In this blog post, we will compare how Augustine and Aquinas proved the existence of God based on their different historical backgrounds and philosophical perspectives.

 

Aurelius Augustine’s Proof of God’s Existence

Augustine’s view, which can be summarized as “I believe in order to understand,” aimed to make theology the ultimate goal of all scholarship. Born in North Africa, he went through numerous pagan religions and religious debates before becoming a Christian bishop. In the process, he was able to combine Neoplatonism with his faith and establish a concept that prioritized faith without separating it from reason.
There are two main proofs of the existence of God in Augustine’s work, the latter serving to support the former, which is the core of his argument. This can be said to stem from his view that faith takes precedence over reason, as mentioned earlier.
Augustine’s first proof of the existence of God is “proof from eternal truth and reason.” This means that the existence of God can be found within humans rather than outside, and is based on the premises that “there is a necessary and unchanging truth” and “the human mind grasps this necessary and unchanging truth.”
Augustine develops his proof of the existence of God based on these two premises. First, according to his argument, “necessary and unchanging” truth, by its very nature, must not be influenced by anything. And according to the second premise, since the human mind has the ability to “grasp” this truth, the human mind must accept this truth as it is. This is because truth is unchanging, and the human mind has the ability to grasp truth, so the conclusion that can be drawn is that the human mind must accept truth as it is. Therefore, truth is a higher concept that cannot be changed by the human mind, and the human mind cannot alter truth. Rather, the human mind can only be altered by truth.
Then, how can the human mind realize the truth? Here, Augustine proposed the “illumination theory.” The “illumination theory” means that God illuminates the truth so that humans can see it. Augustine believed that God reveals the truth to humans, and humans can understand the truth more clearly by using reason as a tool.
Thus, Augustine’s proof of the existence of God does not prove God as an object of the senses. Rather, it may be more appropriate to say that God cannot be proven by the senses. In any case, Augustine saw God as an existence that transcends time and space and is the source of truth itself. And God, the source of this inevitable and unchanging truth, is a concept that exists prior to the human mind, thought, and reason.
Now let’s look at Augustine’s second proof of the existence of God. This is called “proof from creatures and general agreement.” In his book “The City of God,” Augustine argued that “creatures,” represented by the movement, order, change, and arrangement of the world and everything in it, were created by God. His argument is that the natural order of the world is a great work that cannot be created by humans, and that only God can create such a result. Therefore, Augustine argued that humans can feel the breath of God here. This is a “cosmological” and “natural theological” argument.
However, in his second proof of the existence of God, the part related to “creation” can be understood as serving to once again emphasize the inevitability of God’s existence to Christians who already believe in God, rather than as a logical proof.
Furthermore, his second proof of the existence of God, based on “general consent,” is the claim that rational creatures such as humans cannot help but feel the existence of God when they use their reason. He argues that, in this sense, humanity already acknowledges the existence of God. Some people worship various gods, but the God of which Augustine speaks is the God among gods.
However, this proof is also merely an assertion that the existence of God is self-evident, assuming that the world is the result of God’s actions, and therefore does not prove the existence of God itself. Thus, Augustine’s proof of the existence of God is not an academic or rational proof of the existence of God, but merely serves as an aid to remind us of the existence of God. His proof of the existence of God is fundamentally religious.

 

Thomas Aquinas’ proof of the existence of God

Unlike Augustine, Aquinas sought first to explore whether the truth that can be grasped by the human mind and the existence of God through it are self-evident. This is the opposite of Augustine’s view in “Proof from Eternal Truth and Reason” that the existence of God is naturally understood by the human mind. This is because if the existence of God is self-evident, there is no need to prove it. However, according to Aquinas, humans cannot intuitively perceive the existence of God, so his existence must be proven.
Aquinas presented two ideas to prove the existence of God. The first is proof through “cause,” and the second is proof through “effect.” However, Aquinas was a professor of theology, so his belief in the existence of God was already firm. Therefore, for him, God was already an absolute and unchanging concept. This makes the first method of proof through “cause” unusable. This is because God’s “absolute immutability” cannot have a “cause.” For example, if the moon is the cause of the Earth’s axis of rotation, then the Earth’s axis of rotation cannot be an “absolute immutable” entity. This is because if the Earth’s axis of rotation was tilted by the moon, then it would already have changed. If the Earth’s axis of rotation were an “absolutely unchangeable” element, it would remain unchanged even if the sun were next to the Earth. This is the relationship between “cause” and “absolute immutability.” Therefore, due to the nature of God, which is already assumed to be “absolutely unchangeable,” it is impossible to prove the existence of God through “cause.”
In the end, Aquinas attempts to prove the existence of God through “results.” In this process, it is important to consider that Aquinas was greatly influenced by Aristotle. Aquinas borrowed Aristotle’s a posteriori and empiricist ideas and argued that the existence of God is not a priori, known by God himself, but a posteriori, known by humans. Therefore, Aquinas sought to prove the existence of God through the arrangement and order of the sensory world.
Aquinas argued that the existence of God could be proven in five ways through “results.” In Augustine’s proof of the existence of God, the latter was developed in a way that complemented the former, but in Aquinas’ proof of the existence of God, each method proves the existence of God independently.
The first method starts from the sensory facts about the motion that exists in the universe. We can see that all things in the world move. And we know that motion cannot move itself and that each motion has a cause. In other words, just as I was moved by you, you are moved by that person. And that person is moved by another person, and that person is moved by yet another person. If we continue this line of reasoning, we will never be able to identify the origin. Here, through rational reasoning, we come to understand that the first cause of motion is motion itself. This first cause is the primary mover, or God. Therefore, God exists.
The second method is to infer the first cause from cause and effect. This is not fundamentally different from the first method. Aquinas argues that all results in the universe have an “agent.” In other words, everything in the world has a cause for its birth, and this cause must have a highest “agent.” Otherwise, we would have to continue searching for causes infinitely upward. Therefore, the highest “agent” must be God. Therefore, God exists.
The third way is to infer necessary existence from contingent existence. All beings in nature are born and die. This is an endless cycle. And all of them are contingent. Aquinas says that these contingent beings are created by a necessary being. This is because without a necessary being, there cannot be beings in nature that are born and die contingently. Therefore, if the process of beings in nature being born and dying accidentally continues, then beings that exist necessarily must also continue to exist. Aquinas believes that these beings that exist necessarily are God.
The fourth way concerns the concepts of value and perfection in things. This is reminiscent of Plato’s theory of forms. Even if things are identical in concept, they exist with differences in degree. For example, there may be a woman who is considered the most beautiful in a local community, but there may be a woman who is more beautiful when viewed on a national level. In that case, the nationally recognized beauty can be considered more beautiful than the locally recognized beauty. In this way, all things in the universe exist with “various degrees of perfection.” Then, we can assume that there is something that has the highest level of perfection. Aquinas saw God as having the highest level of perfection without any limitations.
The fifth way relates to the purpose of all beings in the universe. This is related to the order of the world. All beings in the universe move toward their own appropriate purposes. Even things without intelligence exist for such purposes. Aquinas asks how this can be explained unless it is planned. Therefore, he argues that a highly intelligent being can be naturally inferred, and that this supreme intelligence can be seen as God.
As a professor of theology, Aquinas believed that everything in the world of experience basically depends on God. Therefore, his proof of God’s existence starts from the experience of things in the world and moves toward a transcendent being. For this reason, although he was an empiricist, he did not become a modern empiricist.

 

Comparison of Augustine and Aquinas’ Proofs of God’s Existence

Augustine and Aquinas existed about 1,000 years apart, but they shared the same worldview of Christianity. In Christianity, God was the answer to the beginning of the world, the cause of the process, and the implication of the end. Under Christianity, Augustine and Aquinas pursued the same goal of “connecting God and humans.” Therefore, they were no exception to the proof of God’s existence that all Christians had attempted.
However, a thousand years is not a short period of time, and Augustine and Aquinas differed in their activities, ideological backgrounds, and the relationship between faith and reason. Augustine was greatly influenced by Plato’s philosophy, while Aquinas accepted many of Aristotle’s ideas. Furthermore, Augustine settled on Christianity through various journeys, while Aquinas spent his entire life learning and studying Christianity and living as a professor of theology. Due to these differences, even though they were both great Christians, there were many differences in their ideas about God and, furthermore, in their views on the proof of God’s existence.
The most striking difference between the two proofs of God’s existence is their approach. Augustine’s proof of God’s existence was a priori and ontological, emphasizing faith and human reason. On the other hand, Aquinas’ proof of God’s existence was a posteriori and cosmological, emphasizing human experience and empirical reality. The change in the method of proving the existence of God over the course of about 1,000 years means that the focus of the proof shifted from faith to reason. It can also be seen that the starting point for proving the existence of God changed from reasoning to experience.

 

Conclusion

I believe that “proof” is based on rationality. However, “belief” transcends rationality. Therefore, from this perspective, Augustine and Aquinas’ proofs of the existence of God can be seen as a means of belief rather than “proof” in the strict sense. Therefore, when discussing their proofs of the existence of God, we must take the perspective of medieval people.
Both Augustine and Aquinas truly believed in God. Before proving the existence of God, they must have truly wanted God to exist. Nevertheless, the reason why I think their proofs of the existence of God are meaningful is because there was a slight modern change between them.
Augustine proved the existence of God based on the idea that necessary and unchanging truths take precedence over human reason, and that there is harmony in the world that humans cannot achieve. For him, God’s existence was a given. If one denied the existence of God, he would have asked, “Then where did all these truths and the harmony of the world come from?”
However, there is room for doubt in his proof of God’s existence. The “illumination theory” he proposed is the source of that doubt. In my opinion, the “illumination theory” is an irrational hypothesis. The idea that God only reveals truths that humans can barely comprehend through reason is illogical. This makes it difficult for me to accept Augustine’s proof of God’s existence.
On the other hand, Aquinas seems to have advanced one step further than Augustine. This is because he presented a much more logical proof than Augustine. He built the foundation of his proof on actual human experience, presented God as the first cause of almost all motion, and argued that God is the first mover. Although his conclusions and proofs were greatly influenced by Augustine, his efforts to find clues in human experience are remarkable. However, he did not become a modern man either.
It is now 2019, and the time gap between Augustine and Aquinas is as long as the time gap between Aquinas and the present. How would the existence of God be proven from a modern perspective? There is an interesting idea here. Elon Musk, CEO of SpaceX, and several scientists argue that this world may be a virtual world. Elon Musk, in particular, says that this world is millions of times more likely to be a virtual world than a real world.
This idea stems from the fact that the graphics we create in computer games are similar to the real world. In realistic game worlds, everything outside the player’s field of vision is frozen to reduce the load on the computer. However, when the player turns their gaze, everything appears to move as it did before. This is very similar to the phenomenon of quantum entanglement in our world. This similarity led to the idea that our world may be virtual.
Considering this point, I wonder if the “God” claimed by medieval theologians is not a programmer or engineer beyond this world who created this world. Of course, this may be a ridiculous claim, but how is this idea essentially different from what they call “God”? They are both the same in that they cannot be verified. Rather, the “virtual world hypothesis” may be verified more quickly.
As someone who has never had a religion and who has an aversion to religion due to my personal upbringing, the reason why I find it difficult to accept Western medieval philosophy is precisely because of the medieval worldview based on “God.” Therefore, the most important thing for me was to find out whether the “God” that medieval people talked about really existed. I needed to know if the “God” they talked about really existed and how they came to believe in “God.” So I read the proofs of the existence of God by Augustine and Thomas Aquinas, who are revered as saints among Christians.
As a modern person, I found Augustine and Aquinas’ proofs of the existence of God very disappointing. It seemed blind to me. Some people say, “We cannot know that God exists, but we also cannot know that God does not exist.” In that case, we should neither reject it as if it does not exist nor believe in it as if it does exist. However, we either believe in it or reject it. In my opinion, “God” is not a concept that should be treated in that way. I believe that we should leave it as it is without attaching any great meaning to it, and that my life should be mine alone.