By Jayson M. Brunelle, M.Ed., CAGS

In Question two of the First Part of the Summa Theologiae, Aquinas proposes arguments or proofs for the existence of God in what are commonly referred to as the “Five Ways.”  These “Five Ways” have been used by apologists for centuries in an effort to demonstrate that God’s existence can, indeed, be philosophically or logically proven.  Note that these are logical proofs, not scientific ones, for God is pure spirit and therefore not subject to the scientific method.  This reality, however, is only a problem for those who subscribe to “scientistism,” which, ironically enough, is a belief system whereby its proponents place what is tantamount to a “religious faith” in science as the only valid source of knowledge, and the “scientific method” as the only viable means of conveying authentic or trustworthy knowledge. This philosophical conviction is also referred to as logical positivism, and, as will be demonstrated, is entirely self-inconsistent.  For, it is entirely impossible to scientifically prove that one ought only to believe that which can be scientifically proven.  Thus, science cannot prove itself, and there certainly are other ways of arriving at true, authentic knowledge.  This is not meant to belittle the scientific method as a valid source of human knowledge.  Rather, it is to say that science provides but one of many ways and means of knowing and attaining truth.  Examples of other valid sources of knowledge are logical, deductive and inductive reasoning; authority/historicity; faith; intuition; etc.  Moreover, the “proofs” for God’s existence might meet with the radical epistemological skepticism of those who claim that it is impossible to know anything.  Of them, one might ask, “But you claim to “know” that you cannot know.  How, then, can you know that?”  For, any time an assertion of any sort is made, the human mind’s ability to ‘know’ is presupposed.  Further, some might assert, “There is no such thing as truth.”  Yet, it is clear that the one making this assertion believes it to be true, otherwise, there would be no point in making the assertion at all.  Yet, if any assertion is true, including this particular assertion, that “There is no such thing as “Truth,” then there is, in fact, such a thing as truth.  Therein lies the self-inconsistency.  

Having anticipated some of the attacks made by logical positivists and extreme epistemological skeptics, let us begin by following the logical progression used by Aquinas in Ia, q.2, a.1 of the Summa, which begins with the question of whether God’s existence is self-evident.  It should be pointed out that prior to Aquinas’ writing of the Summa, St. Anselm had proposed an argument for God’s existence based on the alleged self-evidence of God’s existence.  In the Proslogian, Anselm states, quoting the Psalms, that “The fool says in his heart, ‘God does not exist,’” and argues that all men will agree on the nominal definition of the term “God” as “that than which nothing greater can be conceived of.”  Even the non-believer would agree that this description serves as an appropriate and accurate definition of the term, “God,” even while they, themselves, reject belief in this being’s actual existence.  Yet, as the argument proceeds, it is greater to exist in reality, ontologically, than to simply exist in the mind as an idea.  Therefore, according to this “argument” or “demonstration,” if one conceives of “that than which nothing greater can be conceived of” as simply existing in the mind but not in reality, one is not truly conceiving of “that than which nothing greater can be conceived of.”  And since we can have this idea, this concept of that which nothing greater than can be conceived, it must follow that the thing which it represents – namely, God – must therefore exist.

Aquinas responds to this argument by making a distinction between propositions which are self-evident in themselves and to us, and propositions which are self-evident in themselves but not to us. At this point, an explanation of a self-evident proposition is in order.  A self-evident proposition exists when the predicate is contained within the definition of the subject.  Thus, the statement, “A bachelor is an unmarried man” is an example of such a proposition, for the predicate, “unmarried man” is contained within the definition of the subject “bachelor.”  All of this presupposes that we possess a clear understanding of the definitions of our terms.

Applying this distinction to the proposition, “God exists,” Aquinas states that it is self-evident in itself, for, from a philosophical and theological perspective, it is of God’s essence to exist.  Scripture, one of the two sources of Divine Revelation, bears witness to this philosophical truth, as God reveals Himself as ”I Am.” He Himself identifies His essence with His existence.  He is the necessary being, whose essence is identical with His existence.  Or, in other words, He must exist.  But the proposition, while self-evident in itself, is not self evident to us, as the essence of God is something which the human intellect, while on earth, cannot comprehend.  Thus, the definition of the term, “God,” is not clear to us.  We can know that God is, but this is quite different from knowing exactly what God is.  Thus, due to the ambiguity of the term “God” that results from the limitations of human reason as something finite, we must conclude with Aquinas that the proposition “God exists” is self-evident in itself but not to us.

While Article 1 of Question 2 of Part 1 deals with the above issue of the self evidence of God, Article 2 addresses the issue of whether or not God’s existence is something which can be demonstrated.  Aquinas states that there are two types of demonstration: a priori and a posteriori.  An a priori demonstration is one whereby we argue from cause to effect, while an a posteriori demonstration is an argument from effect to cause.  Speaking on the latter, Aquinas states the following: “When an effect is better known to us than its cause, from the effect we proceed to the knowledge of the cause. And from every effect the existence of its proper cause can be demonstrated, so long as its effects are better known to us; because since every effect depends upon its cause, if the effect exists, the cause must pre-exist.”  Thus, from God’s effects, or His creation, which is better known to us than God Himself, we can, in fact, demonstrate the existence of the cause, which, in this case, is the First Cause, Uncaused, which is God.

Having established that God’s existence can, indeed, be logically proven through a posteriori demonstrations, Aquinas asserts that “the existence of God can be proved in five ways” (ST Ia, q.2, a.3).  In the first way, Aquinas states that it is evident from our experience that things are in motion.  Aquinas employs abstract philosophical terminology to convey relatively common-sense, easily understandable realities.  In this argument, the Aristotelian terms or concepts “motion,”“act” and “potency,” are used.  For clarity’s sake, the Aristotelian term, “Motion,” can be thought of in four senses: 1. Locomotion – change of place; 2. Growth and diminution – getting bigger or smaller; 3. Alteration – change of quality or appearance; 4. Substantial Change – change of substance or nature.  Thus, when we think of Aquinas’ use of the term motion, we understand that this presupposes the various Aristotelian meanings for the word that have been above explained.  “Act” means simply “what is.”  “Potency” is “what is not but is able to be, or has the potential to be.”  With the above in mind, let us read for ourselves the argument put forth by Aquinas concerning motion and the necessity of a First, Un-moved Mover: “whatever is in motion must be put in motion by another. If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover; as the staff moves only because it is put in motion by the hand. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.”  In other words, whatever can undergo change or transformation in any of the four senses listed above must itself be changed by another.  And the very thing causing change was once itself changed by something else that came before it, either temporally or logically.  Now, this process of things being put into motion or changing, whereby each thing is changed by another, which itself has been changed, cannot stretch back indefinitely, or infinitely.  The philosophical way of saying this is that there cannot be an infinite regress.  For, if there were an infinite regress, there would be no first-mover, and without a first-mover, no intermediate movers, and finally no present motion whatever.  And since there is present motion or change, there must exist a First-Mover, itself un-moved.  And this First-Mover is God.

The second way proposed by Aquinas is based on the nature of an efficient cause.  In Aristotelian Philosophy, the “efficient cause” is a phrase used to denote those things that temporally or logically precede and give rise to something else – a new thing, other than itself.  For example, my parents are my efficient causes.  They immediately preceded me and caused me to exist.  In Aristotelian philosophy, the “efficient cause” is one of the “four causes” of all things.  According to Aristotle, any substance whatsoever can be understood and explained by addressing and explaining its four causes.  It’s a concept within Aristotle’s metaphysics, which was wholeheartedly espoused by St. Thomas.  The four causes are the material cause, or that which the substance is materially composed of; the formal cause, which is the form, essence or nature of the object; the efficient cause, which is that which immediately precedes it either temporally or logically and gives rise to the things existence; and the final cause, which is the teleological (goal oriented) nature of the thing, or that for which it was created.  An example will better illustrate this concept.  Take man, for instance.  His material cause is flesh and bone; his formal cause is his soul; his efficient causes are his father and mother; and his final cause, or his goal, is the vision of God in heaven.

The argument proceeds along the same lines as the last, arguing from the effect of an efficient cause to the ultimate cause, the uncaused cause: “The second way is from the nature of the efficient cause. In the world of sense we find there is an order of efficient causes. There is no case known (neither is it, indeed, possible) in which a thing is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible. Now in efficient causes it is not possible to go on to infinity, because in all efficient causes following in order, the first is the cause of the intermediate cause, and the intermediate is the cause of the ultimate cause, whether the intermediate cause be several, or only one. Now to take away the cause is to take away the effect. Therefore, if there be no first cause among efficient causes, there will be no ultimate, nor any intermediate cause. But if in efficient causes it is possible to go on to infinity, there will be no first efficient cause, neither will there be an ultimate effect, nor any intermediate efficient causes; all of which is plainly false. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.”

Put another way, everything that exists receives the gift of its existence from another which precedes it.  Nothing can serve as its own cause because it would have to precede itself, and this is absurd.  As with the first argument, an infinite regress of things is impossible, for to remove the cause is to remove the effect.  It is abundantly evident to us that the observable universe is filled with things which have received the gift of their existence from other things, and this goes on and on.  Yet none of these things would exist, much less be observable, if there were no First Cause, uncaused.  And this is God.

The third way has to do with possibility and necessity.  This argument is based on the notion of contingency.  The cosmos is full of contingent beings, that is, beings that do not have to exist.  They are non-necessary.  And every single thing in the created world is a contingent being. Yet, like in our previous two examples, we cannot have an infinite regress of contingent beings.  There must, then, exist a non-contingent being, a Necessary Being.  And this is God.

“The fourth way is taken from the gradation to be found in things. Among beings there are some more and some less good, true, noble and the like. But “more” and “less” are predicated of different things, according as they resemble in their different ways something which is the maximum, as a thing is said to be hotter according as it more nearly resembles that which is hottest; so that there is something which is truest, something best, something noblest and, consequently, something which is uttermost being; for those things that are greatest in truth are greatest in being, as it is written in Metaph. ii. Now the maximum in any genus is the cause of all in that genus; as fire, which is the maximum heat, is the cause of all hot things. Therefore there must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God” (ST, I, q. 2, a. 3)

It seems that this argument is fairly self-explanatory.  Simply, there is a gradation to be found in things, and this gradation presupposes a standard of perfection, the highest and most perfect expression of which is to be found in God, the sum of all perfections.

Heretofore, we have witnessed examples of the “Cosmological Argument,” which is to say that we have argued a posteriori from the “effect” of the “cosmos” (hence, the name of this type of argument) to its Unmoved Mover, its First Cause Uncaused, it’s Necessary Being, its Standard or Measure of Perfection, it’s God.  The fifth and final of St. Thomas’ arguments (as they are found and assembled in the Summa) is a different type of argument, known as the “Teleological Argument,” or the argument from design.  As apologist Peter Kreeft states in his wonderfully informative book, Fundamentals of the Faith, the first premise is that “where there is design, there must be a designer.”  The second premise is that “there exists design throughout the universe.”  The logical conclusion, then, is that “there must exist a universal designer,” and this is God.  Why, however, must we admit to the veracity of the first premise, that “whenever we encounter design, we can posit the existence of a designer.”  It’s a truth we admit in practice.  If you were to look at the Mona Lisa for the first time, you wouldn’t say to yourself, “Wow, isn’t it great that all that paint randomly thrown at this canvass formed, by pure chance, this stunning, nuanced work of art.”  Design presupposes a designer.

Thomas presents his version differently, referring to the teleology of natural bodies: “The fifth way is taken from the governance of the world. We see that things which lack intelligence, such as natural bodies, act for an end, and this is evident from their acting always, or nearly always, in the same way, so as to obtain the best result. Hence it is plain that not fortuitously, but designedly, do they achieve their end. Now whatever lacks intelligence cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is shot to its mark by the archer. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.”

A more updated version of this Teleological Argument would likely include some version of the anthropic principle, which is the idea that it seems probable that an intelligent force has been guiding the evolutionary process of the entire cosmos specifically for the sake of the emergence of human, intelligent and volitional life.  If the universe’s evolutionary process had not gone exactly as it actually did go, human life would never have emerged.  The chance of intelligent human life emerging into existence was so incredibly improbable.  Statistically, we shouldn’t be here.  And yet, we are.

We have managed to explore the famous “Five Ways.”  Hopefully, this author has been able to make these perennial truths, so brilliantly elucidated by St. Thomas, a bit more understandable.