ACT AND POTENCY. - The doctrine of a. and p., with the principles and applications deriving from it, constitutes the characteristic and the foundation of Aristotle's metaphysics.
I. NOTIONS. - The notions of act and potency arise from the phenomenological-metaphysical analysis of movement, understood in its broadest meaning, as synonymous with change or becoming. This, change, is a fact of universal and immediate empirical evidence. The being that we observe presents itself to us, at every moment of its development and expansion, as bound to a manifold and ceaseless becoming, so that it is not at all identifiable with the one, eternal, immobile Being described by Parmenides. On the other hand, equally untenable before reason and experience was the position of Heraclitus, who, by affirming the primacy of movement, absorbed being as well into pure becoming: for change is not conceivable except in a subject that has an ontological permanence beyond its successive perfectibilities. We must therefore acknowledge, along with the positivity of becoming, the reality of being.
Now becoming presupposes, as its principle and intrinsic possibility, potency. Take the example of the craftsman who carves the statue: for this coming-to-be, this "becoming" of the statue to be possible, there must first of all be in the craftsman a real power, a dynamic principle which, once put into exercise, will bring the statue into being; this is active potency. Furthermore, in the marble too there must be a possibility, a power to become a statue under the artist's chisel; this is passive potency. Both, active and passive potency, constitute the "terminus a quo" of the movement that is realized through them, while they pass over into act: the craftsman is in act when he exercises his art, the statue is in act when it has been brought forth out of the possibility, inert in itself, of the block of marble. Thus act is the reality or the perfection, the end and the term of change; active potency is its dynamic principle; passive potency is the capacity to pass into act; movement or change is the passage from potency to act, or, better, the "act of that which is in potency, insofar as it is in potency." Act and potency are, as can be seen, primary and elementary notions that do not admit of properly so-called definitions, but impose themselves clearly upon thought from the analysis of becoming grasped in experience.
From the Megarians onward there has often been a tendency to recognize only act, and to deny the existence of potency. But it is clear that an architect, even when he is not building, is different from one who is ignorant of the art of building, and is different precisely because he has the power to build well; just as a violinist does not cease to be an artist even when he has stopped playing. Moreover: if everything were act, without potency, everything would stand still, there would no longer be any movement, any change, any progress, any evolution. To suppress the distinction of potency from act would therefore be to suppress no small thing (Aristotle, Metaph., IX, 3, 7).
II. PRINCIPLES. - The principles that flow from the notions of act and potency and that govern the entire field of being are many; here are the principal ones.
1. Act and potency divide being: that is, every being is either act alone or composed of potency and act. For when we speak of a being, we speak of a reality that is, and that consequently has at least the perfection of being: it is therefore an act. If now that same being remains capable of progressing, of changing, of moving, it is therefore in potency to the term of that progress, that change or movement of whatever kind. It is therefore composed of act and potency. If act were wholly actuality, it would be wholly perfection, all perfections, God; God alone is pure act. Every other being is composed of act and potency. One can speak of a pure potency (thus prime matter is described by the Scholastics), but it is not affirmed as a being, but rather as the pure principle of material being, together with specific act or form (v.).
2. Potency and act are really distinct: in fact, if the potency in a being were not really but only conceptually distinct from the act, that being would really be wholly act and act alone, and thus would really have no real principle of change: one would fall back into the error of the Megarians.
3. Connected with the preceding principles and then applied in many cases is the principle that act, in the order in which it is act, is not limited or multiplied unless it is received in a real potency, so that in the order in which it is pure, it is infinite and unique. Here is the reason: act does not limit itself, because limitation does not enter into its concept. Consider, for example, beauty, and suppose that what is thought in that concept were realized separately, without being determined in a beautiful thing, but remaining beauty itself: it is clear that beauty itself is one alone, and that it is not beautiful in a certain degree, but contains within itself the source of all degrees of beauty. To think of beauty as limited or multiplied, one must place it in different subjects, which are as many real potencies to receive it, and in receiving it to limit it according to their capacity.
This conception is substantially the one that informs the dialogues of Plato; in the Phaedo, where he says that the beautiful is that by which beautiful things are beautiful (100, d), or in the Symposium, where, having transcended lower beauties, he speaks of a beauty that stands in itself and for itself, eternally united with itself alone, while other things are beautiful by participation in it (211, b); it is the conception implicit in Aristotle's doctrine of pure act and especially in his identification of the first Being with the act of intelligence subsisting in itself (Metaph., 12, 7); it is the conception of St. Augustine when he affirms: «Si potueris sine illis quae participatione boni bona sunt, perspicere ipsum bonum cuius participatione bona sunt... perspexeris Deum» (De Trinitate, VIII, c. 3, n. 5), that is: «Est itaque bonum solum simplex et ob hoc solum incommutabile, quod est Deus. Ab hoc bono creata sunt omnia bona, sed non simplicia, et ab hoc mutabilia» (De Civitate Dei, XI, c. 10, n. 1); it is the conception that St. Thomas thus chisels out: «Nullus actus invenitur finiri nisi per potentiam quae est eius receptiva» (Compendium Theologiae, c. 18).
The last two principles, however, are not admitted by all the Scholastics. Many of them, with Suárez, think that an act can itself be potency in relation to a higher degree of the same act, and that act can be limited without entering into composition with a distinct real potency, the character of contingency being sufficient for such limitation. Among the other principles, let us further cite that act is prior to potency; that act and potency are in the same genus; that from two beings in act there cannot be made a being that is one: these and other assertions are required by the very notions set out above.
III. APPLICATIONS
The concepts of act and potency are used by the Scholastics in many positions both philosophical and theological. Their use, however, differs according to whether one accepts or rejects the principle that act is not limited and not multiplied unless it is received in a real potency. In the light of this principle, in fact, there is illustrated, among other things, the doctrine of creation, a doctrine that ancient philosophy perhaps ignored, or at most barely glimpsed, and upon which the Scholastics, after St. Augustine and St. Thomas, made the most direct and most decisive application of the principles of act and potency. The passage from the one to the many, the coexistence of the infinite or perfect with the finite, the possibility of contingent beings become in some way intelligible. The act of being is in God pure from every potentiality, one and perfect, but it can be communicated to multiple and limited beings, according to the different degrees of potentiality that will enter into their constitution. An ontological gradation is conceivable, at the summit of which stands pure act, transcendent, infinitely distinct from the universe of which it is the unmoved cause; and subordinate to Him, in descending scale, in proportion as they have less of act and more of potency, the other beings, from pure spirit or angel to inanimate bodies. It is the Platonic conception of participation, but clarified and completed, as the analyses of Aristotelian principles have permitted and as Christian revelation has suggested or confirmed.Explained by the theory of potency and act is also another doctrine important in Thomist philosophy: the real distinction between essence and existence in created beings. Existence being the supreme actuality, if its act were not received in a potency that limits it, it would be unique and infinite; it would be the same absolute and perfect Being, He who is, God. Every limited being therefore is necessarily composed of the act of being and of the potency and capacity of being that befits its nature, that is, it is composed of essence and of existence. Likewise the same principle leads to assigning in the world of bodies as the principle of individuation that element of the essence which is prime matter. Since bodies are multiplicable within the same species, the act that gives specific determination, that is, the substantial form, finds itself multiplied and in each of the many in which it exists it is limited. It is therefore necessary that it actualize a potency or a potential subject, which limits it and permits its multiplication. Such a potential subject is in Aristotelian-Thomist philosophy prime matter, which, having received quantity, can be divided into many potential subjects of as many forms of the same species.
Another important consequence: the real distinction admitted in Thomist philosophy between the soul and its faculties. The soul is in act since it is the act of the living body. If it were identical to its faculty, the faculties too would be in act. But a faculty in act stands in the exercise of its acting. Now experience demonstrates that our faculties are not always in act but that they pass from potency to act; they are therefore distinct from the soul, which is always in act. The being that is its faculty is also its act, and is pure act.
The simplicity of God, despite the union in Him of all perfections, is illuminated by the consideration of the exigencies of pure act. Each perfection must be found in God purely as act: if it were not so, it would retain in itself that passive potency which cannot be found in God, who is pure act. But that which is purely act is nothing other than pure act. If therefore each perfection is identified in God with pure act, one perfection is really identified with all the others, and no real distinction enters into the divine nature, into the order of the absolute: God therefore is simple.
In the mystery of the Incarnation, many theologians hold that the assumption of human nature on the part of the person of the Word is explained by the actualization of this nature by the personal Being of the Word, or at least that this actualization follows necessarily upon the assumption; and this, whether the actualization introduces some created reality or results only from the union with uncreated act. These examples (others could be listed) demonstrate how many consequences and applications the principles concerning potency and act are fruitful of, in philosophy and theology.
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