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date: 14 December 2019


Atomism, a term used of theories that posit the existence of small indivisible particles as the ultimate components of matter. The Greek term atomon, used by some ancient philosophers to describe these ultimate components, means ‘uncuttable' or ‘indivisible'. The theories in ancient philosophy that fall under the general term ‘atomism' share certain features: all posit an infinite number of these microscopic particle-type entities (atoma, atoms) as the physical occupants of the universe; these atoms are in motion through empty space, and the space itself has neither boundaries nor distinct places within it; atoms come in different varieties, which are differentiated in shape and have certain fundamental features such as solidity, resistance, texture, and possibly weight. The atom's intrinsic features never change, but when the atoms gather together to form larger bodies (either collections of several atoms of the same sort, or an assortment of different kinds) their intrinsic or primary qualities account for other secondary effects that are features of larger bodies, including the appearance of colour, flavour, and scent (what we might call secondary qualities). These derivative effects can change as the arrangement of the atoms in a body or collection of bodies change, even though the atoms themselves do not acquire or lose any properties of their own.

Leucippus and Democritus in the early period, and Epicurus and his followers in the Hellenistic period (including the work of the Roman poet Lucretius), are the primary candidates for the description ‘atomists'. For none of them was the atomic hypothesis either prompted or defended by means of experimental investigations into physics, and the atoms that they posited were all supposed to be too small to see and hence could not be detected by observation any more then than they can now. All the atomistic theories were prompted by theoretical questions, including metaphysical puzzles about the nature of reality, and its permanence, and questions about whether things really change, and how we can know. Some were also prompted by puzzles in mathematics and logic, such as Zeno's puzzles about divisibility.

Because these puzzles arise from difficulties raised by other philosophers, the atomistic theories need to be placed in their context. The early atomists Leucippus and Democritus can be treated as a group, since it is hard to disentangle the record of what each separately might have contributed to what has come to be seen as a joint enterprise. Chronologically they occupy a position at the very end of what we call Presocratic philosophy. Democritus' working life actually coincides with that of Socrates. He is regarded as ‘Presocratic’ because he is primarily responding to his predecessors, at least in his work on physics. In metaphysics, the chief concern of the early atomists seems to have been to counter the arguments against plurality and change that had been put forward by Parmenides, and then reaffirmed by other thinkers, including Zeno of Elea and Melissus. Some, at least, of Zeno's notorious paradoxes seem to be designed to show that division into parts is logically impossible, whether that division is supposed to end up with finite numbers of discrete component parts or an unending succession of finer divisions and subdivisions. Leucippus and Democritus respond by proposing finite discrete component parts, themselves solid matter and uncuttable, but separated by portions of empty space or nothingness.

This latter proposal, asserting the existence of ‘nothing' or ‘what is not'—and that this ‘nothing' occupied space between things—was the most controversial. Such apparent nonsense flies in the face of Parmenides' foundational claims (to the effect that only what is something can be included in the contents of the logically possible world). On the contrary, the atomists boldly claim, the world contains what is something and what is nothing, and parts of space, between the things that are something, is occupied by what is nothing. This means that bodies can be distinguished by being detached from each other, so that there can be more than one thing in reality even if all bodies are made of the same kind of stuff.

The suggestion that there is empty space also solves another puzzle, namely Melissus' claim that motion is impossible because things would need empty space to move about in. By positing the void, the atomists make space for the movement of atoms within it, and thereby explain changes in the macroscopic appearance of things. Since arrangements and collections of atoms account for the perceivable appearance, while atoms themselves are too small to see, it is only the appearance of things that changes. There is no change in what is there underneath: atoms themselves never change their shape or their intrinsic features. In this way the atomists deny that anything real has ceased to exist, since the impressions created by conglomerations of things are mere appearances, not genuine parts of reality. This kind of escape route from problems of change, and the consequent distinction between the primary and secondary qualities of things, motivates the sceptical attitude to the senses that is prominent in Democritus' work.

In the Hellenistic period, Epicurean philosophy advocates atomism along similar lines. Developments can be identified in the conception of the void (arguably now envisaged as pure extension, which may be occupied or unoccupied, as opposed to being a place occupied by ‘nothing') and in the idea that atoms themselves contain ‘minimal parts': that is, even though an atom is small, it has some size, and we can think of it having an edge and a middle, a left side and a right side; these parts not only cannot be physically cut apart, but they also have finite size: here too there is a limit to how far we can subdivide the magnitude in our mind, and the result must be a finite number of parts of finite size. These and other features of the Epicurean version of atomism were prompted by work on time, space, and infinite tasks by Aristotle and Diodorus Cronus.

Epicurus also invoked the atomic theory in a range of other areas besides physics and metaphysics strictly understood. Perception, thought, dreams and other psychological phenomena, religious belief, freedom of the will and causation in general are all to be accounted for with reference to a generally materialistic vision, in which the possibilities are defined by what can be supposed to happen to minute bodies falling randomly through an infinite universe of empty space. The most accessible and systematic exploration of this vision that survives intact for us to read as a whole is provided (with missionary zeal) by Lucretius in De rerum natura.


D. Furley, The Greek Cosmologists 1 (1987).Find this resource:

A. Pyle, Atomism and Its Critics: From Democritus to Newton (1997).Find this resource:

S. Berryman, ‘Ancient Atomism' in Stanford Encyclopedia (online, with bibliography).Find this resource:

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