ATOMISM. – Philosophical and scientific theory that resolves reality into an aggregate of indivisible prime elements, called atoms (from the Greek ἄνωσις, “indivisible”).
I. PHILOSOPHY
Atomism, as a philosophical-physical doctrine, first arose in Greece around the middle of the fifth century through the work of Leucippus (probably of Miletus) and his disciple Democritus of Abdera (v.), who developed its theories into a system, taken up and continued in the third century by Epicurus. Between Democritus and Epicurus, tradition gives the following names in continuous succession: Nessa, Metrodorus of Chios, Diogenes of Smyrna, Anaxarchus and Pyrrho of Elis, head of the skeptical school, then Nausiphanes, his pupil and Epicurus’s teacher, and Hecataeus of Abdera; in addition to these, the following are mentioned as belonging to the Democritean school: Apollodorus, Diotimus, and Bion of Abdera.The atomism of Leucippus and Democritus arose as a consequence of the Parmenidean doctrine of being, and was, after that of Empedocles (v.) Anaxagoras (v.), the most grandiose attempt to resolve the problem that the concept of the one and immutable being had opened with regard to the manifold and changing reality of the sensible world. The solution advanced by Empedocles and Anaxagoras, whose work occupies the first half of the fifth century, had been to multiply being and explain change through the union and separation of parts: the former positing the four elements as the foundation of this process, the latter elevating to the rank of originating substances everything that, while quantitatively divided, remains qualitatively one—the so-called “homoeomeries.” This solution, by denying division under the category of quality, may itself be regarded as atomistic, that is, as qualitative atomism. Both Empedocles and Anaxagoras admitted infinite divisibility under the category of quantity.
The solution first put forward by Leucippus was simpler. “Being is, and non-being is not,” Parmenides had said. “Being is being, and non-being is non-being,” Leucippus distinguished, “but non-being exists no less than being: it is the void, whereas being is the full.” Democritus formulated the same proposition as follows: “the existent (τὸ δὲν) does not exist to a greater extent (οὐ μᾶλλον) than nothing (ὃς τὸ μῆδεν)” (fr. 156). The formula “to no greater extent” also recurs elsewhere in the fragments of Democritus and should be considered one of the most important logical principles of atomistic deduction. It was probably on its basis that the multiplicity of entities was demonstrated: if an “existent” exists and is limited by “nothing,” there is no reason why another should not exist, and so on to infinity. In any event, Leucippus and Democritus taught that entities are infinite, just as space is infinite, and that they move ab aeterno in all its directions. Their forms and variations in size, and therefore in weight, are likewise infinite, “since there is no reason why one entity should have one form rather than another.” These entities, excluding nothing from themselves, are indivisible, that is, atoms.
In Democritus we find two arguments demonstrating the necessity of admitting the existence of indivisible bodies. The first is that the two cannot arise from the one, nor the one from the two—an argument typically Eleatic, founded on the identity of the one and being. The second is that, if a body were entirely divisible, since in order to be so it would already have to be divided in actuality, and since the final term of the division would be nothing, the body itself would be nothing. This argument reflects the problem that occupied mathematics in the fifth and fourth centuries, namely that of the infinitesimal, whose solution was achieved only in the Aristotelian theory of the continuum (cf. Met., IX, 6, 1408 b 15 ff.). From this it follows that the atomism of Leucippus and Democritus was physical only, and not mathematical. As regards motion, Aristotle reproached the two philosophers for not having indicated its cause. In some testimonies, impact is given as the cause; but impact is a consequence of motion, and since the motion of the atoms is ab aeterno, it must be concluded that they regarded motion as the immediate consequence of the opposition between the full and the void, and assigned to impact the cause of its determination, not of its origin. But since the atoms move ab aeterno, they collide ab aeterno, and in this sense every aggregation has impact precisely as its immediate cause. Weight, which Epicurus would later assume as the cause of natural motion, in opposition to impact and declination, was regarded by Leucippus and Democritus only as a coefficient, together with form and size, in the separation that determines aggregates. Since the atoms are infinite and space is infinite, worlds too are infinite, succeeding one another as they dissolve into one another.
According to the concordant testimony of all the sources, Democritus attributed the formation and disintegration of worlds to chance (“Democritus, who places the world by chance,” according to Dante’s verse, Inf., IV, 126). That, given the principles, this is in fact true can be denied only by those modern interpreters who exclude every form of teleologism as contrary to the concept of science. Historically, it must be said that the concept of chance was already known and fully defined at the time when Democritus wrote. As for Leucippus, he had asserted that “everything happens according to reason and necessity” (fr. 2). Earlier than Democritus and closer to the Eleatics, he did not yet recognize the opposition between logical and mechanical necessity. His theory was rigorously deduced and rationally intelligible. That, since the elastic identity of being was maintained only for matter, the cosmos, as an order assumed by matter, should derive from non-being and therefore contradict the very principle to which the entire system conformed was something of which he could not be conscious. This cannot be said of Democritus, and his theory of human progress, which he had taken up and developed from Anaxagoras, regarded chance as the natural complement of intelligence and art.
In reality, every atomistic system, reducing the complex to the simple and the whole to its parts, can in no case go beyond matter, and must necessarily sacrifice form, that is, ultimately, spirit. In Democritus’s system (we know less about Leucippus), there is no place either for God or for the soul. Everything is the result of a temporary and contingent aggregation, and everything is mortal. Plato and Aristotle fought atomism on the basis of the same elastic principle from which it had been deduced: if nothing comes from non-being, this impossibility must first of all be affirmed of form; the reason of the part lies in the whole, and not vice versa.
Epicuro, coming after Aristotele and concerned not so much with the scientific as with the practical problem, in taking up the system of Leucippo and Democrito sought to modernize it in accordance with the new concepts introduced by Platonic and Aristotelian speculation. The principal modification was to distinguish in atoms a natural motion, a forced motion, and a free motion. He held the first to consist in falling in a straight line owing to gravity, which naturally brought him into conflict with the concept of the infinite, in which there is neither high nor low. Considering, therefore, that bodies in a vacuum fall with equal velocity, in order to explain encounters and collisions he assumed that atoms could indeterminately deviate “somewhat” from the straight line: this is the second form of motion, which he called declination (πτερέγκλασκ), Lucrezio’s “clinamen.” This second form of motion, which Diogene di Enoanda (second or third century A.D.) calls free motion (“libera potestas” in Lucrezio), enabled him to explain the freedom of the will. The third form of motion is that of collision, necessary and accidental motion at the same time (ἡ κατά τὸ αὐτόμενον ἀνάγκη). Another fundamental modification was to regard the number of atomic forms as finite, whereas his predecessors had made it infinite, in order to explain the fixity of species, that is, the limitation of qualities. With regard to the problem of divisibility, Epicuro, while maintaining the physical indivisibility of atoms on the same grounds as Leucippo and Democrito, professed, in contrast to the mathematics already advanced in his time, a mathematical atomism as well, in the theory of minima, at which every division comes to a halt and which constitute the unit of measurement of magnitudes. For Epicuro the denial of any teleology in the universe is a dogma; but, as a substitute for Aristotelian finalism, he developed in his theory of the universal equilibrium of forces (isonomía) the concept of a constant cyclical identity of becoming, which served him as the basis for the concept of natural necessity.
After the end of the ancient world and until the Middle Ages, no trace is found of any philosophical elaboration of atomism. The Arab philosophers, through their knowledge of the works of Aristotele, revived atomistic theory, maintaining that bodies are composed of point-atoms, devoid of extension and all homogeneous. Through the Arabs, atomistic doctrine reappeared in Western European philosophy among certain realist thinkers: Guglielmo de Conches, d. 1150, a Platonist; Abelardo di Bath, who also in atomism sought a reconciliation between Aristotele and Platone (1115); Ugo da S. Vittore, d. 1141, author of the first Summa; Nicola d'Autrecourt; and others. For them, the material atom is the ultimate residue of division in a chaotic matter which an immanent principle, form, causes to undergo a series of transformations. The four elements are reduced to combinations of homogeneous and invisible particles, and all the works of nature, including the human body, derive their origin from this plasticity of atoms.
In Renaissance thought atomism found an advocate in Fracastoro and later in Bruno (the doctrine of minima); it was upheld by P. Cassendi and opposed by Cartesio. Bacone criticized the doctrine of Democrito, but ultimately came to support a corpuscular theory very similar to that of the Abderite.
Atomism was resumed on scientific grounds by Boyle and Newton in order to explain the constitution and structure of matter. From that time to the present, scientific atomism has undergone continuous development, until, with the hypotheses of Rutherford and Bohr, it attained the status of a general theory accepted by all; it also represents the most fertile field for new discoveries in the modern sciences, for which reference should be made to the articles CHIMICA, FISICA, and MATERIA.
BIBLI: The fragments and reports concerning the first atomists are found in H. Diels, Die Fragmente der Vorsohrather, II, 2ª ed., Berlino 1935, pp. 250-51, which replaced the older collection by Mulbach, ed. Didot, still useful; A. Brieger, Die Urbezeugung der Atome, ecc., Halle 1884; K. Laswitz, Geschichte der Atomistik, Lipsia 1890; L. Mabilleau, Histoire de la philosophie atomistique, Parigi 1895; A. Lange, Geschichte des Materialismus, 1ª ed., Lipsia 1898; Gli Atomisti, translation and notes by V. ALTIERI, Bari 1939 (this is the annotated translation of the material collected in Diels); L. A. Stella, Valore e posizione storica dell'etica di Democrito, in Sophia, 2-3 (1942), pp. 207-58. In addition to specific studies on atomism and on the individual ancient atomists, cf. the general treatises of H. von Arnim, J. Burnet, G. de Ruggiero, P. Deussen, A. Döring, F. Fiorentino, A. Fouillée, Th. Gompers, F. Überweg-K. Praechter, W. Windelband, E. Zeller, etc.
Carlo Diano - Emilio Bodrero
II. SCIENCES
The a. which in the Middle Ages had almost entirely yielded the field to hylomorphism (v.) flourished anew with the rise of the experimental sciences, in which it steadily gained ground until it has come today to permeate every part of physics and chemistry. Yet although contact with the positive sciences led to so vigorous an affirmation of a., this did not occur without serious difficulties and genuine crises, which could be overcome only at the cost of profound changes in its own fundamental conceptions.The reasons why scientists in general showed themselves strongly inclined toward a. were at first predominantly philosophical in nature, and only later were properly experimental motives added to them. Among the former we must include the tendency to visualize one’s own schemes, which naturally led to mechanism, for which a. was especially well suited. One should also add anti-Aristotelianism, due partly to the scholastics’ estrangement from the new scientific currents, and partly to their misunderstanding of the Aristotelian concept of form, with the consequent error concerning occult qualities, and hence concerning every change that could not be reduced to changes of shape and place.
To these principal motives, reasons drawn from the nature of the continuum (v.) were frequently added. Only in the nineteenth century did motives of a scientific character assert themselves, chiefly the kinetic theory (v. dei) and the interpretation of the stoichiometric laws of chemistry.
The atomistic movement in science may be Gassendi (v.), who connected himself directly with Epicurus and attempted to restore his doctrines, replacing eternal atoms governed solely by chance with atoms created by God and directed toward determinate ends according to a divine plan. The same form of eclectic a. was adopted in the seventeenth century by Bacon, Galileo, Hooke, Boyle, Newton... Descartes (v.), despite his rigorous mechanism, was decidedly opposed to II. BOLSCEVISMO (v.) Leibniz (v.) may likewise, in a certain sense, be regarded as forms of a.
Until then, however, a. had remained more a philosophical system than a scientific theory. It acquired this character, instead, with Bernouilli, who in his Hydrodynamica (1783), starting from the hypothesis that a gas consists of particles in disordered motion and applying the laws of mechanics, succeeded in explaining the pressure of a gas as being due to the impact of the particles against the walls, and in mathematically deducing Boyle and Mariotte’s law. Thus the foundations of the kinetic theory were laid; only a century later was it taken up again in the works of Clausius and Maxwell, and it was to have such influence on the establishment of a. in physics. On the other hand, in 1808 Dalton laid the foundations of chemical a. with his New system of chemical philosophy, in which, however, he was compelled to add to the classical atomistic conception a postulate that finds no explanation within it: namely, that the atoms of each element possess their own characteristic weight.
The victory of a. was nevertheless neither easy nor rapid. In the kinetic theory, in fact, a serious difficulty arose when, after interpreting heat as due to the motion of molecules, an attempt was made to explain mechanically the second law of thermodynamics, according to which an isolated body constitutes an irreversible physical system, whereas the laws of mechanics are essentially reversible. This was one of the principal reasons that induced certain physicists—Raikine, Mach, Ostwald, and Duhem—to abandon mechanism and consequently a., taking refuge in energetics (v. DINAMIEMO), a position of more cautious positivism that denies any ontological value to the hypotheses and schemes of physics. The difficulty was brilliantly overcome, however, by Boltzmann on the basis of the calculus of probabilities, through recognition of the statistical value of the second law of thermodynamics.
Even more serious difficulties arose in chemistry when an attempt was made to determine atomic weights. Amid some concordant data, such uncertainties and confusions arose that Dumas declared that, had it been possible, he would gladly have erased the word atom from chemistry; and Berthelot raised even stronger objections. Yet the solution to these difficulties already existed in certain memoirs by Avogadro and Ampère, to which chemists had paid no attention. It fell to a young Italian chemist, Cannizzaro (v.), to draw their attention to this theory (1860), which, while on the one hand marking the definitive triumph of a. in chemistry, on the other constituted a new conception in comparison with the a. of Democritus: simple bodies were no longer composed of absolutely indivisible atoms. With Cannizzaro’s work, a particularly fruitful period began for chemical a. (v. CHIMICA). Not only had the molecule proved divisible into atoms, but the atom itself had proved to be a complex structure. Yet precisely through these marvelous developments, under the pressure of experience and theory, a. was rapidly evolving toward new forms that retained ever less of the old Democritean scheme.
III. ATOMISM IN PRESENT-DAY PHYSICS
Summarizing the results of physics in this regard, it is perhaps not an exaggeration to say that of the original atomism only the name remains,and even this is used in an anachronistic sense. The atom is anything but indivisible, and even its ultimate components, the elementary particles, are something quite different from the simple, immutable, readily visualizable corpuscles of Democritean philosophy. Hence the judgment, still frequent in scientific and philosophical literature, which attributes to Democritus the paternity of scientific atomism must be accepted with considerable reservation.
As regards the atomic structure of matter and many related data, we can readily accept Planck’s statement: «To these objections [against the atomic hypothesis and electronic theory] I oppose the unequivocal assertion (and in this I know that I am not alone) that atoms, even if we know nothing about their nature, are real no more and no less than the heavenly bodies and terrestrial objects that surround us. When I say that the hydrogen atom weighs 1.6 × 10⁻²⁴ g, I have no greater probability of being mistaken than when I say that the moon weighs 7 × 10³⁰ g.» But if one raises the question of the nature of atoms, and especially of their ultimate components, the problem becomes increasingly obscure and compels us to suspend all definitive judgment (v. MECCANICA).
IV. ATOMISM AND SCHOLASTICISM
In general, Scholasticism has shown itself opposed to atomism, insofar as it regarded the system in the materialistic and mechanistic form proposed by Democritus; and this judgment of its remains fully valid. More recent authors ordinarily distinguish between philosophical atomism and atomic theory, but this distinction seems rather vague unless it is specified more precisely what is meant by the name atomic theory. On the other hand, the task of separating out the elements of truth contained in modern theories is, as has been said, exceedingly difficult. Nevertheless, one may attempt to establish certain secure principles that would at least make it possible to delimit the controversial questions more clearly:a. It is certain that the living being possesses substantial unity, and therefore atoms cannot be regarded within it as natural individualities that are complete and independent in themselves.
b. The metaphysical arguments in favor of the hylomorphic composition of bodies in general, at least with regard to their ultimate components, retain their intrinsic value, insofar as they abstract from physical scientific theories (v. ILEMORFIEMO).
c. In principle, there is no opposition between the traditional Scholastic position, which recognizes substantial unity even in macroscopic inorganic bodies, and physical-chemical atomism, which recognizes an atomic structure in them, since this may be due to a simple accidental heterogeneity, like the organic structure of the living being.
d. An attempt has been made to find an interpretation of atomic theory in the theory of the natural minima of the ancient Scholastics: the comparison is perhaps suggestive, but it should be examined more deeply, also in relation to the nature of isotopes.
BIBLI: For the history of atomism in classical physics: K. Lasswitz, Geschichte der Atomistik vom Mittelalter bis Newton, 2 vols., Leipzig 1890; L. Mabilleau, Histoire de la philosophie atomistique, Paris 1907; L. Lowenheim: Die Wissenschaft Democrits und ihr Einfluss auf die moderne Naturwissenschaft, Berlin 1914; A. Mieli, Il periodo atomico moderno, in Scientia, 22 (1917), pp. 178–87; J. Duchesne, Esquisse du développement de l'atomistique classique, in Scientia, 82 (1947), pp. 37–48 (with bibliography). For the conceptions of modern physics: N. Bohr, La théorie atomique et la description des phénomènes, translated from the Danish by A. Legros and L. Rosenfeld, Paris 1932; P. Langevin, La notion des corpuscules et d'atomes, ibid. 1934; L. De Broglie, I quanti e la fisica mo-
derna, translated by U. Richard, Turin 1938; P. Jordan, La fisica del secolo XX, translated by G. Gentile, Florence 1940; M. Planck, La conoscenza del mondo fisico, translated by E. Persico, Turin 1943; W. Heisenberg, Mutamenti nelle basi della scienza, ibid. 1944. — For atomism and Scholasticism: P. Hoenen, Cosmologia, Rome 1944; by the same author, various articles in Gregorianum, 6–10 (1925–29). Mario Viganò