The Dynamics of Potency and Change in Metaphysical Philosophy

Everything around us is in a constant state of transformation. Seeds become trees, water turns to ice, students become doctors. But what exactly happens when something changes? In classical metaphysics, change is not a random event – it is the structured transition from what a thing could be to what it actually becomes. This process, described by Aristotle and refined by Thomas Aquinas, is understood through two foundational principles: potency and act. Together, they provide the metaphysical framework for explaining how and why change occurs, what conditions make it possible, and what categories it falls into.

What are potency and act? 🔗

Before exploring how change works, it is essential to grasp the two principles that make it intelligible. Act (Latin: actus) refers to what a thing currently is – its present reality, its actual state of being. Potency (Latin: potentia) refers to what a thing can become but has not yet become. A rubber ball, for instance, is actually round, solid, and smooth. But it also has the capacity to become flat, squishy, or rough. These capacities are its potencies – they are real features of the ball, even though they are not currently realized.

As Aristotle explains in his Metaphysics, the distinction between potentiality and actuality applies across all categories of being. A person who can see but is not currently seeing possesses the potency of sight without exercising it in act. Potency, then, is not mere nothingness. It occupies a real, if incomplete, place in the structure of being. It is something between full actuality and absolute non-existence.

Thomas Aquinas adopted and extended this Aristotelian framework, making it central to virtually every aspect of his metaphysics. As he writes in his first of the 24 Thomistic Theses, potency and act divide being in such a way that whatever exists is either pure act or necessarily composed of both potency and act as its primary intrinsic principles.

Change as the transition from potency to act 🔗

With this framework in place, change can be defined with precision. In metaphysical terms, change is the actualization of a potency – the passage of something from being in a state of potential to being in a state of actuality. When a green apple turns red, the apple’s potency for redness is actualized. When a student becomes a doctor, the student’s intellectual potency is actualized through study and practice.

This definition matters because it solves a problem that had troubled philosophy since the time of the ancient Greeks. The pre-Socratic philosopher Parmenides argued that change is logically impossible. His reasoning was straightforward: being cannot come from non-being, because nothing comes from nothing. And being cannot come from being, because it already exists. Therefore, there is no room for anything to come to be.

Aristotle’s breakthrough was to show that Parmenides presented a false dilemma. Between absolute being and absolute non-being there is a third option: being-in-potency. A green apple is not yet red (it is not red in actuality), but it is not incapable of becoming red either (it has a real potency for redness). Change occurs not when being arises from non-being, but when one kind of being – potential being – transitions to another kind – actual being. As Thomistic commentators have noted, Aquinas agreed with Parmenides that nothing comes from nothing, but argued that being-in-act can emerge from being-in-potency, since potency is not simply nothing.

Not all potencies are equal 🔗

An important nuance: potency is not unlimited. A thing can only become what its nature permits. An acorn has the potency to become an oak tree, but it cannot become a horse. A block of marble has the potency to be sculpted into a statue, but it cannot become sentient. Potencies are determined by the kind of thing something is – by its substantial nature. This means change is not chaotic or random; it follows the internal logic of what things are.

Conditions necessary for change 🔗

For any change to occur, certain conditions must be in place. These are not arbitrary requirements but follow directly from the nature of potency and act.

The presence of potentiality: Change can only begin in something that has a genuine capacity to become something else. Without real potency, there is no basis for transformation. A stone cannot learn grammar because it lacks the relevant potency altogether.

An actualizing cause: A potency does not actualize itself. Something already in act must bring the potential into reality. In the case of a seed growing into a tree, the actualizing causes include soil, water, sunlight, and the internal biological processes of the seed. In Thomistic metaphysics, the only source that can effect the transfer from potency to act is a being that is already in act – a principle that forms the basis for Aquinas’s arguments for the existence of God.

The absence of impediments: Even when potency and an actualizing cause are present, change can be blocked if something prevents the potency from being realized. A seed in a jar on a shelf has the potency to grow, but the absence of soil and water prevents actualization.

A subject that persists through the change: Every change requires something that remains the same while acquiring new characteristics. In accidental change, the persisting subject is the substance itself. In substantial change, the persisting subject is prime matter. Without this continuity, we would not have change at all but rather the annihilation of one thing and the creation of another.

Positive and negative change 🔗

Not all change moves in the same direction. In metaphysical terms, change can be classified as either positive or negative, depending on whether it involves the gain or loss of actuality.

Positive change occurs when a potency is fulfilled – when something gains a new form, perfection, or actuality it did not previously possess. The growth of a plant, the education of a student, the healing of a wound – these are all instances where a being moves toward greater actualization. The potential is realized, and the being is more fully what it can be.

Negative change, by contrast, involves the loss of an actuality or the movement toward privation. The decay of a living organism, the erosion of a mountain, the corruption of a substance – these represent transitions where a being loses a form or perfection it once had. In negative change, potency is actualized not toward fulfillment but toward diminishment.

In both cases, the underlying metaphysical structure remains the same: there is a transition from potency to act. The difference lies in whether that transition represents a gain or a loss for the subject undergoing the change.

Categories of change 🔗

Beyond the positive-negative distinction, metaphysics recognizes several specific categories of change, each representing a distinct way in which potency is actualized. The three most important are creation, generation and corruption, and accidental change.

Creation 🔗

Creation is the most radical form of change – or, more precisely, it stands at the boundary of what we call change. In creation, something comes into existence from nothing (ex nihilo). There is no pre-existing matter that receives a form; rather, the entire being – both its matter and its form – is brought into existence by an act of pure actuality. In philosophical tradition, creation is associated with divine causation, where a first cause brings something into being without any prior material condition. Strictly speaking, creation is not “change” in the Aristotelian sense, because change requires a persisting subject, and in creation there is no such subject. It is better understood as the absolute beginning of being.

Generation and corruption 🔗

Generation and corruption are the two faces of substantial change – change that affects the very nature or essence of a thing. Generation is the coming-into-being of a new substance. Corruption is the ceasing-to-be of an existing one. These two always occur together: when one substance is corrupted, another is generated from the same underlying matter.

Consider wood being consumed by fire. The wood – a substance with its own nature and properties – is corrupted. In its place, new substances such as ash and smoke are generated. The three principles of change are all present: the substantial form of ash is what comes to be (form), the absence of that form prior to burning is what passes away (privation), and prime matter is what persists throughout the transformation (matter).

We recognize substantial changes because the resulting entity possesses entirely different properties and powers from the original. As commentators on Aristotle’s Physics note, in substantial change the subject of the transformation is matter itself, and the form gained or lost is the substantial form – the form that defines what kind of thing something is. When hydrogen and oxygen combine to form water, a substantial change has occurred: two gases become a liquid with properties neither gas individually possessed.

Accidental change 🔗

Accidental change modifies a substance’s qualities, quantity, or location without altering its fundamental nature. When an apple changes from green to red, the apple remains an apple – only its color, an accident, has changed. When a person grows taller, the substance (the human being) persists, but the accident of quantity changes.

Aristotle identified three main types of accidental change. Qualitative change (alteration) involves a modification in a thing’s qualities – color, temperature, texture. Quantitative change involves an increase or decrease in size or amount. Local motion involves a change in place or position. In all three, the substance remains what it is; only its accidents are modified.

It was precisely through analyzing accidental changes that Aristotle first discovered the principles of matter, form, and privation. The case of a sculptor shaping marble into a statue is a classic example. The marble (matter) loses its shapelessness (privation) and receives the figure of the statue (form). The marble persists throughout – it is the subject that stays the same while its accidental properties are transformed.

The three principles of change: matter, form, and privation 🔗

Running through all categories of change is a consistent three-part structure that Aristotle identified and Aquinas endorsed. Every change requires:

Matter – the subject that persists through the change and is in potency to the new determination. In accidental change, the matter is the substance itself. In substantial change, it is prime matter, the pure potency that underlies all material being.

Form – the new determination or actuality that comes to be. This is what the matter acquires through the change, whether an accidental form (like a new color) or a substantial form (like the nature of a new substance).

Privation – the absence or lack of the form prior to the change. Privation is not pure nothingness but a specific absence in a specific subject. The marble lacks the shape of the statue before the sculptor begins; this lack is the privation. Importantly, privation is only a principle of becoming – once the change is complete and the form has been acquired, the privation ceases to exist.

This triad – matter, form, and privation – is what makes change intelligible. Without it, we cannot distinguish change from creation or annihilation, nor can we explain how something new arises from what already exists.

Why potency and change matter for understanding reality 🔗

The metaphysical analysis of potency and change reveals something profound about reality itself: the universe is fundamentally dynamic. Nothing in the material world is purely actual (with the exception of what classical theists call God, or Pure Act). Everything else is a composite of act and potency, always carrying within itself the seeds of further transformation.

This dynamism is not merely physical or biological. It is a metaphysical principle that governs all finite beings. Every creature, every substance, every entity in the natural world exists in a tension between what it is and what it can become. This tension is the engine of all change – from the growth of a plant to the decay of a star, from the formation of a crystal to the development of a human mind.

Understanding potency and change also helps us see why science is possible in the first place. If nothing ever changed (as Parmenides claimed), there would be no distinct objects or events to study. If everything changed without any stable principles (as the followers of Heraclitus suggested), there would be no repeatable patterns or laws to discover. The act-potency framework shows that change is real but structured – governed by the natures of things and the causal processes that actualize their potencies.

What do you think? Does viewing reality as an ongoing process of potency becoming act change how you understand everyday transformations – whether in nature, in yourself, or in the world around you? And if every change requires something already in act to bring potency to fruition, what does that suggest about the ultimate source of all change?

References

1. https://plato.stanford.edu/entries/aristotle-metaphysics/
2. https://ses.edu/a-summary-of-act-and-potency/
3. https://en.wikipedia.org/wiki/Potentiality_and_actuality
4. https://aquinasonline.com/explaining-change/
5. https://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/potency-and-act
6. https://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/substantial-change
7. https://faculty.washington.edu/smcohen/320/archange.htm
8. https://conciliarpost.com/dialogues/the-necessity-of-contingency-part-3-act-and-potency/