Potency

Potency (from the Latin potentia, translating the Greek dýnamis, “capacity,” “possibility,” or “power”) designates that in a being which is ordered toward an act it does not yet fully possess. It expresses the capacity to receive, become, or participate in a perfection. Potency can be defined only in relation to act: whereas act is the principle of a being’s perfection, potency is the principle of the measure in which it participates in that perfection, that is, of the particular mode according to which it possesses it and of the limits within which it receives it.

More specifically

The distinction between potency and act constitutes one of the foundations of Aristotelian and Thomistic metaphysics. Aristotle introduced it in order to account for change without falling either into the immobility of Parmenides or the absolute becoming of Heraclitus. If a thing changes, it is because it already possesses, in potency, what it will become in act.

Potency should not be understood as mere non-being or pure absence. It is a real possibility inscribed within the nature of a being. The seed is potentially the tree; the child is potentially the adult; the ignorant intellect is potentially knowledge. In each of these cases, potency designates a genuine aptitude to receive a further determination or perfection.

Yet potency never possesses the self-sufficiency of act. It is always ordered toward something other than itself. For this reason Aristotle affirms the priority of act over potency: what is in potency can pass into act only through the influence of a being already in act. Act thus appears as the principle of intelligibility and perfection, whereas potency expresses receptivity and limitation.

In the metaphysics of Saint Thomas Aquinas, potency provides a key to understanding the finitude of creatures. Every created being is composed, in varying degrees, of act and potency. It possesses certain perfections in act while remaining open to others that it possesses only imperfectly or potentially. God alone is Pure Act (actus purus), without any passive potency, since He possesses the fullness of being without limitation or possibility of further acquisition.

Potency manifests itself in various forms. A distinction is commonly made between active potency, which is the capacity to produce an effect, and passive potency, which is the capacity to receive a determination. Fire possesses the active potency to heat; wax possesses the passive potency to receive an impression. These two aspects express different modes of participation in being.

From a metaphysical perspective, potency is the principle of multiplicity, becoming, and limitation. If created beings are diverse and subject to change, it is because they do not possess being in its fullness. Their perfection is received according to a determined measure, and this measure precisely defines their potency. Potency is therefore not merely openness to a future fulfillment; it is also the sign of the finitude of every created being.

This notion also plays an essential role in anthropology and the spiritual life. Man is a being of potency as well as of act: he bears within himself intellectual, moral, and spiritual potentialities that are called to unfold. Education, culture, ascetic discipline, and grace may all be understood as processes through which certain potencies progressively attain their actualization.

Potency thus appears as the necessary correlate of act within the order of created beings. It expresses both their richness of possibilities and their incompleteness. Without potency, no becoming would be possible; without act, no becoming would have meaning. Together, these two notions make it possible to think the graduated participation of beings in the perfection of being.

More specifically

Further reading