brueckner - ~k~sk

Philosophical Issues, 21, The Epistemology of Perception, 2011

∼K∼SK

Anthony BruecknerUniversity of California, Santa Barbara

1. Introduction

Here is a standard formulation of the Cartesian skeptical argument re-garding knowledge of the external world, where ‘H’ stands for the propositionthat I have hands, ‘SK’ for the proposition that I am a handless brain in a vatconnected to a supercomputer that provides me with sense-experience exactlysimilar to that which I actually have, and ‘K—‘ stands for the propositionthat I know that —:

(1) KH → K∼SK(2) ∼K∼SK(3) ∼KH

The argument generalizes in the familiar way. Premise 1 is backed by theprinciple that knowledge is closed under known entailment (given that Iknow the pertinent entailment to hold). Premise 2 is the focus of this paper.I will not consider ways of attacking Premise 1 via attacking closure.

2. Pro ∼K∼SK

Why accept Premise 2? Some people seem to think that this premise canbe taken as a kind of primitive. Keith DeRose, for example, says:

. . .however improbable or even bizarre it may seem to suppose that I am a BIV,it also seems that I don’t know that I’m not one. How could I know such athing?1

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Let us look at some reasons why it might seem so obvious that ∼K∼SK.I surely believe ∼SK. But suppose ∼SK were false. That is, suppose SK

were true. In that case it would again seem to me that I am a normal guy andnot a BIV. I would accordingly believe ∼SK. So if ∼SK were false, then Iwould mistakenly believe it to be true. Thus, my belief of ∼SK is not sensitiveto that proposition’s truth-value. This is why I do not know ∼SK, accordingto Robert Nozick. In general, to know that ϕ, I must meet this Nozickeantracking condition (Sensitivity, as it has come to be known):

∼ϕ �→ ∼Belϕ

As is well known, if the skeptic offers this defense of Premise 2, then he shootshimself in the foot. This is because if he embraces the tracking condition,then he must give up the closure principle which undergirds Premise 1 of ourargument. The failure of closure would arise from the fact that it is possibleto satisfy the tracking condition with respect to an ordinary external worldproposition such as H while failing to satisfy the condition with respect tothe entailed consequence ∼SK. In a possible situation in which the othernecessary conditions for KH are satisfied, we will have KH and ∼K∼SK,violating closure (assuming that I know the entailment).2

Here is a different take on ∼K∼SK which we will examine in somedetail. Stewart Cohen says,

Radical skeptical hypotheses are immune to rejection on the basis of anyevidence. There would appear to be no evidence against the hypothesis thatwe are deceived by a Cartesian demon, or the hypothesis that we are brains-in-a-vat. Radical skeptical hypotheses are designed to neutralize any evidence thatcould be adduced against them.3

If I have no evidence against the skeptical hypothesis embodied in SK, then Ipresumably have no evidence for believing ∼SK. If that is so, and we construethe notion of evidence broadly so as to include sense-experiences in additionto evidential beliefs (as does Cohen), then I lack justification for believing∼SK. If justification is required for knowledge, then ∼K∼SK would followfrom this line of reasoning.

But this might seem to be a rather hasty line of reasoning. Is it reallytrue that I have no evidence whatsoever against the skeptical hypothesis? Afterall, I have “the evidence of my senses”. Why not say that my experientialevidence justifies me in rejecting SK and instead believing ∼SK? If this movecould be made good, then the Cohen-style defense of Premise 2 would beundercut.

At this point, the skeptical defender of Premise 2 can appeal to a furtherepistemic principle, apparently distinct from closure:

76 Anthony Brueckner

(UP) If S has justification for believing ϕ, and ϕ is incompatible with ψ , thenS’s evidence for ϕ favors ϕ over ψ .

Given this Underdetermination Principle, if its consequent is false in a givencase because S’s evidence fails to favor ϕ over an incompatible competitor ψ ,thereby underdetermining the choice between ϕ and ψ , then S is not justifiedin believing ϕ rather than ψ . The skeptic can apply UP to the choice between∼SK and SK, arguing that

(∼F) My experiential evidence for ∼SK does not favor ∼SK over SK.

From UP and ∼F, it follows that I am not justified in believing ∼SK, andso: ∼K∼SK. We will return to this UP-based reasoning below.4

3. Contra ∼K∼SK

Let us now examine some ways of attacking Premise 2. The commonthread of these attacks is this: they seek to show J∼SK ( = I have justificationfor believing ∼SK), or at least to show that my belief of ∼SK has a surrogateform of positive epistemic merit distinct from having justification.

Let us first consider Dogmatism about perceptual justification. Arepresentative Dogmatist is James Pryor.5 According to Pryor, perceptualexperiences have propositional content. When I have a visual experiencecaused by looking at a red cup, that experience has the content that a redcup is present. Suppose that I form the belief that a red cup is present onthe basis of having that experience. According to Pryor and the Dogmatists,my perceptual belief has prima facie justification—justification which couldbe defeated, say by my background belief that I am tripping on LSD.Absent such a defeater, my experience is sufficient for the justification ofmy perceptual belief. No further beliefs are required. On Pryor’s versionof Dogmatism, he emphasizes that my experiences can provide me withjustification in the absence of any independent justification for believingthat I am not involved in a skeptical scenario such as that embodied inSK. Further, Pryor and other Dogmaitists emphasize the following aspectof their view: it makes no difference to the prima facie justification affordedto a believer by his experience whether or not the experience is veridical. Anunveridical experience as of seeing my hands renders my belief of H primafacie justified just as much as does a veridical experience as of seeing myhands.

Suppose that upon having my cup-experience, I instead form the beliefthat a large hadron collider is present. My cup-experience presumably doesnot provide justification for that belief. Why not? Because the content of thatbelief does not match the content of the occasioning experience. Pryor’s idea

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seems to be that the reason why my cup-experience justifies my cup-beliefbut not my collider-belief is that the content of the cup-belief matches that ofthe cup-experience, whereas the content of my collider-belief does not matchthat of the cup-experience.

So on Pryor’s view, is my perceptual cup-belief evidentially justified?This obviously depends upon how we want to use the term ‘evidence’ inepistemology. Some want to hold that evidence always consists of propositionsthat are believed by the pertinent subject (or maybe those beliefs themselvesconstitute the subject’s evidence). On this usage, we should say that forPryor and the Dogmatists, perceptual beliefs are not evidentially justified,since perceptual experiences are neither (believed) propositions nor beliefs.Perceptual experiences are, on the view under consideration, belief-like,in virtue of having propositional content, and they are the justifiers ofappropriately related beliefs formed on their basis. The belief-like characterof experiences takes some of the sting out of the Dogmatists’ violation of theDavidsonian Dictum that only beliefs can justify beliefs.6 If experiences dohave propositional content, then this places them near the space of reasonsof McDowell, Sellars, and Davidson, if not within that space.

What of ∼K∼SK? Pryor endorses closure for knowledge and justifi-cation. Given that my experience as of seeing my hands provides me withundefeated prima facie justification for believing H( = I have hands), andgiven that H entails ∼SK, we can appeal to the following closure principlefor justification:

(CJ) If S has an adequate source of justification for believing ϕ, and ϕ entails ψ ,then S has an adequate source of justification for believing ψ .

Note that S can have an adequate source of justification for believinga proposition without believing it, as when a detective possesses strongevidence for believing that Crippen is the murderer prior to appreciatingthe force of his evidence and thereby forming the belief in question. GivenCJ, and given my experiential justification for believing H, it follows thatI have an adequate source of justification for believing ∼SK. So it is nottrue that I lack justification for believing ∼SK, contra the skeptic. So theskeptic’s route from ∼J∼SK to ∼K∼SK is blocked: the case for the skepticalargument’s Premise 2 is blocked.

But what is my adequate source of justification—call it S∗—forbelieving ∼SK, exactly? The answer that first comes to mind is that S∗

is identical to my adequate source of justification S for believing H. S is justmy experience as of seeing my hands—an experiential justifier. There is aproblem here, however. The propositional content of my hand-experience Eis that I have hands. On the justificatory picture sketched earlier, E serves tojustify a perceptual belief with a matching content—the belief of H (= I havehands). But the propositional content of E does not match that of ∼SK: E


does not have the content that I am not a brain in a vat. E also does nothave the content ∼MC = that I am not a MasterCard account, even thoughH entails ∼MC. Ditto for the entailed content ∼HC = that I am not a largehadron collider. These points suggest that source S, viz. my hand-experience,is not identical to source S∗. The possibility that S is distinct from S∗ is indeedleft open by CJ. But what could S∗ be? Pryor’s view offers no explanation,given that S∗ is not my experience that bears the content that I have hands—acontent that does not match that of my belief of ∼SK.

One answer is suggested by the work of Peter Klein.7 Klein thinks thatmy experience E constitutes an adequate source of justification for believingH but does not constitute an adequate source of justification for believing∼SK. He holds a parallel view of Dretske’s zebra case: as Dretske maintains,my experience as of seeing a zebra in a zoo-pen marked ‘ZEBRA’ is anadequate source of justification for believing Z = The animal is a zebra but isnot an adequate source of justification for believing ∼CD = The animal is nota cleverly disguised mule. But unlike Dretske, Klein upholds CJ. So in eachcase (H and Z) there must be a non-experiential source of justification forbelieving the denial of the pertinent skeptical hypothesis (for believing ∼SKand ∼CD). On Klein’s view, the way all this works is as follows. WheneverS has an adequate source of justification for believing ϕ, and ϕ entails ψ , Shas an adequate source of justification for believing ψ because ϕ, itself, issuch a source. When ϕ becomes justified for S via some adequate source ofjustification, the proposition ϕ itself becomes available as an adequate sourceof justification for whatever propositions ϕ entails, or otherwise confirms.So H itself is an adequate source of justification for my believing ∼SK, andZ itself is an adequate source of justification for my believing ∼CD.

One virtue of Klein’s view is that it is in accord with the intuition thatwhen a proposition ϕ becomes justified for S, he has the right to use ϕ inreasoning, inferring to, e.g., ϕ’s entailed consequences. One vice of Klein’sview is that it seems to embrace a mysterious sort of evidence-generation.At t, S’s total evidence includes a part e that is relevant to believing ϕ.This evidence e, we will suppose, does not provide adequate justification forbelieving ψ , an entailed consequence of ϕ. At t, we will suppose, S has notyet come to believe ϕ on the basis of e. So at t, ϕ is not yet available as anadequate source of justification for suitably related propositions, and henceat t, S has no adequate source of justification for believing ψ (since e is byhypothesis not up to the task). At t’, S comes to believe ϕ on the basis of e,and now S has an adequate source of justification for believing ψ , which helacked at t. A new source of justification for S—the proposition ϕ–is createdat t’ simply in virtue of his coming to believe ϕ at t’—that is all that changesfor S from t to t’.8

So Klein’s view provides a rather unattractive bail-out for Pryor’sMoorean approach to the denial of Premise 2. Let us turn to Klein’sown approach to the denial of this Premise. Suppose, as we have, that

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the skeptic wants to establish Premise 2 (∼K∼SK) by establishing ∼J∼SK.Whatever sub-argument does that work would need to be strong enough byitself to establish ∼JH (and hence ∼KH), says Klein. So the sub-argumentwould need to be strong enough to establish the conclusion of the skepticalargument. Klein calls this virtually begging the question. It is a sin that isdifferent from formal circularity (conclusion is one of the premises) and fromepistemic circularity (conclusion constitutes part of the arguer’s justificationfor one of the premises); but on Klein’s view, it is a sin all the same. So thisis Klein’s take on Premise 2: the skeptic can establish this Premise only byvirtually begging the question. So the Premise cannot be fairly put into play.

But why would the sub-argument for Premise 2 need to be strong enoughto establish ∼JH and hence to establish ∼KH, the argument’s conclusion?Klein’s answer is as follows. Assume the truth of the argument’s closure-basedPremise 1. Thus, if there is an adequate source justification for believing H,it follows, on Klein’s view, that there is an adequate source of justificationfor believing ∼SK (viz. the proposition H itself), contrary to what Premise 2says (contrary to ∼J∼SK). Therefore, any sub-argument for ∼J∼SK wouldneed to be strong enough to establish that there is no adequate sourceof justification for believing H: this is the argument’s conclusion, ∼JH.Otherwise, given Premise 1, we would have it that J∼SK, contrary to whatPremise 2 says.

But it seems that this criticism would equally apply to any Modus Tollensargument:

(1) A → B(2) ∼B(3) ∼A

This argument virtually begs the question, according to Klein’s reasoning.Any sub-argument that rationalizes (2) would need to be strong enough torationalize the conclusion (3). This is because if we assume (1), then if itsantecedent A is true, so its its consequent, contrary to what (2) says. So a sub-argument that rationalizes (2) would need to be strong enough to rationalizethe conclusion ∼A.

I conclude that Klein’s anti-skeptical take on the original skepticalargument’s Premise 2 is not good. Let us now turn to some views that have astructure that is similar to that of Klein’s view of closure. According to bothStewart Cohen and Crispin Wright, closure holds, but the source S of myjustification for believing H is distinct from the source S∗ of my justificationfor believing ∼SK. They both hold that S is just my hand-experience, whileS∗ is non-experiential and non-evidential. Wright speaks of warrant ratherthan justification, but for present purposes we could put his view as follows.9

The positive epistemic status that ∼SK has for me does not derive frommy source S of justification for H (viz. my hand-experience). The positive


epistemic status of ∼SK in a sense has no source—it consists in an unearned,non-evidential warrant that Wright calls entitlement. This entitlement mustbe in place if my hand-experience is to justify, or warrant, my belief of H.On Wright’s view, Wittgensteinian “hinge propositions” (such as that mysenses are reliable, and that the world did not just come into existence) enjoythe entitled status in question in virtue of “the operational necessity, so tospeak, of proceeding on the basis of such far untested assumptions if oneis to proceed at all”.10 Cohen’s view11 is similar. He holds that the positiveepistemic status of ∼SK in a sense has no source—it consists in the non-evidential rationality of believing ∼SK. Cohen does not maintain that theexistence of this non-evidentially rational status somehow enables my hand-experience to justify H. His view is primarily motivated by three ideas: (1)radical skeptical hypotheses are immune to rejection on the basis of anyevidence, and (2) closure holds, and (3) the skeptic is wrong.12

Having sketched these views, I will just say that the skeptic will presum-ably cast a jaundiced eye over them: he will hold that these ways of denyingPremise 2 amount to little more than wishful thinking in epistemology.Wright and Cohen might well reply: “Well it’s either my way, or the lonelyskeptical highway!”

Another well-known way of attacking Premise 2 is the inference tothe best explanation strategy.13 I am justified in rejecting SK and believing∼SK because the hypothesis that there is a physical world which is largelyas I take it to be provides a better—because simpler—explanation of myexperiential evidence than does the skeptical hypothesis. I will not go intothis approach, beyond noting its Klein-like structure. That is, that whichjustifies me in believing H—presumably, my hand-experience E—is not myjustifier for ∼SK. My justifier for ∼SK consists in pragmatic considerationsthat govern theory-choice.

4. More Contra ∼K∼SK: Epistemological Disjunctivism

Following Timothy Williamson, let us call the case in which I see myhands—the case in which both H and ∼SK are true—the good case. Let uscall the case in which I am a brain in a vat and mistakenly believe that Isee my hands—the case in which ∼H and SK are true—the bad case. Theepistemological disjunctivist (to borrow a phrase from Duncan Pritchard14)holds that the epistemic status of my belief of H (and of ∼SK) is different inthe two cases. Let us now use ‘evidence’ in a broad way, so that my evidenceis anything that contributes to my justification for believing propositions. Iwill sketch two forms of epistemological disjunctivism and see how they canbe brought to bear against ∼K∼SK.

The first form of e-disjunctivism (as I will say from know on) isreconstructed from the views of John McDowell15 by Pritchard:

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The key claim made by the epistemological disjunctivist is that in the good casethe rational support available for the agent’s belief is that you see that there is abarn before you [or that your hands are in your lap], where seeing that p entails p.Moreover, the epistemological disjunctivist also claims that the rational basis forone’s belief is reflectively accessible. Accordingly, in the good case the agent hasa reflectively accessible factive reason. In contrast, in the bad case the rationalbasis for the agent’s belief cannot be that she sees that p, since, of course, this isnot the case.16

So in the good case, my evidence (broadly construed) for believing H is afactive reason—it is that I see that I have hands. In the bad case, my evidencefor believing H obviously cannot be the same as in the good case. What ismy evidence in the bad case, then? Presumably it is my unveridical experienceas of seeing that I have hands. As Pritchard says, since there is no factivereason present in the bad case, “the agent will lack this kind of epistemicsupport”. We will return to the question: What level of epistemic supportdoes my mistaken belief of H in the bad case enjoy in virtue of my unveridicalhand-experience?

A view that underlies McDowell’s e-disjunctivism (Pritchard calls theview in question metaphysical disjunctivism) is that the content of myperceptual experience in the good case differs from the content of myexperience in the bad case. The former content is object-involving, while thelatter is not. Pritchard maintains that one can be an e-disjunctivist withoutsubscribing to this metaphysical view according to which the experiencesin the two cases are tokens of two quite different psychological state types,differing as they do in their contents.17

Another form of e-disjunctivism can be found in the work of Williamson.For him, a proposition P is known by me iff P is part of my body ofevidence: E = K. (Note that though for Williamson evidence always consistsin propositions, these are propositions that are believed by the person whoseevidence they are. This follows from E → K, given the belief-condition forknowledge.) Williamson’s view is like Klein’s in the following respect: once Icome to know P (and hence possess a justified belief of P), the propositionP becomes a part of my evidence and is hence available for justifyingfurther suitably related propositions. Given Williamson’s view, we have e-disjunctivism: my evidence in the good case contains the known propositionH, whereas this obviously cannot be so in the bad case, since H is false thereand hence not an object of knowledge and hence not a part of my evidence.18

So my evidence in the bad case cannot be what it is in the good case. What ismy evidence, then, in the bad case? For Williamson, evidence always consistsin (believed) true propositions, and he holds that my evidence in the badcase is, accordingly, the (believed) true proposition that it appears that I havehands. As in the case of McDowellian e-disjunctivism, we will return to thequestion: What level of epistemic support does my mistaken belief of H enjoyin the bad case in virtue of my Williamsonian evidence?


Let us consider how Williamson’s e-disjunctivist view of the good andbad cases can be brought to bear against Premise 2: ∼K∼SK. As we saw,Williamson maintains that in the good case, my evidence contains the knownproposition H. Since H entails ∼SK, by closure I know ∼SK. So Premise 2is false.

The McDowellian e-disjunctivist can argue similarly. In the good case,I have a factive reason for H which enables me to know H. Since Hentails ∼SK, by closure I know ∼SK. So Premise 2 is false.

These ways of attacking Premise 2 are obviously question-begging. Thequestion is whether right now, ∼K∼SK—right now, do I know ∼SK, orfail to know ∼SK? The foregoing ways of answering this question with“K∼SK!” assume that I am now in the good case and therefore have the sortof evidence/reason that the e-disjunctivist claims to be found in the goodcase (a McDowellian factive reason, a Williamsonian known proposition).19

But the e-disjunctivist can tweak the dialectical situation in the follow-ing way. He admittedly cannot fairly address Premise 2 in the foregoingquasi-Moorean manner. Instead, e-disjunctivism can be use to refute whatWilliamson calls the Sameness of Evidence Lemma:

(SEL) I have exactly the same evidence in the good case and in the bad case.

The McDowellian e-disjunctivist holds that my evidence differs between thegood case and the bad case: I possess a factive reason for believing H inthe good case, but I do not possess such a reason in the bad case—I onlyhave unveridical hand-experience. Similarly, the Williamsonian e-disjunctivistholds that my evidence differs between the cases: in the good case, myevidence includes the known proposition H, but in the bad case it does not—my evidence instead includes the known proposition that it appears that Ihave hands, rather than H. So SEL is false, according to these e-disjunctivists.

Let us return to UP and ∼F. We used these assumptions to underwritethe claim that ∼J∼SK (yielding Premise 2 = ∼K∼SK). But it is not obvioushow SEL figures in that defense of Premise 2. So it is not obvious howthe e-disjunctivist’s alleged refutation of SEL bears on the skeptic’s case forpremise 2. I think that the e-disjunctivist should focus upon ∼F.

If is often said that the epistemic subject cannot discriminate between thegood case and the bad case on the basis of his evidence. For example, in mycurrent situation, I cannot, on the basis of my current evidence, tell whether Iam in G = the good case (as I believe) or in B = the bad case. When a subjectis in the good case, according to the e-disjunctivist, and says ‘I know that Ihave hands and hence am in G rather than B’, he says something true. Butwhen a subject is in the bad case and says the same thing, he says somethingfalse. Perhaps this is why even an e-disjunctivist such as Pritchard holds to the“inability to discriminate between G and B” intuition.20 Relatedly, accordingto this intuition, an epistemic subject such as myself cannot discriminate

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between the good good-case-evidence and the bad bad-case-evidence. If hecould do this, then he could discriminate between G and B, which we areassuming he cannot do. Surprisingly, the latter point helps the e-disjunctivistto impugn the skeptic’s claim ∼F.21

To see this, let us return to what e-disjunctivism implies regarding theepistemic status of my belief of H in B. I do not see any grounds for aMcDowellian e-disjunctivist to hold that my evidence in B justifies my falsebeliefs of H and ∼SK. I suppose that a McDowellian could hold this, butwhat would be his rationale? A Williamsonian e-disjunctivist holds thatjustification either attaches to (1) a piece of knowledge, or to (2) a falseproposition suitably related to what is known (e.g., a false proposition thatis highly probable on one’s evidence). Since I obviously lack knowledge ofH and ∼SK in B, I lack justification of type (1) in B for believing H. Thus,H is not available as justifying evidence for the entailed ∼SK. Alternatively,route (2): in B, I know that AH = It appears that I have hands. Williamson,however, shows no tendency to hold that my knowledge of AH constitutesevidence that is sufficient to justify false beliefs of H and ∼SK in B.

So on each version of e-disjunctivism, if I am in B, then my evidence failsto justify me in believing ∼SK. Though it does not follow, it seems plausibleto say that my bad-case-evidence does not even favor ∼SK over SK in B.22

However, if I am in G, then, according to e-disjunctivism, my evidenceobviously does favor ∼SK over SK: on the McDowellian version, my evidenceis a factive reason for H, and H entails ∼SK; on the Williamsonian version,my evidence includes the known proposition H, and H entails ∼SK.

So on each version of e-disjunctivism, we can raise a problem for theUP-based defense of Premise 2. It’s not that we can provide an argumentfor J∼SK, thereby contradicting the skeptic’s claim that ∼J∼SK (the claimthat would yield ∼K∼SK). It is rather that we can undermine the skeptic’scase for Premise 2 that relies upon the combination of UP and ∼F. ∼Fin particular is targeted by the envisaged e-disjunctivist strategy. The anti-skeptic is making a complaint that is similar to that of the skeptic regardingthe earlier question-begging formulation of the e-disjunctivist strategy. Theanti-skeptic says, “According to my e-disjunctivism, whether or not ∼F istrue depends upon whether or not I am in G or in B. If I am in G, then ∼Fis false (even though ∼F is true in B). Therefore, you, the skeptic, cannotuse ∼F in arguing for ∼K∼SK without begging the question as to whetherI am in G or B.” This strategy does in the end involve the denial of SEL,focusing as it does upon the goodness of my evidence in G, which stands incontrast to the badness of my evidence in B.

However, the skeptic clearly will not accept e-disjunctivism. This is notjust because he sees that his case for his Premise 2 will be underminedin the foregoing manner. He will agree with the e-disjunctivist that H and∼SK are true in G and that in G, I see my hands. But that’s it! We sawearlier that it would be silly for the Williamsonian e-disjunctivist to attack


Premise 2 by arguing from the assumption that my evidence in fact containsthe known proposition H; we also saw earlier that it would be silly forthe McDowellian e-disjunctivist to attack Premise 2 by arguing from theassumption that I in fact have a factive, knowledge-grounding reason for H.These assumptions depend in turn upon the assumption that I am in G.The skeptic obviously will not grant any of this. The e-disjunctivist mustaccordingly say, “I make no assumption about which case I am in”. But thenhe goes on to say something weaker which the skeptic will nevertheless deny:“In G, I know H, and hence in G, I know ∼SK”. McDowell’s version of this:“In G, I know H in virtue of having a factive reason, and hence I know ∼SK;thus ∼F is false in G”; Williamson’s version: “In G, H is a known propositionthat constitutes part of my total evidence, and hence I know ∼SK; thus ∼Fis false in G”. The skeptic will deny these weaker claims (weaker than theclaim that I am in fact in G). The conclusion that he wishes to establishis that right now, whichever case I am in, I do not know H. So he willnot accept the Williamsonian e-disjunctivist’s blithe assertion that if I am inG right now, I know H and so H is in G a known evidential propositionwhich I can use to justify ∼SK. Similarly, the skeptic of course agrees thatin G, I see my hands. But he will reject the McDowellian e-disjunctivist’soptimistic construal of that fact, viz. that in G, my seeing my hands consti-tutes a knowledge-generating, factive reason for believing H and hence forbelieving ∼SK. The McDowellian cannot just call my seeing a knowledge-generating factive reason.

5. Problems for the Skeptic’s UP-based Defense of ∼K∼SK

Having raised the foregoing problem for the e-disjunctivist attack onPremise 2, let us try to put some pressure on the skeptic. We have conceivedof his defense of Premise 2 as involving an appeal to UP and ∼F. Let usgrant UP to the skeptic: it’s an epistemic principle with considerable intuitiveappeal. The skeptic’s defense of Premise 2 then hinges upon ∼F. His casefor ∼F does in the end seem to depend upon SEL, the Sameness of EvidenceLemma. He rejects the e-disjunctivist conception of evidence for H and∼SK: my evidence is the experience which is the “common factor” presentin both G and B. Why does that evidence fail to favor ∼SK over SK? Thatis, what is the rationale for ∼F? According to SEL, it is possible that theevidence I have right now for believing ∼SK should obtain in the bad casein which SK is true and ∼SK is false. This is why, according to the skeptic,my experiential evidence for ∼SK fails to favor ∼SK over SK. Given ∼F,then, UP yields the conclusion ∼J∼SK, because UP places the followingrequirement on J∼SK: my evidence for ∼SK must favor ∼SK over SK if I amto have justification for ∼SK. But my experiential evidence does not do thisfavoring.

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Let us go over, rather obsessively, an element in the foregoing reasoning.Let us call my (putative) experiential justifier for ∼SK SE. The reasoningseems to involve the assumption

(∗) ♦(I have SE & SK).

Therefore the proposition I have SE fails to entail ∼SK. In other words: sincethere is a possible world in which I have SE and ∼SK is false (an SK-world),the proposition that I have SE fails to entail ∼SK.

Having noted the foregoing points, let us exit the current dialectic andconsider a view about justification that we can call Infallibilism (IF). IFconsists in the embracing of the following Justification Entailment Principle:

(JEP) J(S,j,ϕ) → (The proposition S has j entails ϕ)

‘J(S,j,ϕ)’ stands for ‘S has justification for believing ϕ in virtue of his justifierj’. JEP is stated in such a way as to allow that a justifier can be somethingother than a (believed) proposition, such as an experience, or a memory,or a rational intuition. An experience, e.g., cannot stand in the relation ofentailment to a proposition ϕ, since only propositions can be the relata ofthat relation. However, the proposition S has (putative) justifier j can besuch a relatum.

The IF principle JEP places a very rigorous constraint on justification.JEP rules out inductive justification, for example. The premises of a stronginductive argument do not entail the conclusion; hence they do not providejustification for believing the conclusion, according to JEP. JEP also rulesout ordinary perceptual justification if such justification is thought to deriveentirely from perceptual experience, as in the Dogmatist view discussedearlier. This is because the proposition I have rich experience as of seeingmy hands, e.g., fails to entail H = I have hands. So by JEP, I lack experientialjustification for believing H. Accordingly, Fallibilism about justification isembraced by a great many epistemologists. Fallibilism, as I am understandingit, consists in the denial of JEP: J(S,j,ϕ) is consistent with the failure ofentailment of ϕ by the proposition S has j. In other words, J(S,j,ϕ) isconsistent with

♦(S has j & ∼ϕ).

To put the Fallibilist view more crudely: justification does not requireentailment.

I would like to think that the Cartesian skeptical argument we have beenconsidering does not simply collapse into IF. On the face of it, the argumentas we have been presenting it does not depend upon IF. It depends upon twodifferent epistemic principles, closure and UP. Neither seems to have much


to do with IF. Sure, we can generate an IF-based skeptical argument (aswe did for KH), but this would seem to be skepticism on the cheap: assumethe ridiculously strong IF—i.e., assume JEP—note the mere possibility ofthe standard skeptical scenarios, and. . .bam! You get the conclusion ∼JH,because the proposition that I have my (putative) experiential justifier failsto entail H.

Bearing these points in mind, let us return to our discussion of ∼F. Wehad the skeptic arguing in the following way. SEL is true: I have the same(putative) experiential justifier for ∼SK—viz. SE—in both G and B. Again,this means that:

(∗) ♦(I have SE & SK [i.e., B obtains]).

Thus, again:

(∼ENT) The proposition I have SE fails to entail ∼SK.

From the considerations embodied in ∗ and ∼ENT, we infer

(∼F) My experiential evidence for ∼SK—viz. SE—does not favor ∼SK over SK.

Given UP, it follows that ∼J∼SK, and, finally, we have ∼K∼SK.The foregoing defense of ∼K∼SK has a distinctly IF air: it looks as if

what is driving the defense is ∼ENT, the failure of entailment thesis. It looksas if the reason why I lack justification for ∼SK—the reason why ∼J∼SK—is the failure of entailment of ∼SK by the proposition I have my (putative)experiential justifier SE. If the now standard Cartesian skeptical argumentultimately depends upon IF’s JEP, then why not skip the details and insteadgo for IF-based skepticism on the cheap? Why all the fuss about closure andUP?

The skeptic can reply as follows. “In my defense of ∼K∼SK, I do notargue directly from ∼ENT (the failure of entailment thesis) to ∼J∼SK.Rather, I argue from SEL—my (putative) experiential justifier SE is presentin both G and B—to ∼F. We noted that SEL trivially implies ∼ENT, inaddition to implying ∼F. Once I have established ∼F, I plug this claiminto UP and then derive ∼J∼SK. So it cannot be said that my reasoningto ∼J∼SK simply consists in an application of AF’s JEP to ∼ENT. Ingeneral, I’m not sure that I believe JEP. But apart from the question ofwhether justification requires entailment, it seems to me that SEL yields ∼F.Again, plugging ∼F into UP will then yield ∼J∼SK and hence ∼K∼SK.”Here is diagrammatic representation of the dialectical situation:

SEL ↔ ♦(I have SE & SK) → ∼ENT → ∼J∼SK (IF line of reasoning)SEL → ♦(I have SE & SK) → ∼F → ∼J∼SK (UP line of reasoning)

∼K∼SK 87

The anti-skeptic can reply as follows. “SEL tells us that there is a possibleworld in which I have SE and yet ∼SK is false, viz. an SK world in whichthe bad case obtains. ∼F is supposed to then follow: my evidence for ∼SKfails to favor ∼SK over SK. But if we are Fallibilists, this line of reasoningwill look unconvincing. You can’t impugn my evidence e for ϕ (holding thate is no better evidence for ϕ than for its incompatible competitors) by merelypointing out there there is a possible world in which I have e and yet ϕ isfalse. Only an Infallibilist will be impressed by that reasoning.”23

This paper seems to end not with a bang but a whimper on the skeptic’spart. It’s just not entirely clear whether the charge that the skeptical argumentcollapses into Infallibilism can be successfully answered by the skeptic. Theanti-skeptic’s ending remarks have some force to them.24

Notes

1. See “Solving the Skeptical Problem” (Philosophical Review 1995). In the end,DeRose says, under the demands of theory, that the sentence ‘K∼SK’ is truewhen evaluated with respect to ordinary conversational contexts, in which thestandards for knowing are more relaxed than in, e.g., philosophical conversa-tional contexts.

2. See my “Unfair to Nozick” (Analysis 1991) for a defense of Nozick againstcharges of question-begging regarding his claim that given tracking, closurefails.

3. See “How to be a Fallibilist”(Philosophical Perspectives 1988).4. See my “The Structure of the Skeptical Argument” (Philosophy and

Phenomenological Research 1994) for discussion of UP and its relation to closure.See also Stewart Cohen’s “Two Kinds of Skeptical Argument” (Philosophy andPhenomenological Research 1998), and Duncan Pritchard’s “The Structure ofSkeptical Arguments” (Philosophical Quarterly 2005). See also Jonathan Vogel’s“Varieties of Skeptical Arguments” (Philosophical Issues 2004). Note that onecan construct a UP-based skeptical argument that bypasses closure and runs asfollows:

(∼F’) My experiential evidence for H does not favor H over SK.(!) ∼JH (by ∼F’ and UP)(3) ∼KH

I will not compare the merits of this argument and that under discussion in thetext. See the papers cited in this footnote for further discussion.

5. See his “The Skeptic and the Dogmatist” (Nous 2000). See also Bill Brewer’sPerception and Reason (Oxford: Oxford University Press, 1999), and MichaelHuemer’s Skepticism and the Veil of Perception (Lanham: Rowman and Little-field, 1999).

6. See Donald Davidson, “A Coherence Theory of Truth and Knowledge”, inE. LePore (ed.), Truth and Interpretation: Perspectives on the Philosophy ofDonald Davidson (Oxford: Blackwell, 1986). The Dictum has its roots in thework of Sellars and Quine.


7. See his “Skepticism and Closure: Why the Evil Genius Argument Fails” (Philo-sophical Topics 1995), and his Certainty: a Refutation of Skepticism (Minneapolis:University of Minnesota Press, 1991). For critical discussion, see my “Skepticismand Epistemic Closure” (Philosophical Topics 1985), my “Klein on Closure andSkepticism” (Philosophical Studies 1995), my “Reply to Coffman on Closure andSkepticism” (Synthese 2008), and E. J. Coffman’s “Defending Klein on Closureand Skepticism” (Synthese 2006).

8. See Dylan Dodd’s “Why Williamson Should Be a Sceptic” (PhilosophicalQuarterly 2007).

9. See, e.g., his ”Some Reflections on the Acquisition of Warrant by Inference”,in S. Nuccetelli (ed), New Essays on Semantic Externalism, Scepticism, and Self-Knowledge (Cambridge: MIT Press, 2003).

10. See paper in footnote 9, p. 68.11. Circa “How to be a Fallibilist”.12. A similar view can be found in Gail Stine’s “Skepticism, Relevant Alternatives,

and Deductive Closure” (Philosophical Studies 1976). She held that one lacksevidence that rules out CD but the irrelevance of that alternative enables one toknow that it does not obtain.

13. See, e.g., Jonathan Vogel’s “Skeptical Arguments”, “Cartesian Skepticism andInference to the Best Explanation” (Journal of Philosophy 1990).

14. See his “Evidentialism, Internalism, Disjunctivism”, in T. Dougherty (ed.),Evidentialism and its Discontents (Oxford: Oxford UP, forthcoming). See also his“Wright Contra McDowell on Perceptual Knowledge and Scepticism” (Synthese,2009).

15. See e.g., “Knowledge and the Internal” (Philosophy and PhenomenologicalResearch 1995), and “Singular Thought and the Extent of Inner Space”, inP. Pettit and J. McDowell (eds.), Subject, Thought, and Context (Oxford:Clarendon Press, 1986).

16. See “Evidentialism, Internalism, Disjunctivism”, p. 11. It is not clear whatPritchard means by ‘reflectively accessible’. McDowellian e-disjunctivism ismeant to be an internalist view of perceptual knowledge, but just how thisinternalism is to be secured is unclear. In a striking quote from “Wright ContraMcDowell on Perceptual Knowledge and Scepticism”, Pritchard says, “. . .ifthe McDowellian proposal could be made palatable then it would constitutethe holy grail of epistemology, in that it is offering a bona fide internalistconception of knowledge which is able to nonetheless allow that the rationalsupport that one’s belief enjoys can be genuinely truth-connected and thussceptic-proof”. (p. 7)

17. Some metaphysical disjunctivists, e.g., McDowell, hold that an unveridicalexperience lacks content altogether.

18. I have criticized the Williamsonian conception of the justificatory structureof perceptual knowledge in “Knowledge, Evidence, and Skepticism Accordingto Williamson” (Philosophy and Phenomenological Research 2005). See alsoWilliamson’s “Reply to Brueckner” (same journal), along with my “E = K andPerceptual Knowledge” (forthcoming in D. Pritchard and P. Greenough (eds.),Williamson on Knowledge).

19. Note that the Dogmatists need not assume that, right now, I am in the goodcase, in order to claim that right now, I have undefeated prima facie justification

∼K∼SK 89

for believing H. This is because on their view I have such justification even if Iam in fact in the bad case.

20. See the papers in footnote 14. Pritchard distinguishes between discriminatingand favoring evidence. In the zebra case, he holds that I lack discriminatingevidence that allows me to tell just from the look of the beast whether it isa zebra or a cleverly disguised mule. But I have favoring evidence for Z and∼CD which consists in my background beliefs about zoos, the unlikelihood ofarcane deceptions, etc. This favoring evidence, together with the look of thebeast, justifies my beliefs of Z and ∼CD. See also Stewart Cohen’s paper infootnote 3. Pritchard seems to hold that although I cannot discriminate thegood case from the bad case purely on the basis of appearances, I neverthelesshave favoring evidence in the G which enables to me to know that I have handsand am accordingly in G and hence not in B. This evidence comes in the formof a McDowellian “reflectively accessible” factive reason.

21. Williamson thinks that when I am in G, I can discriminate G, considered underthe indexical mode of presentation ‘my case’, from B, considered under thedescriptive mode of presentation ‘the bad case’. This is because in G, I knowH, I know that H entails that I am not in the bad case, hence I know that Iam not in the bad case. But when I am in B, according to Williamson, I cannotdiscriminate between B, considered under the indexical mode of presentation‘my case’, from G, considered under the descriptive mode of presentation ‘thegood case’. This is because it is consistent with everything I know in B that Iam in G. See Knowledge and Its Limits (Oxford: Oxford University Press, 2000),section 8.2.

22. See Stewart Cohen’s “Two Kinds of Skeptical Argument” for discussion of therelevance of this lack of entailment to a comparison between closure and UP.

23. Thanks here to Dylan Dodd, Esben Nedenskov Petersen, and Elia Zardini.24. I would like to thank the members of my graduate seminar in epistemology in

winter 2009 at UCSB. I am also indebted to Stephen Schiffer’s “Evidence =Knowledge: Williamson’s Solution to Skepticism” (in the volume cited infootnote 18) for its lucid analyses of Williamson’s views. Finally, I would like tothank the audiences at the Arche conference on skepticism at the University ofSt. Andrews, at the University of Copenhagen epistemology workshop organizedby Mikkel Gerken, and at the Third Brazil Epistemology Conference at PontificiaUniversidade Catolica do Rio Grande do Sul in Porto Alegre.

brueckner - ~k~sk

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