Plantinga's evolutionary argument against naturalism

I’d like to create some discussion around an argument which I find very interesting by Alvin Plantinga. For those who aren’t aware of it, I will do my best to summarise it here, but any who are more familiar with it than I and see some mis-representations, please feel free to correct me. The aim of the argument in a nutshell is to show that if we assume both the process of evolution and naturalism, then we have a defeater for all our beliefs, including naturalism itself. I’d like to point out first that Plantinga is NOT trying to argue against the process of evolution, rather simply showing that if we take both evolution and naturalism as granted, then we run into trouble. Plantinga uses Bayesian concepts in his argument, but I plan to leave out these sorts of formalities at this stage (plus I have no idea how to write equations on a forum post).

So then, the first part of the argument looks at the consequences of evolution on our beliefs, and what we should expect given evolution. The idea then is that our cognitive capabilities have been arrived at after billions of years of evolution, and evolution as we know involves the process of natural selection whereby beneficial mutations with respect to survival and reproductive capability in creatures enable them to suceed better than others in the face of selective pressures. Therefore, one would expect our cognitive faculties to have been produced through this process because they are likely to give us some sort of survival benefit. In other words, we can expect our physical cognitive structures to be such that they fundamentally improve our reproductive fitness. By physical cognitive structures, I mean the arrangment of neurons, their relationship to each other, their behaviour etc. Therefore it is these physical structures of neurons and behaviour that presumably is “on the anvil” with respect to selective pressures (among other things of course).

Now, on the presumption of naturalism, each belief that we have will be associated with a certain neuronal event or state in our brains. This neuronal event or state will have two sets of properties. Firstly, it will have more obviously physical properties such as the rate of firing of a certain set of neurons, the potential between each synapse, a certain physical arrangment of the neurons involved etc. The second property will be the content of the belief which emerges from these neuronal events or states, such as “Apples are either red or green”. Now the main thrust of Plantinga’s argument is, do we have any assurance of the reliability of these beliefs given evolution and naturalism? The main question is, what effect does the truth or falsity of the content of the neuronal event or state (NEorS) have on the actual behaviour of the entity with the NEorS? If the truth content of a belief emerging from a NEorS does not have an effect on the actual survival related behaviour of the organism, then such truth-content will be invisible to evolutionary selective processes. If it is the case that truth-content is not refined by evolutionary processes (or having true beliefs does not confer survival benefit), then why should we consider that our beliefs are actually true given naturalism? There are a number of options to consider here regarding this.

The first is epiphenomenalism, that is, beliefs are mere side effects of NEorSs and actually do not enter the causal chain of behaviour. The more obviously physical properties of NEorSs affect behaviour (i.e. arrangment of neurons, behaviour etc.), but the content properties do not. An overt example of this may be that while I believe I am sitting at a desk typing on a keyboard, I could physically actually be doing something else, say running away from a tiger. If epiphenomenalism is true therefore, I think it is fairly safe to say that the reliability of our beliefs (i.e. how certain we are that our beliefs are true) is low. Another option is to consider that the content of our beliefs actually do affect our phyiscal behaviour, which is probably the prominent view amongst us all. However, do we have any necessary reason to expect that the truth or falsehood of a belief actually confers any survival benefit (therefore making the truth content visible to natural selection)? It’s certainly possible to consider scenarios whereby we can have false beliefs yet these still confer survival benefits. To take a (paraphrased) example from Plantinga, say I have the belief that tigers are harmless and that the best way to play with tigers is to run away from them whenever I see them (i.e. a false belief). This belief would confer on me survival benefits (if I live somewhere near tigers), yet it is completely false. To take a less obvious example, I have heard from many naturalists that they believe that theism is a false belief, and this is a belief held by the majority of people in the world and through-out history. However, I have seen the same naturalists also say that we have a propensity for this belief because it has given us a survival benefit (through promoting social cohesion or whatever) and therefore set NEorSs have emerged from selective pressures which give us a propensity for theistic beliefs. If this is true then we have a false belief (theism) that has given rise to a survival benefit. If this is possible, then why should we necessarily consider the majority of our beliefs to be true, given evolution and naturalism? I think it is safe to say that with epiphenomenalism, the probability of the majority of our beliefs being reliable is rather low. If epiphenomanlism is false (i.e. our beliefs do have a causal effect on our behaviour) then the probability of our beliefs being mostly reliable is more difficult to ascertain. In other words the probability is inscrutable. So if we accept both evolution and naturalism, we can consider the probability of our beliefs being mostly reliable as being either low or inscrutable.

How does this affect a person who believes in both evolution and naturalism? Well, consider this example which Plantinga has offered. A thermometer manufacturer produces thermometers (strangely enough) and the CEO is a devious person who makes some thermometers purposely unreliable. If you obtain a thermometer from said manufacturer, knowing of this practice, then the probability of that thermometer being reliable is inscrutable to you. Would you then go and trust that the temperature really is 30 degrees outside from the results of this thermometer? I think the answer would be no. Therefore, if, given evolution and naturalism, the probability of our beliefs being reliable is either low or inscrutable then this gives a person holding both evolution and naturalism a defeater for all their beliefs, including naturalism.

Anyway, that’s the argument as best as I can put together. I look forward to comments.

shameless bump

No objections to this argument at all?

Given naturalism there is no conceptual “truth”.

There dosn’t seem to be a problem here… I might believe something utterly false and yet survive because of it. In what way is it then “false”? what conception OUGHT I have? there is no “true” conception to compare it with. There is no intelligent personal being who’s concepts the world sprung into being from… so which concepts are then “true” ?

What’s left is this: I concieve of a process in which certain actions yield certain results, and if my actions do in fact yield the results I was expecting then my conception was in effect as “true” as any concept gets. One cannot argue that another conception is “more true”… or “better” or “more accurate” in that there is no universal standard to compare them to.

Sweet, I was just thinking about this. I don’t really have time to get into it right now, but maybe later tonight I’ll give some of my updated thoughts on the issue. I will say that the view Mad Man P is the only one that I think gets out of the problem - a denial of conceptual truth. Of course, one can turn that on it’s head and say,

“If anything is (conceptually) true, than naturalism is false”,

Which is very, very close to what Plantinga wants to say, so I don’t think Mad Man P and Plantinga are opposed in their understanding of the argument, MMP is just jumping for the side of the counterfactual that Plantinga expected to be unappealing- ‘biting the bullet’, in other words. This supports my hypothesis that theists are ultimately going to win the philosophical debate by default, as sooner or later the people saying “Theism is true” will be the only ones saying anything is true.

So, to sum this up for the layman (me), is he arguing that because some of our beliefs about reality are false, and these false beliefs arise through the process of evolution, then we are unable to determine which of our beliefs are true?

That makes no sense…

I don’t see a problem for the atheists here… we would just mean different things when we say “X is true.” (X being a concept)

The atheist would mean “X is true, because X is descriptive of something true” while the theist would mean “X is true because God made X true”.

assuming this isn’t just another “brain in a vat” kind of argument for epistemic skepticism, I really don’t see how this argument poses any threat to atheism

Thanks for the replies all :slight_smile:

Mad Man,

Ok, that is probably a way to get around the argument as Uccisore said. However, I would challenge this concept of truth (or at least try to :slight_smile: ). What I would ask is, what makes you think your conception of what truth is or is not, is in someway better than the alternatives for you? Presumably you do, otherwise you would hold some other position (i.e. it is more “true” for you). For instance you define a kind of “truth”, whereby something is as “true” as it is going to get if you conceive of some sort of idea, perform actions and if the results turn out as you would expect, then this idea is essentially “true”. Does your “definition” of what “true” does or does not mean actually pass this definition of yours then? Do you perform some action with this definition in mind, and then get results which confirm it? If so, I’d like to hear what this action and these results are.

I could conceive of an argument whereby you could arrive at naturalism via your definition, and then once naturalism is accepted as a kind of “truth” (via your definition), then one could move to your conception/definition of what truth is or is not. This is circular however. Let me try to be more rigorous. I see your position being developed in two possible ways.

  1. I conceive of a process, perform actions and get results, if these results conform with this process then they are as “true” as one can get
  2. Using 1., naturalism is true (via some other argument)
  3. Because of 2., there is no conceptual truth, so 1.

Another version could be:

  1. Naturalism is true
  2. Because of 1., there is no conceptual truth, therefore if I conceive of a process, perform actions and get results, and if these results conform with this process then they are as “true” as one can get
  3. From 2., then I conceive of naturalism, perform actions and get results which are consonant with naturalism, therefore 1 (with true being expressed as “true”)

Both of these are circular. The only way I can see your system working is by first accepting something being in some way true (i.e. premise 1 in both arguments), without this something actually going through the process whereby you define what true is or is not. In other words, your position isn’t internally consistent.


Sort of. Basically what he is saying is that if we accept naturalism and evolution, there is no strong reason to believe that the majority of our beliefs are true, in fact the probability that this is the case is either low or inscrutable. Therefore the evolution accepting naturalist essentially has a defeater for all his/her beliefs, and this includes naturalism itself. Plantinga, being a Christian, actually believes that our beliefs about the world are mostly true (given our faculties are operating in the right way and in the conditions they were designed for), so he is arguing that this problem exists only for naturalists who accept evolution.

Poor choice of words on my part… I was basically trying to restate instrumentalism in a messed up way. Concepts are tools… only as valuable or “true” as they are useful.

But that’s not how it works… true/false are tools of language… depending on context I might mean different things.

In logic “X is true” means that X is definatly the case.
but in most anything else we don’t have that 100% certainty… and so no one ever means X is definatly the case when they say “X is true”. Well they might mean that… but that’s an untenable position

So let me define conceptual “truth” as best as I can… That through which we best understand, predict and/or manipulate the world as we experience it.

So in fact there would still be a conceptual truth to be had… but it would depend on how we experience the world… and not on the world itself. Therefor it’s concievable for some alien species to experience the world differently and thus have different concepts that, to them, are as true as ours are to us.

So then here is the argument:

  1. Conceptual truth is that through which we best understand, predict and/or manipulate the world as we experience it
  2. Naturalism is a concept through which we best understand, predict and/or manipulate the world as we experience it
  3. Naturalism isn’t necessarily a true concept, universally.
  4. Therefor Naturalism is a true concept for us.

Mad Man P

Heheh. It’s a matter of philosophical history, and sociology, I suppose. Yes, the theist and the atheist mean two different things when they say “X is true”. Where the supposed problem is, is that they didn’t use to.

The evolutionary argument against naturalism is huge precisely because of this- in the context of Ye Olde Rationalist Atheists of the 20th century, Russell, Flew, etc.; the game is over, Theism won, and the atheists aren’t even on the field anymore. Within the context of what truth was considered to be, and the role that reason played in it’s analysis, this argument beats atheism soundly. So that’s a huge deal. Theists are doing Russell’s philosophy, atheists are Pilates stuck asking “What is truth?”

NoelyG- how does victory feel? You might notice that it’s not a whole lot different than defeat, and the reason is this- it was all along true that if atheism was shown to be completely untrue, the atheist always had at his disposal the ability to just change what ‘true’ is. And so they did. Mad Man P is right that Plantinga’s argument isn’t problematic for an atheist that thinks true is a function of what’s useful. Moving forward, we have to decide if there’s anything to be gained from painting the atheism into an even smaller corner- is pragmatism something that needs defeating, or can we be satisfied with atheists having to begin all their arguments with ‘it depends on what you mean by ‘true’’? Is beating a position back to the point where they have to change what ‘truth’ means in order to sustain themselves far enough?

Mad Man P- Back in the day, you had logical positivism. It was the view that statements that couldn’t be empirically verified didn’t actually mean anything. Thus, it was thought to be shown that when a religious person talked about God, the statements they made were neither true nor false, they were just a sort of poetry at best. A lot of liberal theologians considered traditional religion to be defeated by this argument, and that’s why you have some of the movements that you do - emotional sorts of religions where the facts aren’t as important as the social movements they generate- the idea that Theism is a certain kind of social reform couched in peculiar, beautiful language. In this way, theism was allowed to persist for a while, despite the fact that in the context of all real debate, it was thought at the time to have been shown to have no merit. It’s a historical footnote now- positivism is basically a defeated position that we’ve all moved on from with a few holdouts (faust was one, last I checked). What’s important is, the pragmatic or postmodern atheist is doing the same thing now that the theist was then- coming up with new ways to use the key terms (truth, reason, fact, etc.) so that they can still repeat their favorite sentences with conviction. Within the context of naturalism so-applied, in it’s own private circles, it’s to be expected for naturalists to talk to each other about certain things being true and untrue when all they really mean is “useful to pretend as though they are true”. However, in the broader context, you can’t expect people outside that circle to take it at all seriously, in the same way as no atheist took a theologian saying “God is potential of self-actualization within all of us” seriously. The atheist treated them politely, because they knew they were wrestling the best they could with the demonstrable fact that theism as it had once been was no more, while trying to salvage what they thought was still useful and good about religious talk and tradition. The shoe is on the other foot now- I can treat the pragmatic atheist politely, because I know they’re wrestling with the fact that all claim to knowledge has been taken away from them, while trying to maintain the image that they are serious people, and that the critical thinking they speak so highly of is actually good for something in their framework. But where the rubber meets the road, it’s a dead position as it once was.

Ya, I’d summarize it like this- according to evolution, brains came about from natural selection. Natural selection picks what survives, and ignores everything else. This leaves us with no good reason to think that a brain produced by natural selection would know true things. However, naturalism (belief that the laws of nature and what they act upon are all there is) is one of those things that a natural selection-produced brain has come up with. Ergo, we’ve no good reason to believe naturalism, given that evolution is true.

If it seems hard to believe that the institutions of human thought could be broadly false just because they are survival-oriented and not truth oriented, then all you need to do is check out how some atheists describe the evolutionary origins of religion to get an example.

How are we defining “truth”? If truth is defined in an instrumentalist sense and truth is relative (fallibalism), then I don’t actually see a problem.

Let’s say we think tigers are harmless and the best way to play with them is to run away. That works pretty well. But note, that which is the best at something isn’t necessarily the only option. There are all sorts of local minima (or maxima, depending on how you want to conceive the schema) on the way to the lowest minimum that are often arrived at, both in chemistry (think of conformations and such) and in life (the classic dilemma is relationships is that there is bound to be someone out there that is a better match, yet few people choose to take that fact to its logical conclusions). So the belief that tigers are harmless and that the best way to play with them is to run away would be positively selective, but other factors in the situation may arise that lead the person with this belief to accept a local minima (like teasing the tiger with a string) as opposed to the absolute minimum (running away). On the other hand, someone who thinks tigers are dangerous would adopt a very different, far more selective, set of local minima in response to a tiger. So under ideal situations they can both be said to be equally as effective, but as soon as other factors are included and the situation becomes less-than-ideal, one is substantially more effective than the other.

As for the thermometer, I think it depends on both the level of error and its frequency. First off, the precision of thermometers is limited by the number of significant figures it has been both been calibrated to and can display/can be resolved. A thermometer that I use to gauge the outside temperature needn’t be terribly precise, +/- even four degrees C and I’d be fine. On the other hand, if I am brewing beer even a half a degree can make a huge difference in the final product! And I’m sure chemists and physicists would need an even greater degree of precision for many of their operations. Would the differences here be the same as the case of the devious CEO? After all, the thermometer in my Mom’s backyard did have an error of around +/- 4 degrees (coil thermometers suck) is the CEO making them pumping out an ‘unreliable’ product and distributing it to the masses, especially if he also makes analytic thermometers with an accuracy of +/- 0.005 degrees C? Or is the level of precision needed for those different tasks simply different? I’d argue that errors arising from naturalism are errors of that type and are within range of their need. And I think such an assumption is rational, because of the local minima that I discussed earlier.

What about a thermometer that is just plain off, if it lacks accuracy. Like my brewing thermometer, actually. Again, it is a shitty coil thermometer (but it is pretty precise), reads around eight degrees F too high between analytically measured 145 and 155F (and it is at 8 around 149-151F, which is generally around where I am trying to hit for a beer of average body) and around five degrees F too high between 120 and 140F. But since I’ve compared it to the standard, I know that and can adjust for it easily. Here is the great thing though, I had already done that before I actually broke down and compared my thermometer to a standard. The first beer I made was too thin (I mashed too low) for my tastes. So I gradually bumped up my mash temperature until I found a body and level of sweetness that I enjoyed. The system corrects itself in the case of inaccuracies like that.

Now, if every time I brewed I used a different thermometer, I’d be in trouble. Because of both the unknown precision and the unknown accuracy. But I see no reason to suppose naturalism demands a different thermometer be used each time.


It just smells like a rat, Xunzian. You and I have both been around the block a few times, and we know that the Wiccans, the Holocaust deniers, the UFOologists, the psychics, the anti-moralists...all these sorts are among the first to pull out the 'well, it depends on how you define truth' thing, because let's face it, [i]they need that[/i].  If this argument has atheists doing that, then I'd say that's about as much water as any philosophical argument can be expected to carry.  I mean, to take it to an extreme, if my beliefs get questioned and criticized hard enough, I suppose I can always fall back as "Whatever I happen to believe moment to moment" as a definition of truth, and then my religion would be unassailable! If I did that, could I in good conscience say that "I see no problem here"? In response to the old arguments that pushed me to resort to such a thing?

Sure, but what they are advocating is vulgar relativism, which is decidedly not what I am talking about. This essay by Isaac Asimov illustrates my point. The central thesis of the essay can be summed up in this quip: “when people thought the earth was flat, they were wrong. When people thought the earth was spherical, they were wrong. But if you think that thinking the earth is spherical is just as wrong as thinking the earth is flat, then your view is wronger than both of them put together.”

And that is precisely what I think Plantinga is doing here. He is using an absolute definition of truth that really only make sense in either revealed religions or logic/math. As for defining truth as “whatever you believe at the moment”, I think that is pretty much how solipsists do define truth. And on that ground they can’t be assailed as long as the other party also accepts that definition. But I think we can both agree, that doesn’t make for a very effective epistemology nor is it very good rhetoric.


 I don't see how this advocates any different understanding of truth. I might be mis-reading you, but if you begin by acknowledging that people said the earth was flat were [i]wrong[/i], then I'm going to ask you to tell me what you mean by that, and I'd be surprised if you said anything all that different than what Plantinga (or I) would say. To say that wrong beliefs can get the job done isn't a new understanding of truth to my mind- in fact, it's just an optimistic way of agreeing with P's argument, as far as I can tell. 

I don’t see how. It seems to me that his argument works for any model of truth that deals with approaching the actual nature of things to ANY degree. Sure, the earth isn’t really a sphere, but the REASON why that’s closer to being correct than saying the earth is flat is still wrapped up in the Earth actually being like something, and our notions zeroing in on what that is. I don’t see why Plantinga’s argument doesn’t apply to that just as well- natural selection doesn’t lend itself to beliefs that are almost true any more than it lends itself to ones that are completely false, totally true, or anything else. Or so his argument goes. You’d have to completely abstract truth from external realities altogether, and define it completely in terms of what helps us accomplish our aims to break free of his arguments. Again, I can only point to religion as a supposed example- someone who buys into the idea of religion existing as a set of false beliefs that come about because of some survival benefit in having them isn’t likely to consider theism as being ‘true enough’, they’re going to consider it false, however handy at times.

EDIT: I think you might be making a mistake with your breakdown of the ‘tiger’ example, too. Mathmatically, if you have the series

X 1, 2, ?
Y 2, 3, ?

You could argue that the next element in the series for Y is 4 (X+1) or 5 (listing prime numbers).

It seems to me that you’re arguing that all we need to do is wait for the next element in the series to appear, and then we’d know, but that’s not fair. Certainly, somebody running away from tigers in order to play with them might get into trouble applying that reasoning in some other situation- but this is an analogy after all. Describe that other situation, and I can give you an example of a broadly false belief that would lead to survival-producing behavior. Then you can add some other new factor in which my example isn’t going to work, and we can go back and forth forever. The point that Plantinga is trying to make isn’t ABOUT running away from tigers, though, it’s about how for any (simple or life-long and complex) set of conditions that demand a response to survive, there’s going to be a variety of beliefs that will get the person through unscathed, and an extreme minority of those will have anything to do with the truth. Just like in my mathematical series above- revealing the next element in the series gives the illusion of getting us close to the truth, because it eliminates one of the possibilities I put in front of you. But it doesn’t, really, because the possible explanation of the new series (and any series) is still infinite.

Ahhh, but how were they wrong? Naturalism and selection appear to give us a similar process of refinement that was described in the essay. Is saying the Earth is flat ‘wrong’? Depends on what one wants to accomplish. An unspoken assumption in that essay, and one that I share, is that we can only asymptotically approach the truth. Measurements can always be more precises. So using absolute definitions of ‘truth’ and ‘falseness’ results in us forcing to conclude that everything we know is false, is wrong. Not only is such a formulation unsatisfactory, it is downright nonsensical.

The Earth isn’t ‘like’ anything besides ‘the Earth’. That is what I mean when I talk about the idiopathic nature of truth. The models that we create to understand represent the Earth but they are not the Earth. So we are creating a series of models that model the Earth more closely. A flat Earth models the Earth better over distances than a completely irregular Earth. A spherical Earth better models the Earth than a flat Earth, and so on down the line. Eventually our model could reach a degree of precision that we go back to saying the Earth is completely irregularly shaped because we will have to include all the valleys, mountains, and all of that into it. We already have some models like that, those nifty globes with raised areas for the mountains. We can’t say that a globe like that is a sphere anymore just as we can’t say the pear-shaped Earth is a sphere. But once you’ve reach a degree of precision, it also becomes meaningless. Let’s suppose we get a model that accurately represents the shape of the Earth down to an inch. As soon as the wind blows and a sand dune moves, that model need to be updated.

Sorry for the long, belated edit, I’ll reply in a while. :slight_smile:

I’m out for the evening anyway. I’ll reply to the edit tomorrow. And any additional posts you might make.


Xun is practically speaking for me here… So i’ll just hang back for now, assuming there wasn’t anything in your last post you wanted my comments on…

Also it might be worth adding that when you say:

such people would be irrational people. Given your definition of “true” there is no reasonable way for a non-omniscient being to say anything is true about the outside world. At best they can say “X is likely true”…

Sorry for the absence, I was away over the weekend.

Mad Man,

I think you may have misunderstood what I was getting at, but that’s entirely understandable because it was a bit convoluted.

My problem here is with 1. Your definition of conceptual truth must be taken as a given (i.e. in some sense true a priori) for your system to work. In other words, 1. must be considered to be true in some sense other than what you are actually defining as truth in 1. I fail to see how your definition of conceptual truth (i.e. 1.) can be affirmed by that very definition i.e. it’s not self affirming. In addition to this, the only reason to accept the definition 1. is if naturalism is already given to be true in some sense (i.e. 4.). But then your argument is circular. You could say that 1. is in some way a basic belief or self evident, but then wouldn’t that be saying 1. is a conceptual truth that is not attained by means of the definition itself? That is why I said your position wasn’t internally consistent.


That is it, I think the analogy is so broad as to be useless. As soon as we start actually considering the implications of the analogy and the demands that it makes, we would be forced to conclude that everything we know is wrong due to problems of both precision and accuracy. Furthermore, it demands unknowability because of the changing nature of reality.

I’m arguing that the next unit in the series will appear by virtue of the incompleteness of the knowledge that we have now. You’ll note that I’ve posited that we can only asymptotically approach knowledge unless we are dealing with non-real representations (like logic).