Wade Tisthammer, Spencer Hawkins Discuss The Evolutionary Argument Against Naturalism

On Thursday, February 15, I’ll be hosting a new live discussion between Wade Tisthammer and Spencer Hawkins on The Evolutionary Argument Against Naturalism (EAAN). More info on my guests can be found below. We’ve covered this topic in the past, but this time we’re featuring new guests (and we’re getting a bit more organized). The EAAN has two major theses that need defending: (i) the probability thesis and (ii) the defeater thesis.

The discussion goes live at 8pm Central (6pm Pacific/9pm Eastern) on Thursday, February 15, 2018. Here’s the link to view live (and watch later):

Click Here to View the Live Event

Wade Tisthammer (Christian) graduated from the University of Minnesota with a degree in computer science and a minor in mathematics. He currently works as a software developer and is a philosophy student at the University of New Orleans. He blogs regularly at www.maverick-christian.org.

Spencer Hawkins (non-Christian) studies philosophy at Arizona State University, and he’s the author of the book Contra Christian Apologetics, which takes a skeptical look at many of the common arguments for Christian theism. He also blogs at https://secularstudent.wordpress.com/.


Alvin Plantinga has famously argued that the probability that our evolved brains (given Naturalism) would produce mostly true beliefs is low. But notice, we normally take for granted that our brains are producing mostly true beliefs (e.g.: my belief that I have two hands, that I had Starbucks this morning, that Austin is the capital of Texas, and so on). However, if, on Naturalism, our evolved brains aren’t reliable, that is, they don’t produce mostly true beliefs, then we’ve got a defeater for all the beliefs produced by our brains, including belief in (the conjunction of) Naturalism and Evolution. It follows from this that we ought to give up belief in either Naturalism or Evolution (or both). That’s the basic argument.

Here it is in premise/conclusion form. N&E is shorthand for the claim that Naturalism & Evolution is true. R is shorthand for the claim that our cognitive faculties produce mostly true beliefs:

(1) The probability that R is true given N&E is low.
(2) Anyone who accepts (believes) N&E and sees that (1) is true has a defeater for R.
(3) Anyone who has a defeater for R has a defeater for any other belief she thinks she has, including N&E itself.
(4) If one who accepts N&E thereby acquires a defeater for N&E, N&E is self-defeating and can’t be rationally accepted.

Premise (1) above is what’s called the “Probability Thesis” and (2) the “Defeater Thesis.” It is Wade’s contention that (1) and (2) are true, while Spencer has objections to both.



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  1. I really hope Spencer doesn’t appeal to experience to show that evolved brains produce true belief, or that if he does that Wade calls him on it.

    An evolved brain (Spencer’s) appealing to its own experience to confirm the truth of its experience is circular.

  2. I don’t like the EAAN. I think it successfully establishes (given evolution – naturalism is not required) that what we reason should be doubted. The reply is that, that’s totally true. We should doubt what our intuition and reasoning tells us is true.

    However, in the case of evolution, we don’t just rely on our own reasoning/intuition, but have rigorous scientific investigation which attempts to safeguard against that error.

    The argument then rebounds on beliefs in God: given that there’s valid reasons to believe evolution is true, which avoid the EAAN defeater, so all our innate beliefs should be doubted. In particular, our belief in God cannot be trusted.

    IMHO, excessive skepticism is a problem already (as I think I’ve said here in the comments already) which warps most people’s epistemology. I don’t think the EAAN helps, in that it pushes epistemologies even further towards skepticism, for most people growing up today, they’re already skewed too far that way. What we really need to be doing is the exact opposite – showing people that excessive skepticism is dangerous, and leads to error.

  3. So thank you all for the debate. Here’s my two cents (not that anyone cares, but I enjoy thinking about this sort of thing)….

    In the first part, I don’t understand Spencer’s objection. The argument being offered is one about how we should assess *epistemic* beliefs (ie. Bayesian sense of probability, not a frequentist one). We’re asking “Should we believe naturalism, or not?” or “Should we believe in God or not”. For that question, it’s irrelevant if God is metaphysically necessary (in the sense he exists in every possible universe) or not.

    If you simply take the same argument and apply it to primes, it becomes obvious where it falls apart:

    7 is necessarily prime, in the sense that it is prime in every possible universe. Similarly, every natural number is necessarily (in this sense) either prime or not prime. However, for large numbers, we often *don’t know* for sure whether they are prime or not. So we use probabilistic test (like Rabin-Miller or Fermat) and so conclude numbers are either likely prime, or not. The probabilities we’re updating is our own epistemic probability.

    Someone saying that they believe a large number, n, is likely prime isn’t saying that there’s some universes where it’s prime or some where it’s not. They’re saying it’s either prime in all of the universes, or prime in none of them, they’re just not sure which of these two options is true in reality. They’re definitely not concluding that, because it’s possible that n isn’t prime, that therefore the whole concept of primes is bunk, and we should cease to believe any primes exist. That’s truly a bizarre chain of reasoning, which I think comes from a misunderstanding of what the probabilties represent in the first place.

    On the second part, I was the other way around:

    Evolution gives us reasons to believe, that at least in part, our senses and mental faculties are reliable. Premise 1 is definitely false. A person who accurately ascertains that – in reality – there’s a lion in front of them, not a cream cheese, is more likely to run away and survive. To a certain extent, evolution does choose for accurate mental faculties.

    If I understood correctly, the counter argument was that it’s possible that false beliefs can lead to the same actions. I think the waters were muddied here by saying the same physical brain state can have different beliefs about reality (and because they are the same physical brain state, they necessarily lead to the same actions in a naturalistic world). As Cameron said, it’s unclear if naturalists would even agree that different brain states can have different beliefs.

    But even if we cut through all of that – the counterargument doesn’t really work. Evolution is still slowly selecting for reliable mental faculties, because they give a survival advantage. Of course, that won’t necessarily make our make our mental faculties perfect, they just tend to be reliable, on the whole. So, on evolution, we have reasons to believe our mental faculties largely, reliable, *but* we should also recognise they can sometimes go wrong and lead to error. Perhaps we run away from the lion because we believe it’s a daemon. But that’s not a defeater now – that’s just healthy skepticism.

    Thank you all for the interesting debate!

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