Modern writings on the structure of physical reality usually oppose the Aristotelian doctrine of hylomorphism to the rival theories of atomism and dynamism. Too often overlooked is the great complexity of the questions involved, not to mention the ambiguity that haunts such terms as "atomism," "dynamism," and "mechanism." Quite possibly, by such equivocal or promiscuous logic, even Aristotle can be proved to harbor the sheerest atomism or mechanism, and Descartes, a mechanist if ever there was one, pronounced the complete anti-atomist. Care and circumspection should thus be the watchword in dealing with notions so elastic.
The atomism that cut across the hylomorphism of Aristotle came mostly from Leucippus and his disciple Democritus, and Aristotle's critical examination of their doctrine is perhaps still the best springboard to this whole debate on the structure of physical reality. These two philosophers had devised an atomistic interpretation of nature which for pure consistency and ingenuity it would be hard to better. The material world, they said, was ultimately composed of very minute particles, indivisible and devoid of qualitative content, differing only in shape and figure. The things we see in nature resulted from the particles coming together in varying amounts and combinations; and the changes we see in things were similarly explained as mere rearrangements of these same particles.
Aristotle begins his De Generatione et Corruptione with a close analysis of this doctrine, which he finds he must reject for one compelling reason, namely, that such a doctrine cannot account for the generation or coming-to-be of new substances. A new grouping of atoms is not a new substance. Reclustering does not basically change the things clustered. Yet there are basic or essential changes in nature. "There is," he declares, "absolute generation and corruption, not by association and dissociation [in the mechanistic sense], but by the complete change of this thing to that." 24 Of this Aristotle is sure. "This," he concludes, "may be taken as established, namely, the generation cannot be the mere association some assert it to be." 25
Atomism, therefore, cannot be a total explanation of physical reality because of its failure to account for substantial generation, at least in the traditional sense of the complete passing away of one thing and the coincident emergence of an essentially new thing. Aristotle's argument in De Generatione assumes, of course, that these essential changes do occur, but once we grant this premise the atomism of Leucippus and Democritus falls and hylomorphism, now as then, must stand. Thus, Aristotle's whole case against the Atomists comes and goes with substantial change; but of this the living kingdom, to say no more, offers what appear to be incontrovertible instances. A living thing is a substantial individual, substantially distinct from every other thing; and coming to life or succumbing to death is a substantial change. If not, then nature does indeed belong to the Atomists of old. But for all their ingenuity the Atomists could not long secure the philosophical citadel, and through the ages their partisans have fared little or no better.
As intimated earlier, however, atomism does not mean the same thing to everybody. To some it is only another name for the quantitative analysis of the physical world. This, in general, is what it means to the scientist, whose work consists primarily in sifting and ordering the corporeal world on a quantitative basis, or on the basis of spatial continuity. If this is atomism, there need be no quarrel with it. From his point of view the scientist, as a matter of fact, may well be justified to think of bodily things as though composed of minute particles whose arrangements and movements can be mathematically analyzed. Thus understood the physical universe does indeed assume a mechanistic or atomistic appearance. This conception, moreover, has a solid foundation in reality and is, for that matter, clearly warranted by Aristotle's own doctrine of the primacy of local motion. All other movement in nature presupposes, as we shall see, local motion, a quantitative displacement. What must not be lost sight of, however, is that the quantitative picture of the physical world is bought at an abstraction; hence it affords only a partial, and not a total view.
In sum, both the hylomorphic and the atomistic (i.e., quantitative) explanation have their place. But, speaking philosophically, Aristotle's analysis cuts deeper and gets closer to the heart of things.