferable to so-called prosperity in an autocracy as freedom is to slavery.” By “democracy” he meant a constitutional government, directed by public-spirited, intelligent people in the interest of all citizens.

Democritus was one of the most prolific authors of antiquity, having written, we are told, more than sixty works. The fragments that remain fill about ten pages of ordinary print, of which eight are concerned with ethics, politics, education, and child rearing. (Democritus thought it a risky and thankless business to have children.) Many of the ethical reflections are platitudinous: “In good fortune it is easy to find a friend, in misfortune hardest of all.” Others are shrewd and worldly-wise: “If you cannot understand the compliments, conclude that you are being flattered.” The general tenor of the maxims is advocacy of “cheerfulness,” that is, of prudence, contentment with what one has, not worrying too much.He who would be cheerful must not busy himself with many things, either by himself or in company; and whatever he busies himself with, he should not choose what is beyond his own power and nature. However, he should be so on his guard that when a stroke of fortune tempts him to excess, he puts it aside, and does not grasp at what is beyond his powers. For being well-filled is better than being stuffed.

There are some fragments, however, that embody teachings often credited to others and used unfairly to belabor crude “materialism”: “Refrain from wrongdoing not from fear but from duty”; “The doer of injustice is unhappier than the sufferer”; “Goodness is not merely in refraining from being unjust, but in not even wishing to be”; and “The cause of error is ignorance of the better.”


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Additional Reading

Brumbaugh, Robert S. The Philosophers of Greece. Albany: State University of New York Press, 1981. An important interpreter of Greek philosophy discusses the place of Democritus, atomism, and materialism within Greek philosophical theory.

Burnet, John. Greek Philosophy: Thales to Plato. London: Macmillan, 1953. Burnet’s overview contains a brief but helpful account of Democritus’s philosophy.

Cartledge, Paul. Democritus. New York: Routledge, 1999. An excellent biographical introduction to the thoughts of the philosopher, clearly presented and requiring no special background. Bibliography.

Cleve, Felix M. The Giants of Pre-Sophistic Greek Philosophy: An Attempt to Reconstruct Their Thoughts. The Hague: Martinus Nijhoff, 1969. Cleve concentrates especially on Democritus’s physical theories and his views about sense perception.

Copleston, Frederick. A History of Philosophy: Greece and Rome. Garden City, N.Y.: Doubleday, 1962. Copleston’s brief treatment of Democritus is clear, and it places this pre-Socratic atomist in his historical context.

Curd, Patricia, ed. A Presocratics Reader: Selected Fragments and Testimonia. Translations by Richard D. McKirahan, Jr. Indianapolis, Ind.: Hackett, 1996. This volume includes text fragments from Democritus. Contains insightful editorial commentary.

Guthrie, W. K. C. A History of Greek Philosophy. Cambridge, England: Cambridge University Press, 1965. Democritus has been called an encyclopedic thinker, and Guthrie shows the truth of this remark by exploring many of Democritus’s philosophical concerns.

Hussey, Edward. The Presocratics. Indianapolis, Ind.: Hackett, 1995. This accessible and comprehensive overview of the history of ancient Greek philosophy includes discussion of Democritus.

Kirk, G. S., and J. E. Raven. The Presocratic Philosophers. Cambridge, England: Cambridge University Press, 1960. Democritus’s physical and ethical theories are discussed in this book, which includes the actual Greek texts of the philosophers accompanied by English translations.

McKirahan, Richard D., Jr. Philosophy Before Socrates: An Introduction with Texts and Commentary. Indianapolis, Ind.: Hackett, 1994. An excellent source that contains helpful discussion of Greek atomism and the thought of Democritus in particular.

Taylor, C. C. W., ed. From the Beginning to Plato. New York: Routledge, 1997. Taylor provides a good starting point for understanding Democritus’s contributions to the origins of Western philosophy.

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