Thomas Aquinas: the Fifth Way. Is Aquinas correct?


This Argument is the most important Argument given by aquinas since it seeks to prove that the “uncaused-cause” is also an intelligent cause. Does Aquinas succeed (if not why not)? If not can we improve upon the argument that he has presented

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.


The idea of teleology find its fullest expression in Aristotle. Remember that Aristotle describes the final cause as the “cause of causes”. He uses the example of a saw to illustrate his point: that the wood and metal the saw is made from is to fulfill its purpose as a saw, and its shape (with sharp teeth and etc.) follow likewise.
Aquinas recognises that this final cause is in many cases contingent (i.e. it could be otherwise to what it is). And if final causality is contingent, then it requires an explanation.
But what is the best explanation? Aquinas argues that because the vast majority of bodies that act for ends do not possess intelligence, they themselves are not adequate explanations of their tendencies towards those ends. Thomas says that the best explanation is that there is an intelligence which directs these objects towards a goal. For example, consider an artifact such as a ship – the purpose of the ship resides in the mind of the ship builder(s).
But what of natural objects (such as a man or a bird)? Aquinas argues that these beings are endowed with a purpose (i.e. final causality) by a powerful intelligent being, whom he says we call God.


Even after I began study of Thomist philosophy, the Fifth Way didn’t make sense to me. I had to muse on it, let it stew, and only after some time of that did it really click what Aquinas was saying. And it’s not because Aquinas was being obscure or vague, but it’s because I’m 800 years removed from the philosophical context that he was speaking from. It was something the people of his day would have intuitively understood more easily than myself because they were used to thinking that way. Of all his ways, the Fifth is the most difficult because we are completely unfamiliar with Aristotlean final causes and teleology.

What the Fifth Way is NOT is Paley’s Intelligent Design argument. There’s no “fine tuning” argument or probability argument, and there’s a distinction between substance and artifact as understood by Aquinas that doesn’t fit Paley’s mechanistic world view, in which the Thomist would see Paley as describing everything as artifacts.

What does Aquinas mean by saying an arrow must be pointed at a target? For illustrative purposes, consider an acorn. It has the adult oak tree as its end, as what it’s directed towards becoming. The acorn will not grow into a puppy dog, nor will it grow into a rosebush. In some way, then, the oak tree is the target that the acorn is pointed at. But if the oak tree is a target of the acorn, it must therefore be present in some way. The adult oak tree is not contained in miniature inside the acorn, so we can rule that out. We find oak trees in nature, but it would be true that if all oak trees and saplings poofed out of existence so that only the acorns remain, the acorns would still grow into oak trees. So existing oak trees are not what maintain the target of the acorn either. Aquinas rules out other explanations as well, such as a Platonic third realm. Another explanation is that a mind could hold the target of the acorn, but it could not be a human mind, as the acorn would still grow into an oak tree if there were no humans. (It would help here to understand that Thomas thought the human mind became/took on the form of a thing when it grasped it – not the brain, and not to rule out the brain’s role, but referring to a non-corporeal power that is part of how human reasoning works. Thomists still agree with this, but this isn’t a philosophy of the mind topic). And it could not be the mind of intelligent aliens, or angels, or anything contingent, for what is contingent need not have been nor need be in the future, and if the contingent beings never were or disappeared, acorns would still become oak trees. Aquinas, through better reasoning than what I’ve presented here, concluded that it must reside in a mind that is eternal and necessary, such that it could not not have been. He provides reasons that it must be one, that it must be actus purus, that it must be non-composite, that it must be omnipotent (the cause of all things possible and holding the ends of all things possible), omniscient, etc… (these later attributes I’m just summarizing. I haven’t gone over reasons for them here–i mainly wished to expand on the “arrow must be pointed at a target” line). Essentially, it resides in an eternal, unchanging, omnipotent, omniscient mind that is the source of all existence once all is said and done.

Now, it might be that one would wish to object to the particulars of my example, such as an acorn and an oak tree, but it would hold true for the teleology of anything, whether it be something like a lifeform down to molecules, atoms, gluons, and so on. They “behave” or “react” as they do because their ends/“targets”/what-they-do-when-X-happens is present in some way, that is, within the divine intellect.

I hope that explanation aids discussion. If I’ve misstated the Fifth Way, please correct me.

I don’t think the Fifth Way is the only reason Aquinas argued that the First Cause must be an Intellect, though it is intended to support it, and it’s another argument that is intended, like the cosmological arguments, to show that the eternal, omnipotent, yadda yadda mind must exist.


Thanks for your reply.

Its going to take me a little while to get my head around what you have written. But what would you say to the objection that things just act according to the laws of physics. Why would one need a mind to explain that?

Now, i would be tempted to say that the laws of existence is better explained by an immaterial mind because all physical objects themselves are governed by laws and thus cannot be the first cause of physical law. I would also say that a first cause cannot be a natural cause because that would require potency and thus a mind or will to create is the only other solution.

But these are just my own attempts at philosophy, i would like to know how you think Aquinas would deal with that rebuttal.


Early morning post, so I’m not sure if I’ll be remotely coherent. But I’ll give it a shot.

You use the term “law of physics”, but what does that imply? It’s basically stating that there is an abstract object (the law) that is real and exists in itself. I don’t have an issue with abstract objects in general, but if you have an abstract object, it must be real in some way to have any effect. And if that’s not a mental object and it’s not a physical object floating out there, you’re basically taking a Platonic third real approach, no? [The third realm isn’t this physical space where ghostly forms float around, mind. That would be a misconception.] It’s possible that someone making this objection does take a Platonic approach. Actually, it’s not so uncommon among those who study the philosophy of mathematics, but it’d probably throw the common person who objects to all these types of things through a loop, as they’d be hesitant to affirm it.

The Aristotlean approach doesn’t explain physical laws with a “law of nature” approach, where the law of nature is some type of abstract object (Aristotleans do hold that there are abstract objects: universals (though not always abstract, just in some cases), propositions, mathematics, and other type things, but that’s not how they explain laws of nature). “Laws of nature”, to the Aristotlean, are just ways of describing how things behave in themselves (and this could of course be variable depending upon the conditions it finds itself in). So they’re not abstract and ontological brute facts existing in a Platonic realm of forms, they’re just how we explain the regular behavior of things. It’s in the nature of X to have teleology Y, and it’s in the nature of A to have teleology B, and we regularize the commonalities in formulas and “laws,” and God holds these essences in existence and has them directed towards their ends. Perhaps part of the approach of the fifth way is that this eternal, omnipotent being must also KNOW the essences.

Well, that’s an absolutely terrible go at it on my part, but I’m posting anyway. I’ve never really tried to defend or explain the Fifth Way before, so this is and will be a learning experience for me on how to write about it.


Universe is infinite therefore everything is possible within.


Hi, STT. This doesn’t address the argument being made in the Fifth Way. The argument, if it follows, would apply in a universe that was infinite in matter and energy, infinite in space, and which had no beginning.


Hi Wesrock,

No the argument doesn’t necessary follow when the universe is infinite. Everything is possible in an infinite universe. Could we agree on that? If yes, then it is possible that things to reach to a intelligent state of being as a result of mere chance which they act for an end. This doesn’t however mean that the process which leads to intelligence is intelligent, mere chance which is quite plausible in an infinite universe.


The Thomist argument of the first cause and inteligent design is not the same as our modern day ones, I recommend reading the Summa and see how Thomas argues that it even applies to an infinite universe.


What you write has nothing to do with Aquinas’ Fifth Way, though. As I wrote in my first post yesterday, this isn’t Paley’s intelligent design argument. That’s a common but very incorrect misunderstanding. It’s not about fine tuning or probability or any such thing. It’s not about the chances of life or intelligent life being improbable.


Could you please elaborate how the argument would apply to infinite universe?


So what is the argument about?


I provided some details earlier, but let’s see if I can come up with something pithy.

The Fifth Way is about why anything exhibits teleology at all.

Or perhaps…

The Fifth Way is about why anything exhibits certain, regular patterns of ‘behavior’ as opposed to some other behavior or no patterns of behavior at all.

EDIT: I should rephrase my summary to better speak to the aim of the Fifth Way.

That anything exhibits regular patterns of behavior (teleology) instead of other patterns or no patterns necessarily requires God.


Have you read my first post in this topic? Along with the details IWantGod posted?


As I said I am not a Thomist so I am bad at explaining it myself, but I think it would help if you just download this free book from an actual thomist.
Its in pdf format and easy to read and explains the basic gist of the five ways. He also has free podcasts about each way


That is not true. We know that the oak tree has potentiality to grow from an acorn because of miniature inside the acorn.

What is that reasoning?


Are you saying that there is a whole, miniature, adult oak tree within the acorn?

I presented some of it already. Probably better to resolve the first question you made, though, as that ties into this.


You could say the acorn has potentiality wink wink


No. I am saying that we know that an acorn has potentiality to turn into/grow into a oak tree because of miniature inside the acorn.



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