Abstract
Few philosophers believe that G. E. Moore’s notorious proof of an external world can give us justification to believe that skepticism about perceptual beliefs is false. The most prominent explanation of what is wrong with Moore’s proof—as well as some structurally similar anti-skeptical arguments—centers on conservatism: roughly, the view that someone can acquire a justified belief that p on the basis of E only if he has p-independent justification to believe that all of the skeptical hypotheses that undermine the support lent by E to p are false. In this paper I argue that conservatism does not make trouble for Moore’s proof. I do this by setting up a dilemma concerning the notion of “justification to believe” that figures in conservatism. On one understanding of justification to believe, conservatism is subject to obvious counterexamples. On another understanding of justification to believe, conservatism is consistent with Moore’s “proof” conferring justification upon its conclusion. Since these two understandings exhaust the logical space, the conservative indictment of Mooreanism fails.
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Notes
I say “enabling condition” rather than “premise” since having some perceptual experience cannot itself be a premise in an argument (though, of course, the proposition I am having a perceptual experience as of a hand could be). By enabling condition I simply mean a state that licenses the formation of another belief, here via the use of perception.
Any adequate argument in favor of closure would take us far from the main thrust of this paper. For a full defense of closure, see Hawthorne (2005).
This discussion of the shortcomings of the simple skeptical argument, and the existence of a more powerful alternative, follows Pryor (2000).
The conservative anti-Mooreans White and Wright both embrace some version of rationalism. Wright uses somewhat unconventional nomenclature, however: he refers to apriori “entitlement” to believe anti-skeptical claims; he reserves the term “justification” for bits of entitlement that we somehow earn, rather than possess by default. Cohen eschews both rationalism and Mooreanism in favor of holism; discussion of Cohen’s positive view—which makes a distinction between two levels of knowledge—would take us very far afield.
I won’t assume that all evidence is propositional; as I’ll use the term, sense experience can be evidence.
Many propositions diminish Support(E,p) to some degree. I will use the term underminer, though, only to refer to propositions that eliminate Support(E,p) entirely.
The formulation I have given is in terms of all-or-nothing justification. However, fans of degrees of justification will want to endorse a slightly more general formulation of conservatism, namely:
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Conservatism*: S can additional rational support for p on the basis of E only to the degree that he has p-independent justification to believe anti-underminers for Support(E,p).
For the sake of simplicity, I will stick to the all-or-nothing formulation; the difference won’t matter for the purposes of this paper.
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Not everyone who writes about this issue defines liberalism and conservatism as I do here: while I have represented conservatism as a conditional,
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(S can acquire support to believe p on the basis of E) → (S has p-independent justification to believe all of the anti-underminers for Support(E,p))
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it is common to represent conservatism as some sort of claim involving “because” or “in virtue of”, such as:
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S can acquire support to believe that p on the basis of E only in virtue of having p-independent justification to believe all of the anti-underminers for Support(E,p)
I will focus on the conditional since it is unclear to me just what “in virtue of” means in this context. My way of formulating the issue simplifies the logical space. For instance, Silins (2008) describes his view as non-Moorean liberalism. He argues against conservatism by saying that rational support to believe that p need not be in virtue of justification to believe the relevant anti-underminers, yet he does embrace conservatism in my sense. On my way of describing thing, Silins is just a conservative. Indeed I think Silins’s argument shows why, obscurity aside, the in virtue of claim does not carve at the relevant joints: since the conditional is adequate to block Moorean arguments, making the in virtue of claim needlessly exposes conservatism to additional objections.
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David Christensen, in his unpublished manuscript “Higher-Order Evidence”, describes the distinction between what I call object-directed and reasoning-directed evidence at some length. He uses the term “higher-order evidence” to refer to what I call reasoning-directed evidence. I think his nomenclature is seriously misleading: “higher-order” evidence sounds like evidence about evidence, whereas what he is talking about is evidence about one’s reasoning ability. Beyond that quibble, though, his discussion of the rational response to evidence of fallibility is excellent and far more thorough than my quick remarks here.
We can differentiate the three types of defeater in formal terms. Call O an outweighing defeater for p, U an undermining defeater for Support(E,p), and R a reasoning-directed defeater for S concluding that p on the basis of E. Pr(p|O) < Pr(p), whereas Pr(p|U and E) = Pr(p). Reasoning directed defeaters behave quite differently: Pr(p|E and R) = Pr(p|E), yet my confidence in p upon learning E and R should be lower than my confidence in p upon learning E alone. See Sect. 7 for further discussion of this point.
One might grant this point, but still think that agnosticism about reductio ad absurdum ought to somewhat diminish one’s confidence in there are no even primes greater than 2. I do not disagree with this thought. All that matters is that belief in there are no even primes greater than 2 is doxastically justified in spite of rational agnosticism about the anti-underminer; the counterexample does not require that this justification is completely unscathed by rational agnosticism about the anti-underminer.
The most fully-developed version of the Bayesian argument against liberalism appears in White (2006); a quicker version appears in Schiffer (2004). Pryor, in his unpublished manuscript “Uncertainty and Undermining” and Weatherson (2007) both acknowledge the force of the argument and accordingly urge revision of Bayesianism to accommodate liberalism. Silins (2008) also cites a similar argument which he uses to develop a view that mixes liberalism with rationalism.
I owe this point to Pryor, who makes it in his unpublished manuscript “Uncertainty and Undermining”.
David Christensen makes this argument in his unpublished manuscript “Higher-Order Evidence”.
Is there another species of agnosticism: lacking any object-directed evidence, or more generally, adequate object-directed evidence, for or against a proposition? I think this is just a species of the sort of agnosticism I am discussing. How much object-directed evidence counts as adequate depends upon your reasoning-directed evidence: Detective Smith and Sherlock Holmes require different levels of object-directed evidence in order to have justification to believe that the butler did it. So this final type of agnosticism is not having enough object-directed evidence to clear the bar that your reasoning-directed evidence says you must clear in order to have justification to believe a proposition.
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Acknowledgments
Thanks to an audience at the 2009 Formal Epistemology Workshop as well as Eleonora Cresto, Greg Gates, Dan Greco, Anil Gupta, John McDowell, Jim Pryor, Karl Schafer, Markos Valaris, and, most especially, Cian Dorr and Kieran Setiya.
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Willenken, T. Moorean responses to skepticism: a defense. Philos Stud 154, 1–25 (2011). https://doi.org/10.1007/s11098-010-9517-0
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DOI: https://doi.org/10.1007/s11098-010-9517-0