Possibility and Its Role in Metaphysical Potency

When we talk about what could exist versus what does exist, we step into one of the most foundational discussions in metaphysics. The relationship between potency and possibility shapes how philosophers understand change, existence, and the very boundaries of reality. At the heart of this discussion lies a critical distinction: the difference between something being merely thinkable and something being genuinely capable of coming into existence. This distinction-between subjective (logical) possibility and objective (ontological) possibility-determines how we understand the scope of what can be actualized in the real world.

Potency and actuality: the foundation 🔗

Before we can understand possibility, we need to grasp the framework it operates within. Potency and actuality are two fundamental principles that divide all of being. Potency refers to the inherent capacity of something to change or become something else-it is the “what could be.” Actuality is the fulfillment or realization of that capacity-it is the “what is.” These concepts trace back to Aristotle’s metaphysics, where he used them to explain how change is possible without requiring something to come from nothing.

A classic example makes this concrete. A block of marble has the potency to become a statue. The statue is not yet actual, but the capacity for it is real-it is embedded in the marble’s material nature. When a sculptor carves the marble, the potency is actualized: the statue comes into being. The marble’s potency was not nothing; it was a genuine, though incomplete, mode of being that pointed toward a definite act.

This framework solves the ancient problem posed by Parmenides, who argued that change is impossible because it would require being to arise from non-being. Aristotle’s insight was that being-in-potency is a real middle ground between full actuality and absolute nothingness. Change, then, is the transition from being-in-potency to being-in-act-the actualization of something that was already real in a potential sense.

What is possibility in metaphysics? 🔗

With potency and actuality established, we can now turn to the concept of possibility. In metaphysics, possibility is not a single, uniform idea. It splits into two fundamentally different types, and confusing them leads to serious philosophical errors.

Subjective (logical) possibility 🔗

Subjective possibility-also called logical possibility-refers to anything that can be conceived without self-contradiction. A proposition is logically possible if affirming it does not violate the basic laws of logic, particularly the principle of non-contradiction. As the Stanford Encyclopedia of Philosophy explains, a proposition is logically possible if it is consistent with the laws of logic, and logically necessary if it follows from them.

For instance, it is logically possible that humans can fly without any technology. There is no formal contradiction in the statement “humans fly unaided.” We can think it, imagine it, and formulate it as a coherent proposition. Similarly, a unicorn is logically possible-the concept of a horse with a single horn on its forehead contains no internal contradiction.

However, a square circle is not logically possible. The concept of “square” (having four equal sides and right angles) directly contradicts the concept of “circle” (a continuous curve equidistant from a center point). No amount of imagination can make this coherent because the terms negate each other at the definitional level.

The key point about subjective possibility is that it is about what can be thought without contradiction. It tells us about the limits of coherent conception, not about what can actually exist in the real world. Many things are logically possible but have no grounding in reality whatsoever.

Objective (ontological) possibility 🔗

Objective possibility-also called ontological possibility-is a different matter entirely. This type of possibility refers to what can actually exist or come into being, grounded in the real natures and capacities of things. It is tied to the actual structure of reality, not merely to the structure of our thoughts.

In scholastic metaphysics, objective possibility is further divided into two categories. Absolute (intrinsic) possibility considers whether a thing’s essence is internally coherent-whether the combination of properties that define it are mutually compatible. The existence of a chair, for example, is intrinsically possible because nothing in the concept of a chair contradicts itself. Relative (extrinsic) possibility, on the other hand, considers whether some actual being or agent has the power to bring that thing into existence. A thing might be intrinsically possible in itself but lack any actual cause capable of producing it.

This division matters because it distinguishes between what is possible in principle and what is possible given the actual causal structure of the world. A seed growing into a tree is objectively possible-it is grounded in the biological nature of the seed and the natural processes available to actualize it. But a rock growing into a tree is not objectively possible, even though one could perhaps formulate the idea without a logical contradiction in the strictest sense. The rock lacks the ontological structure, the inherent potency, required for such a transformation.

Objective potency versus subjective potency 🔗

Here is where the terminology can get confusing, because in scholastic philosophy the words “objective” and “subjective” carry meanings almost opposite to their everyday usage. As noted in traditional Thomistic sources on potency and its divisions, the term objective potency refers to mere logical possibility-the capacity of a nonexistent being for existence, considered purely as an object of thought. Subjective potency, by contrast, refers to real potency-the capacity of something that already exists for further actualization, grounded in a real subject.

A unicorn, for example, falls under objective potency. There is no contradiction in the concept of a unicorn, so it is logically or purely possible. But since no real subject in the world carries the actual capacity to become a unicorn through natural processes, it remains a mere possibility-an object of thought, not a real potency. Scholastic writers generally regard subjective potencies as potencies in the proper sense, because they are anchored in the real natures of existing things rather than floating in the domain of abstract thought.

This distinction is not just academic hair-splitting. It carries significant metaphysical weight. Real potencies-subjective potencies-are what make actual change possible. They are the capacities within things that can be triggered and actualized under the right conditions. Mere logical possibilities, objective potencies, have no causal power and cannot, by themselves, bring anything into existence.

How possibility grounds the transition from non-existence to existence 🔗

One of the most significant roles of possibility in metaphysics is explaining how beings transition from non-existence to existence. This transition is not arbitrary. It follows definite paths shaped by the potencies inherent in things.

Consider an embryo. Its development into a mature organism is not a random event but is grounded in the ontological structure of the embryo itself-its genetic code, cellular machinery, and the biological processes that unfold over time. The possibility of this development is objective: it reflects real capacities within a real subject. The embryo’s potency for development is not something merely imagined; it is embedded in the very nature of the organism.

Contrast this with the idea of a rock spontaneously transforming into a living animal. While one might construct a sentence describing this scenario without a formal logical contradiction, the transformation lacks any grounding in the nature of rocks. There is no potency within a rock for becoming an animal. The possibility is at best logical, not ontological. And in Aristotelian-Thomistic metaphysics, only ontologically grounded possibilities correspond to genuine potencies that can be actualized.

This is why the distinction between the two types of possibility is so critical for understanding change. Potency without objective possibility is empty-it cannot ground any real transition. And possibility without potency is mere fantasy-it might be conceivable, but it has no purchase on reality. Together, objective possibility and real potency form the metaphysical foundation for all transitions from non-being to being.

The scope of what can be actualized 🔗

Possibility, understood in its objective sense, defines the boundaries of actualization. Not everything that is thinkable can become real. The scope of what can be actualized is constrained by the natures of existing beings and the causal powers available in the world.

This constraint operates at multiple levels. At the most basic level, intrinsic impossibility rules out anything whose defining properties contradict each other-square circles, married bachelors, and the like. These are impossible not because of any limitation in causal power, but because the concepts themselves are internally incoherent.

At the next level, extrinsic possibility depends on whether actual agents or causes exist that can bring a given potency to fulfillment. Something might be intrinsically possible-internally coherent-and yet never come into being because no cause in the world is equipped to produce it. This is the domain of what scholastic philosophers sometimes call natural or physical possibility, where the laws of nature and the actual powers of existing agents determine what can be realized.

The relationship between these layers of possibility creates a structured hierarchy. Logical possibility is the broadest category-it includes anything that does not involve a contradiction. Metaphysical possibility is narrower, restricted by the essential natures of things. Physical possibility is narrower still, limited by the actual laws governing the natural world. Each successive layer filters out more candidates, leaving only those possibilities that are genuinely grounded in reality and can, under the right conditions, be actualized.

Why this distinction matters for metaphysics 🔗

The distinction between conceptual and ontologically grounded possibilities is not just a technicality within scholastic philosophy. It has far-reaching implications for how we think about reality, causation, and the limits of knowledge.

If we fail to distinguish between logical and ontological possibility, we risk treating every coherent thought as evidence of a real capacity in the world. This confusion has consequences in areas ranging from the philosophy of science to theology. For example, arguments about whether certain outcomes are “possible” often hinge on whether we mean logically conceivable or physically realizable. A perpetual motion machine might be logically possible in the sense that its description contains no formal contradiction, but it is physically impossible given the laws of thermodynamics.

In metaphysics specifically, the relationship between conceivability and genuine possibility remains one of the most debated topics. Can we move from the fact that something is conceivable to the conclusion that it is genuinely possible? Philosophers remain divided. What the Aristotelian-Thomistic tradition offers is a clear framework: genuine possibility must be grounded in the actual natures and potencies of real beings, not merely in the capacity of the mind to form non-contradictory ideas.

This framework provides a disciplined way to think about what the world can and cannot become. It prevents us from inflating the realm of the possible beyond what reality can support, while also acknowledging that reality is richer than what currently exists-that real potencies point to genuine, even if unactualized, futures.

What do you think? Does the fact that you can imagine something without contradiction mean it is genuinely possible in reality? And where should we draw the line between possibilities that are merely conceivable and those that are rooted in the actual structure of the world?

References

1. https://en.wikipedia.org/wiki/Potentiality_and_actuality
2. https://plato.stanford.edu/entries/modality-epistemology/
3. https://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/potency-and-act
4. https://www.catholicphilosophy.info/metaphysics/metaphysics.php?cm=34
5. http://thomism.org/philosophy/theoretical/metaphysics/ontology/act_and_potency.html
6. https://ses.edu/a-summary-of-act-and-potency/
7. https://en.wikipedia.org/wiki/Logical_possibility