The following is the first of Thomas Aquinas’ five ways of
establishing the existence of God. For our immediate purpose, we are merely trying to establish a beginning of causes. That the first cause is known as God, or how or to what
extent we have defined God, is secondary to our immediate discussion. For now,
we are merely interested in establishing a beginning.
Aquinas’ first way, from the Summa Theologica, is as follows:
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. (ST, 1.2.3)
Now many introductory philosophy texts have ridiculed the
sentence which says “ But this cannot go on to infinity, because then there would
be no first mover.” The accusation is that Aquinas assumes a first mover
without proving there to be one. But this criticism misunderstands Thomas’
meaning of movement, for his context is that of ongoing causation of movement. Thomas gives us an explanation when he states “as the staff moves only because it is put in motion by the hand.”
Assume you are in your car, and pull up to a railroad crossing, and you see a series of boxcars rolling past. It would be absurd to say “The boxcars need no engine,
for there could be an infinite series of boxcars.” This is absurd, for boxcars
can only be moved, cannot generate movement, and cannot move themselves. If there is movement in the boxcars, there has to be something pulling the boxcars that is much different from a boxcar, something that can cause movement while itself is not being
moved by another. So a series of things being moved cannot go on to
infinity, for there would be nothing causing the movement in the whole chain. Perhaps
to the modern ear Thomas’ statement should read ‘But this cannot go on to
infinity, because there would be nothing causing the movement.’
Thomas is speaking of motion as continuous and present, as
in the example of the hand moving the staff. To Thomas, if there is motion, it
is immediate and continuous through the entire chain. Increasing the length of
the chain of objects being moved does nothing to eliminate the conclusion that
something is moving the chain of objects. Increasing the length of the chain of
objects to infinity merely increases the need for a cause of the entire set of
objects. If there is movement, something must be currently causing the
movement, while itself is not being moved by another. Posing the boxcars as being in a large circle still does not solve the problem, for boxcars can still not generate movement.
Further, theoretical infinites are no help to us in determining causality in the real world. We readily admit that a theoretical infinite can be placed into a theoretical situation, or plugged into a math formula. But math formulas that calculate things do not prove that the things actually exist in the world. So we find no answers in theoretical infinites that are not attached to actual things.
The question then arises about sequential infinites, or finite things that happen in succession. Suppose we come across a long line of dominoes in the road before us, going to the left and right as far as we can see. We suddenly see the dominoes falling over, each one knocking over the next one in line. Our question is then: “Could there have been an infinitely long string of dominoes that were always knocking the next one over?”
First, we are faced with the fact that something would have had to manufacture and set up this infinite string of dominoes, which defies explanation. We have not an infinite amount of materials to make dominoes with, or an infinite road to place them. Second, proposing the existence of an infinite string of falling objects leaves unexplained how the falling was created in the first place. In everything we observe, such a sequence would have had to be initiated. Supposing an infinite string of dominoes leaves us without an explanation of how the falling action came to exist. Of course, a lack of an explanation here does not prove that the falling did not exist everlastingly, but it does present us with a type of “atheist of the gaps” theory: we have no explanation for an observed sequence, so by golly, it must have always existed with no cause. This is an unacceptable answer.
Third, as we observe this string of dominoes falling over, if it were infinite, we must ask ourselves “how did the falling get to me?” If the line of dominoes were infinitely long, it seems the falling would always be an infinite distance away from me. The atheist might reply, “Well, the ones currently falling over have to be somewhere. It just so happens that it is next to you.” But this misunderstands infinites. If the line were truly infinite, then the falling would always, at all instances, be an infinite distance away from any one point on the line. Pick any domino, and the falling would have been an infinite distance away. Since the falling is happening in sequence, it is impossible to select a domino where the falling is not an infinite distance away. The dominoes are always falling, but never arriving anywhere, which is an absurdity.
So we conclude that both simultaneous causation and sequential causation cannot be infinite. If we observe motion, or causality, in the real world, it cannot have gone on for an infinite sequence in the past. If we observe a cause, logic forces us to conclude that there is a first cause, one that is not being caused by another. This we call God.