Thomas Aquinas’ argument from motion, or “The First Way,” is a cosmological argument found in the Summa Theologiae, and Summa Contra Gentiles. The argument originated in Plato’s Laws and the writings of Aristotle who argued for what he called “the unmoved mover.”
In a nutshell, Aquinas’ First Way suggests that there is a direct link between the existence of change and the existence of God. In order to parse out how this works, we will follow Aquinas’ formulation as it’s presented in the Summa Theologiae, taking time along the way to break down his metaphysics.
The Definition of “Motion”
The argument from motion opens with an acknowledgement that “motion” is an observable fact of reality.
“It is certain, and evident to our senses, that in the world some things are in motion.”
It should be noted that when Aquinas uses the term “motion,” he is not strictly referring to things moving about in the Newtonian sense. The Latin word he uses, “motus,” is often translated as “motion,” but may be better understood as the concept of “change.”
Following in Aristotle’s footsteps, Aquinas defines change as “the actualization of potential.” Here’s how he puts it in the Summa.
“For motion (change) is nothing else than the reduction of something from potentiality to actuality.”
The term “Actuality” refers to all the qualities a thing has in the now, while “Potentiality,” describes the qualities something could have in the future.
Let’s imagine a coffee mug resting on a table. Its “actual” qualities include things like hot, resting on the table, steaming, full, handle, etc. Its potential qualities are things like broken, moved to the left, drunk, cool, or even set on the Great Wall of China.
According to Aquinas, change officially happens when a potential quality becomes an actual quality. So, when the coffee goes from potentially cold to actually cold, we can officially say a change has occurred.
Nothing Can Change Itself?
The next premise argues that the nature of change (the transition from potentially having a quality to actually having a quality) means nothing can be the cause of its own change. In other words, Aquinas claims that nothing can change itself.
“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.”
Let’s go back to the coffee mug resting on the table. As it is, it possesses a near infinite number of potential qualities, but it is powerless to actualize any of them. It can only move if it is moved by some outside force.
In the Summa Aquinas gives us an example from heat transfer. “Thus that which is actually hot, as fire, makes wood, which is potentially hot, to be actually hot, and thereby moves and changes it.” No matter how hard it tries, a cold stick cannot make itself hot.
Even biological organisms experience changes in this way. If you place your hand on a table and leave it to its own devices it will never move. Your hand can only lift off the table if it is moved by the nervous system, which itself is moved by the brain.
These two ideas, “change is the actualization of potential” and “nothing can change itself” are the metaphysical foundation of the mover argument. The next phase explores changes that occur through hierarchical or “per se” causal chains, which will inevitably lead us to the existence of God.
The First Way and Causal Chains
Because nothing can be the cause of its own change, the process of change creates a series of causes, sometimes called causal chains. Philosophers speak about two kinds of causal chains: hierarchical and linear. Most of the time, when we talk about a series of causes, we are thinking about the linear variety. These kinds of chains are created over time by independent but connected events.
For example, in my hometown, there are three Baptist churches within eyeshot of one another. The churches didn’t appear randomly but are the product of a long series of complex causes. The chain began over 2000 years ago with the crucifixion of a Jewish rabí. A later follower of that rabí nailed some grievances onto a church door. This led to the creation of the Baptist denomination and eventually the churches in my town.
Though each event in the chain is separated by time and space, as a series of sequential events, they are all connected. One thing led to another, which led to another and another, which is why this or that happened.
Many cosmological arguments (such as the Kalam, made famous by William Lane Craig) use linear chains to suggest that there must have been a “first cause.” That is to say, there must have been something that began the great chain of causes. This variant has proven potent in the modern era, dominated by Big Bang cosmology.
Thomas, however, lived in a time when most people believed in an eternal universe. Though he himself believed God created the world ex nihilo (from nothing), he admittedly couldn’t prove it philosophically.
“By faith alone do we hold, and by no demonstration can it be proved, that the world did not always exist”
Consequently, Aquinas’ first way relies on hierarchical or per se causal chains rather than the linear sort.
Aquinas’ First Way and Hierarchical Causal Chains
“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”
Let’s go back to the coffee resting on the table. As it is, the coffee possesses the actual quality “resting on the table.” But how does it have that quality? Well, we could say it was placed there by someone, but that would be a linear cause, which we don’t care about. Another place we could look is the relationship between the mug and the table.
The mug has the property “resting on the table” because the table has the power to support it. If the table disappeared, the mug would lose its property. However, this is not the whole story. The table’s ability to support the mug is not its own. It derives the power from the floor, which actively supports it. If the floor vanished, the table would fall and stop supporting the mug. The same is true for the floor, which is supported by the earth. Each link in the chain plays an active role in the mug’s ability to “rest on the table.”
Note, the earth’s role in this chain is different than the floor and tables. The table and floor derive their ability to support from being supported. In contrast, the earth supports the chain but is itself unsupported. It doesn’t sit on turtles or suspend from strings; it essentially rests on nothing. Consequently, its ability to support the floor, table, and mug is not a derived power, but an innate quality. You might say the earth is an unsupported supporter.
This is the basic pattern all hierarchical chains follow. They start with a foundational or “prime” member with an innate ability, who is followed by a series of “secondary” members who derive their abilities from the prime member. Other examples include trains and sticks used for poking.
Trains are made from cars and an engine. In this system, the engine is the prime member who can pull without being pulled. The cars are the secondary members who derive their ability to pull from being pulled.
Here is the classic stick example given by Aquinas.
“As the staff moves only because it is put in motion by the hand.”
To suggest there could be an infinite series of active secondary members with no prime or first member would lead to absurdities. For example, it would be like saying there could be an infinite line of train cars moving down the track with no engine. Or a paintbrush with an infinitely long handle brushing a canvas with no painter. Consequently, hierarchical chains are not subject to the same problems linear chains face.
Conclusion of The First Way
Many forms of change happen through hierarchical chains. Consequently, if we follow the trail of changed changers all the way down, we will find a foundational prime changer. An unchanged changer, from whom all the secondary members actively derive their ability to cause change. Aquinas concludes his argument with the statement:
“This everyone understands to be God.”
A Summary of the First Way
Now that we’ve parsed through the Summa Theologiae and its metaphysics, lets formulate everything into an informal argument.
Because motion (change) is the actualization of potential nothing can be the cause of its own change. The prosses of change, therefore, creates causal chains, both of linear and hierarchical natures. As we’ve seen, in hierarchical chains, the secondary members derive their ability to actualize potential from the prime member. Consequently, if we see potential being actualized by secondary members of a hierarchal chain we must posit the existence of a prime member. That is to say, there must be an unchanged changer or an unactualized actualizer. We could even call it an “unmoved mover.” Whatever we say, this prime member is the active foundation of the hierarchical change we see in the world, and what “everyone understands to be God”
The Argument from Motion by Premise
Here is an informal bullet point presentation of the argument
- Motion (change) exists
- Change is the actualization of potential
- Because change is the actualization of potential, nothing can change itself
- Therefore, the process of change can create hierarchical causal chains
- Hierarchical causal chains must have a prime member
- Therefore, there is an unchanged changer who gives the change changers their ability to cause change.
- This all people call God
Ramification of Aquinas’ First Way
Aquinas’ First Way suggests that God is more than just the one-time creator of the universe. He is its active sustainer, the foundation which gave life to the past and sustains life now. The argument also suggest that God is, as Aquinas put it, “Actus Purus” or pure actuality. That is to say he is not subject to change.
I’m personally very partial to the mover argument. It may in fact be my favorite of the five ways. Once the necessary metaphysics have been laid out, I find it to be explanatory and intuitive. Moreover, it consistently turns my mind to scripture. The conclusion Aquinas draws about God’s active role in the world is, in many ways, reminiscent of Paul’s writing, especially his speech at the Areopagus.
“God did this so that they would seek him and perhaps reach out for him and find him, though he is not far from any one of us. ‘For in him we live and move and have our being.’” (Acts 17:27-28)
Sources on Aquinas’ First Way
- “The Meaning of “Motus” in Aquinas’ First Way,” GONÇALO DO VALE SÁ DA COSTA
- “Aquinas: a beginner’s guide,” by Feser, Edward
- “Five Proofs of the Existence of God,” by Feser, Edward
- “Summa Theologiae, Question 2, Article 3,” Thomas Aquinas (The First Way)
- “Summa Theologiae, Question 46, Article 2” Thomas Aquinas (We cannot philosophically prove the world had a beginning.)
- Summa Contra Gentiles, Chapter 13, Thomas Aquinas
