Aquinas’s Argument from Design Part 3: The End

In the previous post in this series on Aquinas’s Fifth Way, we introduced and briefly defended the reality of final causation as the only possible sufficient metaphysical explanation for the natural order and regularity of cause-effect relationships. We noted that when some being, even a non-rational being, acts, it must have some effect. If it has no effect, then it has not really acted at all. And the effect must be a specific, determinate effect: this effect rather than any other of the infinite number of possible effects. And in order to explain why the action has this specific, determinate effect rather than any other, it is necessary to posit that there is some reason/end towards which the action itself is intrinsically directed.

We must be clear, however, what we mean by an “end”, “goal”, or “purpose” for which natural things act. In ordinary human language, an end/goal/purpose is something we are consciously aware of, something we choose and seek of our own volition. In this sense, one might object, it is just abundantly obvious that non-rational beings such as a rock or an atom or a star do not act for an end/goal/purpose, precisely because they are non-rational and hence not able to have any conscious desires or intentions. But this objection misunderstands Aquinas’ use of language. Aquinas is not suggesting that the moon, in orbiting the earth, is consciously choosing to do so, or even consciously aware in any way at all. That would be preposterous. Rather, he is just insisting that “orbiting the earth” is something the moon is naturally and intrinsically directed towards by its very nature. (Of course, we know the moon actually orbits the earth because it is affected by gravitational forces. But 1) the moon first must be the type of thing susceptible of being affected by gravitational forces in such a way, and 2) those gravitational forces themselves arise from the activity of subatomic particles, so our analysis of action, which we are here applying to a larger, more macroscopic scale, can just be pushed back to the smaller scale).

So when Aquinas (and Aristotelians generally) claim that natural things are acting for an end/goal/purpose, they are using this language to refer to general “directedness” in those things. Human final causality is just one specific instance of final causality broadly. All agent causes act for ends. Rational creatures such as humans, however, are consciously aware of those ends, and can choose or will which ends they seek. Non-rational creatures are inclined towards their ends automatically, naturally, and determinedly. Aquinas notes this distinction:

“Although every agent, both natural and voluntary, intends an end, still it does not follow that every agent knows the end or deliberates about the end . . . in natural agents the actions are determined, hence it is not necessary to choose those things which are for the end . . . Therefore it is possible for the natural agent to intend the end without deliberation; and to intend this is nothing else than to have a natural inclination to something” [1].

Aquinas also points out that even rational creatures, for whom “deliberation is proper”, sometimes act without deliberation. The clearest example of this is in the distinction biologists make between voluntary and involuntary human actions. Breathing, for instance, is something that is mostly done completely outside of our conscious decision and control. Aquinas makes an analogy between such actions and the actions of non-rational beings. Non-rational beings are not consciously aware of the ends they are pursuing. They do not “think” about it, or deliberate, or decide. To say natural agents act for an end is just to say that it has “a natural inclination to something”, to some determinate effect, as we defended in the previous post.

Aquinas gives a fuller explanation of his view of final causality:

“Every agent, of necessity, acts for an end. For if, in a number of causes ordained to one another, the first be removed, the others must, of necessity, be removed also. Now the first of all causes is the final cause. The reason of which is that matter does not receive form, save in so far as it is moved by an agent; for nothing reduces itself from potentiality to act. But an agent does not move except out of intention for an end. For if the agent were not determinate to some particular effect, it would not do one thing rather than another: consequently in order that it produce a determinate effect, it must, of necessity, be determined to some certain one, which has the nature of an end. And just as this determination is effected, in the rational nature, but the ‘rational appetite,’ which is called the will; so, in other things, it is caused by their natural inclination, which is called the ‘natural appetite'” [2].

Here Aquinas actually designates the final cause as the “first of all causes”, meaning that it is causally prior to and more fundamental than the other types of causes (this will be a significant point which we will return to). How so? Recall (harkening back to my very first series of posts on Aquinas’ First Way) that Aquinas, following Aristotle, posited four causes: material, efficient, formal, and final. The “matter” and “form” of a cause can also be considered in terms of “potency” and “act”, respectively. Indeed, in the passage just quoted, Aquinas uses them almost interchangeably. When something is caused to happen, all four of these causes are needed to fully explain it. For something to “happen” is for a potency to be “reduced to act”, or actualized. The efficient cause is the agent which actualizes the potency. The final cause is that for the sake of which the efficient cause acts. As was argued in the previous post, and as is summarized in Aquinas’ quote here, without a final cause, an efficient cause just could not act. If the agent is not directed towards some determinate effect, then there will be no effect, and hence no action. As Edward Feser puts it, “Unless a cause were inherently directed towards a certain effect or range of effects . . . there would be no reason why it should bring about just that effect or effects. In other words, we cannot make sense of efficient causality without final causality” [3]. And so, he writes, “Final causes are prior to or more fundamental than efficient causes, insofar as they make efficient causes intelligible . . . [The final cause is] that which determines all of the other causes. For something to be directed towards a certain end entails that it has a form appropriate to the realization of that end, and thus a material composition suitable for instantiating that form” [4]. Without a final cause, an efficient cause could not act. And without an efficient cause, a potency could never be reduced to act; and hence nothing at all could ever happen. There could be no cause-effect relations whatsoever.

Aquinas continues:

“Nevertheless it must be observed that a thing tends to an end, by its action or movement, in two ways: first, as a thing, moving itself to the end, as man; secondly, as a thing moved by another to the end, as an arrow tends to a determinate end through being moved by the archer who directs his action to the end. Therefore those things that are possessed of reason, move themselves to an end; because they have dominion over their actions through their free-will, which is the ‘faculty of will and reason.’ But those things that lack reason tend to an end, by natural inclination, as being moved by another and not by themselves; since they do not know the nature of an end as such, and consequently cannot ordain anything to an end, but can be ordained to an end only by another . . . Consequently it is proper to the rational nature to tend to an end, as directing (agens) and leading itself to the end: whereas it is proper to the irrational nature to tend to an end, as directed or led by another, whether it apprehends the end, as do irrational animals, or do not apprehend it, as is the case of those things which are altogether void of knowledge” [5].

Here we have reinforced the distinction between tending towards an end in rational as opposed to non-rational beings. But, Aquinas asserts, those natural, non-ratioanl beings cannot tend themselves towards a certain determinate end; they must be directed by another. This is implicit in our descriptions of finality: we say that a final cause is that end towards which a thin is naturally inclined or ordered or directed, all of these verbs being passive in voice, implying that the subject is acted upon. To say that something is “directed towards” is different from saying that it “directs” or “is directing”. Thus our very use of language points towards the reality of this fact. A non-rational thing cannot direct itself towards its proper end, it must be directed by another.

The principle of finality itself was presented as the only sufficient metaphysical explanation of regular cause-effect relationships. If we do not posit that an agent is naturally inclined or directed towards its effect as to an end, then there is no explanation for why the cause would have that particular effect at all. But this just brings us to another problem in need of explanation. Final causality explains cause-effect relationships, but final causality itself is in need of explanation. We can say that the combination of two hydrogen atoms with a single oxygen atom will result in the production of a water molecule because the atoms are inherently directed towards that effect; but then we must ask how or why they are inherently directed towards that effect. When I walk into a buffet, I know which foods I might desire, and choose which foods I eat based on specific reasons I have for wanting those foods. But an acorn planted in the earth has no knowledge at all of an oak tree. It cannot choose to grow into an oak tree. It cannot direct itself towards becoming an oak tree. Aquinas’s frequent use of the example of an arrow being shot is revealing. An arrow is shot from a bow by an archer. The arrow is aimed towards a specific target. The arrow could hardly have aimed itself; it had to have been aimed at the target by the archer.

So from all of this we have established this much of Aquinas’ Fifth Way:

“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” [6].

What comes next is more complicated. For next Aquinas states:

“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” [7].

Before, we indicated the analogy of the arrow as just showing that a cause must be directed to its end by something other than itself. But here Aquinas goes further. The archer, in order to direct and aim the arrow, must know the target, and hence must be “intelligent” or rational. Philosopher Garrigou-Lagrange writes:

“Now, irrational beings cannot tend towards an end, unless they are directed by an intelligence . . . In fact, one thing cannot be directed to another, unless there by a directing cause, which must, of necessity, be intelligent . . . Why? Because an intelligent being alone perceives the raison d’etre of things, and the end is the raison d’etre of the means . . . If, therefore, there were no intelligent designer directing the world, the order and intelligibility existing in things, which science reveals to us, would be the effect of an unintelligibly cause . . . which is absurd. There is, therefore, a supreme intelligent Being, who directs all things to their proper respective ends” [8].

This, however, might seem like quite a leap. To explain and defend it a bit more in depth, we ought to briefly take a step back. We established that it simply must be the case that agent causes are inherently directed towards a determine end. But notice the strangeness of such a statement: the effect of a cause cannot actually exist before the cause itself acts, by definition; for then the effect would be prior to the cause, which is absurd. If an effect were prior to its cause, it would just make no sense to say that it is an effect at all. The cause-effect relationship would be unintelligible. So before the agent acts, its effect cannot actually exist. But the agent must be directed towards the end before it acts, otherwise it could not act at all. But how can something be directed towards something else if the latter does not actually exist? How can an agent cause point towards an end, if that which it points towards is non-existent? It cannot. So we are left with the startling conclusion that the end, as an effect, must somehow, in some sense, exist prior to the action of the cause. If it did not, the cause could not be directed towards it, and thus could not be able to act at all. So in what sense can the effect be said to exist? It cannot actually exist (in the order of “real being), as we said; but it must exist in some sense. The only other option, however, is that it exists in the order of “mental being”, i.e. as an idea in a mind. So philosopher W. Norris Clarke writes:

“The final cause, as determining the action of the efficient cause to produce this effect rather than some other, must be somehow present in the agent, guiding its action, before the effect is actually produced in its own real being. But it cannot be present in the mode of real being, since the effect does not yet exist in its real being until it is actually produced by the agent, at the term of the action. The final cause, therefore, must exist in the agent as a present orientation or dynamic relation to a not-yet-existent-future. Such a presence, as the term of a relation to a not-yet-existent future, cannot itself be that of a real being. Hence it must be present in some mode of mental being, or idea, even though it is not necessarily recognized as such by the immediate agent in which it resides, i.e., in all non-conscious agents . . . Now the only adequate sufficient reason for the presence of this not yet existent future in the form of a mental being within the agent must be that power which alone can make the future present, in the mode of mental being, and that is precisely intelligence, which can make a future effect in its consciousness as a goal to-be-produced and think up appropriate means to achieve this end. The ordering of means to achieve a not-yet-existent end is in fact one of the defining characteristics of intelligence itself” [9].

To go back to my example of the buffet: when I choose to eat, say, the salad, the salad becomes the end/goal of my action, that which causes me to walk up to the buffet, put salad on my plate, and begin to eat it. But as a rational agent, my choice to eat the salad acts as a conscious end because the salad can “exist” as a concept or idea in my mind, which guides my will to choose to eat it. This is how ends work. Edward Feser writes:

“One of the common objections to the very idea of final causation is that it seems to entail that a thing can produce an effect even before that thing exists. Hence to say that an oak tree is the final cause of an acorn seems to entail that the oak tree — which doesn’t exist yet — in some sense causes the acorn to pass through every stage it must reach on the way to becoming an oak, since the oak is the ‘goal’ or natural end of the acorn. But how can this be? Consider those cases were goal-directedness is associated with consciousness, as it is in us. A builder builds a house, and he is able to do so because the effect, the house, exists as an idea in his intellect before it exists in reality. That is the way in which the house serves as the final cause of the actions of the builder as those actions are the efficient cause of the house. Indeed, that is the only way the house can do so. For a cause, to have any efficacy, to must in some sense exist; and if it doesn’t exist in reality, then the only place left for it to exist . . . is in the intellect” [10].

In short, “it is impossible for anything to be directed towards an end unless that end exists in an intellect which directs the thing in question towards it” [11]. What are the implications of this? The only explanation is Aquinas’s conclusion that “some intelligent being exists by whom all natural things are directed to their end”. Or, as Feser puts it, “It follows that the system of ends or final causes that make up the physical universe can only exist at all because there is a Supreme Intelligence or intellect outside that universe which directs things towards their ends” [12].

Several things must be immediately made clear before misunderstanding arises. One instant objection might be: “Well, what directs that agent towards its ends?” But remember that Aquinas’s whole argument only refers to non-rational beings, or “things which lack intelligence.” He is not saying that rational agents require some external cause to determine their ends, because rational agents, qua rational agents, are just by definition things which determine their own ends. Indeed, that was the very distinction he pointed out in the passage quoted earlier, between agents which “move themselves to an end” and agents which “are moved by another to an end”. This Supreme Intelligence, then, is not something which requires a further intellect to determine its ends, since, as an intelligent agent itself, it can determine its own ends, and likewise the ends of all natural things. In short, this argument contends that any action at all requires the principle of finality, but the principle of finality itself is only explicable if there is some Supreme Intelligence in whose Intellect exists all the ends of all natural beings, and who accordingly guides and directs those beings towards those ends, as an archer aiming an arrow. So Clarke concludes:

“This requirement of a planning intelligence, however, can be filled in two ways: (1) if the agent itself is intelligent and can determine itself to its own goals of action; or (2) if the immediate agent itself is not intelligent, then somewhere along the line an intelligent planning cause has constructed the nature of this agent so that it has an innate natural tendency toward the production of this end, even though quite unconscious of why it is doing what it does, since this dynamic orientation is infused deep into its very nature before it can perform the actions leading to this end. These innate goal-oriented tendencies are like incarnate ideas, thought up by another and projected into natures which cannot think their own natural drives — ideas put to work in matter, so to speak, by their intelligent causes, in a way analogously similar to the way a human maker of a machine imbeds the idea of its purpose into the very internal order and ‘being’ of the machine, so that it can carry on its work even if the maker of the machine ceases to exist. Thus every dynamic natural property of a non-conscious agent is an innate ontological ‘intentionality’ toward a determinate type of effect, which it will carry out whenever the conditions of the surrounding environment permit . . . The whole of nature can now be seen in much greater depth as ideas at work in matter, woven into it by a Master Planner” [13].

How astoundingly profound, to come to understand that all of nature, the entirety of the universe, is essentially, in its very being, meaningful, designedintendedintelligible, because, ultimately, idea is more fundamental than physical matter.

But why think this “Supreme Intelligence” is God in the classical sense? Firstly, it just seems obvious that if there is indeed a Supreme Intelligence outside of the universe which is directing all things within the universe towards their particular ends, and is the ultimate guiding cause of all effects, then this Agent could hardly fail to warrant the title “God”.

To move more fully to the God of Classical Theism, however, one would have to already accept the conclusions to the previous four of Aquinas’s Five Ways. Recall what we said earlier about the relation of the four causes, and how the final cause is the most fundamental thereof. The other causes all depend for their operation on the final cause. And so if the other causes point ultimately to a First Cause (as the first and second Ways establish), that First Cause itself would have to be identical to the Supreme Intelligence which directs all final causes. Final causes, as we’ve said, are inherent within the nature/essence of things. A thing, by its essence, is naturally directed towards its determinate ends/effects. But an essence can only be really existent if it has been actualized in existence, if its essence has been joined to an act of existing, by that First Cause whose essence and existence are identical, who is Existence Itself. So it must be that this First Cause, which is Existence Itself, which brings all beings and their essences into existence, is the same Being which is the Supreme Intelligence that imbues those essences with their intrinsic teleology. To actualize an essence is to cause it to exist; and, as we’ve seen, such causal action would require an end. And as Feser points out, “In that case there would have to be a higher intelligence directing that potency to its end, and we would be off on exactly the sort of regress that, for reasons we have already seen, must in Aquinas’s view terminate in a first member” [14]. So the Supreme Intelligence must be identical to the First Cause, Being Itself, Pure Act, who is God. And the Fifth Way alone successfully establishes that this Being is truly personal, in the sense of being intelligent, rational. Indeed, since all beings derive from Him, and derive their action and ends from Him, we can say that this Being is the most truly and fully rational Being in existence. And so Garrigou-Lagrange states that “He must be Thought itself, self-subsisting Intellection” [15]. And this Being we can rightly call God.

But note the significance of this conclusion. It is somewhat common to hear a narrative such as: “People only believed in gods because in ancient times they didn’t understand nature, so they explained everything by way of divine agency.” The idea is that everything now can be explained entirely in natural terms, and hence there is no reason to appeal to divine agency. Take, for example, evolution. Popular atheist writer Richard Dawkins misunderstands the Fifth Way, and takes it as claiming that since life looks designed, there must be a designer. He then responds that life may look designed, but it is explained by way of natural selection and evolution, so we have no need to appeal to a designer. Aquinas actually summarizes this type of objection:

“It is superfluous to suppose that what can be accounted for by a few principles has been produced by many. But it seems that everything we see in the world can be accounted for by other principles, supposing God did not exist. For all natural things can be reduced to one principle which is nature; and all voluntary things can be reduced to one principle which is human reason, or will. Therefore there is no need to suppose God’s existence” [16].

So the question becomes, can we explain everything by naturalistic means only? Is everything ultimately reducible to the one explanatory principle of “nature”? There is a sense in which the answer is possibly yes. For natural sciences work, especially now, on somewhat of a horizontal plane. And on that horizontal plane itself, everything may be ultimately explicable in terms of purely natural means. A biologist, for example, studying the life of trees may not have any need whatsoever to appeal to final causation to explain the growth of an acorn into an oak tree. “God did it” is not only a very shallow scientific explanation, it’s also detrimental to the natural science itself, which studies the realm of secondary causes and their processes. But just because a biologist, for her purposes, can explain the growth of the tree in a completely mechanistic way that is sufficient for her scientific inquiry, does not mean that such a mechanistic description will be the entirety of the explanation. In other words, the biologist has not given a fully complete explanation, at all. As we argued in the previous post, the scientist, for one thing, just assumes the regularity and causal structure of nature and works from there. But a metaphysician is seeking a somewhat deeper, underlying explanation, and so the scientist’s description will not be sufficient. The natural scientist is working on the horizontal realm of secondary causes, but the metaphysician is seeking first causes, which themselves explain those secondary causes. And the metaphysician will discover, as the Five Ways show, that, at bottom, there simply cannot be a purely natural explanation. Nature cannot be the ultimate explanation, for “since nature works for a determinate end under the direction of a higher agent [as the Fifth Way proves], whatever is done by nature must needs be traced back to God, as to its first cause” [17]. But also note that this answer preserves the dignity of secondary causes. The Thomist can fully agree with and support the biologist who concludes that the diversity of life is the result of natural selection and evolutionary processes, because the Thomist agrees that nature really is a principle of things that can be appealed to as explanation. It is just not the ultimate explanation.

And to reiterate, the Fifth Way (contra Dawkins’ interpretation) is just not saying anything at all about the apparent “design” in living things. That, as we explained in the first post, would be an instance of extrinsic teleology whereas the Fifth Way is working with intrinsic teleology, and as a result is far stronger and more certain. The Fifth Way is not claiming “life looks designed so it must have a designer!” Rather, the Fifth Way is arguing that actually, in order for nature to work at all, in order for there to be any sort of cause-effect relationships and hence any sort of causal action whatsoever, there has to be an Ultimate Intelligence guiding all natural things to their proper ends. And this Ultimate Intelligence is what we call God.

And so we have reached the End, having concluded, after over a year, our series introducing and defending Aquinas’s Five Ways.



[1]. Thomas Aquinas. De Principiis Naturae. Translated as THE PRINCIPLES OF NATURE TO BROTHER SYLVESTER by R. A. Kocourek. Html-edited by Joseph Kenny, O.P. <;. 3.19.

[2]. Aquinas, Thomas. Summa Theologica. 1265-1274. Trans. Fathers of the English Dominican Province. Coyote Canyon Press, 2010. ebook. I-II, Q. 1, Art. 2.

[3].  Feser, Edward. Aquinas. London: Oneworld Publications, 2009. Print, 18.

[4]. Ibid.

[5]. Aquinas. Summa. I-II, Q. 1, Art. 2.

[6]. Aquinas. Summa. I, Q. 2, Art. 3.

[7]. Ibid.

[8]. Garrigou-Lagrange, R. God, His Existence and His Nature, Volume I: A Thomistic Solution of Certain Agnostic Antinomies. Translated from the Fifth French Edition by Dom Bede Rose, O.S.B., D.D. St. Louis: B. Herder Book Co., 1939. ebook.

[9]. Clarke, W. Norris. The One and the Many: A Contemporary Thomistic Metaphysics. Notre Dame: University of Notre Dame Press, 2001. Print, 204.

[10]. Feser. Aquinas. 116-117.

[11]. Ibid. 117.

[12]. Feser, Edward. The Last Superstition: A Refutation of the New Atheism. South Bend: St. Augustine’s Press, 2008. ebook.

[13]. Clarke. The One and the Many. 205.

[14]. Feser. Aquinas. 118.

[15]. Garrigou-Lagrange. God, His Existence and His Nature. ebook.

[16]. Aquinas. Summa. I, Q. 2, Art. 3.

[17]. Ibid.


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