ACT AND POTENCY. — The doctrine of act and potency, together with the principles and applications deriving from it, constitutes the characteristic and 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 sense as synonymous with change or becoming. Change is a fact of universal and immediate empirical evidence. The being that we observe presents itself, at every moment of its development and expansion, as bound to a multiplicity of incessant becoming, so that it cannot be absolutely identified with the One, eternal, immobile Being described by Parmenides. On the other hand, equally inconsistent in the face of reason and experience was the position of Heraclitus, who, affirming the primacy of movement, absorbed being into pure becoming: for change cannot be conceived except in a subject that possesses an ontological permanence beyond its successive perfectibilities. It is therefore necessary to recognize, alongside the positivity of becoming, the reality of being.Now becoming presupposes, as its principle and intrinsic possibility, potency. Take the example of the sculptor who carves a statue: for this coming-to-be, this “becoming” of the statue to be possible, there must first be in the sculptor a real power, a dynamic principle that, when exercised, will bring the statue into being; this is active potency. Moreover, in the marble itself 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 sculptor is in act when exercising his art, and the statue is in act when it has emerged from the merely potential state of the marble block. Thus act is reality or perfection, the end and term of change; active potency is its dynamic principle; passive potency is the capacity to pass into act; and movement or change is the passage from potency to act, or rather, “the act of a being insofar as it is in potency.” As we see, act and potency are primary and elementary notions that do not admit of proper definitions but are clearly imposed on thought by the analysis of becoming and/or experience.
From the Megarians onward, there has often been a tendency to recognize only act and to deny the existence of potency. Yet it is clear that an architect, even when not building, is different from one who lacks the art of building, and is different precisely because he possesses the power to build well; just as a violinist does not cease to be an artist even when he has stopped playing. Moreover, if all were act without potency, everything would stand still, there would be no movement, no change, no progress, no evolution. To suppress the distinction between potency and act would therefore be no small matter (Aristotle, Metaphysics, IX, 3, 7).
II. PRINCIPLES
The principles that flow from the notions of act and potency and govern the entire field of being are manifold; here are the principal ones.1. Act and potency divide being: that is, every being is either pure act or composed of potency and act. For when we speak of being, we speak of a reality that is, and that consequently possesses at least the perfection of existence: it is therefore an act. If now that same being remains capable of advancing, of changing, of moving, it is thus in potency to the term of that progress, change, or movement. It is therefore composed of act and potency. If act were all act, it would be all perfection, all perfections—God. God alone is pure act. Every other being is composed of act and potency. One may speak of pure potency (as the prima materia is described by the Scholastics), but it is not affirmed as a being; rather, it is a pure principle of material being, together with the specific act or form (q.v.).
2. Potency and act are really distinct: for if potency in a being is not really distinct from act, that being is really all act and only act, and thus really has no real principle of change; one would fall back into the error of the Megarians.
3. Connected with the foregoing and applied in many cases is the principle that act, insofar as it is act, is not limited or multiplied unless it is received in a real potency, so that insofar as it is pure, it is infinite and unique. The reason is this: act does not limit itself, for limitation does not enter into its concept. Consider, for example, beauty, and suppose that what is thought in that concept is realized separately, without determining itself in a beautiful thing, but remaining beauty itself: it is clear that beauty itself is one, and that it is not beautiful to some degree but contains within itself the source of all degrees of beauty. To think of limited or multiplied beauty, one must place it in different subjects, which are so many real potencies to receive it and, in receiving it, to limit it according to their capacity.
This conception is substantially that which informs the dialogues of Plato; in the Phaedo, where he says that the beautiful is that by which beautiful things are beautiful (100d), or in the Symposium, where, after passing through inferior beauties, he speaks of a beauty that exists in itself and by itself, eternally united with itself alone, while other things are beautiful by participation in it (211b); 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 (Metaphysics, XII, 7); it is the conception of St. Augustine when he affirms: “If one could perceive the good itself, by participation in which things are good... you will have perceived God” (De Trinitate, VIII, ch. 3, no. 5), that is: “Therefore the good alone is simple and for this reason alone immutable, namely God. From this good all things are created that are good, but not simple, and from it all things are mutable” (City of God, XI, ch. 10, no. 1); it is that which St. Thomas thus expresses: “No act is found to be terminated except by a potency that is its receptive principle” (Commentary on the Theology, ch. 18).
The last two principles are not, however, accepted by all Scholastics. Many of them, following Suárez, hold that an act can itself be potency relative to a higher degree of the same act, and that an act can be limited without entering into composition with a distinct real potency, the character of contingency sufficing for such limitation. Among other principles, we may also cite that act is prior to potency; that act and potency are in the same genus; and that from two beings in act one cannot make a single being: these and other assertions are required by the notions set forth above.
ACT AND POTENCY — HEROIC ACT OF CHARITY
### III. APPLICATIONS
The concepts of act (actus) and potency (potentia) are employed by the Scholastics in many contexts, both philosophical and theological. Their use, however, varies depending on whether one accepts or rejects the principle that act is neither limited nor multiplied unless it is received in a real potency. In light of this principle, among other things, the doctrine of creation is illuminated—a doctrine which ancient philosophy perhaps ignored or at best barely glimpsed, but upon which the Scholastics, following St. Augustine and St. Thomas, made the most direct and decisive application of the principles of act and potency. The transition from the One to the many, the coexistence of the infinite or perfect with the finite, and the possibility of contingent beings become, in some way, intelligible. The act of being is in God pure from every potentiality, one and perfect, yet it can be communicated to multiple and limited beings according to the varying degrees of potentiality that enter into their constitution. A gradation of being is conceivable, at whose summit stands pure act, transcendent and infinitely distinct from the universe of which He is the unmoved cause; and beneath Him, in descending scale according as they possess less act and more potency, are the other beings, from pure spirits or angels to inanimate bodies. This is the Platonic conception of participation, but clarified and completed as the analyses of Aristotelian principles permitted and as Christian revelation suggested or confirmed.
Another important doctrine in Thomistic philosophy, explained by the theory of potency and act, is the real distinction between essence and existence in created beings. Since existence is 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 the potency or capacity for being that belongs to its nature, that is, it is composed of essence and existence. Similarly, the same principle leads to the assignment, in the world of bodies, of prime matter as the principle of individuation. Since bodies are multiply instantiable within the same species, the act that confers specific determination—that is, substantial form—is multiplied and, in each of the many instances in which it exists, is limited. It is therefore necessary that it actualize a potency or potential subject, which limits it and permits its multiplication. Such a potential subject, in Aristotelian-Thomistic philosophy, is prime matter, which, when received into quantity, can be divided into many potential subjects of as many forms of the same species.
Another important consequence is the real distinction, admitted in Thomistic philosophy, between the soul and its faculties. The soul is in act insofar as it is the act of the living body. If it were identical with its faculty, the faculties themselves would be in act. But a faculty in act is in the exercise of its operation. Now experience shows that our faculties are not always in act but 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 it is pure act.
The simplicity of God, despite the union in Him of all perfections, is clarified by considering the requirements of pure act. Each perfection must be in God purely in act; if it were not, it would retain within itself that passive potency which cannot be found in God, Who is pure act. But what is purely in act is nothing other than pure act itself. If, therefore, each perfection in God is identified with pure act, one perfection is really identical with all the others, and no real distinction enters into the divine nature, in the order of the absolute; God is therefore simple.
In the mystery of the Incarnation, many theologians hold that the assumption of human nature by the person of the Word is explained by the actuation of this nature by the personal Being of the Word, or at least that this actuation necessarily follows upon the assumption; and this, whether the actuation introduces any created reality or results merely from the union with the uncreated act. These examples (and others could be listed) demonstrate how fruitful in philosophy and theology are the principles concerning potency and act.