In Sect. 3, we looked at all the information about EAD needed to understand the Evolutionary Undercutting Argument. This Appendix will dive a little deeper into epistemic theory, and provide (a) an account of the strength of the defeater described by EAD, and (b) the beginnings of a deeper motivation for EAD.
A.1 Incomplete Explanations and Evidential Strength
Consider the following case: Suppose Tina has a visual experience as of a cat on the mat. We can explain that experience in the following way: Light waves strike Tina’s retina, in such a way that the optic nerve and the visual cortex of Tina’s brain are subsequently stimulated. This is a perfectly good explanation of Tina’s visual experience, but it doesn’t involve either cats or mats; it’s an explanation purely in terms of Tina’s visual sensory system. But Tina learning how her visual sensory system works should not defeat her belief that there is a cat on the mat. So it looks like FPU overgenerates defeat.
It’s easy to see what we need to change about FPU in order to avoid this problem. Tina’s belief is undefeated because the explanation that we’ve given of her visual experience is only a partial explanation. It leaves out portions of the proper explanation of her visual experience, and these portions contain the fact that the cat is on the mat. In order to block counterexamples of this kind, then, we should say that it is only evidence in favor of complete non-P-involving explanations that serves as a defeater, where an explanation is complete just in case (1) the explanans is sufficient for the explanandum and (2) the explanation stretches far enough back in time to cover both proximate and ultimate causes of the explanandum. The information about Tina’s visual sensory system satisfies (1), but it is not complete because it does not satisfy (2). The explanation is not complete in that it does not tell us why light struck Tina’s retina in the way that it did. A complete and accurate explanation of Tina’s visual experience will include the fact that the cat is on the mat, and thus it will be a P-involving explanation. Learning about that isn’t a defeater.
Note that this does not mean that one must be in possession of a complete explanation of one’s evidence in order for that evidence to have justificatory force. That’s unreasonably demanding. What EAD says is that if a subject receives a complete explanation of her evidence, then that explanation had better be P-involving, or else the evidence in favor of this explanation will be an undercutting defeater.
But what of explanations that are less than complete? Will these still be defeaters? They can be, but incomplete explanations will provide weaker defeaters. An incomplete explanation won’t be the kind of thing that can conclusively rule out P being actually involved in the explanation of E, since it’s possible that P would be part of the complete explanation of E. But, given the right kind of incomplete explanation, it might nonetheless still be highly unlikely that P is part of the complete explanation of E. Thus: the strength of the defeater is directly proportional to how likely the defeater makes it that the actual explanation of E is not P-involving. Since the strength of the defeater is proportional to how strong our evidence is that the explanation is not P-involving, the defeater will be stronger the more complete the non-P-involving explanation is. Evidence for fully complete non-P-involving explanations will be a very strong defeater, for it leaves no room for P in the explanation of E. Highly restricted explanations will be very weak defeaters or not defeaters at all (if they are restricted enough not to provide any evidence that the explanation of the original evidence is not P-involving). Most partial explanations will fall somewhere in the middle.
In Sect. 4.1, I claimed that Darwinian explanations are only one large piece of a larger naturalistic explanation of why moral claims seem true to us. Now we’re in a position to see why this matters. Darwinian accounts provide more complete explanations of our moral beliefs than do naturalistic accounts that have no account of the ultimate explanations of our moral beliefs. Darwinian accounts thereby serve to strengthen the general debunking defeater provided by the availability of naturalistic explanations of our moral beliefs.
Adding this qualification about the completeness of explanations to FPU, together with the qualifications about inferential knowledge in 3.2, gives us EAD.
I argued in Sect. 3.3 that EAD is compatible with Bayesianism and is superior to modal accounts. Those arguments make a presumptive case in favor of EAD, but not do not conclusively prove EAD. The best way to provide conclusive support for EAD would be to show that it follows from the correct account of justification, or from the correct account of knowledge. But there is no uncontroversial account of either justification or knowledge. Deeper vindication is, thus, hard to come by.
Since providing a deeper vindication must necessarily fall outside the scope of this paper, I’ll undertake the more modest task of locating EAD in the space of theories of justification and giving some reason to think that this is a good place for EAD to be located.
First, EAD assumes that some kind of epistemic internalism is true about evidence and justification—although not about broader epistemic concepts like warrant 22 or knowledge. Specifically, EAD (as formulated) assumes a view on evidence which we may call attitude-internalism. According to attitude-internalism, evidence for some proposition consists in the beliefs or other mental states of a subject. It is the beliefs themselves, not the contents of those beliefs, which count as evidence (although these beliefs count as evidence in virtue of their content). A second view, that we may call content-internalism, says that in order for a proposition to count as evidence, I must believe it, but it is not my belief that counts as evidence, it is the content of that belief. Accordingly, when my discussion turns to explanations of a subject’s evidence, I have in mind explanations of the subject’s mental states. Those more disposed toward content-internalism may substitute “an explanation of why S believes E” for “an explanation of E” in EAD (and in all subsequent discussion of the principle).
The only position that is inconsistent with EAD is evidential externalism, which holds that epistemic justification depends entirely on features external to the agent. But that’s to be expected—since an agent’s learning new information is a kind of internal change to the agent, externalists cannot account for the existence of undercutting defeat at all (cf. Lasonen-Aarnio (2010)23). So the account of undercutting defeat explored here should be understood as an account of undercutting defeat, assuming that undercutting defeaters exist. Externalists will reject that assumption; so much the worse for externalism. (Lasonen-Aarnio bites the bullet and attempts to argue that undercutting defeaters don’t exist. She does so by offering an explanation of the evidence that supports the existence of undercutting defeat in terms from which one may not infer the existence of undercutting defeat, of course).
There are many compelling arguments in favor of externalism, but these are all good reasons to be an externalist about warrant or knowledge, rather than evidence or justification. And externalism about justification seems to be decisively refuted by the New Evil Demon Problem.24 I wish I could discuss this more.25
EAD is consistent with any internalist view, but it coheres particularly well with explanationist evidentialism, a fairly popular internalist view typically associated with Conee and Feldman, and more recently given an extensive defense by McCain (2014). According to explanationist evidentialism, your belief is justified just in case your belief “fits” the evidence, where a belief, p, fits the evidence, e, at t, just in case “p is part of the best explanation available to S at t for why S has e” (McCain 2014, p. 63). This is just a first-pass formulation of explanationist evidentialism—see McCain’s book for the fully-worked-out account.
It is not the case that EAD is true if and only if explanationist evidentialism is true; the views do not entail one another. Nonetheless, explanationist evidentialism appeals to a lot of the same concepts as EAD, and the bridge principles needed to connect the two views are plausible. So if explanationist evidentialism is true, it is plausible that EAD is also true. The fact that EAD coheres well with explanationist evidentialism may provide indirect support for both views, but the argument of this paper does not presuppose any particular account of justification. I present the connection between EAD and explanationist evidentialism only to show that not only is EAD independently plausible, but it coheres well with a popular internalist account of justification that is itself independently plausible.
This, together with the other support offered for EAD in Sect. 3, should show that EAD is far from ad hoc. Since a deeper vindication for EAD would take a book, this will have to do.