Democritus

1. Of knowledge, there are two types: the one genuine, the other obscure. Obscure knowledge includes everything given by sight, hearing, smell, taste, touch; whereas genuine knowledge is something quite distinct from this. Whenever obscure knowledge can no longer see the objects because of their smallness, and also cannot hear or smell or taste them nor perceive them by touch, one must have recourse to a finer means of knowing.

2. The truth is that what we meet with perceptually is nothing reliable, for it shifts its character according to the body’s dispositions, influences, and confrontations.

3. By convention there is sweet, by convention there is bitter, by convention hot and cold, by convention color; but in reality there are only atoms and void.

4. A dialogue between the intellect and the senses:

5. According to the theory of Democritus, it is the nature of the eternal objects to be tiny substances infinite in number. Accordingly, he postulates also a place for them that is infinite in magnitude, which he designates by these names–the void, the nothing, and the infinite; whereas he speaks of each individual atom as the yes-thing, the dense, and being.

He conceives of them as so small as to elude our senses, but as having all sorts of forms, shapes, and different sizes. [Democritus apparently thinks there are three kinds of real difference. His view is that, while the underlying nature of material body is the same in all instances, bodies differ from one another in surface rhythm (shape), inclination (direction of turning), and intercontact (arrangement).] [The atoms are impassive and unchangeable.]

[According to Democritus, one type of primary nature does not come to be out of another type.] Treating atoms as elements, he conceives of them as combining to produce visible and otherwise perceptible objects.

As they move about in the void, the particles are at variance with one another because of their dissimilarity and the other mentioned differences; hence, in their motion, as they bump or even as they brush against one another, they tend to get ensnarled and interlocked. The process of interlocking never makes them into a single nature, however, for it would be absurd to think that two or more things could ever become one. When these substances remain joined for some time, it is explained by the fact that they fit snugly and so catch firm hold of one another; for some bodies are scalene, while others are sharply hooked, some are concave, others convex, and there are numerous other differences. Democritus’ theory is that they cling together and remain in certain combinations until they are shaken apart and separated by outside forces.

6. Differences of heaviness and lightness are explained by Democritus as ultimately differences of size. For if we could get down to atomic units, we would see that the only standard of an atom’s weight must be its size. In the case of compounds, on the contrary, two bodies of the same size might be of different weights; for the body containing more emptiness would be lighter, while that containing less would be heavier.

He speaks in similar terms of hard and soft. According to his theory, a thing is hard when its parts are compact, soft when they are loose, and differences of degree are explained proportionately. The reason why differences of hard and soft are not always commensurate with differences of heavy and light is that they are not produced by the same positions and groupings of empty spaces. Thus, although iron is harder than lead, lead is heavier than iron. That is because the iron is of uneven composition, and its empty spaces are more numerous and bigger although the particles are more condensed in some places than in others. But its average of empty spaces exceeds that of lead.

As for other sensory qualities he argues that none has objective reality, but that all of them are effects of our sensuous faculty as it undergoes alteration; its is bodily alteration that produces images. Nor does he regard hot and cold as having an objective nature; they are merely a matter of configuration. What we experience as qualitative change within ourselves is the effect of incoming atomic configurations being massed together so as to produce intensity of effect. What is massed together prevails, while what is widely diffused is imperceptible.

His proof of the unreality of sensory qualities is based on the fact that they do not appear the same to all: what is sweet to some is bitter to others, while to yet others it is sour or pungent or astringent; and sense-qualities of other types may be characterized similarly.

Anything sour, he holds, is composed of atoms that are angular, tiny, thin, and twisted. By its sharpness it slips in and penetrates everywhere, by its angular roughness it draws the parts of the tongue together and binds them. … But sweet consists of atomic figures that are rounded and not too hard; it softens the body by its gentle action.

7. Democritus declares that the soul is a sort of fire or heat. For the atomic shapes are unlimited, and those which are spherical he says make up fire and soul. … He says atoms which are spherical compose the soul, because such shapes can penetrate all things, and because being in motion they set things in motion.

The atomists suppose it is the soul that imparts motion to animals, for which reason they regard life as depending on respiration. When the surrounding air presses upon animal bodies and tends to squeeze out those atomic shapes which, being never at rest themselves, impart motion to the animal, they are reinforce by other atoms from the outside to produce the respiratory process. The respiration prevents the escape of atoms that are already in the animals; and, they explain, just so long as it has the strength to do so, life continues.

8. Death occurs when the surrounding air [in the lungs] presses upon the soul to such a degree that the animal can no longer respire, which is to say that the air from outside the body can no longer enter and counteract the compression.

9. Some say that the soul moves the body in which it resides by imparting its own motion to it. Democritus, for example, takes this view, and in such a way that he appears somewhat like Phillipus the comic poet who tells of how Daedelus endowed a wooden statue of Aphrodite with motion simply by pouring mercury into it. Democritus’ account shows a certain similarity to this. For by his theory the spherical atoms, which by their very nature never remain still, tend by their intrinsic movement to set the entire body in motion.

Democritus’ views can best be understood as a response to the philosophical views of Parmenides of Elea, who had argued that whatever exists ("being") has to be one, indivisible, unchangeable, and immovable. Plurality, divisibility, and motion, Parmenides thought, required that beings be separated by non-being, but to posit the existence of non-being would be absurd. Change similarly was held to require that non-being do something (namely, come into existence). The world we perceive does, of course, appear to have precisely the features which the Eleatics reject, but a distinction between appearance and reality was already a feature of Greek thought. Parmenides’ philosophical views were buttressed by the arguments of Zeno, whose paradoxes were designed to show that the defenders of the reality of motion were faced with serious intellectual problems of their own.

Early attempts to offer an account of reality more faithful to ordinary experience than Eleatic monism were offered by Empedocles and Anaxagoras. Better developed responses were offered first by Democritus, then by Plato and Aristotle.

Democritus attempted to explain all the phenomena of ordinary experience in terms of the behavior of the atoms. Although atoms are not subject to changes other than change in place, other kinds of change (such as coming into existence or passing away, or change in size or other properties) are a real feature of the ordinary world. Democritus’ explanation of such change was based on the principle that the objects of ordinary experience are merely aggregates of atoms, arranged in a particular way. Slight rearrangements of the atoms result in qualitative change (for example, in the color of something). Dispersal of the atoms causes the thing to cease to exist. The variability of perception from one observer to another led Democritus to deny that perceived properties such as redness are really in things at all. Rather, such properties are merely the effect that particular arrangements of atoms have on us.

The principle of life (which the Greeks called "the soul") is merely the presence of particularly small and mobile atoms dispersed throughout a body. As long as the body, by respiration, can keep such atoms in the body, life functions continue. If these atoms all leak out, life ends. Since such leaking out would cause a dispersal of the "soul-atoms", there is no possibility of immortality.

Democritus’ atomism was adopted and modified by Epicurus at the end of the fourth century bc. Although Epicurus’ works are also extant only in fragments, the Latin Epicurean poet Titus Lucretius Carus put the ideas into literary form in his De rerum natura (On the Nature of Things), which has survived.

The main line of Greek philosophical thought, however, rejected atomism. Plato ignores Democritus; Aristotle summarizes his work but rejects it as implausible. Aristotelian and Platonic philosophies of nature differ from one another in significant ways, but they share a rejection of Democritus’ attempt to reduce reality to purely material things, variously arranged. In contrast to this materialistic and reductionistic view of reality, Aristotle and Plato, each in his own way, emphasize the importance of "form" as principle that is non-material and essential to the explanation of the behavior of physical objects.

Democritus’ atomism gained a second lease on life with the Renaissance recovery of the text of Lucretius’ poem. Discovered in a Swiss monastery in 1417 and first printed in 1563, Lucretius’ poem was of special interest to seventeenth century practitioners of the new science, who were looking for an alternative to the Aristotelian philosophy of nature that had dominated the Middle Ages. Although initially tainted by its association with atheism, Democritus’ atomism was forged, by Pierre Gassendi, Isaac Newton, John Locke and others, into a Renaissance version usually called "corpusculareanism". That ontology, along with the epistemological distinction between what came to be called "primary" and "secondary" qualities, were important components of the new "mechanical" philosophy.

John Dalton’s attempt to explain the quantitative details of chemical combination by appeal to an atomic theory of matter (1808—10), though it was surely inspired by the Democritean tradition, differs from Democritus in significant details. For example, Dalton’s atoms are not qualitatively the same. Atoms of carbon and oxygen, for example, are different kinds of atoms. Nevertheless, the utility of the atomic theory in explaining the behavior of gases (the kinetic theory of gases) and the ability (indirectly, but by various methods) to count the number of atoms in a given quantity of a chemical substance, led all but the most skeptical scientists to accept the reality of Dalton’s chemical atoms by about 1900.

Twentieth century discovery of sub-atomic particles shows, in Democritean terms, not that atoms are divisible, but that the smallest possible pieces of chemical elements, despite our habit of calling them "atoms", are not really atomic. The 1990’s candidate for "atom" (in Democritus’ sense) are quarks and leptons. Although they, like Dalton’s atoms and unlike those of Democritus, are not all of the same kind, their role in explaining the powers of atoms can be seen as an impressive vindication of Democritus’ general approach to nature. The extent to which particle physics, in which parts (quarks) are more massive than wholes (hadrons), stays within the atomic tradition is a nice topic for philosophical controversy.

More controversial is the applicability of this approach to the explanation of the powers of living things, particularly to perception, emotion, thought and choice. The ability of molecular biologists to describe the physiological correlates of vision, thought, and the like is impressive. Whether these descriptions also explain (that is, give a complete account of) such activity, as is required by the Democritean tradition, is something that is more often asserted than argued for.

The details of Democritus’ explanations of natural phenomena have long ago been superseded. Improvement in techniques of observation and the development of the habit of experimentation made that inevitable. Democritus’ more lasting influence is his attempt to explain the behavior of complex entities in terms of the behavior of their constituents (reductionism) and to explain the qualitative distinctions of everyday experience as mere by-products of purely quantitative distinctions that can be found at the fundamental level of reality (mathematicization of nature). These more general features of his philosophy of nature continue to serve as an inspiration for many modern scientists.