Aquinas states that the existence of God can be proven by reason. Although a Christian, he argues that the individual can arrive at knowledge of God’s existence without recourse to the Christian Scriptures but through the use of reason, logical demonstration. He offers five ways to prove the existence of God through the use of reason. The first way, an argument from change, he argues is the most obvious.
Aquinas writes, “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.”
The first and more manifest way is the argument from motion. Aquinas following from Aristotle uses the term “motion” to refer to any change. He continues by stating that “it is certain and evident to our senses, that in the world some things are in motion”. It is a clear and obvious fact of the world that things can change.
He goes on to explain that every change has a cause. 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.
When something changes, it acquires a new characteristic. A thing cannot change unless it has a potential to acquire the new characteristic and it does not already have that characteristic. In any change, the thing undergoing the change must have the capacity or potentiality to be what it will become, and yet not actually be that which it will become.
In this demonstration, Aquinas uses two examples of change: wood catching fire and a hand moving a staff. For wood to catch fire, it must not actually be burning but must be capable of burning. Wood catching fire involves the reduction of the wood’s potentiality of wood to burn to the actuality of it burning. It must pass from the potential to catch fire to actually being on fire. Wood that is not burning has the potential to catch fire. Wood that is on fire no longer has the potential to catch fire because it is actually on fire.
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.
The cause of change must be something other than the thing changing. A change brings about a new actuality, e.g., wood on fire, from what was first potential to this new actuality, e.g., wood not on fire but capable of being on fire. So the new actuality (burning wood) cannot be the actuality that brings itself to be (wood already on fire cannot set itself on fire). The cause precedes the effect, and therefore the effect cannot be its own cause. A burning match cannot ignite itself. Anything that is changing is being caused to change by something else.
The example of burning wood is an example of a temporal causal series. The heating of the wood precedes in time the wood catching fire. Another example might help. Think of a long line of dominoes, each standing on end with a domino in front of it and behind it. If I push over the first domino in this line, it will knock over the next domino. The second domino will knock over the third and so on. Each domino will knock over the next in sequence. Now once I push over the first domino, my job is done. I can simply walk away and the sequence will run its course without me. Likewise any domino in the sequence could suddenly disappear after it pushed the next domino and the sequence would continue. Each cause precedes each effect in time, but each effect must and does have a cause. In fact, the line of dominos could stretch into infinity in either direction and the principle of “every change has a cause” would still hold true.
Aristotle argued that the universe, the world, was eternal , with no beginning or end. In this demonstration, Aquinas does not refute this even though as a Christian he believed that the world had a definite beginning point. This demonstration is not about a beginning point, a moment of creation, for the world, but is about the fact that every change requires a cause outside of the thing that is changing and that this fact leads logically to the conclusion that God exists.
But if one cannot arrive at God from a temporal series of causes, how can His existence be shown? The answer comes in the next part of the demonstration. Now that Aquinas has established the truth of every change needing a cause, he narrows his argument to a specific type of cause.
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. Here he considers only the case where the cause of a change is itself a process of change or motion. He gives an example of such a case by citing a hand moving a staff.
In the example of a hand moving a staff, we do not have a temporal sequence of causes. The hand does not initiate the staff’s movement as in the case of the dominoes. No, the staff will move only as long as the hand moves it. The cause of the change, i.e., the hand moving, is simultaneous to the change it effects, i.e., the movement of the staff, and continues and sustains the movement throughout the process. Aquinas calls these kinds of causes (that act simultaneously to the process of change they effect) as per se causes. Their effects are essentially subordinated to the causes, not temporally successive.
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.
The staff moves because the hand moves. The effect is the result of a simultaneous motion/change of a prior cause. This motion/change of the cause must itself be the result of a simultaneous motion/change in another prior cause, and so on. It is tempting to think that such essentially subordinated series of causes could stretch out infinitely, just as a temporally successive series of causes could. But this is quite impossible, because we are talking about causes that are simultaneous in time to the effects. There must be something driving the motion/change of the entire system. As an example think of a long line of train cars, each connected to the one in front and behind. This long line of cars is moving steadily along the track through Western Oklahoma. Each car is transferring motion or energy to the other car in line and so on. There must be at some point a locomotive for the train. The locomotive is the initiator of the motion. If the line of cars was infinitely long, there would be no first cause to originate the motion or energy being transferred simultaneously down the line of cars. The point here is simple and logically obvious. In an essentially subordinated series (series of simultaneous causes) the only cause really changing anything is the first cause in the series.
Aquinas then takes the argument to its logical conclusion.
Whenever the effects are the result of the simultaneous motion of prior causes that are themselves effects of prior moving causes, there must be something driving the motion of the system. For example, a series of train cars which is transferring motion cannot be infinitely long because there would be no motion or energy to transfer without a first cause and source for the motion supposedly being transferred. There must at some point be a locomotive for the train. The point is simple and logically obvious. In an essentially subordinated series (series of simultaneous causes) the only cause that is really changing anything is the first cause in the series.
Therefore it is necessary to arrive at a first mover, put in motion by no other
This first mover must be fully actualized, i.e., unchanging, because anything that changes requires a cause for that change. A “first cause” that itself was subject to change could not in fact be the first cause because the fact of it changing requires that something else outside the “first mover” cause the change. Similarly, the first mover cannot be a physical, material being. All physical, material beings are subject to motion/change. The first mover is un-changing. Therefore, the first mover cannot be a physical, material being.
Aquinas then ends the demonstration with a simple statement.
and this everyone understands to be God.
At this point, it is important to point out some important points about this first way. Aquinas never says that everything changes. He points out that change is an observed reality in the world.
He does not argue that the First Mover is the Creator of the Universe in this demonstration. Nor does he argue that every change leads to the conclusion that a First Mover exists. Nor does he argue in this demonstration that all the changes in the Universe demonstrate the existence of a First Mover.
He very specifically argues that an essentially subordinated series (series of simultaneous causes) demonstrates the existence of a First Mover. His argument holds even if we can identify only one such case.
He never states the First Mover verifies or captures all the characteristics and beliefs about the Christian God contained in the Bible. This demonstration did not have as its purpose to fully describe or prove the nature of God as contained in Christian belief.
To summarize the argument:
- Things can change/move.
- Every change is caused by the activity of something else - Nothing is the cause of its own process of change
- If the activity of the cause is itself a change or motion then this per se effect must be caused by another prior, simultaneous cause.
- In a chain of per se or essentially subordinated causes, there would be no last effect if something were not driving the whole chain as the first cause. Since there must be a first initiator of change in essentially subordinated causes, the chain cannot be infinite.
- Therefore there must be a First Mover that acts and causes change, but whose causing activity is not a change or motion.
- This First Mover must be non-physical, non-changing but an actual and active cause of change/motion.
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