The Existence of God - Part 2: Aquinas' First Way

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:

1. Things can change/move.
2. Every change is caused by the activity of something else - Nothing is the cause of its own process of change
3. 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.
4. 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.
5. Therefore there must be a First Mover that acts and causes change, but whose causing activity is not a change or motion.
6. This First Mover must be non-physical, non-changing but an actual and active cause of change/motion.

This First Mover is identified as God.

The Existence of God - Part 1

Change Happens


When we observe the world around us, two fundamental observations can be made. First, it is clear that things exist. Second, it is clear that things can change. I’m not saying that things necessarily have to change but I think it is very clear that some things change sometimes.

The most basic principle in philosophy is that “nothing can come from nothing”. Its corollary is that “something cannot be and not-be at the same time”. Both are very common sensical statements. The table I am sitting at either “is” or “isn’t”. Likewise, I don’t expect coffee to suddenly appear in my empty coffee cup. Nothing is a complete absence of something. Since there is no something in nothing, something cannot suddenly appear from nothing. So, there is either being or non-being.

Now change means that something new comes to be while something old ceases to be. But if nothing comes from nothing, how can something new come to be when it didn’t exist before?

Likewise, how can some new being come to exist from something already in existence? It would seem that no new being can come from another being, since what has being already is and does not begin to be.

You may think these questions to be somewhat silly, but they represent a truly profound problem when trying to explain change. Any explanation of change must address these issues. Parmenides, a Greek philosopher living before Aristotle, arrived at the conclusion that change is impossible and that the change we observe is illusion.

Thankfully, Aristotle solved the dilemma. He agreed with the truth of the statement that “nothing can come from nothing”. However, it is not entirely true that “being cannot come from being”. Aristotle distinguished “being-in-act” from “being-in-potency”. It is true that being-in-act cannot come from being-in-act because it already is fully actualized. However being-in-act can arise from being-in-potency.

As an example, let us consider a sculptor creating a statue. He can carve the statue from a block of marble. This is possible because the block of marble has the “potential” to be shaped into the statue – it has the possibility and capacity for being transformed. The figure of the statue is in potency within the block of marble. This potency is not nothing. It is real – not in the same as the reality of being-in-act, but with the reality of being-in-potency.

Every change implies a duality. A subject in potency, by the action of some agent, passes into actuality. Change presupposes the acquisition of something and the corruption of something else. The subject of change is what stays the same throughout the change. However, through the change, it acquires something new and loses what it previously had. Change implies a passive principle and an active principle intrinsic to the thing that changes.

Thus there are three principles necessary to any change. Something new comes to be (form). Something old passes away (privation). Something stays the same throughout (matter). In the example of the statue, the form, what comes to be, is the shape of the sculptured statue. The privation, what passes away, is the formlessness of the block of marble and the potential for the statue shape. The matter, what stays the same throughout the change, is the marble. This example is an example of an accidental change – what changes are the accidents of the marble, but the substance of the marble stays the same throughout.

There are three kinds of accidental change: change in quality (alteration), change in quantity/size (growth or diminuition), and change in place (local motion). In all cases, change can be defined as the act of a being in potency insofar as it is in potency. Change is the process by which a substance loses one accidental form or actuality and gains another. Change is the act of something that does not yet have, but is acquiring, the full act of a new accidental determination, a new quality, size or position. While the change is happening, the new determination is neither fully actual (because then the change would be over) nor fully potential (for then the change would not have started). In this way, any change is an imperfect act. The implication of this is that there must be a cause sustaining the change as it is occurring.

What we have discussed about accidental change can also apply to substantial change, a passing away and coming to be of substances. For example, iron, a metal, is a different substance from oxygen, a gas. When combined, they form a third substance, rust, that is very different from either iron or oxygen. This is a substantial change. The principles of change described above apply here as well. What comes to be is the form rust. This form comes to be in the matter of iron and oxygen. However, form and matter compose a substantial unity. Form cannot exist without matter nor matter without some form.

But form means much more than a simple arrangement of atoms or molecules. While it is true that form cannot exist without matter, and in a sense, form is realized in matter in a certain configuration, the matter does not all by itself account for its configuration. Form is a cause in the sense that it is constitutive of the thing it Is the form of, just as matter is constitutive of the thing. But form has a certain priority and explanatory value because the form accounts for the matter being in a certain configuration while in that configuration, something matter cannot do. For example, a house can be made of bricks, but the bricks by themselves do not account for the house as opposed to a pile of bricks.

A change in something must have a cause. The change that something undergoes cannot be the cause of that very same process of change. The change results in a new actuality. This new actuality is a result of what is first potential to it. Therefore the resulting actuality cannot be the actuality that brings itself about. Anything changing is being made to change by some other actuating cause, and this actuating cause is an actuality prior to the change which is the effect.

In speaking of causation, we can differentiate two kinds. The prior actuality, the cause, of a change may be prior in time. Example: A cue ball rolls across the pool table and strikes another billiard ball causing the ball to begin rolling. Once the cue ball has initiated the motion of the billiard ball, the cue ball has no further part to play in the continuation or culmination of the change. In fact if the cue ball were to instantly disappear immediately after striking the billiard ball, the motion of the billiard ball would play out in the same way as if the cue ball were still present.

However, some causes of change act simultaneously with the changes they effect. Examples: a hand moving a staff; a series of interlocking gears; or a series of train cars being pulled by a locomotive engine; any system of simultaneous transfer of change or motion with net energy output. In such cases, the change is sustained only by the continued presence of the cause. If the cause is removed, the change could not occur. If the hand is removed, the staff would no longer move.

Aquinas and the Proofs of God’s Existence

Aquinas deals with the question of God’s existence in Question 2 of the First Part of his masterpiece, the Summa Theologiae. The Summa is divided into large sections called Parts. Each part is divided into questions. These questions are more like topics rather than specific questions. Each question then is divided into articles. Each article is a specific question, e.g., “Whether the existence of God is self-evident?” In responding to each article, Aquinas first lays out objections (arguments counter to his own) to the question. Next, Aquinas lays out his answer to the question, and then specifically addresses and refutes each objection.

Question 2 entails three articles. Article 1 asks, “Whether the existence of God is self-evident?” Aquinas concludes that the existence of God is not self-evident to humans. If God’s existence were self-evident, then no one would be an atheist.

Article 2 asks, “Whether it can be demonstrated that God exists?” Aquinas reminds us that there are two kinds of demonstration. A priori demonstration argues from the cause to its effect. A posteriori demonstration argues from an observed effect to its cause. Since God’s existence is not self-evident, God’s existence cannot be demonstrated a priori, for the cause, in this case God, is not self-evident. However, God’s existence can be demonstrated a posteriori, by arguing from His effects observed in the world.

Article 3 asks, “Whether God exists?” Aquinas concludes that God’s existence can be proved in five ways. We will address each of these five ways in separate posts.

However before addressing Aquinas’ first way, it is interesting to note the objections to the existence of God. Aquinas details just two objections to God’s existence. But these are, and have been historically, the strongest arguments against God’s existence.

The first objection noted arises from the existence of evil.

Aquinas writes, “It seems that God does not exist; because if one of two contraries be infinite, the other would be altogether destroyed. But the word "God" means that He is infinite goodness. If, therefore, God existed, there would be no evil discoverable; but there is evil in the world. Therefore God does not exist. “

The second objection is the quite modern argument from the power of science to explain the world.

Aquinas states, “Further, it is superfluous to suppose that what can be accounted for by a few principles has been produced by many. But it seems that everything we see in the world can be accounted for by other principles, supposing God did not exist. For all natural things can be reduced to one principle which is nature; and all voluntary things can be reduced to one principle which is human reason, or will. Therefore there is no need to suppose God's existence. “

It is very interesting to remember that Aquinas was writing in the 13th century. So it is clear that the “new atheism” is hardly new. If anything the arguments it puts forward in defense of itself are simple derivatives and corollaries to these very old objections. That’s not to discount the strength of these arguments. Nor is it to diminish the importance of addressing them head on. We will address each of these objections in its own right following the discussions of the five ways.