Segunda fase: Aprendizaje basado en proyectos, retos y problemas (Curso

The foregoing argument has been that neither the experiential, nor the indication constraints put forward by Beebe should be considered necessary conditions on being a sceptical hypothesis. I now aim to put forward a positive proposal about what could be said to be necessary for being an effective sceptical hypothesis. In developing this proposal, I will draw again on considerations already highlighted in chapter 1, concerning the notion of ‘bad’ possibilities, or scenarios. In this section, I set out the parallels between the indication constraint and characterisations of effective sceptical hypotheses as ‘bad’ possibilities. After pointing towards the limitations of understanding effective sceptical hypotheses in these terms, I use them, in section 2.7, as a springboard for proposing an alternative account.

I think that consideration of the indication constraint could help to explain why claims of the form ‘ifSknows thatp, thenSknows that¬sh’ are plausible for effective sceptical hypotheses. The indication constraint says that it is a necessary condition on any sceptical hypothesisshbeing effective at challengingS’s putative knowledge that

p, thatsh be a scenario in whichSbelieves, but does not know that pon the basis of

their evidence. It is not surprising that virtually all paradigmatic effective sceptical hypotheses fit this pattern: a brain in a vat does not know it has hands, an individual looking at a cleverly disguised mule does not know it is a zebra, and the victim of a complete perceptual deception knows nothing about the world—at least, not on the basis of perception. This might be thought to be obvious given the closure principle, the factivity of knowledge, and the fact that, in each of the aforementioned examples of sceptical hypotheses, these hypotheses entail the falsity of external world propositions. This, however, is not the case with respect to many other well-recognised hypotheses capable of raising a significant challenge to our putative knowledge. The dreaming

hypothesis, for example, does not entail the falsity of many external world propositions, but is capable of raising a sceptical challenge to my putative knowledge of them. Likewise, the hypothesis thathalf of the animals in the pen are cleverly disguised mules, does not entail thatthis animal in the pen is a zebrais false, but itiscapable of raising a sceptical challenge to my putative knowledge that this animal in the pen is a zebra.14

2.6. BAD POSSIBILITIES.

I take it then that an explanatory advantage of the indication constraint, even though it does not quite deal well with my example of thefaulty-monitoreffective hypothesis, is that it goes some way towards providing a more general account of sceptical hypotheses. It applies in equal measure to hypotheses that are not compatible with the targeted propositionp, such as thebrain in a vathypothesis, as it does to those that are compatible withp, such as the dreaming hypothesis. Insofar as the indication constraint is to be rejected on the grounds that it fails to apply to the case of Ellie, this unifying aspect of it will nonetheless be a desirable feature in any alternative account.

In seeking an account of effective sceptical hypotheses, I have suggested that more generality is preferable to less. Speicfically, I take it that it is a desirable feature of an account that it both apply equally to compatible and incompatible hypotheses, in the sense outlined above, and apply to my Ellie case. In seeking an account like this, I think it will be instructive to reconsider some influential characterisations of effective sceptical hypotheses that fall short of having the desired generality. I think that there may be some valuable lessons to be gained from these characterisations, despite their limitations, that can help to shed more light on what an effective sceptical hypothesis must do.

The first account I am interested in considering has been offered by Williamson (2000), who characterises effective sceptical hypotheses as ‘bad’ possibilities in the following way:

In the good case,things appeargenerally as they ordinarily do,and are that way; one believes one propositionp(for example, that one has hands), andpis true; by ordinary standards, one knows p. In the bad case, things

still appeargenerally as they ordinarily do,but are some other way; one still believesp, butpis false; by any standards, one fails to knowp, for only true propositions are known. (Williamson, 2000, 165, my emphasis.)

In the bad scenarios, described by effective sceptical hypotheses,Sstill believes thatp

on the basis of it seeming to them thatp, butSdoes not know thatpbecausepis false.

But what is it about these scenarios that is supposed to be epistemically bad? If there can be knowledge of contingent propositions at all, then surely there will be possibilities in which these propositions are false, and thereby not known. Moreover, it has been continuously stressed here that in order to be effective—at raising a significant challenge to S’s putative knowledge of some external world proposition p—it is not necessary for a hypothesis to entail the falsity of p. It appears that the list of effective sceptical

hypotheses with respect topis not exhausted by the list of bad possibilities with respect topas recognised by Williamson. Specifically, effective sceptical hypotheses such as the

dreaminghypothesis, and the weakerhalf-fakeshypothesis, are not obviously examples of Williamson’s bad possibilities. I submit then that an account of effective sceptical hypotheses in terms of Williamson’s notion of bad possibilities does not provide us with the general account we are seeking.

In contrast to Williamson, Pryor (2000) recognises that not all effective sceptical hypotheses entail the falsity of putatively known external world propositions. And it is from Pryor’s recognition of this fact, and other considerations concerning effective sceptical hypotheses that I now take my cue in pursuing an alternative account. In particular, I take Pryor’s useful insight, with respect to sceptical hypotheses, to be that certain possibilities are not badsimpliciterbut only relative to the propositional content and grounds for—or experiential basis of —a perceptual belief that p.15 In line with the recognition that effective sceptical hypotheses may either entail the falsity of the putatively known proposition or not, Pryor outlines two distinct ways in which a sceptical hypothesisshmay describe a bad possibilityqwith respect to a perceptual belief thatp:

Say that some groundsE you have [for a belief that p] “allow” a possibility

qiff the following counterfactual is true: ifqobtained, you would still possess the same groundsE... So, we might want to count a hypothesis as “bad” for the purposes of a skeptical argument just in case it is (and is recognized to be) incompatible with what you purport to know [p], but it is nonetheless “allowed” by your grounds E..., [or], if it could undermine your experiences.

(Pryor, 2000, 527)

On this view, a hypothesis sh will be effective at raising a significant sceptical challenge toS’s putative knowledge thatponly when it describes a bad possibility with respect topandS’s grounds, E, for believing thatp. A ‘bad’ possibility, in this sense, is one in which Sbelieves thatpon the same groundsEas they do in actuality, but where eitherpis false, or elseEno longer provides any justificatory support forS’s belief that

p.16SinceSdoes not know thatpif eitherpis false, orS’s belief thatplacks justificatory

15_{(Pryor, 2000, 528).}

16_{See (Willenken, 2011, pp.6-7) for an explanation of the function of an ‘underminer’—Pryor’s term for}

a hypothesis that could undermine your experiences. Pryor maintains certain perceptual beliefs about the world are based on grounds or experience, which are what justify these beliefs. Others maintain that beliefs are based upon and justified by evidence, either propositional or non-propositional. For present purposes I remain neutral on whether beliefs are best described as being based on or justified by evidence, experience, grounds, or reasons; requiring only that beliefs are based in some way.

2.6. BAD POSSIBILITIES.

grounds, it is clear that a common feature of bad possibilities with respect topandEis that,in these possibilities,S does not know thatpon the basis ofE.

In this way, Beebe’s indication constraint has clear parallels with this characterisation of sceptical hypotheses in terms of bad possibilities. Bad possibilities are those in which a subject could believe, but not know, a propositionpon some evidential basis, on which they would ordinary base a belief thatp. The close connection between the indication constraint and Pryor’s characterisation of sceptical hypotheses as ‘bad’ possibilities should not be surprising. After all, Pyror explicitly states that he considers a possibility to be bad “just in case it has the special features that characterize the skeptic’s scenarios— whatever those features turn out to be” (Pryor, 2000, 527). If being a sceptical hypothesis simply amounted to describing a ‘bad’ possibility, where a ‘bad’ possibility is just one that has those features that allow it to serve the requisite role in a potentially threatening sceptical argument, then it remains unclear whether the notion of ‘badness’ can help us meaningfully distinguish between sceptical hypotheses that areeffectivefrom those that are not.

Presumably, then, the ‘badness’ of a possibility consists in it satisfying the necessary conditions on being an effective sceptical hypothesis. I think this is a plausible way to interpret Pryor’s view of bad possibilities and effective sceptical hypotheses. So, perhaps the indication constraint is a necessary condition in the following sense: a hypothesis

sh is effective with respect to S’s putative knowledge that p when it describes a bad

possibility, where this notion is explicated in the following way:

a possibility is bad, with respect to an experience and a proposition, iff it is a possibility in which one would have the experience and ordinarily rely on it in believing the proposition but in which one would not thereby gain perceptual knowledge of the proposition. (McGrath, 2013, 535)

This latter-most characterisation of a ‘bad’ possibility, together with the closely related indication constraint, seem to provide some insights into what features of effective sceptical hypotheses are doing the necessary work in challenging our putative knowledge of empirical propositions. I argue, however, that neither provide a satisfactory account of the necessary conditions on effective sceptical hypotheses; neither, I have argued, applies to the example of the effective hypothesis involved in the Ellie case. In what follows, I suggest a weaker alternative constraint on effective sceptical hypotheses, which I argue succeeds where the others have failed in applying to the Ellie case.

Consider again the novel Ellie case I introduced in section 2.4. I have argued that the case involves an effective epistemic challenge, which is an analogue of sceptical challenges. In this case, however, the hypothesis utilised in the raising of a significant challenge to the protagonist’s putative knowledge of some propositiondoes notdescribe a possibility which fits with the above definition of a bad possibility. In any possibility in which the monitor is faulty, Ellie neither has the monitor-related experiences she actually does have, nor does she believe the relevant proposition. But it is obvious that there is some aspect of this hypothesis that is ‘bad’ in the sense that Hammond is able to utilise it effectively in raising an epistemic challenge to Ellie’s belief that Alan is not in the paddock. This case is, however, importantly dissimilar to the various examples of sceptical challenges contained within the cases from recent epistemology which involve extraordinary possibilities (brains in vats, dreaming, or malignant demons). The difference is, as I have noted in chapter 1 and section 2.2, one of scope. I think that this difference in scope is an aspect of effective epistemic challenges that requires explanation. But I think we will be in the best position to give this explanation once we have a general account of the constraints on being an effective sceptical hypothesis, which applies no matter how narrow or wide the range of its epistemic challenge.

Within the next section, I develop an alternative explanation of ‘bad’ possibilities, in terms of the basis for a belief, and then go on to propose an account of the necessary conditions on an effective sceptical hypothesis capable of raising a significant challenge to knowledge of external world propositions. I argue that this constraint captures the common core shared by effective hypotheses, and can accommodate the differences between them in terms of scope.

I noted above that it is an advantage of the indication constraint that it accounted for both those effective sceptical hypotheses that entail the falsity of everyday empirical propositions, and those that do not. I think that this generality is desirable in an account, and should be sought. The indication constraint, however, is not satisfied by the faulty-monitor hypothesis. Instead, I argue that this hypothesis satisfies another necessary condition on effective sceptical hypotheses, and one that also generalises in the desired way. On my view, what makes the faulty-monitor hypothesis an effective sceptical hypothesis is that were it true, then it would be consistent with Ellie believing that Alan was not in the paddockon the same evidential basis as she actually doesthat this belief is false. After setting out my constraint, and applying it to various examples, I go on to argue that it is preferable to the rejected necessary conditions on effective sceptical hypotheses.