ris3n's Apologetics Codex

Argument

First Way - Motion

Intro

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Hold a hot cup of coffee. It is cooling. That is change. Aristotle, and later Thomas Aquinas, looked at change like that and asked a careful question: what does change actually require?

Aquinas's answer is the First Way, and it is not the argument most people think it is. It is not "everything had a beginning, so the universe had a beginner." That is a different argument (the Kalam). The First Way is about right now. It is about what has to be true for that coffee, this very second, to be cooling at all.

The setup uses two ideas. Actual is what something is right now (hot, here, this temperature). Potential is what it could become but is not yet (cool, room temperature). Change is just the moving from potential to actual. A cold room can warm; the cold room is potentially warm. When the heater runs, the potential becomes actual.

Here is the key step. Nothing moves itself from potential to actual on its own. The cold cup does not heat itself. Something already actual (already hot, like the burner) is needed to make the potential heat real. And the burner itself is being kept hot by something already actual, the electric current, which depends on a power station, which depends on something else, which depends on something else.

Aquinas distinguishes two kinds of chains here, and this is where the argument has its teeth. One kind is your great-grandfather, your grandfather, your father, you, your child. That chain can stretch back through time forever without a problem, because grandpa does not need to still exist for you to exist. The other kind is the chain holding up your coffee right now: the cup, the table, the floor, the foundation, the ground. That chain cannot go on forever, because every link is borrowing its power from the next link at the same moment. If there is no foundation at the bottom, the whole stack falls instantly. There has to be something at the bottom that is not borrowing anything from anywhere, something that just is actual, all the way through, with no potential being actualized in it.

Aquinas calls that actus purus, pure act, and says, "this all men call God." That is the First Way. The page below walks through each step, the standard objections (Newton, quantum, infinite regress), and the modern defenses by philosophers like Edward Feser and David Oderberg.

In full

The first of Aquinas Five Ways. From the empirical observation that things in the world undergo change (motion, broadly construed as the actualization of potency), it argues to the existence of a First Actualizer who is pure act, actus purus, identified with God. The argument operates on the act-potency distinction (the foundational metaphysical apparatus of Aristotelian-Thomistic philosophy) and the per-se / per-accidens causal-series distinction (which blocks the obvious infinite-regress objection). Importantly distinct from Kalam: the First Way reasons from the structure of any change-here-and-now, not from the temporal beginning of the cosmos.

Argument structure

# Premise
P1 Whatever is in motion (changing) is being reduced from potency to act.
P2 Nothing can reduce itself from potency to act, a potency is actualized only by something already actual in the relevant respect.
P3 An essentially-ordered (per se) series of actualizers cannot regress infinitely.
C Therefore there exists a First Actualizer who is itself pure act and not in potency to anything, quod omnes intelligunt Deum, "whom all understand to be God."

Form

Modus tollens combined with essential-series reductio. If there were no First Actualizer, no motion could occur (the per-se series would have no source of actualization); but motion does occur; therefore a First Actualizer exists. The argument is a structural-metaphysical claim about what change presupposes, not an inductive generalization. Modality: metaphysical necessity. The denial of a First Actualizer makes change itself impossible.

P1, Whatever is in motion is being reduced from potency to act

Affirmative case (second-order arguments)

  1. The act-potency distinction is the foundational analysis of change. Aristotle (Physics III.1, 201a10-12) defines motion as "the actuality of what is in potentiality, qua in potentiality." Without act/potency, change is incoherent (Parmenidean problem: how can being come from non-being? how can a thing be both itself and not-itself?). The act-potency analysis is Aristotle's solution and remains the standard scholastic apparatus. (Feser, Aquinas: A Beginner's Guide, 2009, ch. 2.)
  2. Universal applicability. Every observed case of change, local motion, qualitative change, growth, alteration, fits the act-potency structure. A cold cup of water has the potency to become hot; when heated, the potency is actualized. The distinction is not optional Aristotelian baggage; it is descriptively adequate to all changes.
  3. The denial of P1 generates Parmenidean paradoxes. If change is not the actualization of potency, then either change is illusory (Parmenides) or being can come from non-being (which violates ex nihilo, nihil fit). Modern attempts to dispense with potency (process philosophy, certain reductionist physicalisms) face this dilemma. (Oderberg, Real Essentialism, 2007, ch. 3.)

Anticipated objections

  1. "Modern physics has dispensed with Aristotelian potency / act." Newtonian / relativistic / quantum physics work without it; the framework is obsolete.
  2. "'Potency' is a vague philosophical term, not a real metaphysical category." Quine-style nominalism.

Rebuttals

  1. Modern physics describes change without naming the metaphysics, but the metaphysics is still presupposed. Talk of "states" and "transitions" presupposes that systems have features they don't currently exhibit but could (potency) and features they do exhibit (act). Quantum superposition is paradigmatic act-potency: the system is potentially in any of several states, actually in one upon measurement. Far from refuting act-potency, modern physics provides striking instances of it. (Feser, Aristotle's Revenge, 2019.) Failure mode: conflating descriptive vocabulary with underlying metaphysics.
  2. Nominalist denial of potency cannot accommodate change. If only what is actual exists, then a thing's capacities (water's capacity to freeze, the seed's capacity to become a tree) have no metaphysical status, but capacities are clearly real (they explain why water freezes when cooled and seeds grow when planted, while air does neither). The nominalist owes an account of capacities; potency is the standard account. (Oderberg.)

Live-cite kit

  • Scripture: Genesis 1.1 (creation as the source of all created change); Hebrews 13:8 (Christ "the same yesterday, today, and forever", contrast with creaturely change); Malachi 3:6, James 1:17 (God's immutability)
  • Scholarly: Aristotle, Physics III.1, Metaphysics IX; Aquinas, ST I.2.3 (Prima Via); Feser, Aquinas (2009) and Aristotle's Revenge (2019); Oderberg, Real Essentialism (2007)
  • Aphorism: "Change is potency becoming act, there's no third option."

Tactical notes

  • Don't sell P1 as obvious; explain it briefly. Most modern interlocutors haven't seen act-potency and will assume the argument fails because the framework is unfamiliar.
  • Quantum-superposition example is the strongest live-debate analogue.
  • Do NOT defend Aristotelian physics (geocentrism, sublunary/superlunary distinction, etc.). Defend act-potency metaphysics, not Aristotle's natural science.

P2, Nothing can reduce itself from potency to act

Affirmative case (second-order arguments)

  1. The act/potency analysis combined with the Law of Non-Contradiction entails P2. A thing cannot be both in act and in potency in the same respect at the same time (LNC). Therefore a thing cannot actualize its own potency in the same respect, that would require it to be already-act-with-respect-to-X (to do the actualizing) while also being in potency-with-respect-to-X (to be actualized). The principle quidquid movetur, ab alio movetur is a direct consequence. (Aquinas, ST I.2.3 ad 1; Feser, Five Proofs, 2017, ch. 1.)
  2. Empirical confirmation: nothing observed actualizes its own latent potency. Cold water doesn't spontaneously become hot; an unmoved billiard ball doesn't accelerate from rest; a seed doesn't germinate without water. Every actualization has an external actualizer.
  3. Self-movers have parts. Animals and humans appear to move themselves, but on analysis: one part actualizes another (the muscle moves the bone, the will moves the muscle, prior causes act on the will). Self-motion at the level of the whole is mediated by part-actualizing-part. Nothing actualizes itself in the same respect at the same time. (Aristotle, Physics VIII.4-5.)

Anticipated objections

  1. "Self-movers refute P2, animals move themselves."
  2. "Quantum events show that things can change without being acted upon." Spontaneous radioactive decay, virtual particles, etc.
  3. "Newton's first law: a body in uniform motion stays in motion without external cause; therefore not every change requires an actualizer."
  4. "If God is pure act, He cannot create, creation would actualize a potency in Him."

Rebuttals

  1. Self-movers have parts; one part actualizes another. Aristotle's analysis (Physics VIII.4-5): in self-movers, one part is in act with respect to the relevant feature and actualizes another part that is in potency. Nothing moves itself in the same respect at the same time. The objection trades on equivocation between "moves itself as a whole" (true; but mediated) and "moves itself in the same respect" (false; impossible). Failure mode: equivocation on "self-motion".
  2. Quantum indeterminism is not uncaused change but probabilistic causation. Radioactive decay has a cause (the unstable nuclear configuration), even if the timing is indeterministic. Virtual particles arise from the structured quantum vacuum (a something, not nothing). The act-potency analysis accommodates probabilistic causation: the unstable nucleus has the potency to decay, and that potency is actualized, sometimes by a process whose triggering is probabilistic rather than deterministic. (Feser, Aristotle's Revenge, ch. 8.) Failure mode: conflating indeterminism with acausality.
  3. Newton's first law concerns inertial motion (continuation), not change-of-state. P2 concerns change, actualization of potency. A body in uniform motion is not changing in the relevant sense; the act-potency analysis applies to changes (acceleration, deceleration, qualitative change), not to constant states. The Newtonian principle is consistent with P2. (Feser; David Oderberg, Real Essentialism.) Failure mode: misidentifying the explanandum.
  4. Creation does not actualize a potency in God. On classical theism, the relation of creation is real in the creature (the creature is really related to God as cause) but only logically in God (God is not really changed by creating). God's act of creation is identical with God's eternal act of being; it is not an additional actualization. (Aquinas, ST I.45.3 ad 1; Feser.) The objection presupposes a temporal-becoming model of creation that classical theism rejects.

Live-cite kit

  • Scripture: Acts 17:28 ("in Him we live and move and exist", creaturely dependence on the divine actualizer); Hebrews 1:3 ("upholding all things by the word of His power"); Colossians 1.16-17
  • Scholarly: Aristotle, Physics VIII; Aquinas, ST I.2.3, I.45; Feser, Five Proofs (2017); Oderberg, Real Essentialism (2007); Wippel, The Metaphysical Thought of Thomas Aquinas (2000)
  • Aphorism: "Quidquid movetur, ab alio movetur: nothing pulls itself out of potency by its own bootstraps."

Tactical notes

  • The "self-mover" objection is the most-common deflection. Have the part-actualizes-part response rehearsed.
  • Do NOT get drawn into Newtonian physics weeds. Stay on the metaphysical question of change-of-state, not constancy.
  • If the opponent goes "but God creating you actualizes a potency in you, doesn't it actualize one in Him too?", explain the asymmetric-real-relation-of-creation move briefly, then refer to Divine Simplicity / Actus Purus for the deep treatment.

P3, An essentially-ordered (per se) series of actualizers cannot regress infinitely

Affirmative case (second-order arguments)

  1. Per Se vs Per Accidens Causation is the load-bearing distinction. Aquinas distinguishes:
  • Per accidens (accidentally-ordered) series, temporal sequences where each member, having received causal power, retains it independently (father → son → grandson; the grandfather can die and the grandson still acts). These can in principle extend infinitely without absurdity.
  • Per se (essentially-ordered) series, simultaneous causal hierarchies where intermediate members have no causal power on their own; they only transmit power from a primary cause (the hand moves the stick that moves the stone, all in one motion). In a per se chain, removing the first cause stops the whole series instantly. An infinite per-se chain has no source from which to transmit anything; nothing happens. But things do happen; therefore the chain terminates in a first member with intrinsic causal power. (Aquinas, ST I.2.3 ad 7; Feser, Five Proofs, ch. 1.)
  1. Instrumentality requires a non-instrumental source. An instrument (a tool, a transmitting medium) has causal power only insofar as a non-instrumental cause empowers it. An infinite series of instruments without a non-instrumental source has no causal power at all, like an infinite chain of train cars with no engine, or an infinite series of mirrors reflecting nothing. The first cause must be non-instrumental, possess causal power intrinsically.
  2. Empirical instances of per-se causation confirm the structure. Every causal chain we observe terminates somewhere with an underived cause. The hand-stick-stone series terminates in the hand (which has its own actualizing source, the will); the will is actualized by reasons / habituated dispositions / divine concurrence (depending on the level of analysis). Termination is the universal rule.

Anticipated objections

  1. "The per-se / per-accidens distinction is contestable; perhaps even essentially-ordered infinite chains are coherent." Oppy, Arguing about Gods (2006); Schellenberg.
  2. "Modern set theory accepts actual infinites; therefore an infinite per-se chain is possible."
  3. "Why can't the chain be circular instead of terminating?" Causal-loop alternatives.
  4. "Even if the chain terminates, why must the first member be God? It could be a quantum field or other physical first."

Rebuttals

  1. The distinction is grounded in act-potency metaphysics, not stipulation. Per-se causation is the structure of simultaneous instrumental dependence; per-accidens causation is the structure of sequential independent power-transmission. The distinction tracks two genuinely different causal phenomena. Rejecting it requires a different metaphysical framework, not just dismissal. Oppy's challenge is that the distinction is non-compulsory; the Thomist replies that it is the best account of observed causal structure, and the burden falls on the alternative. (Feser, Five Proofs, ch. 1; Oderberg, Real Essentialism.) Failure mode: rejecting the metaphysics without offering an alternative.
  2. Set-theoretic actual infinites are abstract, not concrete-causal. Cantor distinguished mathematical infinites (which his theory accepts) from physical-causal infinites (which his theory does not address). The set-theoretic point is irrelevant to the metaphysical question of whether an infinite chain of derived causal power can do causal work without a non-derived source. Failure mode: conflating mathematical existence with metaphysical instantiation.
  3. A circular causal chain is no better than an infinite linear one. In a circle, every member's causal power is derived from another; no member is non-derived. The whole loop has no source of causal power from outside; nothing happens. Circularity does not solve the problem; it makes it more visible. (Pruss, PSR, ch. 6.) Failure mode: moving the regress around the same circle.
  4. A physical "first" is itself contingent and actualizable. Quantum fields have specific configurations; their existence is contingent (they could have been otherwise); they exhibit potencies (they can be in different states). Anything with potency is actualizable from outside, and anything contingent requires explanation (PSR, see Contingency Argument). The Thomist concludes that the first in the per-se chain must be pure act (Actus Purus), having no unactualized potency and no contingency. That conclusion is what Aquinas means by "God." Failure mode: proposing a contingent first.

Live-cite kit

  • Scripture: Romans 11:36 ("from Him and through Him and to Him are all things"); Acts 17:28; Hebrews 1:3; Colossians 1.16-17
  • Scholarly: Aquinas, ST I.2.3 ad 7; Feser, Five Proofs (2017), ch. 1; Oderberg, Real Essentialism (2007); Wippel, The Metaphysical Thought of Thomas Aquinas (2000); Brian Davies, The Thought of Thomas Aquinas (1992)
  • Aphorism: "An infinite chain of instruments with no engine moves nothing."

Tactical notes

  • Take time to explain per-se vs per-accidens, most opponents have not heard the distinction and assume the First Way is just Kalam in medieval clothing. The distinction is what makes the First Way work.
  • Use the hand-stick-stone example or the train-cars-without-engine example. Concrete instances make the structure click.
  • Do NOT defend "infinite regress is impossible in general." Aquinas allows per-accidens infinite regress; the impossibility is specific to per-se chains.
  • Force-commit move: "Granted the per-se / per-accidens distinction, show me a per-se chain that doesn't terminate. (Or, show me how the metaphysics of instrumental causation works without a non-instrumental cause.)"

Conclusion

Therefore a First Actualizer exists who is pure act (actus purus), quod omnes intelligunt Deum. The First Actualizer cannot itself have any potency unactualized, otherwise something would have to actualize it, and it would not be first. Therefore, it is pure act (Actus Purus), and from this follow the divine attributes of immutability (no potency to change), simplicity (no composition of act and potency), eternity (no temporal becoming), and being-itself (Ipsum Esse Subsistens). The terminus is identifiable with the God of classical theism.

Master objections to the argument as a whole

  1. "Even granted, this proves at most an unmoved mover, not the personal God of the Bible." Reply: correct as a standalone, the First Way establishes one aspect of God (pure act). The convergence of the Five Ways (Aquinas Five Ways) and the further apologetic argumentation (moral, historical, comparative-religion) gets to the full Christian God. Aquinas himself notes the conclusion is quod omnes intelligunt Deum ("whom all understand to be God"), a starting point, not a finished theology.
  2. "This is a god-of-the-gaps move." Reply: god-of-the-gaps fills explanatory gaps in physics with God until a naturalistic explanation arrives. The First Way runs from the structure of any actualization-of-potency, here and now; future physics cannot fill the explanatory role of a first actualizer because future-physics would itself involve actualizations of potency.
  3. "The argument depends on outdated Aristotelian metaphysics, modern physics has moved past it." Reply: modern physics describes change without articulating its metaphysics, but act/potency is the most adequate metaphysical analysis of change. Quantum superposition, state-transitions, and probabilistic causation are paradigmatic act/potency phenomena (Feser, Aristotle's Revenge). The claim that modern physics refutes Aristotelian metaphysics confuses the descriptive vocabulary of physics with underlying metaphysical commitments.
  4. "The argument equivocates between the local question (this hand-stick-stone) and the cosmic question (the universe as a whole)." Reply: the First Way doesn't argue at the cosmic level. It argues that any actualization of potency requires a non-derivative actualizer. The argument lands per-se-chain-by-per-se-chain. It does not assume the universe-as-a-whole is one big per-se chain.

Tactical opening / closing

Opening line: "Even right now, things in this room are changing, and every change is an actualization of potency. Want to walk through what that requires?"

Closing landing strip: "Aquinas isn't reasoning from far-off cosmic origins. He's reasoning from change happening right here, right now. The First Actualizer isn't a distant first cause in the past; He's the here-and-now sustaining ground of every change. In Him we live and move and exist."

Connection to Scripture

  • Romans 1:20 (the source's sed contra), "His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made", the warrant for natural theology
  • Genesis 1.1, Creator-creation distinction
  • Romans 1.18-21, general revelation
  • Acts 17:28, "in Him we live and move and exist", Pauline expression of creaturely dependence on the divine actualizer
  • Hebrews 1:3, Christ "upholds all things by the word of His power"
  • Colossians 1.16-17, Christ as the one in whom all things hold together

Patristic / scholarly note

Classical / patristic / medieval:

  • Aristotle (Metaphysics XII, Physics VIII), the unmoved mover; the act-potency apparatus
  • Augustine (Confessions), "You would not seek Him unless He had already moved you", the soul's movement toward God as itself moved by God
  • Gregory of Nyssa, "All motion has its beginning from another"
  • Thomas Aquinas (Summa Theologica I.2.3, Prima Via), the locus classicus

Modern:

  • Edward Feser, Aquinas: A Beginner's Guide (2009); Five Proofs of the Existence of God (2017), ch. 1; Aristotle's Revenge (2019), the contemporary standard defenses
  • David Oderberg, Real Essentialism (2007)
  • Brian Davies, The Thought of Thomas Aquinas (1992)
  • John Wippel, The Metaphysical Thought of Thomas Aquinas (2000)
  • Eleonore Stump, Aquinas (2003)

Critics:

  • Graham Oppy, Arguing about Gods (2006); The Best Argument Against God (2013)
  • Anthony Kenny, The Five Ways (1969)
  • J. L. Schellenberg

Modern scientific parallels (illustrative)

  • Quantum superposition / state collapse, paradigmatic act-potency phenomenon
  • Big Bang cosmology, first transition to motion / change at the cosmic scale
  • Biological development, the unfolding of latent potency into actuality

These are illustrative analogues, not load-bearing. The First Way's metaphysics stands or falls on the philosophical analysis of change, not on physics.

See also