Aquinas’s Argument from Design Part 2: Final Causality

In the first post in this series on Aquinas’s Fifth Way, I introduced and explored several historical examples of different “teleological arguments,” of which the Fifth Way is one. In this post, I will make some final distinctions between the Fifth Way and other teleological arguments, and then begin laying out, explaining, and defending Aquinas’s argument.

For the most part, the majority of teleological arguments make use of what we might call “extrinsic” teleology, whereas the Fifth Way is based upon intrinsic teleology; it is largely for this reason that I think the latter is much stronger and more successful than the former. To grasp this, we might consider an example: Suppose you’re walking along a beach and come across some sticks arranged into a word. The word, qua word, is teleological; it conveys meaning, “points to” some meaning beyond itself. The sticks, on the other hand, in themselves are not teleological, at least in relation to the word. A stick, in itself, does not signify anything beyond itself (what it is), unless such further signification is imposed upon it externally, as in the case when the sticks are arranged to depict a word. So, when you walk on the beach and come across the sticks arranged into a specific word which conveys a meaning, you most likely conclude that some rational agent, some intelligence, some human person, was causally responsible for arranging the sticks. Because sticks in themselves do not convey a meaning beyond themselves, and yet because they have been externally arranged to convey a meaning beyond themselves, you conclude that some intentional and purposeful agent has imposed the meaning.

This is a simplistic example of what many teleological arguments are essentially. Many such arguments take some feature of the world and reason that this feature displays intention, purpose, design, etc. in a way that the world in itself could not unless it received some external teleological imposition. Take, for instance, a version of the the “Fine Tuning argument” popularized by the likes of philosopher William Lane Craig [1]. This argument maintains that the fundamental cosmological constants of the universe have an astronomically narrow and precise life permitting range, and hence must have been “fine tuned” in order to allow for a life permitting universe such as that which we observe. In effect, it argues that the fundamental cosmological constants of the universe were “designed” intentionally and purposefully for life. Notice here, however, that this intentionality comes from without, external to the universe itself. In order to be successful, the argument must maintain that the universe in itself is not the type of thing which could be directed naturally towards life, unless such direction were externally imposed upon it.

Recognition of the Fine Tuning argument as essentially dependent upon extrinsic teleology is not necessarily a critique. After all, there are some obvious cases where one is justified in concluding the agency of some intelligent cause from an instance of extrinsic teleology. In our example of the sticks on the beach, it would just be natural and automatic for one to see the word made out of sticks and reason that some person was responsible for arranging them. Whether teleological arguments which make use of extrinsic teleology, such as Craig’s Fine Tuning argument, are successful is not our purpose to discuss here. Aquinas’s Fifth Way differs fundamentally from other teleological arguments in that it makes no reference to extrinsic teleology, and instead is dependent upon intrinsic teleology.

At its most basic level, the Fifth Way might be thought of as seeking to answer the question of why things happen. Not just why things exist as they do, but why things happen. And in this sense, Aquinas’s Fifth Way is more simple and more fundamental than most other teleological arguments. We notice, via our sense perception and experience of the world, not only that objects exist, but that events take place: Things move, change, act, interact, happen, undergo, etc. Indeed, if this were not the case, our very experience of the world itself would be rendered inert and impossible, since sense perception requires the external objects to act, and their action to somehow interact with our own senses, which receive and interpret the stimulus communications. So we notice that things happen, that events take place, that objects act; and our question begins by wondering why this is so. What explains this?

But our question extends further, for we notice not only that things happen, but that things happen regularly and orderly. This is where Aquinas begins his argument: “The fifth way is taken from the governance of the world”, which governance involves things “acting always, or nearly always, in the same way, so as to obtain the best result” [2]. This is, in fact, the very foundation and heart of all scientific inquiry, really of all intellectual inquiry of any kind. As Aristotle comments in the Physics: “Our first presupposition must be that in nature nothing acts on, or is acted on by, any other thing at random, nor may anything come from anything else.” Nature does not act randomly: This simple yet incomprehensibly profound fact is what enables us to function as beings with intellect, what enables us to interact in and with the world around us in a coherent manner, what from the very beginning inspired thinkers to try to understand reality through philosophy and science and express it through literature and the arts. In perceiving and experiencing physical reality, we become aware of definitive patterns and relationships. If I throw a rock at a window with enough force, it will break. If I drop an apple from a cliff it will fall, not grow wings and fly off into the sunset. It is not the case that anything may come from anything. Cows don’t lay eggs. Gold doesn’t grow on trees. Elephants cannot fly. Rocks don’t shape shift at will. If you light a candle it doesn’t suddenly start performing a beautiful rendition of Handel’s Messiah at the top of its lungs. It is just undeniably evident that in nature, things act orderly and with regularity.

When you smash an egg on a hard surface, it cracks. When you pluck a string on a guitar, it emits sound. When you toss a coin in the air, it falls back down. The moon orbits the earth, the earth spins on its axis and orbits the sun. Combining two atoms of hydrogen with a single atom of oxygen will always produce a molecule of water. The gravitational force attracts objects with mass. The strong nuclear force binds quarks and nucleons at subatomic levels. Eyes see, ears hear, hearts pump blood. Zygotes develop into fetuses and eventually into newborn babies. Babies grow into toddlers, and then into children, then to teenagers, adults, elders. Etc. This regularity is what allows for patterned predictability in scientific experiment, and the creation of theoretical models. It’s what allows for any sort of inductive reasoning. All else being equal, barring any interferences, any and every time I combine two hydrogen atoms with one oxygen atom, I will produce a water molecule. The combination will not result in combustion, or the sound of a violin, or the implosion of a planet billions of lightyears away. Natural is regular and ordered.

So what explains this? Notice that scientific method (as the moderns understand it) is in principle incapable of offering a sufficient explanation for this natural regularity, for modern scientific method just assumes it, works necessarily on the presupposition of its existence, as Aristotle noted. Modern scientific method works on the basis of patterned predictability and creation of theoretical models for testing, as we’ve noted; and this just doesn’t work if regularity isn’t assumed. Since modern scientific method operates on the basis of the existence of natural regularity, it in itself cannot hope to offer a sufficient explanation thereof. Rather, we must find a metaphysical explanation. And as Aquinas argues, the only possible metaphysical explanation of natural regularity is what he calls, after Aristotle, “final causation”.

In short, the principle of final causality is that every agent/efficient cause acts for an end. If this were not the case, then nothing could act at all. There would be no cause and effect relationships, and hence no events. Nothing at all could happen or take place. The principle of final causality is the only sufficient metaphysical explanation of the regular and specific relationship between cause and effect. In other words, final causality explains why this cause always produces/results in this effect, rather than any other possible effect.

To quote extensively from philosopher Ed Feser:

“The universe is filled with natural regularities; this is uncontroversial. These include the regularities manifested in the biological realm–the way the heart pumps blood, thus keeping an organism alive, or the way a species is so adapted to its environment that its members can reliably find sources of food, reproduce themselves, and so forth–but Aquinas is not especially interested in these over any others. Indeed, unlike [William] Paley and ‘Intelligent Design’ proponents, he is not, for the purpose of the Fifth Way, particularly interested in complexity per se at all. The regularity with which the moon orbits the earth, or the regularity of the way a struck match generates fire–both very simple examples compared to eyes, hearts, species, and the like–are no less important. Indeed, they are more important for his argument. For life is a fairly rare phenomenon, confined so far as we know only to the earth. But the far simpler causal regularities I have been speaking of are completely general, and pervade the physical universe. Indeed, they largely constitute the physical universe, which can be thought of as a vast system of material elements interacting according to regular patterns of cause and effect. But there is no way to make sense of these regularities apart from the notion of final causation, of things being directed toward an end or goal. For it is not just the case that a struck match regularly generates fire, heat, and the like; it regularly generates fire and heat specificallyrather than ice, or the smell of lilacs, or the sound of a trumpet. It is not just the case that the moon regularly orbits the earth in a regular pattern; it orbits the earth specificallyrather than quickly swinging out to Mars and back now and again, or stopping dead for five minutes here and there, or dipping down toward the earth occasionally and then quickly popping back up. And so on for all the innumerable regularities that fill the universe at any moment. In each case, the causes don’t simply happen to result in certain effects, but are evidently and inherently directed toward certain specific effects as toward a ‘goal’ . . . This doesn’t mean they are consciously trying to reach these goals; of course they are not. The Aristotelian idea is precisely that goal-directedness can and does exist in the natural world even apart from conscious awareness” [3].

So now we are in a better position to understand the beginning of Aquinas’s presentation of the 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” [4].

The natural regularity of causal relationships in objects necessitates the principle of final causality as sufficient metaphysical explanation.

This, of course, is quite contrary, even extremely so, from the modern framework of thought, where acting “purposefully”, goal-directedly, for an “end”, is resigned to the domain of rational agents, namely human beings. Human beings have goals, intentions, purposes, and ends for which they act; rocks and atoms and trees do not. But consider here what the goal-directed behavior of rational agents partly consists of: choosing between a vast range of possible options for actions by way of seeking some ultimate purpose. To see this, let’s examine a very simplistic example. Imagine you walk into a restaurant which is an “all-you-can-eat” buffet dinner. You pay once and now are allowed to eat a nearly unlimited amount of food–whatever you want. At the buffet are a large plethora of various foods: salads, breads, meats, pastas, fruits, etc. And you can choose absolutely whatever you want. On what basis will you make your choice? Why do you choose one food item over another? Consider the possibilities: Perhaps lasagna is your absolute favorite food, so you choose the lasagna. In this case, the reason to explain your action is your desire for taste satisfaction. This end “drives” your choice/action; it explains and even causes your action, by moving and directing it towards itself. But suppose, despite your fervent love of lasagna, you are trying to eat healthily, and hence choose salad instead. Here there is a different end which moves and motivates your action, but an end nonetheless. Or suppose you love all the foods equally, and have no principle of choosing between them, and so you close your eyes and point at random, at whatever food you see when you open your eyes again, that’s the food you choose. You might think here that your action has no end, that it is essentially random. But that is not the case. Perhaps you ending up pointing at chicken, and choose to eat that. Here your action still has an end, an explanation–the pointing–even if you did not consciously “pick” it over the others.

In short, any action we purposefully choose to undertake can only be explained by some end which directs it. What is unique to rational agents specifically is the ability to know different ends and choose between them. But all actions, even of non-rational things, must ultimately be for some end, or else they would just be inexplicable. Go back again to the example of combining hydrogen and oxygen atoms to form a water molecule. Here, you, as the conductor of the experiment, are the efficient cause, the agent which brings together the atoms. But why does brining together hydrogen and oxygen atoms always result in the creation of a water molecule? After all, there are theoretically an infinite number of possible effects or “results” that an action qua action could have. Turning into cheese is an effect; undergoing nuclear fusion is an effect; mooing is an effect; growing is an effect; orbiting is an effect; and so on and so on. What is it that ties all these effects to their specific causes? What is it that binds the relationships between causes and effects? What is it that explains why hydrogen and oxygen atoms when properly combined always result in a molecule of water, rather than a molecule of acetic acid, or a star, or a horse? There are an infinite number of possible effects, so why do causes only result in specific, determinate effects? The only metaphysical explanation is that the causes, by their very nature, are inherently directed to those certain determinate effects as to their ends. If causes did not by nature inherently have specific determinate effects, then there just would be no possible cause-effect relationships at all, and hence no natural regularities.

Feser writes elsewhere:

“It is the existence of any causal regularities at all that [Aquinas] takes to require explanation . . . For Aquinas, the fact that A regularly brings about B, as B’s efficient cause, entails that bringing about B is in turn the final cause of A. For if we did not suppose that A inherently ‘points to’ or is ‘directed towards’ the generation of B as its natural end, then we would have no way to account for the fact that A typically does generate B specifically, rather than C, or D, or E, or indeed rather than no effect at all. Of course, some interfering factor might prevent A from bringing about its typical effect, or from bringing it about fully or perfectly; this is why Aquinas speaks of a cause bringing about the ‘best’ or perfect result at least ‘nearly always.’ But these unusual cases can only be understood against the backdrop of the typical case, and in particular in light of the fact that a cause inherently points to the best or most perfect realization of its effect, even if it might sometimes be prevented by circumstances from bringing it about” [5].

The ends towards which a particular thing is directed are limited and determined by its nature. An acorn planted in the earth has the potential to grow into/become a tree, but not an elephant. The potencies are contained within its nature. As a human being I can choose to walk or run down the street, but not to flap my arms and fly. A thing’s nature contains only a limited number of potencies, and it is directed towards the realization of these potencies as the fulfillment of its nature and being.

Philosopher Reginald Garrigou-Lagrange writes:

“This terminus of their action, precisely because it is something determinate and in complete conformity with their nature, is entitled to the name of end; for the end is the good in view of which an agent acts . . . The necessity and universality of the principle of finality are evident truths” [6].

And Aquinas states that, “Were it otherwise [that every agent cause acts for an end] . . . one thing would not follow from the action of the agent more than another . . . For the natural agent to produce an effect which is determinate, it must be determined for some particular effect, and this is what is meant by the word end” [7].

Philosopher W. Norris Clarke explains:

“If the efficient cause at the moment of its productive action is not interiorly determined or focused toward producing this effect rather than that, then there is no sufficient reason why it should produce this one rather than that. Hence it will produce nothing at all: indeterminate action is no action at all, hence can produce no determinate effect. But the effect as a real being must be determinately this or that, and this determination must be explained by, or find its sufficient reason in, the cause which brings it into being. This dynamic pre-ordination or predetermination of the cause toward this determinate effect, as precontained in the cause at the moment of its action and perduring throughout the action as its guiding form, is precisely what is meant by final causality, or focused efficient causality, efficient causality focused toward a determinate end or goal = the effect-to-be-produced as guiding the action of the efficient cause as it produces its effect. The final cause resides, therefore, in the efficient cause but as focused toward its future effect-to-be-produced . . . Every effect of an efficient cause must be some determinate being or mode of being. But precisely because it is an effect depending on its cause, with its sufficient reason for existing located in its cause, its efficient cause must contain the sufficient reason not only for its existence but for its particular mode of existence, for its being this particular effect and not some other. Otherwise, it would have no sufficient reason for its being as it is. It follows that the agent at the moment of its action, and throughout the execution of the same, must contain within itself an interior determination or pre-ordination of its power toward producing this effect rather than some other . . . [Therefore] every efficient cause, in order to be an efficient cause in action at all, must act for an end, i.e., its action must be finalized, directed, focused from within toward the effect to be produced as end or goal to be attained” [8].

To go back to our “buffet” example: you will either choose to eat a food, or not choose to eat, in which case you will not eat anything. If you do choose to eat, you must choose something to eat. But in order to choose one food over another, you must have some reason or principle which explains choosing one over the other. This is reflected in non-rational beings which act as causes. When beings act, they must have some action which is their effect–if not, there is just no real action at all. But if there is an effect, it must be some specific effect, this fact rather than some other effect. And in order to explain why it is this specific, determinate effect rather than any other, there must be some reason/end which directs the cause towards itself.

This is “intrinsic” teleology, which must be distinguished from the extrinsic teleology discussed at the start of this post. Aquinas is here referring to the natural, inherent tendency of things in our universe to act for determinate ends with order and regularity, which can only be explained by this principle of final causality; not for some extrinsic “design” imposed upon thins externally.

So we have reached the conclusion of the reality of final causation. In the next post we will delve into the rest of the argument, which moves from the reality of final causation to the necessary existence of God as explanation thereof.



[1]. For an introductory or “beginner’s” presentation of the argument, see Craig’s animated video here.

[2]. Aquinas, Thomas. Summa Theologica. 1265-1274. Trans. Fathers of the English Dominican Province. Coyote Canyon Press, 2010. ebook. I, Q. 2, Art. 3.

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

[4]. Aquinas. Summa Theologica. I, Q. 2, Art. 3.

[5]. Feser, Edward. Aquinas. London: Oneworld Publications, 2009. Print, 113.

[6]. 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.

[7]. Aquinas, quoted in Ibid.

[8]. Clarke, W. Norris. The One and the Many: A Contemporary Thomistic Metaphysics. Notre Dame: University of Notre Dame Press, 2001. Print, 200-201.


5 thoughts on “Aquinas’s Argument from Design Part 2: Final Causality

  1. I think one is placing a different emphasis on “goal” by presuming it has something to do with personal goals. But in the cosmos death is as common as life, and more species have gone extinct than survive today. So there are many goals to take note of depending on where one looks. Humans are a late arrival in the cosmos, very late, and might not be here tomorrow, or they might be changed, or even devolve. Religions change as well, compete, and form new branches or schismatic divisions, leaving many ancient sects now extinct. What does all this constant movement of matter and energy and social evolution mean?

    One can of course assume all sorts of goals via enough imagination. One could assume the nose was placed in the middle of the face in order to support eyeglasses. Or that cork trees exist for the goal of making glass bottle stoppers.


    • Aquinas in no way “presumes” that natural goals have something to do with “personal” goals. He makes very clear that in this argument he’s referring to non-personal, non-intelligent, non-rational agents. His conception of “goals” or “ends” is much broader than our normal use. It isn’t restricted to conscious goals/ends. Instead, using goal/end to refer to the action of non-rational beings is analogous, as I explained in the article. It refers simply to determinate effects of agent causes. For example, hydrogen and oxygen molecules interact and result in a water molecule. This is the type of end being talked about. One doesn’t have to assume that the nose was “placed” in the middle of the face in order to support eyeglasses; one can fully accept that a nose developed naturally, perhaps even by nonguided evolution, and still maintain that the nose has a natural end in smelling, simply by virtue of the fact that that is what it actually does


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