Thomism: Act & Potency

Everything actual acts, everything potent is powerful, everything passive receives.

Now that we have explored being and essence, form and matter, substance and accidents, it is time to tackle act (actus) and potency (potentia)—the conceptual toolkit that coordinates our understanding of these foundational principles of being and becoming. Though act and potency are notionally prior to these other principles, insofar as they are needed to adequately understand each of them (both individually and in their relation), it is natural to explore act and potency only after we have attained an understanding of these others, for the concreteness of these real principles gives us the traction we need to grapple with the abstractness of act and potency. The reason for this abstractness is that act and potency are ‘second order concepts’ which are not directly derivable from or attributable to any thing in particular, but which are nonetheless applicable to all things in general. In fact, for Aquinas, these concepts are so foundational that with them in hand we can literally grasp and articulate the whole of reality in a most universal way.

Act and potency were initially crafted by Aristotle in order to grapple with being (esse) and becoming (fieri), and everything included under the umbrella of being and becoming, for to grapple with with reality in such a foundational and universal way, we needed concepts that are equally foundational and universal. Act and potency are precisely these concepts because they fittingly capture the way the above-listed basic principles of reality—being and essence, form and matter, etc.—are set in relation to one another, at ontological, essential, and substantial levels, and on all other levels whatsoever. Thus, we can applying this insight immediately to the whole of reality and say that while God is the fullness of being (esse tantum) and thus the fulness of actuality (actus purus), all other beings possess something of non-being and thus stand before us as an admixture of act and potency, and in all sorts of ways—in perfect correspondence to the subtle structuration of reality.

act and potency: how small acorns become great oaks… unless their rising toward the sun is foiled by chubby little squirrels… who can themselves then rise into the fulness of being

Grounding Application

As already mentioned, these principles are first applied in the ontological order with respect to being and essence, and then in the essential order with respect to form and matter, before finding an application across all other areas of being in its beautifully variegated structure. Let us here look at their primary application at the level of the ontological and essential:

• In the order of being: All finite beings are ontologically composed of the co-relative principles of being and essence, where being functions as the principle of actuality and essence as the principle of potentiality. This means that an essence that can be (i.e., is essentially possible) is in potency to its actualization by an act of being that makes it an existent substance. In this relation, the essence contracts and limits the act of being to this very being, while the act of being establishes the essence in existence as as something subsistent, with its own power and action in the world.

• In the order of essence: All bodily beings are essentially composed of the co-relative principles of form and matter, where form functions as the principle of actuality and matter as the principle of potentiality. This means that a portion of matter that can be some or other bodily thing is in potency to being formed, and that this potency can be actualized by a proportionate form that determines the matter to be a bodily substance. In this relation, the matter contracts and limits the formal actuality to this very substance, while the determinate form establishes this matter as a bodily substance of a specific kind.

From this we see a number of things, namely: 1) that while some substances are form alone (i.e., separated substances or angels), others are form-matter composites (i.e., material bodies); 2) that being comes to an essence of a substance through its form, whether the substance be form alone or a form-matter composite; and 3) that all bodily substances are first a composition of being and essence (ontologically), and then a further composition of form and matter (essentially). And we also see that being, essence, form, and matter are not themselves beings but the principles of beings, and that precisely as such principles they are co-constitutive of beings through their characteristic union with one another. The designation of these real principles (being-essence, form-matter) as associated with one another as act to potency then evidently reveals that they bear a profound relation to one another: Since they possess an asymmetrical relation, where one of each pair represents a principle that is indeterminate yet determinable, while the other a principle that provides the determination of the indeterminate yet determinable, when these principles are conjoined with their complementary opposite they form the highest kind of unity.

Explanatory Power

And thus we see that while act represents a kind of fullness of being, either as the act of being itself, or as the formal determination of being, potency represents a kind of relative non-being, inasmuch as it undergirds all actuality as an open substratum that admits of being determined, either ontologically or essentially. And it is in precisely this way that act and potency can explain all being, for together they account for the evident multiplicity of being, in kind and number, by explaining how there can be many different kinds of beings, and many individuals of each kind, as well as the corresponding stability of these same beings through time and change.

Moreover, act and potency can then also account for all becoming, for the change by which becoming is wrought is nothing else than the process by which potency is actualized. For any being to undergo change, it must have a privation (lack) of some determination, as well as the passive potential to receive that same determination; and for any being to produce a change, it must have the power to introduce the needed determination that overcomes the privation. Change then evidently requires a being in potency to receive the change, as well as a being in act to produce the change, so that act and potency, together with privation, are necessary principles of change—whatever its kind, whether local, quantitative, or qualitative (the three species of change). And from this we see that every finite being is apt to produce actions through the power of its actuality, and every finite being is apt to suffer the actions of another through its passive potentiality to receive further determination.

And it is in precisely this way act and potency help us to understand all being and becoming, for together they account for the evident multiplicity of beings, in kind and number, as well as their relative stability through time, together with the further becoming of being through their derivative capacity to undergo change by a process of added actualization—according to all of which we get the inherent flux of reality).

as Heraclitus first noted, all the world is flux… through the correlation of act-potency introduced by Aristotle

Primacy of Act over Potency

Now, given what has been detailed, we must then ask: Which kind of principle has priority, the principles of act or the principles of potency? Or, more simply: Which is prior, act or potency?

This is an extremely important question, since how we answer it will determine the superstructure of our metaphysics, while also determining whether we become a philosophical theist or atheist—for one answer gives us a bottom-up explanation of reality (even if incoherently), and the other a top-down explanation that ultimately tops-out in God.

the old riddle solved with some clear thought

Now, though at first sight it appears that potency comes before act, for in every change privation and potency come before the process of change and the resultant actuality, Aquinas recognizes that this priority is limited to one particular dimension, the singular undergoing change, and that act is prior to potency in general, both simply and absolutely.

Let us look at the three decisive ways act is prior to potency:

• Ontologically: Since change is the actualization of potency by an already actual being with an actuality apt to produce the change in question, act is prior to potency in the order of becoming, and thus is ontologically prior to potency, while also being naturally prior by way of substance and (usually) time.

• Teleologically: Since potency is for the sake of its actualization, potency is ordered toward act, with the result that act is prior to potency in view of the end (telos) toward which the potency is oriented; with the further consequence that act makes potency understandable by accounting for ‘why’ it is a potency.

• Epistemologically: Since potency is intelligible in view of the act toward which it is ordered, and only in view of this actuality, potency can be understood and defined only in relation to act, which makes act prior to potency in knowledge and the articulation of knowledge via definition.

Thus, while potency is prior to act in one narrow sense—in the particular subject undergoing change—act is prior to potency in all other ways, since act, so to speak, surrounds potency on all sides. As a result, we come to an important conclusion, that we cannot give a full account of any being or becoming if we do not conclude to a first being that is pure act. And this being we call God.