We have seen now that in the real order the potential presupposes the actual; for the potential cannot actualize itself, but can be actualized only by the action of some already actual being. Nor can we avoid this consequence by supposing the potential being to have had no actual beginning in time, but to be eternally in process of actualization; for even so, it must be eternally actualized by some other actual being—a position which Aristotle and some scholastics admit to be possible. Whether, then, we conceive the actualization as beginning in time or as proceeding from all eternity, it is self-contradictory to suppose the potential as capable of actualizing itself.
It is likewise true that the actual precedes the possible in the order of our knowledge. The concept of a thing as possible presupposes the concept of that thing as actual; for the possible is understood to be possible only by its intelligible relation to actual existence. This is evidently true of extrinsic possibility; but our knowledge even of the intrinsic possibility of a thing cannot be the first knowledge we possess in the order of time. Our first knowledge is of the actual; for the mind's first cognitive act must have for object either itself or something not itself. But it knows itself as a consciously acting and therefore actual being. And it comes to know things other than itself only by the fact that such other things act upon it either immediately or mediately through sense-consciousness; so that in every hypothesis its first known object is something actual.[79]
The priority of the actual as compared with the potential in the real order, suggests a proof of the existence of God in the manner indicated above. It also affords a refutation of Hegelian monism. The conception of the world, including all the phenomena of mind and matter, as the gradual self-manifestation or evolution of a potential being eternally actualizing itself, is a self-contradictory conception. Scholastics rightly maintain that the realities from which we derive our first most abstract and transcendental notion of being in general, are actual realities. Hegelians seize on the object [pg 068] of this notion, identify it with pure thought, proclaim it the sole reality, and endow it with the power of becoming actually everything. It is manifest, therefore, that they endow purely potential being with the power of actualizing itself.
Nor can they fairly avoid this charge by pointing out that although their starting-point is not actual being (with which the scholastic philosophy of being commences), yet neither is it possible or potential being, but being which has neither of these determinations, being which abstracts from both, like the real being of the scholastics (7, 13). For though real being can be an object of abstract human thought without either of the predicates “existent” or “non-existent,” yet it cannot be anything in the real order without either of them. There it must be either actually existent or else merely potential. But Hegelians claim absolutely indeterminate being to be as such something in the real order; and though they try to distinguish it from potential being they nevertheless think of it as potential being, for they distinctly and repeatedly declare that it can become all things, and does become all things, and is constantly, eternally transforming itself by an internal dialectic process into the phenomena which constitute the worlds of mind and matter. Contrasting it with the abstract “inert” being which they conceive to be the object of the traditional metaphysics, they endow “indeterminate being” with the active power of producing, and the passive potentiality of becoming, actually everything. Thus, in order to show a priori how this indeterminate being must evolve itself by internal logical necessity into the world of our direct and immediate experience, they suppose it to be subject to change and to be at the same time self-actualizing, in direct opposition to the axiom that potential reality, reality which is subject to change, cannot actualize itself: Quidquid movetur ab alio moveatur oportet.
11. Kinds of Change.—Following Aristotle,[80] we may recognize a broad and clear distinction between four great classes of change (μεταβολή, mutatio) in the phenomena of our sense experience: local change (κίνησις κατὰ τόπον, φορά, latio); quantitative change (κατὰ τὸ πόσον, ἀύζησις ἤ φθίσις, augmentatio vel diminutio); qualitative change (κατὰ τὸ ποίον, ἀλλοίωσις, alteratio); and substantial change (κατ᾽ οὐσίαν, γένεσις ἤ φθορά). The three former are accidental, i.e. do not reach or affect the essence or substance of the thing that is changed; the fourth is substantial, a change of essence. Substantial change is regarded as taking place instantaneously, as soon as the condition brought about by the accidental changes leading up to it becomes naturally incompatible with the essence or nature of the subject. The accidental changes, on the other hand, are regarded as taking place gradually, as realizing and involving a succession of states or conditions in the subject. These changes, especially when they take place in corporeal things, are properly described as [pg 069] movement or motion (motus, motio). By movement or motion in the strict sense we therefore mean any change which takes place gradually or successively in a corporeal thing. It is only in a wider and improper sense that these terms are sometimes applied to activity of whatsoever kind, even of spiritual beings. In this sense we speak of thoughts, volitions, etc., as movements of the soul, motus animae; or of God as the Prime Mover ever in motion, the Primum Movens semper in motu.
With local change in material things, as also with quantitative change, growth and diminution of quantity (mass and volume), everyone is perfectly familiar. From the earliest times, moreover, we find both in science and philosophy the conception of matter as composed of, and divisible into, ultimate particles, themselves supposed to admit of no further real division, and hence called atoms (ἄ-τομος, τέμνω). From the days of Grecian atomism men have attempted to show that all change in the Universe is ultimately reducible to changes of place, order, spatial arrangement and collocation, of those hypothetical atomic factors. It has likewise been commonly assumed that change in mass is solely due to change in the number of those atoms, and change in volume (of the same mass) to the relative density or closeness with which the atoms aggregate together; though some have held—and it is certainly not inconceivable—that exactly the same material entity, an atom let us say, may be capable of real contraction and expansion, and so of real change of volume: as distinct from the apparent contraction and expansion of bodies, a change which is supposed to be due to change of density, i.e. to decrease or increase in the dimensions of the pores or interstices between the smaller constituent parts or molecules. However this may be, the attempts to reduce all change in physical nature to mere mechanical change i.e. to spatial motions of the masses (molar motions), the molecules (molecular motions), and the atoms or other ultimate components of matter (whether vibratory, undulatory, rotatory or translational motions), have never been satisfactory.
Qualitative change is wider than material change, for it includes changes in spiritual beings, i.e. in beings which are outside the category of quantity and have a mode of existence altogether different from the extensional, spatial existence which characterizes matter. When, for instance, the human mind acquires knowledge, it undergoes qualitative change. But matter, too, has qualities, [pg 070] and is subject to qualitative change. It is endowed with active qualities, i.e. with powers, forces, energies, whereby it can not merely perform mechanical work by producing local changes in the distribution of its mass throughout space, but also produce physical and chemical changes which seem at least to be different in their nature from mere mechanical changes. It is likewise endowed with passive qualities which appear to the senses to be of various kinds, differing from one another and from the mechanical or quantitative characteristics of size, shape, motion, rest, etc. While these latter are called “primary qualities” of bodies—because conceived to be more fundamental and more closely inherent in the real and objective nature of matter—or “common sensibles” (sensibilia communia), because perceptible by more than one of our external senses—the former are called “secondary qualities,” because conceived to be less characteristic of the real and objective nature of matter, and more largely subjective products of our own sentient cognitive activity—or “proper sensibles” (sensibilia propria), because each of them is apprehended by only one of our external senses: colour, sound, taste, odour, temperature, material state or texture (e.g. roughness, liquidity, softness, etc.). Now about all these perceived qualities and their changes the question has been raised: Are they, as such, i.e. as perceived by us, really in the material things or bodies which make up the physical universe, and really different in these bodies from the quantitative factors and motions of the latter? Or, as such, are they not rather partially or wholly subjective phenomena—products, at least in part, of our own sense perception, states of our own consciousness, having nothing really corresponding to them in the external matter of the universe beyond the quantitative, mechanical factors and motions whereby matter acts upon our faculties of sense cognition and produces these states of consciousness in us? This is a question of the first importance, the solution of which belongs to Epistemology. Aristotle would not allow that the objective material universe can be denuded, in the way just suggested, of qualities and qualitative change; and scholastic philosophers have always held the same general view. What we have to note here, however, in regard to the question is simply this, that even if the world of matter were thus simplified by transferring all qualitative change to the subjective domain of consciousness, the reality of qualitative change and all the problems arising from it would [pg 071] still persist. To transfer qualitative change from object to subject, from matter to mind, is certainly something very different from explaining it as reducible to quantitative or mechanical change. The simplification thus effected would be more apparent than real: it would be simplifying the world of matter by transferring its complexity to the world of mind. This consideration is one which is sometimes lost sight of by scientists who advance mechanical hypotheses as ultimate explanations of the nature and activities of the physical universe.
If all material things and processes could be ultimately analysed into configurations and local motions of space-occupying atoms, homogeneous in nature and differing only in size and shape, then each of these ultimate atomic factors would be itself exempt from intrinsic change as to its own essence and individuality. In this hypothesis there would be really no such thing as substantial change. The collection of atoms would form an immutable core of material reality, wholly simple and ever actual. Such an hypothesis, however, is utterly inadequate as an explanation of the facts of life and consciousness. And even as an account of the processes of the inorganic universe it encounters insuperable difficulties. The common belief of men has always been that even in this domain of reality there are fundamentally different kinds of matter, kinds which differ from one another not merely in the shape and size and configuration and arrangement of their ultimate actual constituents, but even in the very substance or nature of these constituents; and that there are some material changes which affect the actual substance itself of the matter which undergoes them. This belief scholastics, again following Aristotle, hold to be a correct belief, and one which is well grounded in reason. And this belief in turn involves the view that every type of actual material entity—whether merely inorganic, or endowed with life, or even allied with a higher, spiritual mode of being as in the case of man himself—is essentially composite, essentially a synthesis of potential and actual principles of being, and therefore capable of substantial change. The actually existing material being scholastics describe as materia secunda, the ὕλη ἐσχάτη of Aristotle; the purely potential factor, which is actualized in this or that particular kind of matter, they describe as materia prima, the ὕλη πρώτη of Aristotle; the actualizing, specifying, formative principle, they designate as forma substantialis (εἶδος). And since the purely potential principle [pg 072] cannot actually exist except as actualized by some formative principle, all substantial change or transition from one substantial type to another is necessarily both a corruptio and a generatio. That is, it involves the actual disappearance of one substantial form and the actual appearance of another. Hence the scholastic aphorism regarding substantial change: Corruptio unius est generatio alterius: the corruption or destruction of one kind of material thing involves the generation of another kind.
The concepts of materia prima and forma substantialis are concepts not of phenomenal entities directly accessible to the senses or the imagination, but of principles which can be reached only mediately and by intellect proper. They cannot be pictured in the imagination, which can only attain to the sensible. We may help ourselves to grasp them intellectually by the analogy of the shapeless block of marble and the figure educed therefrom by the sculptor, but this is only an analogy: just as the statue results from the union of an accidental form with an existing matter, so this matter itself, the substance marble, is composed of a substantial form and a primordial, potential matter. But there the analogy ceases.
Furthermore, when we consider that the proper and primary objects of the human intellect itself are corporeal things or bodies, and that these bodies actually exist in nature only as composite substances, subject to essential or substantial change, we shall realize why it is that the concept of materia prima especially, being a mediate and negative concept, is so difficult to grasp; for, as the scholastics describe it, translating Aristotle's formula, it is in itself neque quid, neque quantum, neque quale, neque aliquid eorum quibus ens determinatur.[81] But it is through intellectual concepts alone, and not through imagination images, that we may hope to analyse the nature and processes even of the world of corporeal reality; and, as St. Thomas well observes, it was because the ancient Greek atomists did not rise above the level of thinking in imagination images that they failed to recognize the existence, or explain the nature, of substantial change in the material universe[82]: an observation which applies with equal [pg 073] force to those scientists and philosophers of our own time who would fain reduce all physical processes to mere mechanical change.