In the Summa Theologica, Thomas Aquinas uses the philosophical method to theology and addresses the question of whether God’s existence can be demonstrated as well as the question of whether we can know God completely. For Aquinas, the question of proving the existence of God is always bound up with the question of how, and to what extent, we can know God at all. St. Thomas Aquinas believes that yes, God’s existence can be demonstrated but that no we cannot know God completely. St. Thomas believes that God’s existence can in fact be demonstrated and that it can be done so in two ways.
“One is through the cause, and is called “a priori”, and this is to argue from what is prior absolutely. The other is through the effect, and is called a demonstration “a posteriori”; this is to argue from what is prior relatively only to us” (Aquinas 15). In other words, to demonstrate that God exists is done in a cause and effect manner. For the question as to whether or not we can know God completely, St. Thomas answers that no, we cannot know God completely. According to St. Thomas one can know the essence of God, but to completely know God would be impossible.
The differences between these two questions are that the question as to whether or not God’s existence can be demonstrated addresses God’s existence whereas the question on whether or not we can know God completely does not question God’s existence, just the amount of knowledge one can have on God. St. Thomas Aquinas proposed five proofs in which humans can use natural reason to prove the existence of God through extrinsic evidence. Through the use of natural reason we can logically conclude in the existence of God. Yet strictly speaking, God’s existence cannot be definitively proven through laboratory tests and experimental science.
Experimental science and intrinsic evidence cannot definitively prove historical events, and yet by reason we know they have occurred. And surely were science falters and extrinsic evidence fail, reason and intrinsic evidence can prove the spiritual which cannot be measured by material sciences. The first way begins observing the movement all over the world and ends up asserting the existence of God as Immovable Motor; the second way observes the existence of causes in the world and concludes the existence of an ultimate Cause.
The Third Way emphasizes one of the most important features of all finite objects, the radical insufficiency of their being, their contingency: the beings of the world exist but they could equally not exist, they have specific features which they could equally not have. If they do exist but could not then we can think of a time in which they didn’t; and if they were the only beings of the world, then nothing would have existed. As this is obviously not the case, then we should conclude that along with those contingent beings there must exist a necessary being, a being which has its origin in itself instead of in another being, and that being is God.
St. Thomas states, “Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God” (Aquinas 16). In the next paragraph Aquinas says, “Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God” (Aquinas 17). Clearly, St. Thomas Aquinas is making his point that God is the source of everything. Since God is the cause we see the effects. The effects had to have come from a cause, which is God, and therefore God must exist. St.
Thomas Aquinas starts off his discussion on whether or not one can know God by discussing the senses and their role in how humans know things. “Our natural knowledge begins from sense. Hence our natural knowledge can go as far as it can be led by sensible things” (Aquinas 86). St. Thomas states, “It is impossible for God to be seen by the sense of sight, or by any other sense, or faculty of the sensitive power” (Aquinas 74). What this passage is saying is that we cannot see God and because we cannot see God, it is impossible for us to know him.
As humans we can know human beings because we can see them physically, however we cannot do this with God. Aquinas says, “when any created intellect sees the essence of God, the essence of God itself becomes the intelligible form on the intellect” (Aquinas 77) and this means that for what we can see with our human eyes that is what is going to portray to us what God is like. This means that we cannot fully know God and that we can only know of him or about him. God is an infinite being and we are finite beings which mean that we can only contain so much knowledge within us.
Due to the fact that we are limited with our knowledge, it is impossible for humans to ever be able to fully encompass and know God because there is too much to know about Him. God is infinite, he has always been and humans cannot understand this because there is nothing else that we know of that has forever been and always will be. For these reasons, St. Aquinas believes that humans will never be able to fully know God like how they know one another. One can also compare these two questions not just by what they are based on (existence and knowledge) but also by looking at the differences between faith and knowledge.
As stated previously when discussing whether or not we can know God completely, the basis of knowledge is derived from the senses. Knowledge has factual evidence from the world around you and has to do with reason and science. “We have a more perfect knowledge of God by grace than by natural reason…the knowledge which we have by natural reason contains two things: images derived from the sensible objects; and the natural intelligible light, enabling us to abstract from them intelligible conceptions. Now in both of these, human knowledge is assisted by the revelation of grace.
For the intellect’s natural light is strengthened by the infusion of gratuitous light” (Aquinas__). On the other hand, Faith (or a belief) in something you take without question or evidence. An example of this is if someone is inside of a building and cannot see outside and someone comes in from being outside and tells the person that it is raining. Since the person inside has no way of knowing that it is raining outside since they cannot see or hear it, then they must believe the person telling them that it is raining.
“Faith does not involve a search by natural reason to prove what is believed. But it does involve a form of inquiry unto things by which a person is led to belief, e. g. whether they are spoken by God and confirmed by miracles” (Aquinas__). Teachings by St. Augustine and Pseudo-Dionysius agree with the teachings of St. Thomas Aquinas about knowing God. All of them agree that it impossible to be able to fully and completely know God. Alternatively, the three of them believe that one can only know about and of God; knowing only the different aspects of God.
Dionysius describes God as “wholly unknowable” and has as “incomprehensible presence” (Pseudo Dionysius 119) which is him saying that God cannot be understood completely. Dionysius also says that God is made up of infinite characteristics, which Dionysius combines to call the “Godlike oneness” (Pseudo Dionysius 36). He says that one can better know God through knowing that he has characteristics such as “good”, “fair”, and “existent” (Pseudo Dionysius 39-40) but that he is so much more than just these. This relates to St.
Thomas Aquinas’ thoughts that through our senses, we can come to know more about God because of what he created, but it is still impossible to completely know God. Similarly with St. Augustine, he states that God is “high above all, uncontainable and immeasurable” (Augustine 32) which means that God is beyond our reach. Due to the face that we cannot see God, then it is impossible for us to know him fully. St. Augustine also states that God is “incorruptible, inviolable, and unchangeable’ (Augustine 90). The meaning of this passage states that God is perfect.
If he were to be changed, he would no longer be perfect. This is a concept that humans cannot comprehend because humans are not perfect and perfection is an abstract thought. They can have an idea as to what perfection is, but it is impossible to fully understand. In conclusion, knowing that God exists and knowing God are two completely different questions. St. Thomas Aquinas states that one can know that God exists and that it can be proven philosophically through the effects. On the other hand he also states that one cannot know God, only aspects of Him.
These two questions correlate with the different of faith and knowledge. Faith is associated with the question of knowing God (cannot be proven) and knowledge is associated with the question of knowing that God exists (can be proven philosophically). St. Thomas Aquinas, St. Augustine and Pseudo Dionysius all state that it is impossible to fully know God. They all agree on the fact that it is possible to know aspects of God and know partially who he is through using our senses, yet God is still seen to be infinite so it is impossible for our human minds to fully comprehend God.