The Fifth Way: Argument from Design

Not sure because first of all there is always some uncertainty in the initial cause. Over the short run, this uncertainty is not noticed, but over the long run of millions of years you may notice different results as we see in the evolution of life into different species.
Secondly, take the same roulette wheel and the same ball. This same roulette wheel and this same ball will tend toward giving different results so that in some cases you will win on red, whereas in other cases you lose. Similarly with a slot machine.

Take the roulette wheel. There are some who would say that if every exact mechanical part of the roulette wheel, the weight distribution of the ball and its initial momentum, the exact distribution of air, and all such things were kept exactly the same and ensured to have absolutely no variation from previous experiments, the result would be the same.

Even if there is some indeterminacy the roulette wheel will behave in the same general way, insofar as it will physically will spin and repeatedly transfer momentum to and from the ball until the ball either lands on red or black somewhere on the board, or the ball is thrown off the board altogether. That you can attempt any physical model of physical interactions at all underscores the point. The roulette wheel doesn’t transmute the ball into a pigeon, or cause it to disappear, and if the circumstances are the same as previous experiments the ball isn’t going to change color or melt instead of just bouncing around when put into a roulette wheel.

Organisms are under selective pressures by which they either go instinct or become more competitive in a niche. It’s not that the pressures or biology is pointed towards creating this specific organism or that specific organism, as the confluence of many different events creates chance. It’s that the causal factors of these different contributors proceed in a regular fashion.

What you’re basically trying to reject is the idea that a cause has any determination (or even relation) to its effect or vice versa. That I can’t model any systems because that presupposes predictive behavior. That I can’t know whether one billiard ball striking another on a pool table will actually cause a transfer of momentum between the balls or a bunny to appear, even if a similar set of conditions has resulted in a transfer of momentum once or twice or a million times. And if a bunny did appear, we would assume it was due to that there was something very different about what actually occurred that resulted in the different effect.

It is that there is any regularity at all that is important to St. Thomas.

What i am claiming is that there is always some small uncertainty in the original cause. There is an overriding cause which we know, but there is always an infinitesimally smaller epsilon cause added on (i.e., we have C + epsilon, not just C). Epsilon generally will not affect anything so that the effect will remain “basically” the same. However, even the effect has a small uncertainty. In the short run, these uncertainties will not be noticed. However, over longer time periods these uncertainties will come into play so that the results will differ.

But according to the uncertainty principles you cannot know with exactness both the momentum and position simultaneously.

Stating that effects can be interfered with by other causes doesn’t undermine the point. It’s exactly what you’d expect. St. Thomas was actually very much aware of the fact that if A tends to B then it means that B will mostly obtain unless other secondary causes prevented it from occurring.

Stating that a roulette wheel (perhaps) might slowly get dinged up and damaged over time or that on one spin you might have a stronger wind than on a previous spin and that these types of things could change the results misses the point. I don’t want to get too bogged down in differentiating between substances and accidental form, either (of which the roulette wheel is the latter), but in terms of the substances the wheel is made of and the regularities we expect from a roulette wheel we’re looking at things impacting each other and the transfer of momentum in such cases as being regularities of the materials involved.

The intent of science is to figure out what effects things produce under certain circumstances. Circumstances are controlled in experiments precisely (to the best of the scientist’s ability) to determine what effects are due to the substance alone apart from other causes (which also behave with regularities). If we did not expect to find tendencies then science and its ability to predict things would be bunk.

I’d like to get into this with more depth when I approach the third proposition. I’ve started on a response but am still near the beginning.

I think i might be interpreting the fifth way differently (not necessarily as Aquinas intended). But even if we assert that the first premise is wrong if it infers or asserts a teleology, i think the argument can still work without mention of a teleology. So lets keep it simple. Here is a restatement of the argument as i understand it.

1. There are laws of physics. Things have a regularity and direction in their activity. Particular things have a tendency towards particular effects. This is not by chance that natures produce effects according to their natures insomuch as they do not randomly produce any number of effects. For example a goat doesn’t randomly transform into a dining room table.

2. Natural activity is blind to any end. It lacks knowledge and understanding. So we need to explain why natures have laws of behaviour, why there is regularity in their behaviour since they do not intelligently move to any possible end.

3. But as an arrow reaches its target because it is directed by an archer, what lacks intelligence achieves goals by being directed by something intelligent.

4. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.

Now the obvious rebuttal to this is simply to assert that the laws of physics is existentially-necessary. But for sake of argument Aquinas has already established in the first 3 ways that physical reality is not necessary and therefore the laws of physics is not natural. Therefore the fact that things move to particular ends and produce particular effects and have regularity in their behaviour, can only be explained by an intelligent cause.

So, i would argue that the fifth way taken by itself suffers some difficulty, but taken together with the other ways i find that the fifth way succeeds.

Well, to quote St. Thomas directly.

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.

He has not structured the Fifth Way as a formal syllogism in the Summa the way @IWantGod did in the first post. But if I can snip St. Thomas’ words a little to better fit the start of a syllogism:

  • We see that things which lack intelligence, such as natural bodies act always, or nearly always, in the same way, so as to obtain the best result.

Or to break it apart further.

  • We see that there are things that lack intelligence.

  • We see that there are things that act always, or nearly always, in the same way, so as to obtain the best result.

Best is a problematic word nowadays, as “who judges best!?” St. Thomas just means a thing will better obtain what a thing naturally tends towards the fewer the interfering causes are.


It’s not that water froze at a certain temperature that Aquinas or i find significant. It is the fact that water always freezes at a particular temperature. It is the fact that there are regularities that needs to be explained.

The problem with effects following perfectly from given causes is that we have free will. If all our actions and choices are determined by pre-existing causes, would that not mean that there is no free will?

And just to head off certain types of objections, we realize that the freezing temperature of water is dependent also on other factors such as air pressure, “impurities” in the water, etc… But even when accounting for these other circumstances there is a regularity.

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Let’s not get sidetracked in this topic regarding the Fifth Way. At least not until after we beat the topic to death.

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But this is not a sidetrack since it concerns what is meant by cause and effect and if these causes and effects really are what people think they are. Not every effect has a pre-existing cause. Otherwise, why should you lock up a man who just killed his neighbor in an argument over a barking dog? There were pre-existing causes which determined his tendency to act that way and since these causes were pre-existing, they were beyond his control and his responsibility. He did not have a free choice because it was the Devil, i.e., the pre-existing causes, that made him do it. All his actions are determined by pre-existing causes over which he has no control.

Well, it’s not by chance that a ball roles down a hill. It will always happen so long as there is gravity and all the right conditions are met. Also, effects do not randomly follow their cause. What is mean’t by this is that particular natures tend to produce particular effects. A cow will not randomly transform into a cat or a mountain for example. Effects tend to consistently occur according to the nature of their cause and not by chance.

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Aside from the whole broader discussion of the difference between transient and imminent causality and that the reality (or lack thereof) of free will has no impact on whether the Fifth Way follows, the Fifth Way concerns the acting of entities lacking intelligence. The acting of intelligent agents, then, is not in its scope. Perhaps we can make a broader argument, but it’s not necessary here and goes beyond what’s stated in the Summa as “the fifth way…”

Please see the quotation from the Summa in post 32: The Fifth Way: Argument from Design

So again, let’s not get sidetracked.

Unfortunately, there are reasons to believe that not all natural bodies work toward some goal, and even if they did, the end could come about by chance. It has not been proven that there is always a pre-determined end to which natural bodies are working. BTW, are humans considered to be natural bodies or are they unnatural in some sense?

This is my fault. The title of the OP is a bit misleading. It’s not an argument against evolution.

I don’t even think Aquinas would be against evolution if he were here today.

I don’t think there is anything problematic with the idea that particular natures have particular effects, and it is not by chance. Even if you say that some things happen by chance, the statement is still true.

The OP is focused primarily on natural bodies. The question of freewill doesn’t come into it.

As you and I have stated, we know that a chance confluence of different causal factors is involved in the production of many particular effects. That’s not the type of chance you were referring to in the first proposition (I say this for the benefit of others; I’m not correcting you).

What we mean is that cause A tends towards effect Y (or even different, but not random, effects depending upon the circumstances) instead of A having no tendency and just producing unrelated random effects at any given moment. St. Thomas’ point is that there is causal regularity even in entities lacking intelligence.

And that point is just the first and second proposition, not the whole argument.

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Should we rule out entities with intelligence (free will) or do we count them as being governed by these causal principles.

Is free will a natural or an unnatural property? Is it governed by pre-existing causal principles or can it override them.
Since the human being is a natural phenomenon, why would it not be governed by the same principles as everything else found in nature?

For the third and final time, the question has nought to do with the argument. The argument concerns entities lacking intelligence exhibiting causal regularity.

Your question isn’t a bad one in itself, but it is a major tangent away from the subject of the topic. So this is the last time I’ll respond to you bringing it up until we’ve beaten the actual topic’s subject to death.

If I’m not burnt out by 8PM tonight I’ll have time to comment on the actual argument instead of its starting premises.


Free agent can override the chain of causality. In simple word, free agent can initiate and terminate chain of causality. The effect of decision looks random from third perspective point but it is not intrinsically random.

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