HYLEMORPHISM. — From 8.7. (matter) and 10.7. (form) (shape), it denotes the philosophical theory, attributed to Plato and Aristotle, which holds that corporeal substance is composed of an indeterminate element (matter) and a determinate one (form).
The earliest Greek philosophy, with its attempts to explain becoming, prepared the way for hylemorphism. Against the mobilism of Heraclitus, Parmenides affirms immobility: “For being exists, while nothingness does not” (frg. 6, 1-2); this being is immobile. Indeed, change is either from being or from non-being; but both are impossible, “since being cannot come to be (for it already is), nor can anything come to be from non-being” (frg. 8, 7-8). Plato, in his doctrine of ideas, posits matter as the indeterminate principle of becoming, while form is the principle of determination and intelligibility. Aristotle systematizes this doctrine in his theory of substance (ousia), where matter (hyle) is the indeterminate substratum of change, and form (morphe) is the determining and actualizing principle.
Hylemorphism is not merely a metaphysical theory but also a response to the problem of the unity of composite beings. It explains how a substance can be both one and many: one in its substantial unity, many in its potential parts. This theory has been contrasted with other metaphysical systems (v. dynamism, phenomenism, idealism, etc) for general metaphysical reasons.
Assuming the objective reality of extended bodies, not a few authors ground hylemorphism on Aristotle’s argument concerning substantial change. In the face of difficulties raised by scientific atomic theory, others attempt to derive hylemorphism from the fact that the body is a spatio-temporal reality with energetic and inertial properties. The actual unity and potential multiplicity of the continuum, they argue, cannot be adequately explained without admitting in corporeal substance a principle of unity and determination (form) and a principle of multiplicity and indetermination (prime matter; cf. St. Thomas, *Summa Contra Gentiles*, II, cap. 65; P. Descogis, *Essai critique sur l'hypermorphisme*, Paris 1924, p. 237). A similar argument is drawn from the consideration of corporeal existence, which is characterized by both unity and temporal diffusion (cf. F. Renoirte, *Eléments de critique des sciences et de cosmologie*, Louvain 1947, p. 227). Finally, hylemorphism is further supported by the dual and opposing series of properties of corporeal substance: on the one hand, quantity and energy; on the other, quality and activity (electromagnetic forces, etc.; cf. P. Descogis, op. cit., pp. 269 ff.). These last three considerations are interconnected and may be regarded as a single foundation of hylemorphism from different but complementary perspectives.
Other authors, assuming as evident the principle that pure act is unique and infinite and is multiplied when participated in a potential subject, deduce from the fact that there exist multiple corporeal individuals of the same species that these bodies are composed of a participated substantial act and a substantial potency that receives it (cf. St. Thomas, *De spiritu creato*, a. 1, ad 9; *Physics*, VIII, lect. 2). This argument is much debated, since others maintain that the principle of participation is itself grounded in hylemorphism.
Hylemorphism seems to be opposed by modern science, according to which matter is constituted of particles that some physical theories consider ontologically distinct and sometimes even spatially separate. In this regard, it is observed that if bodies were to be understood as aggregates of particles (and thus as distinct individuals), hylemorphic theory could still be applied to them. Indeed, it cannot be admitted, as some assert (St. Albert the Great, P. Descogis, M. Fatta, etc.), that particles, while remaining unchanged, are assumed by a higher substantial form into a substantial metaphysical unity, nor that metaphysical unity could consist in physical discontinuity. Yet the activity of the living body strongly persuades us of its substantial unity, from which it follows that in the assimilation of food as in the destruction of the living being after death, substantial changes intervene. This argues, in the elements taken into the unity of the living being and, by extension, in bodies in general, the essential composition of matter and form.
Even in physics, if one sets aside theoretical constructions, observations of nuclei, atoms, and crystals, understood in their concrete experimental value, indicate a heterogeneous particulate constitution of matter (i.e., with different properties in different parts), so that it is not necessary to think of particles in a compound as distinct ontological individuals (cf. P. Hoenen, *Cosmologia*, pp. 316 ff.). In the atom, in chemical compounds, and even in crystals, a heterogeneous continuity is therefore possible, which allows for the ontological substantial unity of higher bodies. Moreover, the most recent physical theory of quantum mechanics, by rejecting the intuitive notion of the corpuscle as a material point, rejects mechanical theories of discontinuous matter, namely: “it rejects the presupposition, inherent in all previous theories, that atoms, photons, and other entities of the atomic world had to be conceived as bodies or mechanisms of immensely small size” (E. Persico, *Fondamenti della meccanica atomica*, Bologna 1945, p. 68, cf. p. 87). Consequently, it affirms that the corpuscle, for example the electron, when entering into higher complexes, loses its physical individuality, cannot be marked or followed, and remains as a modification of the complex. “The property of individuality in this case does not correspond to any physical reality” (ibid., p. 467; cf. P. Langevin, *La notion de corpuscules et d'atomes*, Paris 1935); L. de Broglie (*Materia e luce*, Milan 1940, p. 274) writes: “In quantum physics, the system is a kind of organism in whose unity the constituent elementary units are almost absorbed.” This concept is similar to that of the virtual existence of components in a compound, developed by Aristotle and Thomas Aquinas. It may therefore be concluded that physical experiments do not seem to exclude hylemorphism, and in particular quantum mechanics develops concepts favorable to II.
By analogy with the concepts of hylemorphism, the terms “matter” and “form” are often used in disparate fields. E. Kant generally calls the manifold “matter,” while “form” is that by which the manifold is ordered (cf. *Critique of Pure Reason*, Italian trans. by G. Gentile and G. Lombardo-Radice, Bari 1945, p. 64). There are “forms” of intuition: external (space), internal (time), of thought (categories), of pure reason (ideas), etc. In sacramental theology, the masters of the 12th and 13th centuries formulated the general doctrine according to which every sacrament, as a sensible sign, is composed of things (res) and words (verba). Guided by analogy and observing that the res has an indeterminate meaning while the verba have a precise sense, they called the former the “matter” and the latter the “form” of the sacrament.