How do the Thomistic arguments depend on the metaphysics of act and potency, and does this metaphysics remain defensible in light of contemporary natural sciences?

The five Thomistic arguments — especially those from motion, efficient causation, and possibility/necessity — depend essentially on Aristotelian act-potency metaphysics. This metaphysics faces two challenges today: criticism from within philosophy (Hume, Kant), and challenges from contemporary natural sciences. However, contemporary Thomists (Edward Feser, David Oderberg, Eleonore Stump) are developing a systematic defense, claiming that this metaphysics remains necessary for understanding reality.

Inadequate Responses to Avoid

From some defenders of Thomism: "Modern science doesn't understand metaphysics" is unproductive condescension. Physicist-philosophers like Mario Bunge and Carlo Rovelli critique act/potency with deep understanding. "Aristotle and Aquinas are infallible" is a position that doesn't serve philosophical discussion.

From some critics: "Act and potency are outdated medieval concepts" is superficial historicist judgment. "Modern physics has abolished metaphysics" confuses levels — physics describes, metaphysics explains.

Structure of Dependence: How the Thomistic Arguments Use Act/Potency

In the argument from motion (First Way):
Everything moved passes from potency to act. What is in potency cannot become actual except through something actual. Nothing can be simultaneously actual and potential in the same respect. Therefore: the chain of movers requires a first mover in pure act.

The dependence is essential: without the act/potency distinction, the argument collapses. "Motion" for Aquinas is not merely spatial change, but any transition from possibility to actualization.

In the argument from causation (Second Way):
The efficient cause brings the effect from potency to act. What does not exist (only potentially) cannot cause itself to exist. The chain of efficient causes requires a first cause in complete act.

In the argument from possibility/necessity (Third Way):
The possible = what can be or not be (mixture of act/potency). The necessary = pure act without potency. If everything were possible, nothing would exist. Therefore: there exists a necessary being.

The Challenge from Contemporary Physics

From quantum mechanics:
- Uncertainty principle: particles don't have determinate properties before measurement. Does this negate "determinate potency"?
- Quantum superposition: electrons in multiple states simultaneously. Does this negate "cannot be actual and potential together"?
- Quantum vacuum: virtual particles appear and disappear. Is this "act from nothing"?

From relativity:
- Relativity of simultaneity: no "cosmic now." Does this challenge "motion" as an absolute concept?
- Spacetime as fourth dimension: do things "exist" at all points of their worldline? Where is "potency" then?

From thermodynamics:
- Second law and entropy: does "act" naturally decay into "potency"?
- Complex systems: emergence of new properties. Is this "act" that wasn't "potential"?

Contemporary Thomistic Defense

Edward Feser (in "Aristotle's Revenge" 2019):

Physics implicitly assumes act/potency:
- Physical laws = descriptions of things' "powers"
- Potential energy = literally Aristotelian "potency"
- Physical transformations = transitions from potency to act

Quantum mechanics doesn't refute but confirms:
- Wave function = mathematical description of multiple potencies
- Wave function collapse = transition from potency to act
- Uncertainty principle = limits of our knowledge, not denial of determinate powers

David Oderberg (in "Real Essentialism" 2007):

Distinction between levels:
- Mathematical physical description ≠ metaphysical explanation
- Physics equations describe "how," metaphysics asks "why"
- Act/potency is an explanatory framework for physical data

Counter-Criticism from Philosophy of Science

Mario Bunge:
Act/potency are vague concepts that add no explanatory power. Modern physics dispenses with them through precise concepts (energy, fields, probabilities). Aristotelian "potency" is a misleading analogy to potential energy.

Carlo Rovelli:
In loop quantum gravity, there are no "things" but "events." Reality is processes, not substances. Act/potency assumes stable substances = macroscopic illusion.

Tim Maudlin:
Laws of nature are primitive, needing no "powers" in things. Physical necessity ≠ Thomistic metaphysical necessity.

The Middle Position: William Simpson

In "Hylomorphism" (2021), Simpson (physicist turned philosopher) proposes:
- Accept that modern physics has changed our understanding of matter
- But philosophical explanation still needs concepts like act/potency
- Develop "neo-Aristotelianism" that accommodates scientific data

Example: electron in quantum superposition:
- Copenhagen interpretation: no determinate properties before measurement
- Neo-Aristotelian interpretation: electron has multiple powers, measurement actualizes one

Assessment of Current Position

Strengths of Thomistic defense:
1. Physics uses concepts (potential energy, possibilities) close to act/potency
2. Philosophical explanation of physics needs metaphysics
3. Alternatives (Laplacean determinism, pure randomness) are problematic

Weaknesses:
1. Act/potency are classical concepts that may not suit quantum reality
2. Danger of "forced interpretation" of physics to fit preconceived metaphysics
3. Alternative metaphysical frameworks may be more suitable

From the Perspective of Rational Preponderance (rajḥān ʿaqlī)

The Thomistic arguments retain philosophical strength, but must:
- Not tie themselves to ancient Aristotelian physics
- Remain open to reformulation in contemporary language
- Acknowledge that the physics/metaphysics relationship is complex

Act/potency as explanatory framework:
- Is neither "proven" nor "refuted" definitively
- But remains a reasonable philosophical option
- Needs development, not abandonment

Where We Stand in This Debate Today

The period 2020-2026 witnessed concrete developments in the debate. From the neo-Aristotelian side: Feser, Koons, and Simpson continued developing hylomorphic models that accommodate quantum mechanical results, especially within interpretations like "pilot wave" (de Broglie-Bohm) that suit act/potency structure better than Copenhagen interpretation. Collective works appeared like "Neo-Aristotelian Perspectives on Formal Causation" (2023) showing that formal causality, not just efficient, finds applications in evolutionary biology and information theories. From the critics' side: ontic structural realism strengthened with Ladyman and French, offering a metaphysical alternative that dispenses with substances and powers in favor of a network of structural relations. Similarly, Rovelli continued in his recent works deepening event ontology against thing ontology. Today's debate remains unsettled: neo-Aristotelianism has proven it's not merely historical residue, but structural and process alternatives are also advancing strongly. The question remains philosophically open, and any claim of resolution from either side is premature.

From the Angle of Rational Preponderance

This debate reveals an important structure in cumulative methodology:
— Thomistic arguments don't fall merely through physics changing, because they operate on a metaphysical level different from mathematical equations.
— But they don't automatically survive either: if an alternative metaphysical framework (structural or processual) proves to explain physical data with higher efficiency without needing act/potency, then preponderance shifts.
— Currently preponderant: act/potency remains a reasonable and defensible explanatory framework, but it's not the only reasonable framework. Its strength lies in internal coherence and capacity to accommodate phenomena (causation, change, possibility) that are difficult to explain without similar concepts.
— Within cumulative weighing: even if dependence on act/potency weakens in its classical formulation, cosmological arguments can be reformulated with other frameworks (principle of sufficient reason, metaphysical necessity), meaning the theological content of the arguments is broader than the specific Aristotelian framework in which they were first formulated.

For Reading

- Edward Feser, Aristotle's Revenge (Editiones Scholasticae, 2019)
- David Oderberg, Real Essentialism (Routledge, 2007)
- William Simpson, Robert Koons & Nicholas Teh (eds.), Neo-Aristotelian Perspectives on Contemporary Science (Routledge, 2018)
- Tuomas Tahko, Contemporary Aristotelian Metaphysics (Cambridge UP, 2012)
- Mario Bunge, Causality and Modern Science (Dover, 2009)
- "Formulation: Five Ways (Aquinas)" page on the website