To answer the question concerning God’s existence, St. Thomas Aquinas presented five ways or proofs in his most notable work, the Summa Theologica. This is also called “Aquinas’ Five Proofs for God’s Existence”. These five arguments draw proof or evidence from man’s experience with the world, which are noticeably influenced by Aristotle and his concept of the four causes.
The first argument that Aquinas formulated is the argument from motion. After observing objects in motion, Aquinas was convinced that whatever is currently in motion were once at rest but had changed states when it was moved by something else. This mover was something once at rest as well but was also moved by something else. This line of thought would go on and on until it forms an almost infinite series of concurrent events where the objects are both movers and moved. But if this series of events needed something to begin the movement, then, it is logical to assume that at the very beginning of this infinite series is the first mover, which starts the movement. Aquinas describes this first mover as the “unmoved mover,” a label which is quite similar to Aristotle’s “prime mover.” As we can see, both see this mover as one that is not caused or moved by anything other than itself. And for Aquinas, this is God.
The second argument is the argument from causation, which builds upon Aristotle’s concept of the efficient cause. The main idea here is that every object, action, or event, according to Aristotle, has an efficient cause or an entity or event responsible for its creation or change. Just like how a baby finds their efficient cause in their parents and their parents in their own parents and so on and so forth, Aquinas uses these examples of dependent relationships to show that every person or object in the world depends on a creator (efficient cause) and that this creator also has its own creator, and this new creator also has its own efficient cause. This cycle, much like the argument from motion, can go on infinitely but, according to Aquinas, it should not be so since in the first place the series would not have begun.
It is then logical to assume that at the very beginning, there is the existence of a “First Maker” or an “Uncaused Cause,” which, as the name suggests, is the efficient cause that is not caused by others or anything but itself. This “Uncaused Cause” is, of course, attributed by Aquinas to the Christian God.
The third argument is the argument from contingency which necessitates the distinction between “necessary” and “possible” beings. “Possible” beings, simply put, are beings that can be created and corrupted or are beings that can exist and not exist. An example of a possible being is man. Man is a possible being because we have the potential to exist (birth) and the same potential to not exist (death). Plants, animals, and structures are among some of the other beings included in this category.
With this in mind, it is then reasonable to think that since most beings in the world are possible beings, then there must have been a time that they had not existed at all, which means that nothing ever existed. And if there truly was a time of pure non-existence, then nothing could currently exist because nothingness can only yield nothingness. The only way that our existence at this very moment could be explained, for Aquinas, is if there was a being that already exists despite the nothingness of the possible beings.
This being is called a necessary being. Necessary beings, on the other hand, are beings that necessarily exist or are beings that cannot be nonexistent. For Aquinas, there must be at least one necessary being to exist at the very beginning for the rest of the beings to be able to exist. This being is, of course, God.
The fourth argument is the argument from degrees of perfection. This argument makes use of man’s knowledge of perfection and his tendency to judge or evaluate whether an object or person is more or less perfect. This action of judging something to be more or less perfect means that there is a standard that is used for the said evaluation. But how could man ever have such standards unless there is a being that is all-perfect to compare it to? Aquinas affirms the existence of such a perfect being and says that if any other being would be compared or evaluated against such perfection, they would always be judged as less perfect. He calls this all-perfect being God.
The fifth and last argument in St. Thomas Aquinas’s five proofs for God’s existence is the argument from final causes or design. Some scholars would also call this as the teleological argument. Aquinas once again drew on the notions of causality as presented by Aristotle to justify this argument. The “final cause,” as described by Aristotle, is the fourth cause and is one that refers to “the end, that for the sake of which a thing is done.” Some scholars would describe it, rather simply, as the cause that refers to the purpose of which a specific object or entity has been created to fulfill.
Humans and most natural beings in the world have been “designed” to have a purpose and we behave or act according to that purpose. For instance, the bird’s wings behave in accordance with its design which allows it to fly. Humans talk using their mouths because this is in accordance with their body’s design which allows them to utilize air and various muscles in their body to create sounds.
For Aquinas, if there is some sort of design that is set in our world, then there must be a designer. This designer cannot possibly just be humans or other natural beings themselves as he describes man as imperfect and not intelligent enough to set such a grand design. Some of the natural beings, Aquinas tells us, are not even capable enough to know what their end is. The design of the world, therefore, must have been set by a being that is vastly more intelligent than humans and knowledgeable enough to guide them towards their end. This, of course, is God.
Aquinas’ five proofs for God’s existence, during, of course, Aquinas’ time, were found to be compelling enough and soon grew to be influential in religious discourses. For some religious denominations, these arguments still remain significant in defense of the Faith up until the 21st century, where most of them have been incorporated into doctrines and statements. But as groundbreaking as St. Thomas Aquinas’ arguments were and are, there is still room for critique.
St. Thomas Aquinas’ Five Proofs for God’s Existence: A Brief Critique
The main criticism that one can immediately infer from these arguments is the fact that a majority of them remain as assumptions. Though St. Thomas Aquinas did invoke observations from man’s experience with natural phenomena as well as logic to prove his point, there is no concrete way of knowing whether these events do happen in the manner that the theologian-philosopher has described it. In the case of the first proof, there is no concrete explanation as to whether every single movement in this world can be traced back to one single cause nor is there enough proof to determine that an event or an object is necessarily moved or affected by the simultaneous movement of another object or entity. In the case of the fifth argument, it is simply too illogical to immediately assume that just because the bird’s wings are aerodynamic or that humans are capable of speech it automatically suggests the presence of both a grand design and of a grand intelligent mind when, in the same paradigm, the notion of spontaneity and adaption exists.
Interestingly, he did speak of this same point in the Summa Theologica as Objection #2 and his response to this response is as follows: “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. Therefore, there is no need to suppose God’s existence.” Though the reduction does serve the purpose of trying the establish concrete principles where he can root his arguments on, the idea that natural and voluntary things can be reduced into just nature and reason is still an assumption by itself.
It is tempting to think that there is indeed such a connection between the beings in the world, but as far as human knowledge is concerned, these conclusions are merely a product of inference and are not concretely proven.
This then leads to the second point of my criticism. Should a person not be satisfied with the assumptions forwarded by St. Thomas Aquinas and decides to do away with them, then Aquinas’s five proofs will become irrelevant. The arguments would not be able to stand once you remove the assumptions, such as the assumption that the one thing is caused by another or that if the notion of a grand design necessitates the existence of a grand designer, as these are the logical links between his premises. To continue to believe in these arguments without said assumptions, one must somehow either see it in a dogmatic light or ignore contrary logical proof.
Despite these criticisms, St. Thomas Aquinas’ philosophy has withstood time and continues to play a significant role in the development of both the Church and modern theology. By incorporating human experience, logic, and Aristotle in his attempt of proving His existence, he not only formulated five succinct and insightful arguments but he had also brought theology further than what his time had expected.