In "Perceptual Variation and Ignorance" I make a claims about evidence and perceptual justification that might sound controversial, but aren't. In this appendix I distinguish them from more controversial claims

Morrison, John Ross

Columbia University Academic Commons

Appendix to“Perceptual Variation and Ignorance”John MorrisonBarnard College, Columbia UniversityDecember 28, 2020In “Perceptual Variation and Ignorance” (forthcoming) I claim:perceptual defeasibilityIf your evidence assigns a low probability to your perception that pbeing accurate, you cannot justifiably believe that p based on yourperception.I also claim that, once you learn about perceptual variation, your evidenceassigns a low probability to your perception being accurate. Both claimsshould be uncontroversial. If they sound controversial, it’s because theysound like claims that have been rejected by Pryor (2000), Wright (2002),Goldman (2008), Williamson (2014), Lasonen-Aarnio (2014), Kelly (2010)and Wedgwood (2007). Let’s distinguish them.Pryor (2000) (a “liberal”), Wright (2002) (a “conservative”), and Gold-man (2008) (a “reliabilist”) all deny that you must have evidence for theaccuracy of your perception in order to justifiably believe that p based on it.For example, according to them, you can justifiably believe that you havetwo hands even if you lack evidence that you’re not hallucinating hands. In-deed, on Pryor’s view, your perception can itself justify the belief that you’renot hallucinating hands. But these philosophers also say that, once you getevidence assigning a low probability to your perception being accurate, youcan no longer justifiably believe that you have two hands. If you learn thatyou’ve ingested hallucinogens, your perception alone can’t justify the beliefthat you have two hands.Williamson (2014) and Lasonen-Aarnio (2014) describe examples in whichyour evidence assigns a high probability to your belief that p being accu-rate, and a low probability to your belief that p being justified. But theyaren’t counterexamples to perceptual defeasibility. To appreciate why,consider Williamson’s famous clock example (p.979–980).1 Suppose you’re1While the original example is about knowledge, he later says that it works just as wellfor justified belief (p.981–982).looking at the second hand on an unmarked clock, and that the most exactproposition you can justifiably believe is that the second hand is between8 and 12. Because your belief is justified, your evidence must assign a highprobability to the second hand being in that range. As a result, your evidencemust assign a high probability to your belief being accurate. Nonetheless,Williamson argues, your evidence assigns a low probability to your beliefbeing justified. According to Williamson, your belief is justified only if thesecond hand is at 10. If the second hand were at 11, the most exact propo-sition you could justifiably believe is that the second hand is between 9 and13. More generally, if the second hand is at x, the most exact propositionyou can justifiably believe is that the second hand is between x−2 and x+2.Because your evidence merely assigns a high probability to second hand be-ing somewhere between 8 and 10, it assigns a low probability to it being at10. Williamson infers that your evidence assigns a low probability to yourbelief being justified. Your evidence assigns a high probability to your beliefbeing accurate and a low probability to its being justified.This isn’t a counterexample to perceptual defeasibility, becauseperceptual defeasibility applies when your evidence assigns a low prob-ability to your perception being accurate, not when your evidence assigns alow probability to your belief being justified. The antecedent of perceptualdefeasibility is about a different kind of mental state (perception, not be-lief) and a different kind of assessment (accuracy, not justification). It mighthelp to note that, in Williamson’s counterexample, you presumably believethat the second hand is between 8 and 12 because that’s what you perceive.In that case, your evidence assigns a high probability to your perception be-ing accurate. To be a counterexample to perceptual defeasibility, yourevidence would need to assign a low probability to your perception beingaccurate.perceptual defeasibility should thus be uncontroversial. Let’s nowconsider its application to perceptual variation. I claim that, once you learnabout perceptual variation, your evidence assigns a low probability to yourperception being accurate. Kelly (2010) and Wedgwood (2007) might seemleast likely to agree (as “anti-conciliationists”), so let’s consider their views.Kelly (2010) claims that if you justifiably believe that p, and discover adisagreement about p with epistemic peers who have the same evidence, youcan still justifiably believe that p. For example, if you justifiably believe thatit will rain tomorrow on the basis of the meteorological data, you can stilljustifiably believe that it will rain, even if an epistemic peer believes that it2won’t based on the same data. Kelly says that this is because the evidencefor your belief includes more than just the psychological facts about what youbelieve and what your epistemic peer believes. Your evidence also includesthe meteorological data itself, and that might still be enough to justify yourbelief. Thus, even when you discover the disagreement, your evidence stillassigns a high probability to your belief being accurate (p.132–134). Butwhen your disagreement is based entirely on different perceptions, there is noother evidence. Your evidence is exhausted by the psychological facts aboutwhat you perceive, what the other person perceives, and your reliabilityin uncontroversial cases. There is nothing analogous to the meteorologicaldata, no further evidence that grounds your belief that the lemon is pureyellow rather than greenish yellow. Thus, according to Kelly, when youlearn that someone else perceives things differently, your evidence assigns alow probability to your perception being accurate, and you should suspendjudgment (p.150–152).Wedgwood (2007, p.257–266) claims that if you have a normative intu-ition that p, and discover that others have different intuitions, you can stilljustifiably believe that p. For example, if you have the normative intuitionthat eating meat is ethically permissible, and discover that another personhas the intuition that it’s impermissible, you can still justifiably believe thatit is permissible. Even so, Wedgwood insists that your justification can bedefeated, either by incoherence with the rest of your beliefs, or by evidencethat the other person’s normative intuitions are at least as reliable (p.244,258). With respect to your normative intuitions, this second kind of evidenceis rare. Wedgwood’s only example is when the other person has previouslybrought about significant changes in your own normative intuitions (p.263).In most cases, you don’t have any evidence about the reliability of your ownnormative intuitions or the other person’s normative intuitions, and thusyour evidence doesn’t assign any probability to the accuracy of your intu-ition. When that happens, Wedgwood thinks that you’re justified in relyingmore on your own intuition. Thus, your intuition can still justify your be-lief. Wedgwood doesn’t say as much about perceptions, but he does saythe justification for beliefs based on perception can be defeated in the sameways: either by incoherence with the rest of your beliefs, or by evidence thatthe other person’s perceptions are at least as reliable (p.259, 262). Unlikenormative intuitions, this second kind of evidence is plentiful. You can, forexample, confirm that others perform equally well on standard perceptualtasks, such as the Farnsworth-Munsell Hue Test. You also know that percep-3tions of fine-grained colors are the result of haphazard genetic mutations andenvironmental interactions, much like your exact height, skin pigment, andhair density. Thus, with respect to perception, the situation is quite differ-ent; you have a lot of evidence about the reliability of your own perceptionsand other people’s perceptions, and that evidence assigns a low probabilityto your own perception being accurate.For these reasons, it should be uncontroversial that Perceptual De-feasibility is true and applies to perceptual variation.2ReferencesGoldman, Alvin I. (2008). Immediate justification and process reliabilism. InSmith, Quentin, editor, Epistemology: New Essays, pages 63–82. OxfordUniversity Press.Kelly, Thomas (2010). Peer disagreement and higher-order evidence. InFeldman, Richard and Warfield, Ted A., editors, Disagreement, pages 111–174. Oxford University Press.Lasonen-Aarnio, Maria (2014). Higherorder evidence and the limits of defeat.Philosophy and Phenomenological Research, 88(2):314–345.Morrison, John (forthcoming). Perceptual variation and ignorance. Synthese.Pryor, James (2000). The skeptic and the dogmatist. Noûs, 34(4):517–549.Wedgwood, Ralph (2007). The Nature of Normativity. Oxford UniversityPress.Williamson, Timothy (2014). Very improbable knowing. Erkenntnis,79(5):971–999.Wright, Crispin (2002). (Anti-)sceptics simple and subtle: G. E. Moore andJohn McDowell. Philosophy and Phenomenological Research, 65(2):330–348.2Thanks to David J. Barnett for many discussions of these authors and views.4

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