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The Argument from Change

From the reality of change to a first, unchanging cause of it. Its heart is a distinction between two kinds of causal chain: the per accidens chain, which can run back forever, and the per se chain, which cannot. Aristotle's argument, Aquinas's First Way, defended today in rigorous form by Edward Feser.

Premises & Hinge

The Argument

The numbered form is ours, after Aristotle (Physics VII–VIII) and Aquinas's First Way; cf. Edward Feser, Five Proofs (2017) — the words themselves are the philosophers', below.

  1. P1 Some things are changing — a potential in them is being made actual.
  2. P2 Whatever is changing is being changed by something else already actual; nothing actualizes its own potential.
  3. P3 The chain of changers here is essentially ordered (per se) — each changes only while the one before it is acting, right now — and a per se chain cannot regress to infinity. the hinge
  4. Therefore there is a first, unchanging cause of change — something purely actual, "and this everyone understands to be God."

The sources

The Argument Saint Thomas Aquinas 1259
It is clear to the sense that something, the sun for instance, is in motion. Therefore it is set in motion by something else moving it. Now that which moves it is itself either moved or not. If it be not moved, then the point is proved that we must needs postulate an immovable mover: and this we call God. If, however, it be moved, it is moved by another mover. Either, therefore, we must proceed to infinity, or we must come to an immovable mover. But it is not possible to proceed to infinity. Therefore it is necessary to postulate an immovable mover.

Source — Saint Thomas Aquinas, Summa Contra Gentiles I, ch. 13

Continued Saint Thomas Aquinas 1274
The first and more manifest way is the argument from motion. It is certain, and evident to our senses, that in the world some things are in motion. Now whatever is in motion is put in motion by another, for nothing can be in motion except it is in potentiality to that towards which it is in motion; whereas a thing moves inasmuch as it is in act. For motion is nothing else than the reduction of something from potentiality to actuality. But nothing can be reduced from potentiality to actuality, except by something in a state of actuality. Thus that which is actually hot, as fire, makes wood, which is potentially hot, to be actually hot, and thereby moves and changes it. Now it is not possible that the same thing should be at once in actuality and potentiality in the same respect, but only in different respects. For what is actually hot cannot simultaneously be potentially hot; but it is simultaneously potentially cold. It is therefore impossible that in the same respect and in the same way a thing should be both mover and moved, i.e. that it should move itself. Therefore, whatever is in motion must be put in motion by another. If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover; as the staff moves only because it is put in motion by the hand. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.

Source — Saint Thomas Aquinas, Summa Theologica I, q. 2, a. 3 — the First Way

Objection David Hume 1779
In such a chain, too, or succession of objects, each part is caused by that which preceded it, and causes that which succeeds it. Where then is the difficulty? But the whole, you say, wants a cause. I answer, that the uniting of these parts into a whole, like the uniting of several distinct countries into one kingdom, or several distinct members into one body, is performed merely by an arbitrary act of the mind, and has no influence on the nature of things.

Source — David Hume, Dialogues Concerning Natural Religion, Part IX (Cleanthes)

Objection Immanuel Kant 1781
The transcendental principle: "Everything that is contingent must have a cause"—a principle without significance, except in the sensuous world. For the purely intellectual conception of the contingent cannot produce any synthetical proposition, like that of causality … But in the present case it is employed to help us beyond the limits of its sphere.

Source — Immanuel Kant, Critique of Pure Reason — the causal principle

Argument hinges on:

The per-se causal chain The chain of changers here is essentially ordered (per se) — each changes only while the one before it is acting, right now — and a per se chain cannot regress to infinity. What does that mean?
The library's note

Start with what "change" is. A cup of coffee is actually hot and potentially cold; when it cools, that potential is made actual. Aristotle's basic claim is that a potential cannot actualize itself — the coffee does not cool itself; the cold air does. So whatever is changing is being changed by something else that is already actual.

Everything then turns on what kind of causal chain is in play, because there are two, and they behave very differently. The first Aquinas calls accidental (per accidens). A father begets a son, who grows up and begets a son of his own. Here each cause, once it has done its work, is no longer needed: the grandfather can die and the grandson is born all the same; the son becomes a cause in his own right. The links do not depend on the earlier ones still operating. A chain like this, Aquinas freely grants, could in principle run back forever — he does not think reason alone can prove the world had a beginning.

The argument depends on the other kind, which Aquinas calls essential (per se). Picture a hand pushing a stick that pushes a stone. The stick moves the stone only because the hand is moving the stick, right now — the stick has no power to push on its own; it merely passes along power it is receiving this instant. A choir holding a note only while the conductor beats time, or a chandelier hung from a chain whose every link is held up by the one above, is the same: each member is borrowing its activity, at this moment, from the one before it. The defining mark of such a chain is simple — the instant the first cause stops, everything stops. The stone halts the moment the hand does; the note dies the moment the conductor's hand falls.

A chain like that cannot run back forever, because if every link were only passing along borrowed power — if there were no first member actually supplying it — there would be no power in the chain at all, and nothing would move. Yet things are moving. So an essentially ordered chain must rest on a first cause that is not itself being moved by another: something with no unrealized potential to be actualized, "purely actual." And because such a cause has no potential left to be actualized, there is nothing prior that could actualize it — which is the reply to "then what changes God?" That first, unchanging cause is what Aristotle and Aquinas call God.

Written for this library — not a quoted source. It reports how the premise is argued and answered; the philosophers' own words are above.

If you accept it

Accept it, and you take on the whole Aristotelian framework — real potentials, a sharp act/potency distinction, essentially ordered causal series — a metaphysics much of modern philosophy set aside after the rise of mechanical science (and which the argument's defenders say was abandoned too quickly).
Edward Feser, Scholastic Metaphysics (2014) ↗

The reply

The critique holds that things may simply persist in existence without anything sustaining them — existential inertia — in which case no here-and-now chain needs a first member.
Joseph Schmid, "Existential Inertia and the Aristotelian Proof" (2020) ↗

If you deny it

Deny that a changing (or existing) thing needs something already actual sustaining it here and now, and the regress can stop early: the "existential inertia" thesis holds that things simply persist on their own, with no need of a moment-to-moment sustaining cause.
Joseph Schmid, "Existential Inertia and the Aristotelian Proof" (2020) ↗

The reply

The reply is that inertia is asserted rather than argued, and that a thing composed of potential and act cannot account for its own continued actuality.
Edward Feser, Five Proofs of the Existence of God (2017) ↗

Where it leads

Accept that this is a per-se causal chain, one that cannot run back forever, and this argument leads to a first, unchanging cause of change — something purely actual.

Beyond the public domain

The modern revivals and their critics are under copyright, so we don't host them — the reading doesn't stop at the public-domain record. Follow it at the sources:

Edward Feser, Five Proofs of the Existence of God (Ignatius, 2017) Joseph Schmid, "Existential Inertia and the Aristotelian Proof" (2020) — the main critique Stanford Encyclopedia of Philosophy — Aristotle on Causality

You have read the premise, the objection, and the cost of each move. The library draws no conclusion.