Apr 25

Is naturalism a type of faith?

In this essay, I’m going to take on a common claim that a form of narrow naturalism can rightly be called faith. The form of naturalism I have in mind is one that says for any given unexplained event, it is overwhelmingly likely that the real explanation will be a naturalistic one. So, for example, such a person would claim that something natural probably caused our universe via the Big Bang or other means. Or they would claim that something natural probably brought about the origin of life on this planet. These are events currently not explained by science, but the narrow naturalist is confident that science can one day explain them, if the opportunity actually presents itself.

I don’t want to get too mired in a discussion of what we may rightly call faith, so I’ll just consider whether that confidence in science’s explanatory capability is justified and to what extent it is justified. If the belief is very justified, say at a probability of 0.75 or higher, then I don’t think we can rightly call it faith under any definition except those that are too all encompassing to be useful.

What will be our method of determining this probability? You probably guessed it, if you’re a regular reader—Bayes’ Theorem! If you just read that and thought, “WTF is Bayes’ Theorem?” then you may want to start here, here, and here to see my attempts at instruction.

As a reminder, here is Bayes’ Theorem, and the sections below will attempt to replace these abstractions with real numbers so we can run the formula:

p(h|e.b) = p(h|b) x p(e|h.b)  /  [ p(h|b) x p(e|h.b) ] + [ p(~h|b) x p(e|~h.b) ]


Prior Probabilities: p(h│b) and p(~h│b)

To determine our prior probability, we’ll use Laplace’s Law of Succession. This offers a great advantage in determining our prior probability compared to situations that require more subjectivity. Laplace’s Law is p = (r + 1) / (n + 2) where r is the number of times in past trials that an outcome has occurred and n is the total number of trials. I’ll give a quick explanation: If you were rolling a die that you knew was biased, but weren’t sure toward which number, you could test it by rolling it several times. Let’s say that the 6-side is rolled 47 times out of 100 rolls. The expected prior probability of rolling a six is 1/6, but on this particular die we see it’s 48/102 or simplified is 8/17. When you have past data, Laplace’s Law is a good way to provide an objective prior probability.

Now, in the case of naturalistic explanations, we have an extensive track record. In fact, everything that has ever been conclusively explained has been done so by a naturalistic process. This includes the birth of every person, the formation of rivers and mountains, diseases, genetics, the outcomes of wars, and on and on. All of these things used to be attributed to the acts of gods or other divine creatures, but are now understood as natural phenomena. This means that using Laplace’s Law, r and n are the same. This can quickly get out of hand because so many things have happened like these in the history of Earth. I’m going to limit my occurrences to 100 billion. That’s the number of people estimated to have ever lived. So, even if we were only counting the number of sneezes that have ever occurred, we would be justified in using this large of a number. If we run Laplace’s Law, we get a result of p(h│b) = 0.99999999999. This is the probability that our hypothesis of narrow naturalism is true given our background knowledge of history and science.

The other number we want here is simply derived from the previous number: p(~h│b) = 1 – p(h│b) = 0.00000000001. Now we have two of the four terms necessary to calculate an answer.


Consideration of Evidence: p(e│h.b) and p(e│~h.b)

We’ve just seen that prior to considering any particular example, like the Big Bang, naturalism has a significant statistical advantage in its potential to explain based on a strong track record. What this tells us is that even if we are very generous to the opponent (like a supernaturalist) in the consideration of evidence, h (narrow naturalism) should still come out as much more probable. So, let’s try and be generous so that no one can accuse me of bias. I’m going to offer three sets of possible numbers that stack the deck in favor of supernaturalism by making the likelihood of evidence given ~h way more probable than the likelihood of evidence given h.

  • Scenario 1
    • p(e│h.b) = 0.01
    • p(e│~h.b) = 0.99
  • Scenario 2
    • p(e│h.b) = 0.001
    • p(e│~h.b) = 0.999
  • Scenario 3
    • p(e│h.b) = 0.0001
    • p(e│~h.b) = 0.9999



Now, we are able to solve for p (h│e.b), which stands for the probability our hypothesis of narrow naturalism is true given available evidence and background knowledge. I’m going to show the outcome for all three scenarios:

  • Scenario 1
    • p (h│e.b) = 99.999999901%
  • Scenario 2
    • p (h│e.b) = 99.9999990009999%
  • Scenario 3
    • p (h│e.b) = 99.9999900010002%

Even in the best case scenario, the result of the confidence we should place in narrow naturalism being true given history is practically 100%. And that is with the likelihood of available evidence being 9,999 times more probable under supernaturalism!

Unless someone can start coming up with confirmed supernatural causes in the past (and it had better be a whole lot of them if they plan to make a dent in the probabilities), then narrow naturalism is incredibly well justified. To call this level of confidence faith is misleading at best, dishonest at worst.


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  1. Grundy

    As a semi-pro poker player, I’m a bit of a probability nerd. Needless to say, I enjoyed this post.

    To me, naturalism is just trusting that anything is understandable, even those things we don’t yet understand. Evoking the supernatural means we might as well throw out everything we know about reality. If something can over-rule a natural concept of biology, we might as well throw out biology. And since biology rests on a foundation of chemistry which rests on a foundation of physics, we might as well throw everything out.

    Saying God caused the Big Bang is one thing, but admitting that how God caused it is forever beyond the reach of human understanding is another–even though it is implied since God is apparently supernatural. I’d rather focus on contributing to human knowledge instead of trivializing human knowledge.

  2. Mike

    I actually started writing a how-to post for bayes using poker once. I was running through a scenario of a hand against Dan Harrington where I imposed on him his recommended probabilities from Harrington on Hold Em. It started getting really complicated, though, and I thought anyone who didn’t play a lot of poker would get lost in my thought process.

  3. Lee

    As clear and understandable as your explanation is to all, I can readily see how the theist will approach a rebuttal: “There but for the grace of God, go I.” Regarding the “faith” of naturalism, It seems to me that the theist who makes this charge is not disagreeing over the probabilities, if we assume that past events are ipso facto natural in origin, but whether that assumption itself is the case at all. That is to say, many (western) theists believe, on faith, that providence is a person to be named, and that name is ______. To the believer, a naturalist is one who believes, on “faith”, that providence is nature herself.

    Notwithstanding the above, thank you for the post! It got my mind cranking, as all your posts inevitably do. Keep up the good work.


  4. Grundy

    I could see that Harrington example losing nonplayers. Harrington on Holdem is a good book though.

  5. Mike

    Thanks Lee.

    It might help if I explain my motivation for writing this. I’m in a class right now on the history of science that contains a mix of graduate students in history and in philosophy. The professor, who is pretty much an atheist, recounted a story about going to a Buddhist temple and seeing some monks floating off the ground. He said he was waving his hand under them and thinks he remembers everything correctly and is unsure what to make of the experience. Lots of claims came up in class (ironically from the philosophy students) about being prejudiced toward scientific explanations. After class, another student emailed me to ask what I thought of the situation. I compared it to someone seeing a remote control for the first time and waving their hand between it and the TV. I said it bothered me a bit, but I wouldn’t lose sleep over it. If this is something real and not a trick or mistaken perception, then I think we’re actually justified in saying science would be able to explain it given the right opportunity. I think we’re in this situation given any particular event brought before us (a different, stronger claim would be needed to say every event is/has been/will always be natural). This post basically became an expanded version of my email response to him.

    I’m honestly not sure what I could say about someone with a religious presupposition. I’d probably say that such a starting point for belief is precisely the opposite of what we observe throughout history in every reliable area of knowledge. Of course, that’s the whole point of the post so they probably won’t accept it! At that point, I don’t know what to do except say “oh well” because I probably won’t make much headway if they aren’t willing to at least attempt to start from an objective standpoint and see where the evidence leads.

  6. Lee

    I think we’re actually justified in saying science would be able to explain it given the right opportunity. I think we’re in this situation given any particular event brought before us (a different, stronger claim would be needed to say every event is/has been/will always be natural).

    Precisely. I think the misunderstanding is in being “prejudiced toward scientific explanations.” That, in itself, as you pointed out, does not entail naturalism, only uniformity of phenomena. Theism presupposes such uniformity in it’s rights and rituals, and it’s claims to metaphysical truth(believe or behave a certain way, receive a certain reply). So to claim someone is prejudiced for applying the scientific methodology is a little like saying someone is prejudiced towards reliable historical methodology when considering historical claims. It’s basically meaningless. Even supposing that Buddhism is true, and certain meditative states produce certain naturalism-denying results, using the tools of science to explore and/or explain the phenomena is something, I would hope, we can all objectively agree to as being the right course of action to obtain an understanding thereof.

    Or they would claim that something natural probably brought about the origin of life on this planet. These are events currently not explained by science, but the narrow naturalist is confident that science can one day explain them, if the opportunity actually presents itself.

    Here, I think you subtly shift the topic from “naturalism” to “science”, from “natural in origin” to “uniform in character”.

    All I was pointing out was that, rather than “science” being naturalistic and therefore a “faith” position, the assumption that the uniformity upon which science is predicated can either be a result of a naturalistic presupposition or a theistic one. Both, as far as I can tell, cannot be rationally justified in a non-circular way. I certainly agree with you about the truth naturalism, but I don’t see how you presented a case in support of “naturalism is not a faith position” rather than “uniformity of phenomena is not a faith position.”

    Does that make more sense? I’m plagued by the thought that something in what I’ve said above is wrong, but having read it through many times, I can’t quite put my finger on it (zero formal training in philosophy, to my shame). As always, I appreciate your feedback on these issues!



  7. Paul So

    There is a documentary on Buddhist Monk Levitating with a link below with a scene of a Buddhist Monk towards the end of the documentary “levitating”. I’m not sure whether it’s real or not but I hope you guys would at least see it. I personally think it’s not “magic” but something else….


  8. Mike

    Thanks for the comment Lee.
    I wonder if we are miscommunicating just a bit. When talking about naturalism, we could have the narrow form that I proposed that is probabilistically justified or we could have the idea that there are only such things as natural causes, which is less justified (though I still believe it).
    The difference is subtle, but the latter is making a claim that requires proof and the former makes a claim that requires confirmation (past confirmation counts as it probabilistically predicts future confirmation). I’m not trying to justify the truth of a full scope naturalism in this post. As you said, that’s not really feasible. What I’m trying to say is due to the level of confirmation given to a narrow naturalism hypothesis in the past, we are probabilistically justified in assuming the level of confirmation will continue.
    The only big assumptions going into it are these: 1) that probability can be a guide to whether belief in something is justified; 2) that we have in fact discovered natural explanations for a wide variety of things (not just from science but also from other “knowledge” producing areas like history); and 3) that we don’t have the same sort of results from non-natural claims about explanations. In fact, for 3, I’m saying there isn’t a single case of the kind of consensus knowledge present in saying something like “sneezes proceed from natural causes.”  If you agree with me on those three assumptions, then my conclusion should follow from Bayes’s Theorem as I’ve presented it.
    Remember, though, it’s not about all out naturalism, but about saying for any given situation that is presented, you are justified in saying it probably has a natural explanation. So, when I’m told about the monk story (or I see the video Paul posted) I am justified in thinking it probably has a natural explanation just given what we know about the past. I’m not ruling anything out; I’m just saying this is probably true (overwhelmingly so!) and it doesn’t require a position of faith to make that claim because I’m making a probability claim that is in fact justified by the probability.
    Does that clear things up or have I made it worse?

  9. Lee

    You’re talking about methodological naturalism, not philosophical naturalism. I misread you, my apologies! Carry on 🙂



  10. Mike

    Thats correct. It does serve as a defense of doing science, history, etc. with an assumption of methodological naturalism.

  11. efrique

    interesting post.

    However, your algebraic fraction there:

    p(h|e.b) = p(h|b) x p(e|h.b) / [ p(h|b) x p(e|h.b) ] + [ p(~h|b) x p(e|~h.b) ]

    is – while clear enough to someone who is familiar with Bayes theorem – not strictly correct:

    As written, this is of the form a / [a] + [b]

    Under the conventional rules of order of operations, that’s (a/a) + b = 1+b

    what you intend is a / [a+b].

    The simplest way to achieve that is to remove the inner square brackets (they’re superfluous for grouping the products).

  12. Mike

    Thanks, efrique. I get what you’re saying. I prefer to show it with a horizontal line to divide the operations and then it’s clear between numerator and denominator but I don’t have a good way of writing that out. I’m glad you enjoyed the article, though!

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