The purposes of this paper are threefold: First, to provide a Thomistic critique of the arguments put forth by proponents of “Intelligent Design” (ID); secondly, to investigate whether Aquinas's “Fifth Way” is an alternative design argument; thirdly, to evaluate how the Fifth Way fares in the face of claims made by atheist evolutionists. The two main ID proponents whose views I will examine are William Dembski and Michael Behe.

Dembski's key notion is “specified complexity”. The presence of specified complexity is grounds for inferring an intelligent designer has been at work. Dembski often illustrates what he means by specified complexity by giving an example of how we would determine that radio signals we received had been sent by an intelligent life form. First, the signal would have to be complex; a sequence of ones and zeros that was only twelve digits long is too short to be complex. A sequence that was 1126 digits long would be complex, but would not necessarily be specified. Specification means that the sequence contains “a suitable pattern”, e.g., the sequence of prime numbers or something else that one can specify, and not just a random pattern. The probability that such a pattern arise by chance can be mathematically calculated. It turns out to be so small that it would be unreasonable to think that such a sequence originated by chance. Intelligence is the obvious alternative explanation for such a sequence.

What is crucial in Dembski's notion of specified complexity is that of mathematical probability. Dembski is quite clear on this point:

The method of looking to mathematical representations that treat different natural things as if they were uniform entities, rather than as beings endowed with distinctive causal abilities following upon their forms, is not an adequate way of determining the effects these beings can or cannot extend to. One can take the chemical formulas for water, vinegar, salt, and baking soda, and figure out mathematically that they can be grouped in six different pairs. But doing so is not going to allow one to determine which pairs are going to cause a chemical reaction. Dembski is far from being the first to attempt to solve questions about what is possible in the living realm by looking to the realm of mathematics. Michael Denton, author of a couple of provocative books concerning evolution, also talks about the statistical improbabilities of a cell arising by chance,Footnote ² as if natural things did not have natures that incline them to act in certain ways, but were indifferent subjects of juxtaposition to one another, like cards in a shuffled deck.

At this juncture ID proponents will say “not so fast”, the order of base pairs in DNA are like cards shuffled in a deck in that their position relative to one another is arbitrary. DNA is not a crystal, like salt, where there is simply a repetition of the same sequence over and over. While cytosine on one strand of the double helix is always united to a guanine on the other, and similarly for adenine with thymine, on the same strand any base pair can follow another. This is what allows segments of DNA to code for different proteins, instead of repeating the same message over and over.

The chances that the correct order of base pairs arises to form the genes needed to code for say the hemoglobin molecule are something like 1 in 10¹⁹⁰.Footnote ³ According to Dembski this gives us ample reason to infer that an intelligent designer has been at work. Would a Thomist fault Dembski's argument, which after all seems very persuasive?

Again, we must insist upon the differences between the mathematical realm and the realm of nature.Footnote ⁴ The order of base pairs in DNA seems to lend itself to mathematical analysis without any residue. However, it is a little premature to assume that there is not material and efficient causality involved which removes some of the apparent arbitrariness from the base pairs’ arrangement. For example, it would seem if the order of base pairs is entirely arbitrary, then mutations would take place arbitrarily at any location. However, this is not the case, mutations actually take place preferentially, e.g., at certain cytosine residues.Footnote ⁵

An analogy with games is helpful here. Compare the letters one picks in a game like Scrabble to the cards one picks from a standard playing deck. In Scrabble there is not the same frequency of letters, as there is of fives, sixes, Jacks, etc. in a deck of cards. In Scrabble, there are more “e's” than other letters (e.g., there is only one “q”), because “e” is the letter most often needed to spell a word. Do we know so much about DNA to know that it is like a deck of cards? Perhaps it is rather the case that there are natural causes that bias the order of DNA in such a way that it is more likely to produce “words”, i.e. sequences that will code for functional proteins. Until we know which way nature is, probability calculations have no solid basis. So it may turn out that it is not so far-fetched that non-intelligent natural causes produce DNA after all. Again, the capabilities of a group of natural things pooled together cannot be determined by mathematical analyses that treat them as if their ability to act and to undergo change was uniform; such analyses also ignore the possibility that they may have causal abilities that are yet to be discovered. This is the major flaw in Dembski's approach.

Another problem with the Dembski's ID argument is that it is based on “probability and complexity theory”. As other authors have pointed out, since Dembski's argument is based on theory it is subject to revision like any theory. Dembski's design inference by his own admission is only one of high probability. He goes so far as to say that he is simply putting forth a research project for science which may prove to be fruitful or unfruitful, but which makes no claims to being true:

So much for Dembski's version of ID putting the argument from design for God's existence on a firmer foundation.Footnote ⁷

Yet another problem with Dembski's view lies in the false dichotomy upon which it is based, a dichotomy that inappropriately pits natural causes against intelligent ones. Dembski's version of ID claims to identify features of organisms whose production could not be explained by natural causes. His ID argument by his own admission loses its cogency if it turns out that the Intelligent Being uses natural causes to achieve its ends:

Let us turn now to Michael Behe, whose key notion is irreducible complexity.Footnote ⁹ Irreducible complexity is present in functional wholes that have to have all their parts in place or they will not work at all. An example Behe gives of this is the mousetrap; remove a single piece from a mousetrap and it won't catch mice. Irreducibly complex things cannot arise in a stepwise fashion from simpler systems that do the same thing; they thus require an intelligent agent to assemble them.Footnote ¹⁰ Behe goes on from there to show that in natural things there are irreducibly complex features such as the flagellum and the clotting system — if one component isn't there, the system is non-functional; whence the need for an intelligent designer to assemble it.

Behe is widely criticized for appealing to ignorance, using God to fill in what he perceives to be gaps that nature cannot navigate across.Footnote ¹¹ Yet Behe's inability to figure out how a given irreducibly complex system arose may be simply due to his lack of imagination and experience. This has proven to be the case. Behe claimed that Factor XII was part of the irreducibly complex clotting system. However, as biologist Kenneth Miller point outs: “Once again, however, a nasty little fact gets in the way of intelligent design theory. Dolphins lack Factor XII (Robinson, Kasting, and Aggeler 1969), and yet their blood clots perfectly well.”Footnote ¹² In the case of the flagellum it turns out that it contains within itself the equivalent of a smaller functional unit that is found in other organisms serving the purposes of translocating proteins.Footnote ¹³ The flagellum then is not irreducibly complex, but can in principle be broken down into a simpler functioning system. Another paper shows how one hormone receptor which binds cortisol could have evolved from a more promiscuous ancestral receptor by two point mutations; and this despite the irreducibly complex appearance of the system supposedly ruling out such stepwise evolution.Footnote ¹⁴ What if all the systems that Behe thinks are irreducibly complex turn out not to be? Gone would be Behe's reason for concluding to an intelligence behind nature.

Note that the way Behe and Aquinas formulates their arguments are quite different. Behe's argument stands to lose ground each time science discovers natural causes that can account for the formation of systems that he could see no natural explanation for;Footnote ¹⁵ the more science discovers natural causes can do the job, the less there is a need for God. Aquinas's argument, on the other hand, is unaffected by scientific discoveries of the said sort. This is because Aquinas does not reason to God based on a surmise of what effects natural causes cannot extend to as immediate efficient causes, but rather reasons to God on grounds that are sure, namely, that there is an ordering to an end in nature.

Behe and Aquinas also part company in their views concerning secondary causes. For Behe, if natural causes marking out traceable biological pathways were discovered to explain how the foot and eye arose from simpler precursors, his argument for an intelligent designer would no longer have any cogency.Footnote ¹⁶ Ironically Behe appears to agree with Richard Dawkins. Both seem to think that if natural efficient causes can be discovered to account for the original assembly of organisms’ parts, then there is no need for an intelligent designer.

What both fail to distinguish is that causes which physically produce the object may be other than the causes responsible for the plan according to which the object is made. Planning and construction may both be the work of the same agent, but need not be. The architect may never touch any component of the house, but is certainly responsible for its construction; whereas the artisans who actually assemble the house may have no idea of its overall layout, but simply follow instructions. Aquinas makes this distinction when speaking about divine providence:

To give another illustration of the mistake both the IDers and Dawkins are making: it is like saying that if the feature of my computer that saves my documents automatically after a certain period of time can be fully explained in terms of the mechanism by which this is accomplished, then there is no need to bring in an intelligent being. But of course someone had to design the mechanism. Many other illustrations of beings working to an end they have no knowledge of can be given: a bread maker, the assembly line worker who has no idea of the design of the finished product, but simply inserts a given part, etc. The final product, however, plainly requires someone who determined how to organize the device or the assembly line, and what the various parts or workers would do. The one who plans an assembly line need never handle part of the finished product. And again, as Aquinas notes, the architect or engineer responsible for the design of a building, as such, never puts a single part in place.Footnote ¹⁸

We have to ask: Are those who deny design doing so simply because they have found agents which account for the organism's completed assembly (Dawkins and company)? Are those who are trying to defend design, seeking to show that there are no natural causes capable of assembling organisms so that a Designer has to intervene directly (Behe and Dembski)?

Dembski and Behe see the only path to concluding to an intelligent being to consist in showing the inadequacy of natural causes as immediate causes of organisms with their complex features.Footnote ¹⁹ Aquinas would squarely reject this view on the grounds that it fails to distinguish planning an order from executing it; that natural causes suffice as immediate causes bringing about a complex functional feature does not eliminate the need for an intelligent being to plan that feature.

Aquinas would also level a far weaker sort of argument against the ID position, an argument by fittingness. The aim of the ID project is basically to show that natural causes are deficient when it comes to the production of new species. It is true that there are forms of causality that God cannot impart to creatures because this would imply contradiction, e.g., God cannot give a creature the power to create. The IDers, however, do not deny that God could have organized the universe so that new species would be produced by natural causes; and indeed this is not inherently impossible, for the origin of new species by such causes would come about by change and not by creation.Footnote ²⁰ Aquinas would regard the view that God withheld a sort of causal ability that he could have endowed creatures as unbefitting God's perfect governance:

In other words, Aquinas, who insists that God “not only makes things to be, but to be causes”, and this reveals “the abundance of his goodness”,Footnote ²² would regard the ID position to be implausible insofar as it subtracts from the causality that could in principle be imparted to natural things,Footnote ²³ and by doing so detracts from God's beneficence.Footnote ²⁴

It is time to ask whether Aquinas thinks there is another argument from design, one which is viable. This is a hard question. Some Thomists reject speaking of the Fifth Way in terms of design.

Certainly, one would not want to define design in terms of a designer; such a definition would be question-begging when used in an argument from design.

I also agree that design is sometimes used simply to refer to a pattern apart from any reference to final causality. Usually such designs are decorative. In this case we speak of a design as being pleasing or ugly. But there is another sense of design which we speak of as being good or bad (or poor), and we determine this by seeing how well the thing achieves its end.

Design in the latter sense refers to a plan for something that is to serve a purpose as it exists in the mind of an intelligent being or as it realized in the thing actually produced. Design in the mind of an intelligent being seems to be the equivalent of idea or exemplar which according to Aquinas “has in a certain manner the notion of end”.Footnote ²⁵ Design in the thing is that plan as realized in the thing allowing it to achieve some end. Design for an electric mixer involves a handle, a motor which is arranged to rotate beaters, and so forth. The design within the thing is what allows the device to achieve its end of mixing foods more rapidly and with less effort than stirring with a spoon. It seems to me that design as a plan realized in a thing allowing it to achieve an end is what Aquinas is speaking in his commentary on the Physics at the very end of the discussion of final causality in nature: “nature is nothing other than the plan (ratio) of a certain art, namely, the divine, placed in things, by which things move to a determinate end; as if the ship-builder could give to the wood something so that the wood of itself would move to bringing about the form of the ship.”Footnote ²⁶

In any case, I think people are right to resist too readily assimilating the Fifth Way to arguments from design such as Paley's. Let me set out Paley's argument, and we can think along the way about how the Fifth Way is like or unlike it. For Paley a thing manifests design when it has a multiplicity of parts ordered and adjusted to achieve a goal.Footnote ²⁷ Paley takes as evident, at least to the wise, that anything manifesting design is ultimately the product of intelligence.Footnote ²⁸ Given that organic parts, such as the eye, manifest design, Paley concludes that they are the product of intelligence. Now let us look at the Fifth Way:

There are two syllogisms in the overall argument:

1. (1) Everything that always or frequently operates in the same mode such that what is obtained is the best acts for an end, and not by chance.

   Natural bodies, lacking knowledge, operate in the same mode such that what is obtained is the best.

   Natural bodies, lacking knowledge, act for an end, and not by chance.

2. (2) Everything which tends to an end, lacking knowledge, is a thing that is directed by some knowing and intelligent being.

   Natural bodies are things that lacking knowledge act for an end.

   Natural bodies are things directed [to an end] by some knowing and intelligent being.

The first premise in the first syllogism harkens back to the discussion in Aristotle's Physics as to whether natural things act for an end. Aristotle takes up the arguments of philosophers like Empedocles who says that rain is not for the sake of helping the plants grow, but material causes necessarily result in water evaporating and eventually falling again, regardless of the plants’ needs, and also that teeth and other parts of living things which allow for eating and other life activities did not arise to serve those purposes, but arose by necessity and by chance happened in some cases to be useful to organisms in which they arose, and these organisms survived as a consequence. Aquinas response to this is:

It is noteworthy that Aquinas picks the foot as a premier example of nature acting for an end; the examples that had been given were teeth and rainfall, and Aquinas sees the organic parts of animals as the clearer examples of nature acting for an end.Footnote ³¹

Empedocles’ response to this, or that of his modern-day contemporaries, would be to say, sure, there is a difference between a foot well adapted for walking and a foot that is not. However, even a poorly adapted foot may offer an advantage over no foot, and with time natural selection may lead to better and better adapted feet. A rudimentary, poorly functional organ is sometimes due to a defect of nature, but sometimes it is nature's way to the production of a new species.

Nor would Empedocles be fazed by Aristotle's insistence that teeth and other organic parts come up regularly, and so they cannot be a product of chance, but must be for the sake of something. Empedocles does not think that it is just chance that lungs proved to be useful on land, and that animals that had them survived and had offspring that had the same useful feature. Empedocles’ position is that these features arose by chance. He doesn't think it chance that certain features are adaptive in a given environment nor does he think that reproduction infrequently and by accident reproduces adaptive features. And the modern day followers of Empedocles are insistent on this point: it is random variation and natural selection that replace God, chance and necessity, chance alone is not enough.Footnote ³²

Let us look more closely at the Fifth Way to see whether Aquinas and Empedocles cannot be brought closer together and at what point they definitively part company, beginning with the first syllogism: “We see that some things which lack cognition, namely, natural bodies act for an end; which appears from this that they always or frequently act in the same manner such that what follows is the best; whence it is manifest that they arrive at the end from a tendency, and not from chance.”

Empedocles or at least his contemporary counterparts would want to qualify “the best”. Natural selection does not always produce an ideally designed organism, but rather it tinkers together organisms with what random variation makes available. Aquinas is aware that intelligent agents sometimes choose things suited to their purpose despite certain unavoidable drawbacks that accompany the employment of those things, e.g., iron holds an edge, but also rusts. He makes explicit reference to this sort of thing occurring in the case of the human body.Footnote ³³ If Aquinas had been aware of evolution, he would have recognized the available options for producing new species are more limited than if each species was specially created, and consequently would have expected to see more imperfections in evolved organisms than would be found in those produced directly from the drawing board.Footnote ³⁴

Empedocles would point out that chance is a needed element in the production of new species, for if organisms always reproduce true to type there would be no new species,Footnote ³⁵ and so bodies acting in the same manner are not the only source of good things (this is assuming that Empedocles would regard the diversity of life forms as a good thing) — and Aquinas would not disagree with him that chance events can have good results. Let us examine further what Aquinas holds regarding chance causes.

Aquinas thinks that causes that act in a contingent way are a desirable feature in the universe. Without chance causality, however, there would be no contingency. For contingent causes differ from necessary causes in that “they can fail in the fewer number of cases”, and “fortune and chance are said in regard to those things that happen in the fewer number of cases”.Footnote ³⁶ Aquinas says that contingency contributes to the beauty of the universe which consists in there being various grades of beings, some more like God who never changes, and some less like God and more subject to change.Footnote ³⁷ Chance causes increase the order of the universe by increasing the interactivity within it.Footnote ³⁸ In a world without chance, natural causes could not occasionally interfere with each other, but all would unchangeably follow fixed paths.

Aquinas maintains that in nature there are occurrences that are chance at one level, but are aimed at or tended towards at another level. For example, he holds this to be the case in regard to the production of female offspring. For him, semen, the efficient cause of generation, is tending to produce something like itself, namely, a male. If it produces a female, it has failed due to some sort of interference. What is bad luck from the point of view of the semen, is, however, aimed at by nature at a more universal level.Footnote ³⁹ It is not a matter of luck that the sex ratio is maintained as this good outcome occurs frequently. Let us not be sidetracked by the fact that Aquinas's understanding of reproduction is inaccurate. What is important to see here is that Aquinas acknowledges cases where a more global end that nature tends towards is realized by chance events at the level of the immediate causes.

Now what evolutionists are saying is that chance occurrences are involved in the development of every new species. We have seen that the mere introduction of chance is not a reason for Aquinas to deny tendency to an end at another level. Why then the following categorical rejection of Empedocles' evolutionary views?

It is certainly true that the same thing cannot occur as the result of chance and as a result of tendency, in the same respect. Thus, if Empedocles is saying that the origin of new species does not result from natural tendencies to an end at any level, then he is saying that it must be purely the result of chance. Why though doesn't Aquinas make plain that Empedocles’ error lies in denying finality at any level, and why does he not suggest that Empedocles should have considered the possibility that chance and finality are operative at different levels? It seems here that, unlike the case of the sex ratio, he fails to consider the possibility of different levels of causality because he has no evidence that new features arise, aside from two kinds of cases. The first is the production of individuals afflicted by birth defects; the second are some of the seemingly spontaneously generated animals.Footnote ⁴¹ In the vast number of cases, however, what is observed is that like produces like, which is to be expected given that agents act according to their forms.Footnote ⁴² One can hardly blame Aquinas for being ignorant of the fossil record which reveals a vast number of species arising (and sometimes disappearing) over immense periods of time, as well as being ignorant of evidence that points to this occurring by natural causes, rather than through direct divine intervention. It seems to me it is this ignorance which elicits his categorical rejection of Empedocles, for again, he thinks that it is possible for chance at one level to be compatible with finality at another level, as is evident in the case of the semen, and also in the case of spontaneously generated organisms, as we shall now see:

Aquinas is plainly saying here that certain animals can arise by chance at the level of particular causes while be tended towards by more universal causes in nature,Footnote ⁴⁴ causes that tend towards the universal effect of actualizing all the forms material is capable of. The forms in question here, unlike the case of birth defects, are a goal. The same basic position can be fitted to the evidence we have for evolution without in any way undermining the Fifth Way.

Is there a universal tendency of nature to actualize all the potencies of matter? If indeed it is correct to infer that action for an end is present when the same good result is achieved frequently, and not rarely, we can ask does nature regularly or rarely tend to fill up available niches?Footnote ⁴⁵ It is generally thought that 99% of species once extant are now extinct; if so, this indicates that throughout evolutionary history niches were continually being filled. Moreover, after each mass extinction, the number of life forms subsequently proliferated so as to either eventually exceed pre-extinction numbers or at least to return almost to them,Footnote ⁴⁶ again indicating that where there is an open niche an organism will generally evolve to fill it. If it is rare that a new species forms compared to how often species remain stable before going extinct, it is rare that a seed grows to maturity compared to how often seeds fail to do so. Yet seed-bearing plants regularly replace themselves, and species give rise to new species to fill available niches, despite the rarity of these outcomes for the particular causes involved in these events.Footnote ⁴⁷

Whether or not chance causes alone can lead to speciation, they are involved in it, and while individually they occur unpredictably, as a group they regularly contribute to the production of new species. In other words, while environmental changes, the migration of part of a population to new areas, changes required for the various sorts of reproductive barriers to form, etc. may be chance occurrences, they happen often enough to account in part for the continual filling of unoccupied niches by new species.Footnote ⁴⁸

We see then that we can adjust Aquinas's argument to take in account the evidence for evolution. Aquinas in light of this evidence would say, yes, there is chance involved in the production of new species; without chance like would keep reproducing like, and no new species could originate. However, part and parcel of evolution is a tendency towards something good, the wondrous diversification of life forms. Evolution, then, substantiates the first syllogism in the Fifth Way.

It might seem then that the updated version of Aquinas and Empedocles’ evolutionary views are entirely compatible. Empedocles would not necessarily disagree that chance produces new species with a certain regularity, and so it is not chance that all available niches tend to get filled with species. Some neo-Darwinians might say that there is no tendency here, it just happens by accident as a by-product of copying errors or the like. But what factually happened/happens? Niches are regularly filled, and when new niches open up, new species arise to fill them (e.g., with the apparition of trees, mosses had a new habitat to colonize, and many new species of mosses appeared).Footnote ⁴⁹ That it is through contingent events that niches are filled, and that if conditions were somewhat different, different organisms would have arisen to fill those niches, does nothing to show that there is no tendency.Footnote ⁵⁰ And evolutionary biologists are not in the habit of denying that biodiversity is a good.

Where some evolutionists diverge from Aquinas is when it comes to attributing the production of biodiversity to intelligence. The good that is biodiversity consists in a number of diverse species, each of which has its own parts ordered to its survival and reproduction. Just as some deny that the latter is a work of mind, attributing it exclusively to blind causes, so too some attribute the production of biodiversity to blind causes alone. Aquinas thinks they lack insight:

Blind forces cannot account for the coordination of their activities requisite for forming the functional parts that insure the good of the animal, such as feet, teeth, and eyes, or DNA for that matter; an intelligent agent must be responsible for such order.Footnote ⁵² Here we seem to be back to Paley's argument, an argument which finally does not seem that different from the Fifth Way which says: “Those things which lack cognition do not tend to an end unless directed by someone knowing and intelligent, as the arrow by an archer.” Paley would agree with Aquinas that the foot is a good example of something in which the parts are arranged in such a way as is suited to an end (namely, walking), and that this arrangement requires an intelligent cause to explain it. As the natural causes immediately responsible for the foot lack knowledge, this ordering of the foot's parts to an end must be traced back to a being that is intelligent and knowing.

This is exactly where Empedocles and/or his followers are going disagree with Aquinas: “Those things which lack cognition do not tend to an end unless directed by someone knowing and intelligent, as the arrow by an archer.” Sure, there is a difference between something acting according to an innate tendency, “a program” as opposed to chance (e.g., the parts that result in normal fetal development are due to the DNA blueprint and other determinate factors in the cell, and not to chance), but the blind forces of nature are capable of doing the programming.

I think a person can say this, but he can't really think it. I think it is self-evident that where non-intelligent causes are coordinated to achieve an end, this must be the work of intelligence, and that all one can do is try to show the absurdities that follow from saying other.Footnote ⁵³

This latter claim is borne out when one examines one of Richard Dawkins's arguments in The Blind Watchmaker. Dawkins is trying to convince us that the God that Paley argues to starting from his example of a watch is superfluous for explaining organs such as the eye or molecules such as hemoglobin. Dawkins first speaks of the statistical improbability of the hemoglobin molecule arising by pure chance (one chance in 10¹⁹⁰). To show us how a hemoglobin molecule could be arrived at by blind causes, he presents an analogy with a computer. Keep in mind he is trying to show how one can get something of “specified complexity” or a determinate complex order without any input from intelligence. He takes a target sentence, “methinks it looks like a weasel”, and he admits that if he had his computer randomly generate a string of letters, that the chances of coming up with even such a short sentence are astronomical. He then asks, what if the computer retained those of the randomly generated letters that happened to fall in the right places, and then generated random letters only for the remaining places? He programs his computer thus, and indeed in a very short period of time his computer arrives at the target sentence. Voilà complex order without any input of intelligence, just random letter generation and the automatic retention of the correct letters. Dawkins goes on to say that blind forces in nature have set up a similar process, whence the hemoglobin molecules, eyes, etc.

How, though, was the computer able to retain the correct letters? Dawkins programmed it. The whole point of his analogy was to show that natural causes can produce hemoglobin and the eye without the input of intelligence. But what his analogy has in fact indicated is that intelligence is required in order to generate complex forms of order. Intelligent beings do programming; non-intelligent ones do not.

When something is self-evident, all one can do is show the absurdities in the positions of those who maintain the opposite. The failure of Dawkins’ argument supports my thesis that it is self-evident that “those things which lack cognition do not tend to an end unless directed by someone knowing and intelligent, as the arrow by an archer.”

So ultimately I think that people cannot fail to see that if it is unbelievable that a computer capable of word processing, showing DVDs, etc. arose by the action of blind forces that a fortiori the human body could not have so arisen. One can show the absurdity of the various scenarios concocted to get around this. One cannot make a person see the obvious by presenting an argument based on something better known. As Thomas Reid notes, the typical defense for reasoning from finality to intelligence is by reduction to the absurd. For example, people will point out the DNA of an organism contains more information than an encyclopedia. They go on to point out that if something like that arrived from outer space, everyone would acknowledge that this was the work of an intelligent extra-terrestrial. Whence the absurdity of denying that the ordering to an end in DNA must ultimately be traced back to some intelligent being.

We have seen then that St. Thomas's Fifth Way stands up to challenges posed in the name of evolutionary biology. We have also seen that the second syllogism contained therein is quite similar to Paley's argument from design. At this point, it is worth articulating from a Thomistic perspective the respective roles that the intelligent being and chance play in evolution. Ironically, examining Dawkins’ computer analogy is helpful for understanding how an intelligent being can get something complex that is ordered to an end by using both chance and necessary causes. A shortcoming in Dawkins's computer analogy is that evolution cannot aim at future goals (the equivalent of Dawkins's target sentence). God does though. God then in principle can “program” the universe such that lucky combinations arise through chance, but then those combinations are retained due to causes acting from tendency that God has put in place to insure an evolving biosphere. It is sometimes overlooked that God needs to order the causes acting by tendency in such a manner that the sorts of chance events conducive to the origin of new species are possible. Chance causality is not independent of natural things acting in a determinate way.Footnote ⁵⁴ Digging a hole for a tree can be the cause of finding lost treasure. It cannot be the cause of an eclipse of the moon. For the right sort of chance events to be possible, namely, for ones that lead to evolutionary novelty, there have to be specific tendencies present in natural things. In addition, God needs to set a balance between the chance events and ones proceeding from tendency. Chance is part of the design;Footnote ⁵⁵ it is a way of getting novelty, but it must be held within certain limits. If chance were to run completely wild — if the biosphere was continually flooded with a variety of mutant beings such as Empedocles’ “man-faced ox-progeny” — species would scarcely be possible, as it would only be the odd individual that would produce offspring like itself.Footnote ⁵⁶ When one reflects that causes acting by tendency and those acting by chance need to be carefully orchestrated if they are to produce the amazing array of organisms that has evolved on our planet, it is obvious that the evolution of new life forms must have an intelligent cause; one either acknowledges this or one doesn't.

A distinction Aquinas makes when speaking of plans will help clarify what I mean by saying that chance is part of the design. There are two senses of “plan” or “design”. To plan or design is to figure out appropriate means to achieve an end which one has fixed upon. A plan for a desk involves a writing surface, storage space, etc. In addition to this plan, one needs another sort of plan, namely, directions for how to bring about the desired arrangement. These two plans are not the same, as anyone who has put together ready-to-assemble furniture knows. Accordingly, Aquinas notes that for understanding a thing it suffices to know the order of its parts, whereas for making a thing one has to also know by what operations the parts can be so ordered.Footnote ⁵⁷ When I say that chance is part of the design, I am speaking of design in the second sense. Chance is a means used by an intelligent being to get novelty.Footnote ⁵⁸ It is not chance that the intelligent being uses chance for this purpose, as by doing so it can involve secondary causes in the production of new species. Nor is it chance that there are other natural causes present that are able to channel chance so as to in some cases produce a viable new species. The design of new species in the first sense of design is a plan including features that make it possible for individuals of a species to occupy a given niche (e.g., the gills of fish). That chance is part of the design for getting this design means that the latter is often imperfectly realized (e.g., the inferior wiring of our photocells compared to those of mollusks) and includes features that are somewhat arbitraryFootnote ⁵⁹ (e.g., the number of toes humans have), not to mention that it often produces organisms that are not viable. Notice how an evolving biosphere as opposed to one created ex nihilo requires two levels of planning rather than one, and thus two reasons to posit “aliquid intelligens”, as opposed to one.

Aquinas says in one place: “It is necessary that the entire work (operatio) of nature be ordered from some knowledge, and this certainly must be reduced to God in an immediate or mediate way.”Footnote ⁶⁰ An explanation of the production of the diversity of life forms which calls upon natural causes, both those that operate by tendency and those which are chance causes, must ultimately be reduced to God's wisdom, but in a mediate way. God is the source of the ordering of natural things to their ends in such a way that the things acting by tendency both make it possible for chance causes to bring about novelty capable of leading to the develop of new species and provide a framework within which the novelty that arises by chance (and perhaps also from other natural causes) can be retained. He is thus not only responsible for the ordering of means to end in the parts of the rose, the frog, etc., which order he realizes through intermediary causes, he is also immediately responsible for the ordering of universe which allows the intermediary causes to continually tend to produce new organisms with their appropriate parts. The use of intermediary causes in the realization of the order to an end found in the diversity of life forms points even more strongly to the need for a governor. Again the parallel with a person who sets up an assembly line to produce some useful artifact is helpful here. Not only does such a person have to know how the parts of that artifact are ordered to the artifact's end, the person also has to know how to organize a group of people or things that lack knowledge of this ordering in such a way that they produce the artifact nonetheless. Thus, Aquinas says:

The activity of ministers or secondary causes, including contingent ones, does not speak against the governance of providence, but bespeaks of greater wisdom on part of the governor. Thus, evolution through natural causes (including chance causes), far from being a refutation of the Fifth Way, offers pre-eminent evidence of its truth.