St. Thomas Aquinas is broadly held to be the greatest thinker in the Catholic tradition. In one of his many works, he offers five proofs for the existence of God. Of the five proofs, the 4th is often the most ignored and misunderstood. However, I don’t think it should be. This proof deserves far more credit than it traditionally receives. Not only can it be readily understood by common sense, but it actually proves a lot about God in one fell swoop.
I don’t plan to go through a slow and painful exegesis of the text. Nor will I be starting with all of the metaphysical principles that ought to be prerequisite to understanding this argument. Here at thegordianknot.org , that is not our style. I think we can cut through the confusion swirling around this proof of God if we use some creativity in our explanation and present the answers as simply as possible. Here is the primary text from the Summa Theologiae:
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.
Let’s jump right into some examples:
If you notice there are things that are more and less salty, what can we conclude from this? Aquinas would say if things can be “salt-y”, in other words “like salt”, this must mean that salt exists. Otherwise, the “salty” would have no ontological referent. It would be incoherent to say there could be things that were “like salt”, or “salty”, if salt didn’t exist. It would be like saying this pretzel is _____-y very much like ______.
These conclusions should be pretty obvious: things can’t be salty unless salt exists. This is not to say salt must exist or that it causes its own existence. Certainly not. Salt is, however, the reason for its own saltiness. Aquinas follows Aristotle and states, “the maximum in any genus is the cause of all in that genus”. Let’s look back to our example. Salt, being the maximum of saltiness is the cause of all saltiness. Does this mean the platonic form of salt is high above us, zapping pretzels with magic saltiness rays from its place in an ethereal platonic heaven? Does this mean there is a ‘most salty’ chunk of salt floating through space, which if destroyed would make pretzels, olives, and potato chips everywhere disappointingly bland? Of course not.
Here is another example: If things can be more or less red, or in other words, if things can have “redness”, this means there is such a thing as red. Red is therefore the cause of all in the genus of redness. Why? Because if the nature or essence of red stopped existing, then there could not even in principle be such a thing as redness. Again, this is not saying there is a most red firetruck, or a most red “Clifford the big red dog”, who happens to epitomize what it means to be red and somehow beams the power of redness to all other things in the genus. Nor does this mean perfect redness exists in the platonic heaven and beams redness down from there. No silly claims like this are being made, just common sense ones outlined above.
Let’s provide a final example: Salt is a material object and redness is a property of a material object. However, the number 1 is an abstract reality. Nevertheless, we see in the world things can be more or less singular or unified. Singularity of unity means to share in the nature of “1”, just like salty mean to share in the nature of salt and redness means to share in the nature of red. If the number 1 somehow stopped existing, things could no longer be singular. To rehash what must be tiresome to the reader at this point, to be singular means to be like or share in the nature of “1”. That would be impossible if 1 did not exist. On the flip side, since things can be singular, we know that 1 exists.
How does this relate to God? For Aquinas, God is “The pure act of To-Be”. He is existence as a verb, totally unlimited being Himself. The examples he gives of things that are more and less, like truth and goodness, belong to a group called the transcendentals, all of which are philosophically convertible into being. What he is getting at is that there are things with more or less existence. You could say that things can be exist-y or have existence-ness. You have more existence than your shadow. The shadow really exists; after all, we can make true predictions about it, and only existing things can ground a true statement. Likewise, you have more existence than a thought which you hold in your mind. If you stopped existing, so would your thoughts and your shadow, but not the other way around. Your shadow can disappear and, I assure you, you will be just fine.
So if things can have more and less existence or be ‘exist-y’ as we could say, what does this let us conclude? Easy; the maximum of the genus of existence exists. The interesting thing about existence versus the other things we explored is that if there is a being that has within its nature the reason for its own existence, then it explains itself. Salt by reason of its own nature was the reason for its own saltiness and likewise with red and the number 1 with respect to redness and singularity. But there is no reason that red, or salt, or the number 1 must exist.
With this understanding, let’s deal with the argument against God’s existence that never seems to die, even though it is embarrassingly bad: “If God is the reason for everything's existence, then what caused God to exist?”
Substituting Aquinas's definition of God in for the word God unravels this objection pretty quickly: “If ‘the pure act of existence’ is the reason for everything's existence, then what caused the ‘pure act of existence’ to exist?”
Such a question is like asking, “If salt make things salty, what makes salt salty?” It’s fairly simple; salt contains within its nature the reason for its own saltiness. Why? Because to be salty means to be like salt, and what can be more like salt than salt itself? Insert any of the other examples if you prefer.
So the answer is, God contains within Himself the reason for His own existence. Why? Because to be ‘exist-y’, or to have ‘existence-ness’, is to participate in/be like ‘the pure act of existence’/God...and nothing can be more like God than God Himself.
This pure act of To-Be is the cause of all existent things, because He is the maximum of the genus of being. Since truth is made true by that which exists, He is the cause of all truth. Furthermore, goodness is the possession of everything proper to one’s nature; again, this is rooted in existence. Therefore, He is the cause of all goodness, and by being the maximum of existence and having all existence as an extension of His nature, He is maximally good. A maximally good, maximally existent being that causes all things to exist would be called God.
If somehow this maximally good, maximally existent, maximally perfect being failed to exist, there would be no such thing as goodness, truth, being, or perfection. But there are these things, therefore we can conclude God exists.
Objections and Answers:
Objection: This is a circular argument. You start from the idea that existence exists and arrive at the fact that existence exists, but later you call it God.
Answer: First, I started with the claim that things have more or less existence, which is an obvious fact. Then I reasoned to the concept that the maximum of the genus is the cause of all in that genus, again, once properly understood, this is pretty self evident. I identified God as the maximum of the genus of "being" and therefore the cause of all of those things that participate more or less in being. There is literally nothing circular about that.
Objection: Clearly you haven’t read enough of Aquinas. God is not part of any genus, not even the genus of being. So which is it? If He isn’t part of the genus of being, your argument falls apart.
Answer: He is the maximum of the genus as a ‘limit simpliciter’. For instance, if I continue to add sides, a polygon could move from a triangle with three sides, to a square with four, up to a octagon, then to a polygon with a thousand sides, and beyond. What do these polygons become more and more like? A circle, which would be the limit simpliciter of the set. And yet the circle is radically different from these polygons. In fact, with only one side it could be argued it is most like the triangle, even though it more closely physically resembles the polygons on the other end of the set. So no, God is not like the most sided polygon; He is not in the set in that way, for instead He is the limit case that no finite being could ever reach.
Answer: Aquinas understood that no category can contain God because any limit, or containment, must first exist to do the limiting of containing. Yet God is is the cause of all existence and therefore would be the only thing that could contain Himself. No external force could do so because they would all have to be first derived from God. This is what he is trying to say, not that he rejects his own 4th way.
Objection: You say only an existent thing can make a statement true. However, it is true that unicorns have one horn, yet unicorns do not exist.
Answer: The concept of unicorn is what you are referring to, and yes, the concept of a unicorn does exist. If there were no concept of unicorn, then you would have been speaking nonsense which related to nothing at all and the statement would have no truth value. I could not make any true prediction about a “skfjskj”, because no such concept yet exists.
Objection: What about Dawkins' response, which says, using this argument, if stinky things exist, there is a peerless stinky stinker?
Answer: What Dawkins’ argument proves is if stinkyness exists, then stink exists. Stink doesn’t explain its own existence, just its own stinkyness. Where he goes wrong is imagining that the maximum of the genus of stink would be a being which happens to be very stinky, rather than the nature of stink itself. All this proves is that Dawkins stinks at philosophy. And of course, there is nothing in the nature of stink that entails its own existence. It is fully possible that there could have been a reality where stink did not exist. The genus of stink is very different from the genus of Being (or its fellow transcendentals like goodness of truth) in this regard.
Objection: Things can’t have more or less being. It’s like on or off; either there is being or there isn’t. No gradations.
Answer: Which has more being, you or the totality of reality? Clearly one has more being than the other, by whatever measure you choose. How about quantum fields? They seem to have properties which make them seem real and other properties which make it seem they might not be. Looks like Quantum fields are less real than regular objects.
Answer: Aquinas offers truth as a clear example of gradations. As we have mentioned earlier, this is convertible into being. Ask anyone you wish to rank the following statements from more to less true: 2+2= 4, 2+2= 5, or 2+2= potato. It is clear that some of those statements were more true than others. If things can only be true insofar as they are grounded in existence, then there are your gradations of being. If that is not clear enough, I would offer gradations of goodness as yet another example, like truth this is also convertible into being.
Objection: The maximum of a genus does not cause all in that genus. The natures you are supposing are causally inert and can’t do any causing at all. Material processes like taste buds make salt salty. Our reception of certain light wavelengths in our eyes make things red to us and oneness of unity is just an arbitrary grouping, not a real feature of the universe. This argument is just pre-scientific superstitious trash that doesn’t understand actual causal processes.
Answer: All of your examples regard material or efficient causation, which isn’t what we are addressing. This argument relates to formal causation.
Answer: Causally inert? These aren't platonic forms, as I reiterated in each of my examples. The form is in the thing. How is the form of a cat causally inert? Go ahead and removes its form and see what happens to the cat. How is the form of a chair causally inert? It seems to me the form allows for the function of the chair to be possible. Again, a chair without the form of a chair is a pile of wood. Even modern philosophy is against you on this one. Such reductionist materialism is not a tenable position, especially in areas like biology, where the arrow of causality does indeed point from the whole down to its parts.
Answer: If salt did not exist, then there would be no way your taste buds could register saltiness. If red did not exist, then there would be no redness for your eyes to witness. And no, not all things are arbitrary groupings. There is nothing arbitrary about grouping the material of the cat into one group and the matter of the cup he slides off a shelf into a separate group. What removes the arbitrariness in grouping is immaterial form. This form is marked by new causal powers which are irreducible to the sum of its parts. For instance, the cat by nature of his form can imagine a future where the cup falls off the shelf and then intend to make it fall. Matter has neither imagination nor intention in its nature. Cats do, not by virtue of their material composition, but because of their form which shapes and determines the material they are made of.
Answer: Those in Medieval times had both taste buds and salt and were fully away of what happened when the two came together. Likewise they had prisms, eyeballs, and an ability to count things. They weren’t the morons many moderns suppose. The real superstitious and non-scientific trash is a position that denies salt causes saltiness or red causes redness. This objection, while appearing scientific, is just a smokescreen to help the objector deny painfully obvious facts in order to avoid accepting the clear conclusion of the argument.
Objection: Fine. Some type of unbounded limit simpliciter type of existence, which has its existence by its very nature, must exist. I’ll grant all of that, but it can’t be God. Maybe it’s a particle or a quantum field. Heck, what if it’s many gods and not just one.
Answer: The conclusion of this argument can’t be a set of material things, be they super-strings, tiny particles, fields, or any other material reality, because they have objectively less being than the things they make up. For instance, people have greater goodness, perfection, truth, and being than the collection of material that constitutes them. Don’t believe me? Think of your favorite person. Are they good? Do they have more goodness than an equal mass of quantum particles? Or an equal number of super-strings? Of course they do.
Take the way of truth as another example. I can make many more true statements about my friend Bob than about a set of basic material. In fact, since Bob is made up of these particles, I could make all of the true statements about those particles plus all of the true statements about Bob. Therefore, the “Bob set” is greater by definition. And that’s not all, for the type of truths Bob as Bob makes to be true are much more grand and important than those made true by whatever basic material makes up his body. To say, “Bob is a material being who is contemplating his materiality using his immaterial intellect”, or, “Bob is probing the great mysteries of the universe”, or, “Bob has grasped the existence of a transcendent moral law, binding on all free and rational creatures and seeks to live in accordance with it”, are far less trivial than those regarding the basic material constituting his body, because they relate to Bob as a whole and unified being.
For these reasons and others, when looking for God who is All-Good, All-Truth, and All-Existence, going towards basic material looks less and less like God. Instead, moving up the chain of being from plants to animals to humans starts to look more like God, because each of these levels has greater goodness, truth, and being. It is not a bad instinct to look for God at that basic level of existence any more than it would be a bad instinct to look for the circle in a set before the triangle. In a way, the circle belongs at the beginning of the polygon set, having only 1 side. On the other hand, the instinct to find God at the height of the chain of being in our universe is like searching for God among the polygons with the most sides. Yes, these beings more resemble the circle, but in another way they get further from it because they are adding sides rather than having only one. This is why we speak of God as radically transcendent, the First and the Last, the Alpha and the Omega. He is not another being among many, but rather the Cause of all beings.
Answer: Say what you will about a particle or a field but, all good? Fullness of truth? Perfect? These qualities are entailed by the 4th way and much expanded on by the other ways. None of these qualities are present in a basic substance.
Answer: There can only be one God. If there were two candidates, then in order to distinguish between the two, one would have to have something the other did not. After all, if they had every single possible feature the other had, they would not be two beings, but one. Alternatively, if one candidate lacked something, it could not be an infinite being, nor would it be the cause of all that exists. Furthermore, if one lacked something that is proper to its nature, it could not be all-good. So either it would have a different nature from the definition of God and thereby not be God, or it would not be all good, which is a defining feature arrived at by this argument and others, and for that reason not be God. Either way, there can’t be more than one such being.
If you have more questions or comments on this argument, comment on the article or email me at email@example.com. I would love to hear from you. If you liked this argument, I encourage you to look into other explanations of it by others in the Thomistic tradition. There is plenty I left out, skipped over, or just don’t know to tell you about. What Aquinas wrote was a brief summary, not a fleshed out argument. He expands on this proof in the Summa Contra Gentiles, which would be a great next thing to read if you like the 4h way. This is far from the only proof of God's existence and far from the strongest one. I didn't take much time to systematically pull out the reasons for each of the divine attributes. All this to say, if you are looking for resources on the philosophy of God, Email me and I can point you to some great resources, don't think for a second that this little article is all that there is in the way of proofs for God.