Greg Krehbiel's Crowhill Weblog - Content

Thoughts on life — News, culture, politics, beer, art, science, education, religion and ethics

Other Crowhill sites:
Crowhill PublishingGreg's Book Publishing blog
Greg's Marketing blogGreg's Home Brewing blog

Weak and Strong Plantinga

by Greg Krehbiel on 17 December 2011

As you may know, Alvin Plantinga is a well-known Christian philosopher who recently wrote Where the Conflict Really Lies: Science, Religion, and Naturalism. There’s a short interview with Plantinga here, which is somewhat interesting.

Plantinga defends an argument that I first encountered through C.S. Lewis, many years ago. In brief, it goes like this. If your mind is a product of your brain, and your brain is a product of random natural selection, you have no grounds to trust it.

The argument is much more detailed than anything I’m going to say here, but by way of simple summary …

… if this is true, if our minds are aimed at mere survival, not at truth, then it’s not probable that our minds should be reliable….

Plantinga points out (rightly, I think) that you wouldn’t expect unguided evolution to produce a brain that is a reliable arbiter of truth.

But “not expecting it” is not the same as “this can’t happen.”

As I’ve thought through some of this it seems to me that we have two versions of this arument — “weak Plantinga” and “strong Plantinga.”

Weak Plantinga might go like this. Naturalism doesn’t explain a brain ordered towards truth. The human brain is ordered towards truth. Therefore naturalism doesn’t explain the human brain.

That seems like a reasonable argument to me, with some caveats I mention below.

Strong Plantinga might go like this. Naturalism can’t explain a brain ordered towards the truth. If a brain is ordered towards truth, naturalism must be false. The human brain is ordered towards truth. Therefore naturalism is false.

That bugs me, because I don’t think you can move from “we wouldn’t expect naturalism to be able to do this” to “naturalism can’t do this, therefore something else is required.”

Another thing that bothers me about this line of argument is that I don’t think we’re dealing with binary choices. Our brains are neither entirely reliable nor entirely unreliable. (Maybe I should just speak for myself?) And I’m not sure it’s fair to say “naturalism leads to an unreliable brain” and “design (or whatever) leads to a reliable brain.”

How do we know, anyway?

Plantinga may cover these objections in his longer treatment of this argument. I have only read some of his essays.

One final thing. As I was reading the Q&A with Plantinga (linked above), I had an odd feeling … like I’d heard this kind of thing somewhere before. And then it struck me that the logic was similar to evolutionary psychology. Something along the lines of “we expect A to lead to B, we see B, therefore A.” But when I tried to elaborate on the connection it kinda fizzled. It’s like when have a genius idea in the shower and can’t remember it when you have pen and paper.

Oh well.

-- 2011-12-17  »  Greg Krehbiel

Talkback x 28

  1. John Krehbiel John K
    17 December 2011 @ 8:43 am

    As usual, Plantinga is best at showing that he has no clue about evolution.

    1. Natural selection is the opposite of random. Period.

    2. How could natural selection supply us with a system of perceiving the world that was not reliable? Yes, there are built in biases, like our tendency to assign agency to things that can’t have agency, but if you see a tiger and think it’s a bunny rabbit, you’re out of the game.

    3. I suspect, but am not sure, that “truth” as he is using it is some nebulous metaphysical concept, and has little to do with gaining reliable information about the world.

    4. Why on Earth would you assume that a created mind was any better at finding “truth” (whatever that may mean)?
    For instance, I was once in a political argument with a soldier. He claimed to be in the know, because they tell the soldiers stuff the public never hears. Although that is possible, I consider it much more likely that they tell the soldiers what they want them to believe to further the geopolitical goals of whomever promoted the military conflict they want the poor dumb schmuck to die in.

  2. Greg Krehbiel Greg Krehbiel
    17 December 2011 @ 9:04 am

    Apparently you didn’t read the link. It was me who said natural selection is random, not Plantinga, and I stand by it, since “random” means “having no definite aim or purpose.” It also means “lack of predictability,” which also applies.

    The sense in which biologists say natural selection in not random was entirely irrelevant to my point or the issue at hand.

    Plantinga is, of course, speaking of “truth” in a sense beyond “that’s a rabbit.”

    And it seems fairly obvious that a mind that is specifically designed to do a task is more likely to be good at it than a mind that accidentally developed in an organism whose real business lay elsewhere. It’s also possible to imagine a “designed brain” that is clueless — made by some evil djin or something.

  3. John Krehbiel John K
    17 December 2011 @ 3:49 pm

    It is easy in population genetics to predict gene frequencies that natural selection will produce, given the selective advantage of a particular genotype in a particular environment. (sickle cell anemia is an example)

    So he’s using “truth” in a way that is basically meaningless, which is what I suspected.

    Just because something “seems obvious” doesn’t make it so. Lots of computers make better paperweights than computers, thanks to ever-so-clever programming :-)

  4. Greg Krehbiel Greg Krehbiel
    17 December 2011 @ 4:43 pm

    Natural selection may be predictable in a controlled environment, but it’s not all that predictable in the real world.

    Re: truth, you don’t seriously mean that the only sense of “truth” that matters is “that’s a rabbit.”

    Why, for example, should the human mind be able to comprehend advanced mathematics, when it’s only been relevant for the last few centuries? Why would evolution have created a brain with such a useless capacity (considering the overall history of man)?

    I’m not saying there’s only one answer. But it is definitely a valid question.

    So I could rephrase “weak plantinga” as …

    Naturalism doesn’t explain a brain that can understand advanced mathematics. The human brain can understand advanced mathematics. Therefore naturalism doesn’t explain the human brain.

  5. John Krehbiel John K
    18 December 2011 @ 2:48 pm

    First, not all human brains can comprehend advanced mathematics. I suspect that the number of adults who can do actual algebra (not the crap on the state assessments designed to give dunces passing grades, but real algebra) is about 50% of the total population.

    To see how some brains might be able to do higher math as a consequence of natural selection, look at singing as an example. I very strongly suspect that the ability of humans to sing is a sexually selected trait. Singing is considered, in at least some contexts, as courtship behavior. Better singers are more successful at attracting mates.

    But this doesn’t mean that everyone is a Pavarotti. It means that most people can at least hold a tune. Many are tone-deaf, or nearly so, and many are capable of singing somewhat better than average.

    The amount of mathematical ability that is necessary to get along is probably a bit below the average. But the natural variation includes some who can do a whole lot better.

    And the computed frequencies for a great many allele frequencies are quite close to their actual frequencies in the real world. Natural selection is among the three most successful scientific theories, the other two being general relativity and quantum mechanics.

    As for a useful definition of “truth,” see this (at least the beginning).

  6. Greg Krehbiel Greg Krehbiel
    18 December 2011 @ 4:32 pm

    It’s possible that there is an evolutionary explanation for the human brain’s ability to understand incredible things, to think about things way deeper than “there’s a rabbit,” etc. I don’t think weak Plantinga is a slam-dunk argument by any means. But I think it’s a respectable argument.

    I don’t much like the article you link to about truth. It just seems to reiterate “science as a cult” talking points.

    For example, he says “What science … provides is a set of investigative methods that everyone regards as legitimate.”

    I think that takes things too far. People regard science as a legitimate tool for investigating some things, but science has clearly gone beyond that in many ways. For example, modern science assumes philosophical materialism, and everyone does not regard that as legitimate.

    Further on, it seems to me he’s missing the point about math. Mathematical reasoning precedes science, and his arguments to the contrary seem very weak.

    Same with his arguments about morality.

    The more I read of the science blogs, the more they remind me of a mind-control cult. Rather than admit their weaknesses, they bend and twist language, come up with rather weird positions on things, pound the table insisting their side is right, establish an incredibly strong “us” vs. “them” culture, and excommunicate people who don’t toe the doctrinal line.

  7. Dave Krehbiel Dave K
    18 December 2011 @ 6:24 pm

    John and Greg: it seems to me that you are ignoring a fundamental question which is central to this discussion: “what is truth?”

  8. Greg Krehbiel Greg Krehbiel
    18 December 2011 @ 10:29 pm

    I think it’s odd that you think we’re ignoring it, since we’ve been talking about it.

    Anyway, I think we agree that “truth” is “what corresponds to reality.”

    Sometimes John sounds as if believes that the only truths that are worth worrying about are truths that can be objectively verified. I don’t think he really believes that, because I believe there are a number of things he (and all the rest of us) believe to be true that we can’t verify.

    In addition to things that we actually believe that we can’t verify, there’s also “higher order” stuff, like math and physics and even philosophy. We can verify some math and some physics objectively, but not all of it. We nevertheless believe it’s true. (At least in the case of math.)

    And a lot of philosophy we can’t verify at all. It’s a story we bring to the evidence.

    I don’t think the question is “what is truth?”

    I think the question is “what kinds of things can be considered true?”

  9. Dave Krehbiel Dave K
    19 December 2011 @ 8:44 am

    I think there is a very important difference and a very real difference between natural truth and spiritual truth. 1 Corinthians Chapter 2 is well worth reading in its entirety.

    Verse 14 says, “ The person without the Spirit does not accept the things that come from the Spirit of God but considers them foolishness, and cannot understand them because they are discerned only through the Spirit.”

    An argument by an atheist that he or she does not understand spiritual truths with their natural mind should not cause believers to doubt Scripture.

  10. kdeb
    19 December 2011 @ 9:07 am

    @John – I read the article and it really doesn’t define truth at all. It just gripes about an “issue.” (his words I believe)

    So I have a few questions:
    You said: ” Natural selection is the opposite of random. Period.” Does that mean that the destruction of life due to cataclysm is not Natural Selection at work? Or do you argue that since the tidal wave or meteor or what-have-you happened because of non-random causes that it is tied to the process of Natural Selction in a non-random way?

    You said: “How could natural selection supply us with a system of perceiving the world that was not reliable?” Of course it could give us a completely unreliable brain in all regards except the “success” measure – producing offspring, right? So we could have brains that excel and are attracted to rape, child molestation, cuckolding, etc. And please do not tell me how societies root out such behaviors over time because the society as a whole benefits…. I can just as easily blame church attendance. ;)

  11. Greg Krehbiel Greg Krehbiel
    19 December 2011 @ 9:08 am

    That’s true (@Dave). And the person who is (for whatever reason) convinced of the reality of such spiritual truths doesn’t have any reason to be worried by people who don’t believe in them.

    A person may have perfectly valid reasons for believing something that he can’t explain or justify to someone else. Or, to put it another way, it’s wrong-headed to believe that someone else’s beliefs are unjustified unless they can convince me of them.

    But some people believe the only relevant truths are those that can be verified objectively. I don’t think they really believe that for themselves, or in their own personal lives, but they may believe it for “public truth.”

    So, for example, a person might say “the only truths that are admissible for public matters, like law, are those that can be objectively verified.”

    That is a reasonable position to hold, but many people who believe it think it is the only reasonable position, and that is the error of the secularist.

    Many secularists think that because they have taken a stand that only things that are objectively verified can be used for public matters that everybody else is obligated to follow that rule as well. But why should they?

  12. Greg Krehbiel Greg Krehbiel
    19 December 2011 @ 9:14 am

    @Deb — yes, it seems that the best claim natural selection can make is that it would lead to a brain that is reliable enough to get the creature to survive to successfully pass along its genes. Any number of wrong-headed ideas might be “successful” in that respect.

    But … isn’t that sorta the way the world is? Lots of human cultures have completely wrong-headed ideas about lots of things. And they survived. Natural selection didn’t weed them out.

    ISTM that Plantinga’s point can’t rely on “man as he is,” but on “man as he can be.”

    “Man as he is” is a crazy mess. But “man as he can be” is a pretty impressive thing that seems to go beyond anything you’d expect from natural selection.

    (The major weakness in that argument is the “seems.” How do we really know?)

  13. John Krehbiel John Krehbiel
    19 December 2011 @ 11:39 am

    @Deb, random events do change gene frequencies, and are outside of natural selection. For instance, if a small population migrates out of the home range of a species it will not have the full range of variation that the original population contains most of the time. Subsequent generations descended from that population have different gene frequencies than the parent population due to the Founder Effect, which is not natural selection.

    And not all behaviors that naively seem to increase reproductive success actually do so. There was an amusing (if mean-spirited) article recently about how the Duggers (that family on the “reality” show with a seemingly endless parade of kids whose names all start with the same letter) are a demonstration of the tradeoff between number of offspring and quality of offspring. In some species rape pays off. But in humans the absence of both parents in a stable relationship is demonstrably negative for the well being of the offspring.

    @Dave, the problem with that kind of “spiritual truth” is that there is enormous disagreement over just what those “truths” are, and no good way to differentiate between them.

    Truth ought to be reliable, and part of that is being able to verify it.

  14. Greg Krehbiel Greg Krehbiel
    19 December 2011 @ 12:32 pm

    >Truth ought to be reliable, and part of that is being
    >able to verify it.

    Yes, but there are annoying situations in which a truth claim can’t be verified. The movie “Contact” played on that theme very well.

  15. John Krehbiel John Krehbiel
    31 December 2011 @ 11:58 am

    Just saw (heard) this on Youtube yesterday. It’s an hour and 45 minutes long in total, and you have to listen in segments, but it’s very interesting.

  16. kdeb
    31 December 2011 @ 12:18 pm

    Geez, John, it would have to be the freaking YouTube of the decade to watch something for 1:45~~~~~

    Lol Happy New Year!

  17. John Krehbiel John K
    31 December 2011 @ 3:57 pm

    Plantinga certainly makes clear that he means something other than “reliably true information” when he talks about a mind capable of holding, or coming to, true beliefs. But my question to him would be “Who says any of those ‘true beliefs’ are in fact true?”

    I find nearly all of his arguments circular.

  18. kdeb
    31 December 2011 @ 4:30 pm

    Well who says any of anyone’s true beliefs are in fact true?
    You aren’t turning into a Scientologist on us are you?

  19. Greg Krehbiel Greg Krehbiel
    1 January 2012 @ 12:07 am

    John, this is an interesting debate, but I’m surprised you posted it because of the way Dennett comes across.

    My overall reaction is that Plantinga engages in serious, careful, logical argument, and Dennett mostly engages in posturing, story telling and polemic. Compared to Plantinga, Dennett sounds like a jerk and a clown.

    I listened to their whole statements, but not the Q&A. Here’s my summary of their major points.


    The conflict is between naturalism and science, not theistic religion and science.

    The question is whether evolution is unguided. (unplanned, unintended) Some people claim it is essential to evolutionary theory to say that it is unguided.

    Can mutations be random and also intended? There’s nothing essential in the use of “random” that excludes a cause or an intention. The randomness involved in Darwinism does not require that it is not designed or planned.

    People who claim evolution shows man is not designed are confusing the scientific theory with a metaphysical add-on (naturalism).

    Does evolution undercut the argument from design? — Not if you look at the complicated nature of a cell. Biological science might seem to take away the design argument at the macro level while restoring it at the micro level.

    Does evolution (which relies on waste and suffering) undercut the idea of a good or intelligent God? — People have known that nature is ugly and nasty well before Darwin. Evolution doesn’t offer much new to the argument.

    Is evolution without God “simpler”? — In one sense it might be, but that’s not the only consideration. When Plantinga breaks down the propositions into their individual components, it’s very hard to see why the “no God” theory is more probable. However, even the argument that evolution without God is “simpler” starts by presupposing a non-theistic universe, which is the question at issue.

    Plantinga says a naturalism that includes materialism is incompatible with science. This discussion gets pretty technical, but it revolves around the problem of reducing the mental to the physical. He also goes into the problem of believing that naturalism would lead to a mind that knows something true.


    Dennett agrees that evolution is compatible with theistic belief. He agrees that the sense of “randomness” used in evolution does not have to mean “not planned.” He also says evolution by itself (without naturalism) does not lead to an anti-God position.

    He then goes into a series of anecdotes about Pekinese and Cheetahs and such, arguing that it’s hard to tell what is produced by natural vs. artificial selection.

    He says a failure of our ability to imagine something is not evidence against it.

    Dennett says any biologist who says he can rule out intelligent design is overstating the case. But he calls belief in a designer a gratuitous fantasy for which there is not a shred of evidence.

    He makes a very telling comment. He says “without naturalism Behe is just a theological speculator.” IOW, he is contradict himself and equating science with naturalism.

    He tries to demonstrate that Behe must be wrong this way. He says if Behe was anywhere close to right, scientists would be rushing to their labs to demonstrate his theories and win the Nobel prize for proving irreducible complexity. Since they’re not, Behe must be wrong.

    He argues against Plantinga’s argument — “the probability that your cognitive faculties are reliable given natural selection is low” — by saying there wouldn’t be much of a market in the real world for senses that weren’t reliable.

  20. Greg Krehbiel Greg Krehbiel
    1 January 2012 @ 12:16 am

    One illustration of Plantinga’s seriousness vs. Dennett’s clownishness is the “supermanism” discussion.

    Dennett says sure, belief in God is compatible with evolution, but so is a belief that Superman formed life on the earth.

    Rather than calling Dennett a clown and a jerk, Plantinga points out a couple of the differences between belief in God and belief in Superman, and says that Dennett’s criticism only makes sense if he intends to argue that belief in Superman is just as reasonable as belief in God.

    Dennett’s argument is the kind of sloppy, clownish reasoning I’ve come to expect from that crowd. It would be interesting to hear somebody debate Plantinga who is actually on his level.

  21. John Krehbiel John K
    1 January 2012 @ 11:14 am

    Dennett does come across as very flippant, but while Plantinga sounds serious, his arguments deserve nothing more.

    He says that there is nothing in evolutionary science to rule out the idea that God guided all of the supposedly random events (mutations, geologic upheavals, whatever). Dennet’s reply is basically “So what? There’s nothing in evolutionary science to rule out the idea that Superman did it all either.” So what Dennett is pointing out is that, given our understanding of the evolutionary history of life on Earth, positing a manipulator to guide the process is superfluous.

    Plantinga calls Behe serious, and Dennett points out that Behe is anything but serious. His math is seriously flawed, his attempt at logic attacks naturalism at the same time it depends on it. (You made the same point about the fine tuning argument– it depends on Big Bang cosmology) It is entirely true that if Behe had anything to contribute, scientists would be rushing to confirm it, as they tried to with Cold Fusion.

    Plantinga engages in a serious sounding kind of symbolic reasoning which is just about impossible to follow in the audio, but comes across as a device to make him sound impressive, rather than a device to illuminate his points. (Like Vox Day’s Latin phrases)

    Plantinga’s response to the critique that creationism inserts an unnecessary entity into the argument is revealing, though. He essentially says “But we aren’t inserting anything that we didn’t already assume in the first place.” He didn’t say it in so many words, but it does reveal the underlying circularity of his arguments.

  22. Greg Krehbiel Greg Krehbiel
    1 January 2012 @ 12:22 pm

    I think you’re neglecting to take into consideration the context. The question of the debate was whether there is a conflict between science and religion. On that topic, Plantinga’s approach was right and Dennett’s approach was ridiculous.

    Plantinga’s response to the critique that creationism inserts an unnecessary entity into the argument is revealing, though. He essentially says “But we aren’t inserting anything that we didn’t already assume in the first place.”

    That’s my point. The topic wasn’t “can we prove religious belief,” but “is there a conflict.” Plantinga is taking exactly the correct approach given the topic under consideration.

    To the question “is there a conflict between science and religion” Dennett wants to say “oh, well, of course we start by denying religion and making silly caricatures of if, and we go from there.”

  23. John Krehbiel John K
    1 January 2012 @ 1:04 pm

    But Plantinga’s argument is essentially “There is no conflict between a materialist account of dynamics and a belief that there are little demons driving atoms so that they conserve energy and momentum in the way that physicists insist is naturalistic.”

    It’s a silly argument, and the correct response is “So what?”

    It’s not that different from Dennett’s argument that, while our future actions may be in fact completely determined, we do have a kind of free will in a make-believe act-like-we-have-it-even-though-we-don’t way. IIRC, I lent you that book, and we both found it unsatisfying.

  24. Greg Krehbiel Greg Krehbiel
    1 January 2012 @ 2:25 pm

    First, you’re still not getting the point. The question is not “is it reasonable to believe that God controls the material world?” The question is “is there a conflict between science and religion?”

    Second, comparing the theism that Plantinga is defending to “little demons driving atoms so that they conserve energy and momentum” is offensive to the people who believe it and absurd.

    Imagine a debate on the ability of random mutation to create enough material for natural selection to work on, and one of the debaters said “what you’re saying is no different from believing that lots of little elves are rolling dice and tinkering with DNA.”

    In one respect, … well, yes, it sorta is analogous. But it’s irrelevant and intentionally insulting.

    And it’s definitely not a “so what?” issue. There are lots of so-called scientists who believe that philosophical naturalism is necessary component of modern science. Dennett has the sense to realize it is not, and that is a very significant point.

  25. John Krehbiel John K
    1 January 2012 @ 6:02 pm

    But the point is that the conflict only disappears when the actions of the supposed supernatural entity precisely mimic those events which can be just as well explained by completely natural means. There’s no conflict between saying that lightning struck someone at random verses saying that God intended for that person to be struck by lightning, but actual events show no evidence of any such guidance.

    Claiming that God presented just those mutations that actually happened, dropped meteors when it was necessary to get dinosaurs out of the way, turned the thermostat up or down when necessary, in the service of removing the contingency of Earth’s evolutionary history is no more absurd than saying that atoms follow their particular paths because of supernatural guidance.

    And incidentally, recombination of existing genes does an awful lot of the heavy lifting in providing variation for selection to work on. There are a surprisingly small number of actual genes, mostly present in prokaryotes, that are used by just about all living things. It’s not whether such variation occurs that is at issue, but how particular variants were available when “needed” for the history of life not to be contingent upon random events.

  26. Greg Krehbiel Greg Krehbiel
    1 January 2012 @ 10:54 pm

    Okay, but that is a different question.

    If the question is “does religion add anything to the discussion” then all those points may be apt. In that discussion, it’s reasonable to ask whether postulating a god helps resolve anything, or adds any knowledge that we otherwise wouldn’t have.

    But if the question is “is there a conflict between science and religion,” then those points are complete non sequitors.

  27. kdeb
    2 January 2012 @ 6:16 am

    Of course, religion in this case is not a cargo cult, trying to produce by strange and unproductive and clearly misguided means what was demonstrably produced in another way. It is seeing a “third party,” if you will, whose very suggested presence causes people to feel required to argue vehemently against it. Plantinga’s point is – isn’t it? – that this is not an inconsistency between science and religion. It may make people get gripey and they may moan and they may insist it is unnecessary, but it is not inconsistent in the sense that believing that there is a God active in creation would necessarily imply that no other part of the scientific understanding of creation could then work.

  28. Greg Krehbiel Greg Krehbiel
    2 January 2012 @ 8:37 am

    Yes, the question was whether religion and science are inconsistent, not whether religion is necessary.

    There are people going around saying that “science proves” that man has no purpose or meaning and that God could not have made man “in his image” because we’re not “made” in any meaningful sense.

    But science doesn’t “prove” anything of the kind. Most modern scientists assumes it, but that’s a different matter. And a person can be a perfectly good scientist and reject that assumption.

    To me, the fact that Dennett admits that point (even though he backpedals on it) is the most interesting think in the debate.

    Having said that, a person could legitimately argue that science makes religion unnecessary. That’s what Dennett was getting at. And I would very much like to hear Plantinga argue that point with someone.