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Aquinas’ Fifth Way: The Proof from Specification


Editor’s note: See also, “Introducing Aquinas’ Five Ways,” by Michael Egnor. For Dr. Egnor’s previous posts in this series on Aquinas’ Five Ways, see herehere, here, and here. For more on Thomas Aquinas, intelligent design, and evolution, see the website Aquinas.Design.

Aquinas’ Fifth Way is the proof of God’s existence that is easiest to grasp in everyday life. The order of nature points to a Mind that gives it order. This obvious order is the substrate for all natural science — after all, without natural order, scientific study of nature would be an exercise in futility. And the natural order is the framework for everyday life. We could not take a breath unless our lungs and nerves worked consistently, and unless oxygen had the chemical properties that it has. Order in nature is ubiquitous. We have become so accustomed to it that we fail to notice how remarkable it is. 

That this natural order points to God is obvious. But what are the characteristics of this order? In living things, ID theorists describe this order as specified complexity. Specified complexity means that a pattern has substantial independently specified information (specification) that has a low probability of occurrence by chance (complexity). Aquinas would agree that such specified complexity points to a designer, but he understands natural order in a way that is rather different from the understanding of many ID theorists. 

Specification Rather than Complexity

For Aquinas, it is the specification, rather than the complexity, that is at the heart of the Fifth Way. Aquinas understands specification in an Aristotelian sense: as final cause (teleology). The Fifth Way is often called the proof from Final Cause, or the Teleological proof. 

Final cause is fundamental to Aristotelian-Thomistic metaphysics. One may ask: “What is the cause of a thing?” St. Thomas answers that to completely understand a cause in nature, we really must know four causes:

Material cause: the matter out of which something is made. The material cause of a statue is the block of marble from which it is carved.

Efficient cause: the agent that gets the cause started. The efficient cause of a statue is the sculptor. 

Formal cause: the structure of the system that is caused. The formal cause of a statue is the shape of the statue.

Final cause: the end or purpose for the cause. The final cause of a statue is the purpose in the mind of the sculptor — to use the statue to decorate a garden, for example. 

In nature, final causes and formal causes often overlap. The formal cause of an acorn growing into an oak tree is the form of the oak tree, which is also the final cause of the growth of the acorn — the end or telos of the growth of the acorn is the form of the oak tree it will become. 

The Cause of Causes

The four causes have reciprocal relations. Material cause and formal cause work together, in the sense that form provides structure to matter. Efficient cause and final cause work together, in the sense of a push-pull relationship. An efficient cause “pushes” while a final cause “pulls” simultaneously. Efficient causes point to ends — regular causes in nature tend to specific outcomes. When you strike a match (efficient cause), it bursts into flame (final cause). Efficient causation is incomprehensible without final cause: regular cause-and-effect in nature is directional, in the sense that cause is consistently from one specific state to another specific state. It makes no sense to speak of “cause from” unless we also speak of “cause to.” Causes have beginnings and ends. 

For St. Thomas (following Aristotle), final cause is particularly important, because it provides direction to natural causes. Final cause is the essential principle by which causes in nature happen. We moderns tend to ignore final causes—we think in terms of cause as a “push” — efficient cause, rather than cause that “pulls” — final cause. For St. Thomas, it is the pull of final cause that is fundamental to the regularity of nature. Final cause is the cause of causes. 

With this in mind, let’s look at the proof from the Fifth Way. St. Thomas notes that causes in nature are more or less consistent. Causation is the actualization of potentiality, and causation follows patterns. Things fall down, not up. Cold weather causes water to freeze, not boil. Acorns become oaks, but oaks don’t become acorns. Aquinas notes that the final cause of an acorn is in some sense in the acorn itself: that is, in order for an acorn to reliably grow into an oak tree, the form of the oak tree must have some sort of existence while the acorn is still an acorn. A process of change can’t point to an end unless the end pre-exists in some sense. But how can an oak tree “exist” when it is merely an acorn?

The Form of the Oak Tree

What exists is the form of the oak tree. The form of the oak tree can exist in two ways. It can exist in an object as a substantial form — that is, the form can exist in the oak tree itself. This is the way forms ordinarily exist in objects. 

A form can also exist in an intentional sense — that is, the form can exist in the mind of a person who thinks about it. When I know an oak tree, the form of that oak tree is in my mind as well as in the oak tree. That is, in fact, how I know it. My mind grasps its form. 

For change to occur in nature, the form of the end-state of the change must in some way exist prior to the completion of the change. Otherwise, the change would have no direction — colloquially, the acorn wouldn’t “know” what to grow into. 

But of course most things in nature — and all inanimate things — don’t “know” anything. An electron doesn’t know quantum mechanics, but it moves in strict accordance with quantum mechanical laws. A rock knows nothing of Newton’s law of gravity, but it falls in strict accordance with Newton’s law. A plant knows nothing about photosynthesis, but it does it very well every day with an expertise exceeding that of the best chemist. 

Since the form of the final state of a process of change can’t be in the thing being changed — the acorn is not yet the oak tree — and change routinely occurs in things that have no mind to look forward to the final state, where is the form of the final state of change in nature?

Aquinas asserts that the form of the final state — the telos or final cause — must therefore be in the Mind of a Superintelligence that directs natural change. That is what all men call God. 

So you can see that in the Thomistic Fifth Way, it is the specification of change, not its complexity, that is at the heart of the matter. It’s reminiscent of the quip about a dog that can recite Shakespeare. It’s not that the mutt knows Shakespeare that’s remarkable; it’s remarkable that he can talk at all. What’s remarkable in nature is not so much that nature follows complex patterns, but that it follows any pattern at all. Any pattern in nature, even the simplest, cries out for explanation, and it is the fact of natural patterns that is the starting point of the Fifth Way. 

From the Thomistic perspective, even the most simple natural process — a leaf falling to the ground — is proof of God’s existence. The fall of the leaf is specified prior to the fall — leaves fall to the ground, rather than doing any of countless other things a natural object might do (like burst into flame or grow a tail). This specification — this telos — requires a Mind in which the fallen state of the leaf is conceived prior to the actual fall of the leaf. Change in nature requires a Mind to look ahead and direct it. Complexity (or simplicity) of the change is irrelevant. 

It is the consistent directedness of change in nature that points to God. Atheists, with much handwaving and dubious science, claim to explain biological complexity by Darwinian stories. Yet, even on its own terms, Darwinism fails. Adaptation by “natural selection” may account on some level for the fixation of a particular phenotype in a population, but it offers no explanation for the fundamental fact of teleology in nature. In fact, Darwinian theory depends on teleology in nature. If natural causes were not consistent and mostly directed, there would be no consistency to evolution at all. There is no evolution in chaos. Without teleology, “chance and necessity” would be all chance and no necessity, and therefore no evolution.

Explaining Chance

Actually, atheists can’t explain chance either. Chance is the accidental conjunction of teleological processes. A car accident may be by chance, but it necessarily occurs in a matrix of purpose and teleology — the cars move in accordance with laws of physics, the road was constructed according to plans, the cars are driven purposefully by drivers, etc. There can be no chance unless there is a system of regularity in which chance can occur. Chance by itself can’t happen — it is, by definition, the accidental conjunction of teleological processes. Both “chance” and “necessity” point to God. Pure chance, without a framework of regularity, is unintelligible. 

From the perspective of the Fifth Way, necessity permeates nature. But it is specification, rather than the complexity, that characterizes necessity and points to God’s existence. The specification need not be complex. The simplest motion of an inanimate object — a raindrop falling to the ground — is proof of God’s existence. 

No Mere Watchmaker

Teleology is foresight, the ability of a natural process to proceed to an end not yet realized. Yet the end must be realized, in some real sense, for final cause to be a cause. The foresight inherent in teleology is in God’s Mind, and it is via His manifest foresight in teleology that we see Him at work all around us.

This rules out the God of deism. The God of the Fifth Way is no watchmaker who winds up the world and walks away. He is at work ceaselessly and everywhere. The evidence for a Designer is as clear in the most simple inanimate process as it is in the most complex living organism. The elegant intricate complexity of cellular metabolism is certainly a manifestation of God’s glory — the beauty of biological processes is breath-taking. But the proof of His existence is in every movement in nature — in every detail of cellular metabolism, of course, but also in every raindrop and in every blown grain of dust.

Photo: An oak tree, by Abrget47j [CC BY-SA 3.0], via Wikimedia Commons.