The Hand, the Stick, and the Stone: Aquinas's Five Ways Reconsidered

The Hand, the Stick, and the Stone

Picture a man pushing a stone with a stick. The stone moves because the stick moves it; the stick moves because the hand moves it; the hand moves because the arm, the muscles, the nervous system, the will all conspire in a single present moment. Remove the hand and the whole sequence collapses at once — not eventually, but now. Thomas Aquinas chose exactly this image to anchor the first and most famous of his arguments for God: "the staff moves only because it is put in motion by the hand."¹ Everything in his case for God hangs on what kind of series this is. Misread the picture, and you will spend your life refuting an argument Aquinas never made.

The Five Ways — the Quinque Viae — occupy a single dense article of the Summa Theologiae (I, q. 2, a. 3), written around 1265–1268. They are not Aquinas's whole natural theology; they are five compressed sketches, each closing with a deceptively casual tag — "and this everyone understands to be God." The real work of identifying that conclusion with the God of classical theism comes in the questions that follow. To read the Five Ways fairly, we must first read them as written, and then defend the strongest of them against its most serious critics.

The Five Ways in Brief

The First Way, "more manifest" than the rest, argues from motion — better translated as change. Things change; whatever changes is changed by another; an infinite series of such changers (of the right sort) is impossible; therefore there is a first, unchanged changer, "and this everyone understands to be God."²

The Second Way runs the same structure on efficient causation: we observe an order of causes; nothing is the efficient cause of itself; the series cannot regress to infinity; so there is a first efficient cause, "to which everyone gives the name of God."³

The Third Way argues from possibility and necessity (contingency): some things can be or not be — they come to be and pass away. If everything were like that, then at some point nothing would exist, and nothing would now exist either, which is absurd. So there must be something necessary, and ultimately something whose necessity is uncaused — God. (As literally stated, the Third Way faces a well-known quantifier-shift worry — the slide from "each contingent thing can fail to exist at some time" to "there is some time at which all contingent things fail together" is invalid as it stands; the argument rests its weight on the First and Second Ways, with the Third needing repair before it can be leaned on.)

The Fourth Way argues from degrees of perfection: we speak of more and less good, true, noble; such comparatives imply a maximum, which is the cause of all such perfection in others.

The Fifth Way argues from governance: natural bodies lacking intelligence act toward an end, hitting their mark regularly; what lacks intelligence cannot tend to an end unless directed by an intelligent being, "and this being we call God."

The First Way is the paradigm, so we will dwell there. Everything important — and every common error — is visible in it.

The Single Most Important Point

Here is the interpretive key, and it is the one most often missed: the causal series Aquinas has in mind does not stretch backward in time to a first event. He is not arguing that the universe must have had a beginning and that the first domino is God. Aquinas, remarkably, did not think reason could prove the universe began at all. In his treatise De aeternitate mundi (c. 1271) and in the Summa itself, he held that the world's beginning is "an object of faith, but not of demonstration or science."⁴ This put him in open disagreement with his Franciscan contemporary Bonaventure, who insisted the world's temporal beginning could be philosophically proven. Aquinas thought a beginningless universe was philosophically possible; we know it began only because Genesis tells us so.

So the Five Ways cannot depend on a beginning. They concern a different kind of series altogether. Medieval and modern Thomists distinguish two:

A series ordered per accidens ("accidentally ordered") runs through time: a father begets a son, who begets a grandson. Each member, once it acts, no longer needs its predecessor. Abraham can be long dead while Isaac fathers Jacob. Such a series could, for all philosophy shows, regress forever — which is precisely why Aquinas conceded the universe might be eternal.

A series ordered per se ("essentially ordered") operates simultaneously, here and now. The stone's motion depends, at this very instant, on the stick, which depends on the hand. The later members have no causal power of their own; they move only insofar as something is moving them right now. Take away the first member and the entire series ceases instantly. As Edward Feser, the foremost recent defender, puts it, in such a series the intermediate causes are mere instruments; their causal power is "borrowed."⁵ A series of borrowers with no one who owns the power outright explains nothing — like a paintbrush moving a paintbrush moving a paintbrush, with no hand. This is the series that cannot regress to infinity, and it requires a first member acting now: not a starter long ago, but a sustainer at the foundation of present reality.

The Metaphysics Beneath the First Way

Why must whatever changes be changed by another? Aquinas's answer rests on Aristotle's distinction between potency and act. A thing changes when a potential it has becomes actual — cold water becomes hot. But a mere potential cannot actualize itself; the cold water does not heat itself. Something already actual (the flame) must do it. "Nothing can be reduced from potentiality to actuality, except by something in a state of actuality."⁶ Trace the present chain of actualizers, and you reach something that actualizes without itself being actualized — something with no unrealized potential, pure actuality (actus purus). That, Aquinas argues across the following questions, must be one, immaterial, unchanging, and the source of all being.

The Objections — Steelmanned

1. "If everything has a cause, God needs a cause too"

Bertrand Russell pressed this in his 1927 lecture Why I Am Not a Christian. Crediting John Stuart Mill's Autobiography, he wrote: "If everything must have a cause, then God must have a cause. If there can be anything without a cause, it may just as well be the world as God, so that there cannot be any validity in that argument."⁷ It is a clean, memorable objection — and it has persuaded generations.

But it answers an argument Aquinas did not give. Aquinas never claims "everything has a cause." His premise is narrower: whatever is being changed is being changed by another; whatever is contingent requires a cause. What is purely actual has no potential to be actualized and so needs no actualizer; what is necessary in itself needs no cause. God is not an exception smuggled in arbitrarily — He is the one thing the argument's own logic says cannot stand in the dependent series. To his credit, Russell elsewhere grappled more seriously with these arguments; but the famous one-liner, repeated endlessly, simply misses the qualifier in the premise.

2. Hume and Kant

David Hume argued that causation is not a rationally intuited necessary connection but a habit of mind: we see one billiard ball strike another and infer a "power," but we observe only constant conjunction. If so, the causal principle behind the Ways loses its self-evidence. Immanuel Kant, in the Critique of Pure Reason (1781), pressed a different line: the cosmological argument, in inferring from a necessary being to the supremely real being, secretly relies on the ontological argument, which Kant thought already refuted — and in any case the categories of cause and necessity apply only within possible experience, not beyond it.

These are formidable, and a fully adequate reply requires defending an entire realist metaphysics against empiricism and transcendental idealism — more than any essay can do. The Thomistic response is that Hume's analysis describes how we come to know causal connections without showing there are none, and that the principle "a potential cannot actualize itself" is not an empirical generalization like "fire is hot" but a metaphysical truth about the nature of potency and act. Against Kant, Thomists deny that the argument depends on the ontological proof at all: it argues from features of the world to their required cause, not from a concept to existence. Whether these replies fully succeed is contested, and honesty requires saying so: the dispute is live among serious philosophers.

3. Newton's inertia: the most serious objection

Here is the objection that should keep a Thomist up at night. Aquinas's premise "whatever is moved is moved by another" looks like exactly what Newtonian physics overturned. By the principle of inertia, a body in uniform motion stays in motion with no mover at all. Anthony Kenny, in his careful and skeptical study The Five Ways (1969), pressed the point hard, concluding that the First Way fails in light of modern dynamics, which dissolves the medieval premise that sustained motion needs a sustaining mover.⁸ If the paradigm Way rests on dead physics, that is a grave problem.

Feser's reply, and that of contemporary Thomists, turns on what "motion" means. For Aristotle and Aquinas, motus is not merely local motion (change of place) but any actualization of a potential — change of quality, quantity, substance. Inertia concerns only local motion, and — on this view — even there it does not touch the deeper principle. Inertia, the Thomist replies, describes that bodies persist in motion; it does not explain what grounds the existence of that motion, or of the body, or of the law itself, from moment to moment.⁹ The Thomist relocates the argument from "what keeps the cannonball moving?" to "what sustains in being, right now, every actualized potential — including the persistence the law describes?" One may judge the reply successful or strained, but it is not a dodge: it reflects what Aquinas meant by change all along.

4. Oppy: must the per se regress really stop?

The atheist philosopher Graham Oppy, perhaps the most rigorous contemporary critic, grants the per se / per accidens distinction more than most — but asks whether an essentially ordered series must terminate in a single first member, or whether reality's "causal shape" might simply bottom out in a necessary initial state of the universe with no need for God. Oppy argues that on the plausible naturalistic options — an infinite regress, a contingent brute starting-point, or a necessary one — non-theism is at least as defensible as theism.¹⁰

The Thomist answers that a brute necessary physical state is not enough: anything composed of parts, or having unrealized potential, still requires actualization and so cannot be the terminus; only something purely actual and absolutely simple can be. Whether the universe could itself be that — purely actual, with no potency — is the crux, and here the argument shades into the full doctrine of divine simplicity. Oppy is owed the last word on the narrow point: he can coherently maintain that the regress stops at a necessary cosmos rather than at God. The Thomist's rejoinder is that such a cosmos, being changeable and composite, fails the very test that forced us up the series in the first place. That exchange, not a slogan, is where the real debate now lives.

5. The Fourth Way: conceding the weak link

Candor demands it: the Fourth Way is widely regarded, even by sympathetic readers, as the weakest. The inference from "there are degrees of goodness and truth" to "there exists a maximum that causes them" looks, as Kenny noted, like a fragile echo of Platonic Forms, and the premise that a maximum in a genus causes all lesser instances strikes many as a dated piece of metaphysics. Some Thomists rehabilitate it via the doctrine of transcendentals and participation in being; but no one should rest the case on it. The First and Second Ways carry the weight; the Third, given the quantifier-shift worry noted above, can join them only in a repaired form.

The Honest State of the Scholarship

The Five Ways are not a museum piece. A genuine revival of analytic Thomism — Feser, David Oderberg, and others — has put rigorous versions back into peer-reviewed debate, met by equally rigorous critics like Oppy and Kenny. There is no scholarly consensus that the arguments succeed; neither is there consensus that they fail. What no longer survives careful reading is the lazy dismissal — the Russell one-liner, the "God needs a cause" reflex, the bumper-sticker assumption that "Newton settled it." Those are misreadings. This is not to wave away the inertia objection itself: as section 3 granted, the underlying worry about whether sustained motion needs a sustaining mover is a serious one that a Thomist must answer with real work, not a slogan. What collapses is only the cheap version of it. The burden has shifted to the harder questions: the reality of potency and act, the legitimacy of essentially ordered causation, and whether a purely actual being is required or merely one option among several.

What the Five Ways Do and Do Not Establish

Aquinas himself was modest. Each Way concludes only with a label — "this everyone calls God" — not with a full theology. The arguments, if sound, establish a purely actual, necessary, sustaining first cause of present reality. They do not, by themselves, establish that this cause is good, personal, triune, or the God of Abraham; that is the work of the subsequent questions of the Summa and of revelation. Nor do they prove the universe began in time — Aquinas insisted they don't, and didn't need to.

What they offer, at their best, is not a knockdown proof that ends all argument but a serious and still-living case that the changing, contingent world we touch and push and watch cannot be the whole story — that beneath the stone and the stick and the hand there must be a hand that nothing moves. Whether one finds that case finally compelling is a matter for honest, careful thought, pursued, as Peter urged, "with gentleness and respect" (1 Peter 3:15). The argument deserves nothing less, and neither do those who reject it.