St. Thomas Aquinas’
The Way of Motion
Thomas’ Proof from Motion
The fulfillment of what exists potentially
The actualization of what exists potentially
(insofar as it exists potentially)
Examples of Change
(in the widest possible sense)
Getting a suntan
Becoming a doctor
A meteor crashes to earth
A shooting star
Riding a bicycle
Learning a trade
Teaching a concept
The agent cause is not only moving the
block to its new form, he himself is
moving or changing as he moves or
changes the block.
The two are really different. Potentiality is NOT
Actuality is MORE than potentiality.
Nothing moves itself from potency to act, except by
something already in act.
At rest At rest
Potentially moving Potentially moving
Not actually moving Not actually moving
To say: “Nothing moves itself from potency to act, except by
something already in act” is to say that “from nothing comes
nothing”, or “one cannot get something from nothing”.
A thing cannot give what it does not have.
If a ball is at rest, it is NOT moving. It does not have motion.
And so it cannot impart motion to itself.
A thing must receive a perfection that it does not have from
something that actually has it.
The ball at rest receives motion from something actually moving.
Moving in this direction
Imagine a moving freight train that is infinitely long,
one that has no engine.
Each one receives motion from a principle. The principle
has something that is received by the one. The receiver
initially has less.
The cause of motion in the receiver is the principle. The
principle is the cause, and thus the explanation. The
principle accounts for the motion. From something comes
If the series goes to infinity, then there is no principle, no
cause, of the motion in the series. The whole series lacks a
cause. We are expected to accept that each part on the series
has a cause and explanation of its motion, but that the motion
originally came from nothing, not something, and that the
movement of the whole series lacks a cause. In other words,
something came from nothing. The caboose moves, but there
is no engine, no first cause of the movement.
But if there is no first cause of the movement, then the caboose
does not move, in fact, it never moves. Neither does any freight car
on the series move, for it is preceded by an infinite series.
To say that it moves, but that there is no first cause, is to say that
potentiality and actuality are NOT different, that something can
come from nothing, that something and nothing are the same thing,
that potentiality and actuality are the same thing.
A terminal. An end.
Infinity means “without end”, “without term”. But one cannot
divide infinity in half and speak of a series that is half infinite. If
the motion comes to an end, then the series is not infinite. It is
finite. Hence, there is a First Unmoved Mover or Principle.
Every part of the series is dependent, every part receives what it has
from something, but the whole does not receive what it has.
The whole series is nothing but the sum of every part of the series.
Every part of the series is dependent, but the whole is not dependent,
but is independent.
The motion of every part of the series is explained and accounted for, and
thus caused, but the whole series is uncaused and unaccounted for.
The motion of every part of the series comes from something, but the
motion of the entire series comes from nothing.
An infinite series is both finite and infinite at the same time.
Hence, there is no infinite regress. There is not an infinite
series of movers that precedes a moving thing. The series is
If the series is finite, then there is a First Mover that is
unmoved by anything prior to itself. If not, then this first
mover is not absolutely first.
Hence, there is an Unmoved Mover, a mover that is unlike
any mover within the series. For every mover within the
series is a moved mover.
The Unmoved Mover is not moved in the act of moving.
The Unmoved Mover is not in a state of potentiality.