Existence of God

by brianpetry on


There are two different ways that something can be self-evident.  The first type of self-evidence is that which you cannot deny its existence. An example of this is that it is self-evident that you are reading this paper right now.  The second type of self-evidence is that it is evident to itself but not to those around it.  Knowledge of God’s existence is not self-evident in the first sense.  God’s existence is, however, self-evident to Himself but not completely to us.  Thomas Aquinas says that we understand God’s existence naturally in a weak and confused way[1], and that we can only properly understand if it is proved through reason and demonstration.

The first question regarding the existence of God ought to concern if it is possible to demonstrate His existence.  First we must look at the two ways that anything can be demonstrated.  The first is a priori, which is knowing from cause to effect, and the second is a posteriori, which is knowing from effect to cause.  If God exists we can only demonstrate God’s existence a posteriori, which means that we must first look at the effects of God and only then can we can link these effects to Him, and conclude that He exists and is the primary efficient cause of everything.

In order to prove if God exists, I believe it is important to look into a variety of different sources to show us how it is necessary for God to exist.  I have selected four philosophers, Aristotle, Plotinus, Augustine of Hippo, and Thomas Aquinas to give insight on why God must exist and a little glimpse of what this God is like.  Each philosopher offers a relatively unique way of proving the existence of God and who He is.



Aristotle was a Greek philosopher who lived in the years of 384 BC – 322 BC. Aristotle is one of the greatest philosophers of all time.  Some of Aristotle’s works are still an important aspect of academic study today.  He had great influence on philosophical as well as theological thinking, especial in Islam and Judeo-Christianity.  Aristotle was known for taking scientific approaches to obtaining truth.  Aristotelean Physics were in use as science for nearly two-thousand years, until they were replaced by Newtonian physics.  Aristotle paved the way for western philosophy as well as furthering studies of metaphysics.

Cosmological Argument

Aristotle explains that there are four causes to answer the question “why”.  These causes are the material cause, the formal cause, the efficient cause, and the final cause.[2]  The cause that is important for the cosmological argument is the efficient cause.  The efficient cause is that which causes change or motion.  In Aristotle’s example he uses the metaphor of a house being built.  The efficient cause would be the agent that caused the event and, in the case of building a house, the agent would be a house builder.  The cosmological argument states that everything that has motion must have been moved.  In our cosmos everything moves: the planet we are on, the sun, our galaxy, etc.  If all of our cosmos are in motion then something must have put it in motion.  But this could not go on infinitely, if it were to go on infinitely then nothing would have moved anything and nothing would be moving today.  So he concludes that there must be one substance that first moved without itself having been moved.  This is what Aristotle calls the prime mover.

Aristotle describes three types of substances.  The first is material and perishable, the second is material and eternal, and the third is immovable, immaterial, and eternal.[3]  The prime mover must be the third type of substance.  The prime mover must be eternal because it “is impossible that movement should either have come into being or cease to be (for it must always have existed), or that time should. For there could not be a before and an after if time did not exist.”[4]  Furthermore, the prime mover must be immovable because the prime mover is immaterial and in order for something to be moved it must have material.  Because it is immaterial and cannot be moved it, is pure actuality or pure Act.[5]

Aristotle then identifies the prime mover as God.  His reasoning is that there is a prime mover, the prime mover is the highest being, and the highest being is God.  Therefore the prime mover is God.  Aristotle’s definition of God is a “self-subsisting and eternal Act.”[6]


Plotinus was one of the most influential philosophers of ancient times.[7]  He lived in the years 204 – 270 AD and he studied both Plato and Aristotle’s work and he made it his task to interpret the work of Plato.  He was most well-known for creating three fundamental principles for metaphysics.  These three principles where the “One”[8], the “Intellect”[9], and the “supreme Soul.”[10]

The One

Plotinus says that it is necessary that there be a “necessary being.”  This theory of God builds off of Aristotle’s prime mover.  God is self-causing and the source of existence and must have existed before the world and will continue to exist for all eternity.  Plotinus maintains that God is immovable, immaterial, and eternal.  Plotinus also made the connection between the “One” and Plato’s Idea of Good.  This stated that God is the “universal author of all things beautiful and right, the parent of light, and lord of the visible world, and the immediate source of reason and truth in the intellect, and that this is the power on which he who would act rationally either in public or private life must have his eye fixed.”[11]  The “One” being the existence of all beings begot the first derivation from the “One” called the “Intellect.”

The Intellect

The “Intellect” is the principle of essence of the “One” is the principle of being. This God builds off of the self-thinking thought that Aristotle previously built.  The “Intellect” has two main attributes, first he is the locus of all Ideas,[12] and second he is the actualization of thinking which constitutes the being of all forms.[13]  Without the “Intellect” nothing exists because without knowledge of existence, it really doesn’t exist.[14] The “Intellect” is so important that it could be said that the “One” needs the “Intellect” to make things truly exist.[15]  So we can know that the “Intellect” exists because forms exist and also because we have human intellect which derives from the “Intellect.”  The word he used for “Intellect” was nous, which meant between being and matter which would be called the “supreme Soul”.  The “supreme Soul” comes from the “Intellect “and forms the connection between the “Intellect” and the material world.

The Supreme Soul

Plotinus reasoned that the “supreme Soul” must exist because if there was just the “One” from which all existence is, and the “Intellect”, how would our material world exist?  So the “supreme Soul” is the bridge that connects the Intellect with the material world.    What the “Intellect” is to the “One”, the supreme “Soul” is to the “Intellect”.  The supreme “Soul” is brought the material world into existence through the “One” and with the “Intellect”.

Augustine of Hippo

Augustine of Hippo was one of the greatest Early Church Fathers.  He live in the years 354-430 and he was a brilliant theologian as well as philosopher.  A lot of his philosophy served as a cornerstone for modern Christian Philosophy.  He studied heavily under Plato, and wrote The City of God, with a similar style to Plato’s Republic.  He also developed a new way to approach theology and philosophy by mixing a variety of methods and perspectives.[16]

Fulfillment of Plotinus

When Augustine of Hippo read the works of Plotinus he understood it better than many philosophers before his time.[17]  Many philosophers were confused as to how it should be possible that there should be three Gods and that without either the “One”, the “Intellect”, or the “supreme Soul” nothing would be, and yet they all relied on each other for anything to actually exist.  Augustine saw that this was surely the Christian God.  He saw that the “One” was clearly God the father, the first person of the Holy Trinity, the being who himself is existence.  He saw that the “Intellect” was Jesus, the second person of the Holy Trinity, He to whom all Ideas and Form exist.  He also saw that the supreme “Soul” was clearly the Holy Spirit, the third person of the Holy Trinity, the creator of the material world.


Hierarchy of Existence

Augustine made a rather compelling argument that God must exist.  His argument began with a common truth.  This common truth is that we exist, and if a person argued that he didn’t exist that would be proof that he did exist.  He then created a Hierarchy of Existence.  He would point to a rock and say that the rock is merely a substance that is not alive but just merely exists.  Then he would show that the rock exists on a much lower level than a plant because a plant at least has a “nutritive” soul, which meant that the plant would actually be alive.  Then he continued to show that animals are yet above plants because animals have a “sensational” soul which encompasses the “nutritive” soul but also adds movement and sense.  He then reasons that humans are yet above animals because we have a “rational” soul, that is we are alive, we can move, we can sense, and we can reason.  Augustine then makes a point that if it were possible for us to prove that there is yet something above mankind then that higher existence would be that which is called God.  Augustine would prove that there is something more than mankind by asking a simple mathematical question.  He would say, “What is seven plus three?”  The answer was generally ten, save a few who weren’t good at math.  He would ask, “Why does seven plus three equal ten?”  It is not that way because one wills it to be that way.  So because of this we can say that there is something above human reason and what is above human reason is God.


Thomas Aquinas

Thomas Aquinas was an Italian Dominican Friar who lived in the year 1225-1274.  He was one of the most brilliant philosophers of all time.  He studied heavily the works of Aristotle and worked to synthesize Aristotelian Philosophy with Christian Philosophy.  This is very apparent in one of his most famous works Summa Theologica.  Thomas Aquinas was honored with being a Doctor of the Church for the tremendous work he did, especially in furthering metaphysics.  Aquinas proved that God existed in five ways that did not require faith, only reason.[18] Aquinas’ five proofs were built off of Aristotle’s cosmological argument but went into much more depth about why it is necessary that there must be a God.

First Mover

Aquinas argues that everything that is in motion must be in motion because something put it in motion.  This is very similar to Aristotle’s cosmological argument.  This series of objects being put into motion could not go on infinitely, because if it did go on infinitely then there would be nothing to move anything in the first place.  Since it is impossible then there must have been a first mover.  “Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.”[19]  The first mover has the immobility of actuality, which means that “God acts by himself, who is his own action, and consequently his own being … and the mode of operation the mode of being.”[20]

First Cause

Thomas continues to build off of Aristotle and his first proof.  He says that everything that exists has a cause.  In order for something to have caused itself, it must have existed before it existed, which he concludes is impossible.  He also argues that efficient causes could not go on infinitely or else there would be no cause to begin with, in which case nothing would ever have been caused.  Since can see there are many things that have causes we can conclude that at one time there was a first cause.  This first cause is God.[21]  As Fr. Wallace says:

The first cause is not a body, and does not have parts on which it depends for its being and acting. It is not composed of matter and form, nor of potency and act. It is not capable of being moved or having motion, either by itself or by something else, but it is the unmoved mover of other things. Because it is unmoved, it is not a temporal being but eternal.[22]


Necessary Being

This argument is similar to Aristotle’s argument that some substances must be eternal.  Aristotle states that if all substances are perishable then all the substances would have perished and there would no longer be anything in existence, and since there are substances in existence then it must be necessary that there be some eternal substance.[23]  Aquinas echoes this by saying that if “if everything is possible not to be, then at one time there could have been nothing in existence.”[24]  If this were true then everything would have already perished, but since there are substances that are alive there must be something that is already existing in actuality not mere potentiality.  Since there are substances in existence it must be that there was a being that existed out of pure actuality or Act, and that this pure Act “is self-existent, it follows that His essence is not only something capable of existing of receiving and limiting existence, but that this necessary being is the self-subsisting Being.”[25]

Greatest Being

Thomas has yet another brilliant proof of God’s existence.  He says that the quality of something that is said to be hotter isn’t actually in and of itself hotness but rather it resembles hottest.[26]  “Among beings there are some more and some less good, true.” [27]  These “levels” show that they are not good or true in and of themselves but rather that they have resemblance of the transcendental of good or true.  The fact that they resemble these transcendental means that there is an absolute Good or True.  That which is the maximum in whatever level it stands for becomes the cause of all that quality.  In this case the Ultimate Good, or rather the Perfect, is the cause of all things that are good.  This also applies to truth, as there is an Ultimate Truth from which causes all things that are true.  Jesus made claims about goodness and truth: he said “your heavenly Father is perfect”[28] and, “I am the way, and the truth, and the life.”[29]  By these two statements Jesus made we can see that God is the Perfect Being as well as truth itself.

Intelligent Designer

Thomas has one last yet still profound argument that proves God’s existence as necessary.  Thomas states that objects with no intelligence act for an end.  In order for this to be possible there must be an intelligent designer that makes such things act for an end.  He tells us that as intelligent beings we act for a purpose, for an end.  We act “always, or nearly always, in the same way, so as to obtain the best result.”[30]  Proof that we act to achieve an end is in the fact that we eat every day and sleep every night.  We take certain actions to take care of ourselves, which fulfills our purpose in life: happiness.   The fact that we take care of ourselves to be happy makes sense, but it does not prove that God exists.   Let us now observe something that doesn’t have intelligence, say a tree.  Why does a tree grow a seed and drop the seed to the ground?  It does so for an end, which is for creating a new tree.  But since the tree has no intellect it makes you reason that there must be some intelligence that directs the tree to do so, just as when a gun is shot, it is not the bullet that goes to the target on its own but rather the one who fired the gun that directed the bullet.  “Therefore some intelligent being exists by whom all natural things are directed to their end, and this being we call God.”[31]




There certainly must be a God.  Aristotle does a great job of proving that there must be a Prime Mover.  He also begins describing God as self-subsisting and eternal pure Act.  Plotinus shows us that this God must be existence itself and everything that exists, exists through it.  He also describes the first derivation of this God.  This being is the being through which all forms and ideas come forth.  Then there is the last being that connects the first being of existence and the being of form with material.  From there Augustine of Hippo explains that these beings are the Trinity and that the first being is God the Father, the second being is Jesus, and the third being is the Holy Spirit.  Augustine also adds a very unique proof of God’s existence by creating a hierarchy of existence.  Then from there Thomas reiterates and cleans up Aristotle’s Cosmological argument with his five proofs of God’s existence.

So far we can be certain that there is a God and this God is immaterial, immovable, and eternal.  We also know that this God is the being through which of all existence comes, the form through which all form comes, and the bridge between these principles and matter.  We can also see that these are three individual person of God.  God does not have parts, God is one and cannot be divisible.  God is the efficient cause of everything, and He is Perfection and Truth itself.  Through this study we are literally reaching at the very ends of metaphysics and what we can rationalize about God.  There is only one way to go any further and know more about this God, which is through His revelation.  The only rational step I see from here is to look to where he has already revealed himself, namely the Catholic Church.  The Catholic Church teaches of a God that perfectly fits this metaphysical description of God and has so much more to offer.

Works Cited


Aquinas, Thomas. Summa Theologica. Coyote Canyon Press , 2010.

Aristotle. Aristotle Metaphysics. Oxford: Oxford University Press, 1994.

—. Physics or Natural Hearing. Indiana: St. Augustine’s Press, 2005.

Fr. William Wallace, O.P. “Philosophy of Nature.” (n.d.).

Garrigou, Rev. Reginald. The One God. San Bernadino: Ex Fontibus Company, 2014.

Gerson, Lloyd. “Plotinus.” The Stanford Encyclopedia of Philosophy (Summer 2014 Edition). 2014. http://plato.stanford.edu/entries/plotinus/.

Gilson, Etienne. God and Philosophy. Indiana: Yale University Press, 2002.

Plotinus. Enneads. n.d.

TeSelle, Eugene. Augustine the Theologian. London, 1970.



[1] (Aquinas) Part I Question II Article I

[2] (Aristotle, Physics or Natural Hearing) Book II Chapter 3

[3] (Aristotle, Aristotle Metaphysics) Book XII

[4] Ibid

[5] Ibid

[6] (Gilson) pg.32

[7] (Gerson)

[8] (Plotinus) Book VI 7, 87

[9] Ibid

[10] Ibid

[11] (Gilson) pg. 25

[12] (Gilson) pg. 46

[13] (Gerson)

[14] (Gilson) pg.47

[15] (Gerson)

[16] (TeSelle) pg. 347–349

[17] (Gilson) pg. 49

[18] (Aquinas) Part I Question II Article 3

[19] Ibid

[20] (Garrigou) pg. 141

[21] (Aquinas) Part I Question II Article 3

[22] (Fr. William Wallace) 6th Lecture Part 7

[23] (Aristotle, Aristotle Metaphysics)Book IX Chapter 8

[24] (Aquinas) Part I Question II Article 3

[25] (Garrigou) pg. 145

[26] (Aquinas) Part I Question II Article 3

[27] Ibid

[28] Mat 5:48

[29] John 14:6

[30] (Aquinas) Part I Question II Article 3

[31] Ibid

Written by: brianpetry

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