The Library · Arguments for God's Existence

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.

Summary of the argument

This is the oldest of the arguments — Aristotle's, taken up by Aquinas as the first of his Five Ways, and defended today by Edward Feser as "the Aristotelian proof." It begins from the plainest fact there is: things change. Aristotle analysed any change as a potential being made actual — cold coffee becoming hot — and argued that nothing makes its own potential actual: whatever is changing is being changed by something else. The whole argument then turns on a distinction most people have never named but instantly recognize once it is drawn: there are two very different kinds of causal chain, and only one of them can run back forever. The kind this argument depends on cannot — and where it must stop is what Aristotle and Aquinas call God.

A plain-language summary to get oriented — not a verdict. The sources below are the argument itself.

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

P1 Some things are changing — a potential in them is being made actual.
P2 Whatever is changing is being changed by something else already actual; nothing actualizes its own potential.
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
Therefore there is a first, unchanging cause of change — something purely actual, "and this everyone understands to be God."

The dispute turns on one premise: That this is a per-se (essentially ordered) chain — one that cannot run back forever.

Set out this way, the conclusion follows if the premises hold. The dispute is over the premises — above all the Aristotelian claim about change — not the logic. A valid argument built on a false premise establishes nothing.

What the hinge means

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.

The cost — weighed both ways

The per-se causal chain

If you keep the premise — the cost some name

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) ↗

If you deny the premise — the cost some name

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) ↗

Every line is attributed to a named thinker. Neither column is refereed — the reader weighs them.

Where it leads · what it does not reach

Where the other arguments reach "a necessary being" or "a first cause," this one aims at something more immediate: not a first cause in the distant past, but a cause holding every changing thing in being right now, at the top of every per se chain. Its defenders argue that this first cause must be immaterial, unchanging, one, and intelligent, since anything with unrealized potential would itself need actualizing. It is the most metaphysically ambitious of the arguments — and the most demanding: it stands or falls with the Aristotelian account of change and causation on which it is built.

The sources · in their own words, across time

Scholastic c. 1100 – 1500

1259

A.D.

Thomas Aquinas Catholic

1225–1274

“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

1259

A.D.

Thomas Aquinas Catholic

1225–1274

“That which is stated to be moved by itself is moved primarily. Therefore if one of its parts is at rest, it follows that the whole is at rest … Hence that which was stated to be moved by itself, is not moved by itself. Therefore whatever is in motion must needs be moved by another.”

Source

1274

A.D.

Thomas Aquinas Catholic

1225–1274

“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

505 years pass — nothing from this stretch is hosted yet

Post-Reformation c. 1650 – 1900

1779

A.D.

David Hume

1711–1776

“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

1781

A.D.

Immanuel Kant

1724–1804

“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

The living debate · after 1953

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.