- The basic nature of atomism
- Various senses of atomism
- Diverse philosophical characterizations of atomism
- History and major representatives of the various atomisms
- Foundational issues posed by atomism
Extensions to other fields
Whereas classical atomism spoke mainly of material atoms (i.e., of particles of matter), the success of the atomic doctrine encouraged the extension of the general principles of atomism to other phenomena, more or less removed from the original field of application. Rather plausible, for example, was the extension of atomism to the phenomena of electricity. There were reasons to suppose the existence of an elementary charge of electricity associated with an elementary material particle, the electron (19th century). A second fruitful extension concerned energetic processes (20th century). Some experimental data suggested the hypothesis that energy can exist only in amounts that are whole multiples of an elementary quantity of energy. Extensions of the idea of an atomic structure to amounts of gravitation and even to time have been attempted but have not been sufficiently confirmed.
More removed from the original field of application of atomism is a theory known as logical atomism (developed by the eminent philosopher and logician Bertrand Russell and by the philosopher Ludwig Wittgenstein in his early period), which supposes that a perfect isomorphism exists between an “atom” of language (i.e., an atomic proposition) and an atomic fact; i.e., for each atomic fact, there is a corresponding atomic proposition. An atomic proposition is one that asserts that a certain thing has a certain quality—e.g., “This is red.” An atomic fact is the simplest kind of fact and consists in the possession of a quality by some individual thing.
Another application of atomism (albeit in a moot sense) lay in the monadology of the philosopher-scientist G.W. Leibniz. According to Leibniz, the atoms of Democritus, who provided the paradigm case of ancient Greek atomism, are not true unities; possessing size and shape, they still are divisible in principle. The ultimate constituents of things must, therefore, be points, said Leibniz, not mathematical but metaphysical points—i.e., points of real existence. They are indeed a kind of soul, which he came to call “monads.”
In psychology, atomism is a doctrine about perception. It holds that what human beings perceive is a mosaic of atomic sensations, each independent and unconnected with any other sensation. According to the early modern empiricist David Hume and the pre-World War I father of experimental psychology Wilhelm Wundt, the fact that humans nevertheless experience an ordered whole formed from the unordered “atoms” of perception is caused by the mind’s capacity to combine them by “association.”
Diverse philosophical characterizations of atomism
The intrinsic nature of the atoms
In 1927 the Belgian astronomer Georges Lemaître formulated the hypothesis that the present high degree of differentiation of matter in space and the complexity of forms displayed by the various astronomical objects must have resulted from a violent explosion and subsequent dispersal of an originally highly compressed homogeneous material, a kind of “primitive atom,” containing all of the matter that exists. From the philosophical viewpoint this hypothesis is interesting. By its attempt to reduce the manifold to unity, it recalls the beginning of Greek philosophy, which was also inspired by a thesis of the unity of being, propounded by the Eleatic philosopher Parmenides. Even apart from their respective contexts, there is, of course, a great difference between Lemaître’s and Parmenides’ conceptions of the unity of being, for the latter combined the thesis of the unity of being with that of the immutability of being.
Although it would be wrong to classify Parmenides among the atomists, it is nonetheless appropriate that, in an introduction to the diverse forms of atomism, his conception of reality as just one being should be mentioned. Parmenides’ thesis is not only historically but also logically the cornerstone of atomistic thought. Any atomic theory can be interpreted as an attempt to reconcile the thesis of the unity and immutability of being with the fact that the senses observe multiplicity and change. The different ways in which the unity and immutability are understood characterize the different forms of atomism.