Thomas Aquinas and 5 Arguments for the Existence of God

Thomas Aquinas (1225-1275) was an early academic theologian during the Middle Ages. Francis Schaeffer has noted that Aquinas “changed the world in a very real way.” In his last work, which was left incomplete at his death, Summa Theologiae Aquinas quickly tackles the discussion about the existence of God. In this discussion he posits five ways of proving Gods existence. To read the full article by Aquinas on these proofs click here.

In the time of Aquinas the Holy Scriptures were not as commonly possessed by the common man as they are today. Indeed, today translations of the Scriptures abound not only in their ability to be accessed but also in the variety of renderings of the original languages. This was a time where social hierarchy was evident and lords ruled over their peasants. The common man did not have in common such things that the more affluent persons, such as those born into wealth and abundance, often took for granted or even gloated over. It was a very impressionable time for those who knew poverty as their closest relative. After all, they regularly did the bidding of their lords without question.

Today the effectiveness of simply being able to quote Scripture as an absolute answer to the complaints and skepticisms of our post-modern society has been weakened. Certainly individuals exist where this method suffices but likely they are already devout believers or are those who have already vested some authority in the Holy Scriptures by way of reason or intellect. Many wonder about, doubt or even totally disbelieve that God even exists much less an inspired Word exists from God Himself.

For some simply quoting from the Scriptures is equivalent to quoting from Shakespeare or Chaucer. It has been demoted, in their eyes, as simply another work of literature. Since Nietzsche God is dead in the minds of some. Once God is—again—made alive we can then begin a discussion about submission to the divinely inspired Book of God.

For example, does a freshman student of medicine begin by studying specified diseases or disorders? Do they begin by starting their own clinical practice? No, it is likely that they start with anatomy 101 or learning medical terminology to get a firm foundational grasp of the human body and terms associated with its treatment.

After studying philosophy with Albert Magnus, in Cologne, much of his early theological training was received at the University of Paris. Aquinas owes much of his philosophical and theological outcomes to Aristotelian methods. In fact, Oxford scholar Jonathan Hill has noted that he was “foremost amongst those making efforts to assimilate Aristotelian methods and tools in the discussion of Christian theology.”

Aquinas begins this article by listing two objections. The first is the problem of evil and how the existence of evil cancels out the existence of a God who is infinite in goodness. The second supposes the existence of God to be redundant since nature and human reason can account for natural and voluntary things. At the end of the article Aquinas answer these objections concisely. We shall examine the five ways of proving Gods existence offered by Aquinas.

The first three ways discussed by Aquinas can be called cosmological arguments. There are different forms of this argument but essentially it posits that “since there is a universe rather than none at all, it must have been caused by something beyond itself.” This argument has its roots in Aristotle and Plato but essentially argues that whatever begins to exist has a cause. Therefore, whatever exists has been caused or set in motion by God, the uncaused cause. For example, if we were to count to 100 we had to begin somewhere—at 1. There is no infinite series of events. Each cause has an effect and therefore in the Thomistic arguments God is not a cause but the “first mover”; the one who has created the initial cause that has set matter into motion.

First Way: This argument refers to the Unmoved Mover based on the idea of motion. Newton’s first law of motion essentially states that an object will remain at rest unless force is placed upon the object. Aquinas says, “motion is nothing else than the reduction of something from potentiality to actuality.” Each object has the potential for motion. For example, a book sitting on the very edge of a table has potential for motion if force is exerted.

Aquinas analogously refers to heat and wood. Wood has the potential to be hot but not until the heat has acted upon the wood. He also notes, “whatever is in motion must be put in motion by another.” In other words, the wood cannot heat itself but must have some force to act upon it. This setting into motion cannot go on to infinity because then there would be no first mover. As mentioned earlier, once we arrive at 100 we must concede a starting point. He concludes that “it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.”

Second Way: This argument refers to causality. Although Aquinas is referring to the causality of existence, consider the book near the very edge of the bookshelf. It has the potential of causality but must have force exerted upon it to see it fall to the floor. The cause of this effect could be someone shaking the bookshelf or simply a child nudging it to fall. God is eternal and without cause or else He would not be God simply by Biblical definition (Deuteronomy 33:27; 1 Timothy 1:17). According to the second argument everything that exists must originate from an initial cause. Human beings and the universe are effects which must have a cause. Since these exist then there was a cause.

It would be impossible for a human to exist prior to his existence. Aquinas notes, “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.” The point is that nothing can be self-caused because existence would be bestowed upon itself. Since this is obviously true everything that has a cause is or was caused by something other than itself. For a human to exist there were a series of causal events in order to come to conscious existence.

Human life did not simply appear without cause. Our human existence is dependant, then, upon other causes. “Therefore, there must be a first, uncaused, efficient Cause of all efficient causality in the world. Everyone gives to this the name of God.”

Third Way: This way of proving Gods existence argues for the existence of necessary and possible beings. Possible beings are those that begin to exist and cease to exist. A necessary being would be just the opposite—without ability to non-exist. The existence of human beings is not necessary but possible. This is demonstrated daily by the human death that has occurred since its beginning. A necessary being would always exist.

Aquinas notes, “that which does not exist only begins to exist by something already existing.” Since things in our temporal universe have been caused to exist or are not necessary then there must be an absolutely necessary being. According to Aquinas then, “we cannot but postulate the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity. This all men speak of as God.”

Fourth Way: This argument has been called “the argument from gradation (Perfection) in things.” William L. Craig suggests this argument is a type of “moral argument.” Aquinas notes that “among beings there are some more and some less good, true, noble and the like.” Here he refers to the varying grades of things. For example, there are various cuts of meat, e.g. chuck, sirloin, ribeye, prime rib, T-bone, porterhouse, New York strip or filet mignon. All parts of these choice cuts come from the same beef, however, even beeves raised for such purposes vary in their quality or breed. To many the filet mignon is the best of the best.

Another way to illustrate this would be a diamond. The value of a diamond is determined by four factors: color, shape, blemishes, and weight. As anybody who has visited a jewelry store has noted, diamonds too, have various grades. This effect of gradation is apparent in everything in some sense. There exists within everything a “superlative standard: the most good, most true, and so forth.” The result then is that within all things there exists something is the best or truest. Aquinas concludes, “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.”

Fifth Way: This final argument is a type of teleological argument—an argument from design. For example, the nautilus shell has certain design patterns in each and everyone that is repeated in nature. In nature we observe that all things grow and move towards some end or goal. Craig uses poppies and acorns as an illustration. He states, “poppy seeds always grow into poppies and acorns into oaks.”

Fibonacci numbers (from Italian mathematician Leonardo Fibonacci (1170-1240) are widely used in mathematics. In nature design patterns, such as the spiral growth of leaves on some trees, often exhibit the Fibonacci series. Each sequential number is the sum of the two preceding numbers. For example, a series beginning 0, 1 ... continues as 1, 2, 3, 5, 8, 13, 21, etc. Many things in nature duplicate their pattern and design each time a new one emerges.

Aquinas notes, “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.” Here he points to the archer who aims his arrow towards a mark. The arrow does not arrive at its mark without some intelligence that has selected the arrow, placed it and then aimed and shot. Aquinas concludes, “. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.”

1. Schaeffer, Francis A. Escape from Reason. © 1968 by Inter-Varsity Press. London, England
2. Hill, Jonathan. Zondervan Handbook to the History of Christianity. © 2006 by Jonathan Hill. Published by Lion Publishing Plc. Oxford, England
3. Geisler, N. L. 1999. Baker encyclopedia of Christian apologetics. Baker reference library . Baker Books: Grand Rapids, Mich.
4. Craig, William L. Reasonable Faith © 1994 by William Lane Craig Published by Crossway Books Pg. 88

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