Asher Sisneros

Saint Thomas Aquinas developed numerous theological works during his life and advanced scholasticism, an academic movement to synthesize worldly reasoning and biblical faith. Today, he is most remembered for his Quinque Viae (the five ways). In his book Summa Cuma Gentiles, Aquinas made five logical proofs for the existence of God. The unmoved mover argument was one of the logical proofs, but it is largely misunderstood. Despite the philosophical nuance in the argument – what can be perceived as gibberish by some people – it makes sense when dissected. 

The potency-act distinction that Aristotle developed is the first step to understanding the unmoved mover argument. In modern English, it could be rephrased as the potentiality-actuality distinction. Potency is understood as unrealized potential, whereas act is understood as realized potential. People who have gone through physics will understand the difference between realized energy and potential energy. Things can possess the potential to do something, however, the object needs external stimulation to transform that potential into actuality. In the Western civilization course on the Ron Paul Curriculum, historian Tom Woods uses the analogy of cold food to explain this relatively basic Aristotelian concept. As the analogy goes, a cold bowl of food possesses the potency to become hot. However, it cannot become hot by itself. The bowl of food requires the external stimulation of a stove, microwave, etc., to become hot. Before being heated by the stove, the food had the potency (potentiality) to be hot. After being heated by the stove, the food had the act (actuality) of being hot. The distinction between potency and act can be seen everywhere in life. 

If a man has a son, that son can have another son. The first son needed his father to exist. However, from there, the first son can have another son without the continued existence of his father. His father’s death does not restrict his ability to have offspring. More offspring can come, and the series can continue without its original member. In other words, the series acts independently from its first member. Aquinas calls this phenomenon an accidentally ordered causal series, but the term “independent series” will suffice in conveying its meaning.  

Aquinas contrasts accidentally ordered causal series with essentially ordered causal series, which depend on the continued existence of the first member. Aquinas uses an analogy between a stick and a rock to demonstrate the position an original member has in an essentially ordered series. As the analogy goes, a man walked down a road holding a stick. There was a rock on the road, and the man used his stick to push the rock. The rock continued to move forward. However, if the stick disappeared, the rock stopped moving, and the essentially ordered series ended. The essentially ordered series directly contrasts with the accidentally ordered series because, unlike its accidental counterpart, the series cannot continue without its first member. In terms of the stick and rock analogy used by Aquinas, he then points out how the stick was not the first member. For the stick to move, it needed the person’s hand. However, a hand cannot move independently from the body. For the hand to move, it needed an arm, nerves, and a brain. The series can continue to the microscopic level in search of the original member, but the original member seems to be elusive, as no matter how closely one looks, there is always something preceding the apparent original members. In other words, the search for an original member is an eternal process. 

It is now relevant to revisit Aristotle’s potency-act distinction. Aristotle defined motion as the transition from potency to act. One of the laws of nature that Aristotle discovered was that nothing could cause itself to have motion. All of creation needs an external stimulator to turn its potential into actuality. Take the food on the stove example that was previously used. The food was capable of becoming hot, but it could not make itself hot. The food could only capitalize on its potency through the external stimulation of the stove. However, if nothing can cause itself to have motion (turn its potency into act) then the essentially ordered causal series could not have an original member. But the series cannot exist without its original member, as already illustrated. What is the point of the matter? Logic and reasoning prove that no essentially ordered causal series can exist. 

The prior conclusion seems absurd because even a relatively sensible mind can blatantly see that essentially ordered causal series do exist. The question is how they can exist without an original member being identified. After all, an essentially ordered causal series without an original member is an oxymoron. The very concept is self-contradictory. Aquinas agreed but rejected that there was no original member. There was an original member and that was God. God was the original member. As stated before, nothing on Earth can cause its own motion. Nothing on Earth can actualize its own potential. The potential can only be realized by an external force. However, God is the one exception. He must have been capable of actualizing his own potency because He is God. If God had a potency that needed external stimulation to be actualized, He would not be all-powerful. The all-powerful Jehovah is the one exception to Aristotle’s rule that nothing can cause its own motion. He can cause His own motion. He must cause His own motion and all motion in the world, for that matter. With that understanding, Aquinas argues that God is the answer for every essentially ordered causal series, concluding his logical unmoved mover argument, proving God’s existence. 

The argument for the unmoved mover was only one of Aquinas’ five arguments. The others are harder to understand. Despite the philosophical arguments people can make both for and against the existence of God, the best and most theologically correct argument is that God exists because He said so. Dr. Greg Bahnsen articulated in his debate with R.C. Sproul that philosophers can only arrive at the conclusion that God exists from a logical argument if they start with the presumption of God’s existence. It should be noted that Bahnsen was a huge advocate of Christianity and arguably one of the most powerful preachers in American history. However, he believed that logical cases for God’s existence were secondary to faith, and someone would only arrive at the logical conclusion for God’s existence if they already believed God existed. To put it simply, a smarter philosopher can always create a more logically sound argument for why God cannot exist, and the only true evidence for God’s existence is His divine Word.