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The Existence of God: My Thoughts On Thomas Aquinas' Argument From Motion

Updated on March 13, 2012
St. Thomas Aquinas
St. Thomas Aquinas | Source

Many philosophers throughout history have tried to prove the existence of God, but it can be argued that none of them have come as close to succeeding as Thomas Aquinas, a thirteenth century Italian Dominican Catholic Priest. While Aquinas’ may have one of the best arguments for the existence of God, I believe the argument is still flawed significantly.

Aquinas’ cosmological argument for the existence of God is divided into five ways, but this essay will focus only on the first way, also known as “The Argument from Motion”. The first premise in the argument is that motion exists in the natural world. Before one can fully understand Aquinas’ argument, “motion” must be defined. To Aquinas, the term “motion” refers to any type of change. More specifically, “motion” is the act of something changing from potentiality to actuality. For example, if a pencil has the potential to fall off of the edge of a desk, and then it actually falls off of that desk, it has exhibited motion. While the example of a falling pencil is very easy to comprehend, it is important to realize that motion does not always have to be a physical motion. Something intangible, such as an individual’s thought process, can also be considered motion. If an individual has the potential to think about squirrels, and then they actually begin thinking about squirrels, they have exhibited motion. Aquinas also makes clear that something cannot exhibit potentiality and actuality simultaneously in the same respect. For example, a pencil that is actually in the air cannot simultaneously be actually on the ground, but a pencil that is actually in air can simultaneously be potentially on the ground

The next few premises in Aquinas’ argument say that motion in the natural world must be triggered by a mover, who must also already be in motion. For example, an individual cannot move a ball without first moving himself in some way. Whether they throw the ball with their hands, kick the ball with their feet, or build a contraption which remotely moves the ball for them, all of these methods require some previous movement from the mover to initiate the new motion in the ball. Given these premises, it is impossible for something in the natural world to move itself.

These premises, or rules, that exist in the natural world set up a chain a motion. Object “Z” must have been moved by object “Y”, and object “Y” must have been moved by object “X”, and so on and so forth. According to Aquinas, this chain of motion cannot possibly go infinitely in reverse. In other words, it must have a beginning. There must be a first initial mover that started the entire chain of motion. Following the premises of Aquinas’ argument, this presents a problem. How can an initial mover exist within the natural world and trigger motion, if there was nothing in prior existence to set him in motion? This is Aquinas’ point exactly, which leads to his conclusion. Aquinas states that there must be an UNMOVED mover which exists OUTSIDE of the natural world and does not have to follow the rules of motion.


At first glance, this seems to be a very strong argument, but there are undoubtedly objections to be raised. One objection that should be raised is that even if Aquinas’ argument did prove the existence of God, who is supposedly necessary for the existence of this chain of motion and the universe itself, his argument could also be said to prove the existence of multiple gods. Seeing as how Aquinas’ was a Catholic priest, his objective was obviously to prove the existence of, not only A God, but to prove the existence of THEE God. In other words, he wished to prove the existence of the one and only all-powerful, all-knowing, and all-benevolent God. For obvious reasons, of this type of god, there can only be one. But seemingly, Aquinas fails to reflect on that point and his argument can easily be taken as an argument for multiple gods or supreme entities. In this sense, Aquinas’ argument fails.

Some may argue against this claim by using Occam’s razor, which states that simpler explanations are better than more complex ones, assuming that all other things are equal. Occam’s razor can be applied to Aquinas’ conclusion by stating that you should not multiply entities beyond what is necessary for explanation. The argument would go as follows: Can the universe and this chain of motion exist as a result of the actions of only a single supreme being? Yes. Therefore, you should not assume that there is more than one supreme being or unnecessarily multiply the number of supreme beings, because you are simply complicating the argument more than you have to. Well, using this mindset, Occam’s razor can be used make the claim that this chain of motion exists without a single supreme being at all. Just as one supreme being would be more simple than two, zero supreme beings would be more simple than one. Of course, if one were following all of Aquinas’ premises diligently, at least one supreme being is necessary by the time they reach the conclusion…but who’s to say that the premises themselves are not flawed?

If motion and the universe exist naturally, the concepts of potentiality and actuality may be irrelevant when dealing with natural phenomenon. Natural occurrences may not need to have a beginning, middle, and an end. The ideas of a beginning, middle, and an end can be viewed as concepts constructed by mankind. Furthermore, the scheme of putting everything on a timeline may be a result of the natural human thought process, and it may not necessarily be accurate.

With this in mind, is seems that Aquinas simply assumes that the chain of motion must have a beginning. Motion clearly exists in the natural world, but by assuming that it has a clear-cut beginning triggered by a single event, you must also be implying that it will have an end. The real question is: Can the chain of motion ever be stopped? Theoretically, in order to stop the chain of motion, one must perform a single action that is devastating enough to erase the entire universe. On top of that, when the universe blinks out of existence, it mustn’t have even one repercussion. If motion cannot be stopped, then it can conceivably exist infinitely in both directions. Meaning that this “chain” of motion does not need to have a beginning or an end, it has simply always existed. Returning to Occam’s razor once more, it is simpler to assume that motion has always existed than to assume that it is a new phenomenon that came from a supreme being.

Also, when looking at Aquinas’ argument, one must ask to what extent motion, in and of itself, is necessary. Is it possible that the universe could have existed without motion? From tiny atoms vibrating against one another to giant planets orbiting around in space, they all meet Aquinas’ criteria of motion, so it seems that motion is absolutely necessary for anything to exist. In assuming that this chain of motion has a beginning, Aquinas seems to also be assuming that the universe has a beginning which coincides with the start of this motion. It is almost as if he is using his religious belief of creation to prove the existence of God, which is essentially begging the question.

Yet another problem with Aquinas’ argument is that when placed under close scrutiny it seems to be awfully circular. Aquinas states that nothing in the natural world can move itself. A mover, who is also moving, must cause the motion. More specifically, the mover must reduce an object from potentiality to actuality, thus causing “motion”, or change. This means that potentiality can only be moved by actuality. For example, the pencil that rolled off of the desk was only reduced from potentiality to actuality because another force actuallymoved it. Once again, potentiality is moved by actuality. If God is an exception to this rule, an unmoved mover that is already all that he could be, then he couldn’t have any potential. If God consists of pure actuality then he wouldn’t be able to do anything. If God can’t even move himself, than how can he move other things? If God were to have the potential to move something and then he actually moved it, God himself would be demonstrating motion and he is no longer an exception to the premises’ of the argument. The concept of an unmoved mover seems to tear itself apart in the circularity of the argument.

As made apparent, there are many issues with Aquinas’ argument that need to be addressed. Overall, Aquinas’ argument from motion is constructed quite well, but I believe he fails to accomplish his goal of proving the existence of his ideal Catholic God.


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    • WretchedRapture profile imageAUTHOR


      5 years ago from California, USA

      1) I presented Aquinas' argument for the existence of an unmoved mover (i.e. God). I then objected that this argument does not necessarily lead to the conclusion of a single God, so it seems that I did refute the argument that was presented.

      2) I was not attempting to disprove any and all gods. I was merely presenting possible objections to Aquinas' argument. As a matter of fact, I clearly acknowledged that his argument could lead to the conclusion that there are multiple divine entities.

      3) First, your analogy is not constructed as a valid argument. If you claim that every baby comes from a mother and that a baby is born, the only valid conclusion from those two premises is that the baby has a mother. Nothing else can be said. Second, your analogy is disanalogous is more ways than one. Most significantly, childbirth is a completely natural phenomenon that modern science is rather familiar with. This is in no way analogous to an argument about the initiation of a chain of causation by an unmoved mover that exists outside of the natural world.

      4) I agree! Readers beware! Don't automatically believe what I say or what anyone says. Think critically and be diligent. I'm not here to convince you to take any particular standpoint; I am simply here to encourage intellectual thought.

    • profile image


      5 years ago

      Just wanted to shine light on what you formulated as an objection. I believe you said the following, "Even if Aquinas’ argument did prove the existence of God ... his argument could also be said to prove the existence of multiple gods." 1) You refuted a different argument than the one presented 2) You never point at a flaw that disproves ANY gods. 3) Here's an analogy of your argument: Every baby comes from a mother. We have a baby. Therefor the mother never existed because the argument doesn't disprove the existence of multiple mothers. (makes no sense). These counter-arguments tend to always dodge around the main argument because of an inability to provide an answer. Readers beware!

    • penofone profile image

      Anish Patel 

      8 years ago

      what does it mean to say tomorrow never dies?

      Thomas Aquinas is the world's worst painter in disguise.

      An explorer of magnificent mankinds gentleman works.

    • Seeker7 profile image

      Helen Murphy Howell 

      8 years ago from Fife, Scotland

      Fascinating hub and I enjoyed Thomas's argument as well as your own. I think the interesting aspect about most arguments for/against a supreme being is that depending on what belief mode you belong to, you may lean towards accepting some arguments but against others. It may well be that we are wrong and right at the same time - but I guess this is making it too complicated for many if taking it from Occam's razor point of view.

      My own belief for what it's worth, is that I do believe that there is a source of higher consciousness. That ultimately everything is mind and energy and we certainly don't need religion to tap into it, although I respect the fact that people find comfort in an organised belief of sorts.

      This was a very interesting and absorbing hub. Voted up!


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