Abstract
Dogmatists often exploit the skeptical argument based on the brains-in-a-vat (BIV) scenario as a test case for their epistemological enterprises. I argue that this ‘argument’ does not deserve our attention, so it should not be used as a test case. I first show that the possibilities of empirical knowledge and of skeptical scenarios are inconsistent (the Inconsistency Thesis). If so, the BIV-skeptic must make the case for preferring such scenarios over the possibility of empirical knowledge. The central argument of my paper is that the BIV-skeptic can neither rely on any selection principle (e.g. conceivability) for this purpose, nor can she claim that she needs no such principle. Then I will show that we can even dispense with the Inconsistency Thesis: if the skeptic wishes, she may allow for the possibility of empirical knowledge. The essay concludes with considering the morals of the above argument for the dogmatist (or simply, epistemological) endeavor.
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Notes
The proper symbolization of the claim would be, of course, ∃p∃sK(s,p), but for our purposes the simplified version will do.
The claim that the skeptic cannot directly prove that such knowledge is impossible requires some further qualification since the Knower Paradox aims to show just that. That paradox, as fascinating as it is, is outside of the scope of the paper and won’t be discussed here. It should also be added that while the phrasing of our claim seems to suggest the reliance on logical possibility and necessity, it can easily be adjusted to claims about metaphysical possibility, once the set of background beliefs, Γ, is introduced.
It is a broadly held view, nonetheless erroneous, that the accessibility relation corresponding to S5 is homogenous, i.e. each world is connected to each others. In fact, it is sufficient for S5 if the accessibility relation is an equivalence one, and so the set of all possible worlds might be partitioned into disjoined equivalence classes. To rule out this possibility the skeptic must assume a semantically restricted version of S5 in which all worlds are in fact interconnected.
Actually, we can present a more sophisticated description of the situation. Instead of □(◊SK⊃~Kp) we can begin with the premise that □((◊SK & ◊SK1 & ◊SK2 & … & ◊SKn &…) ⊃ ~Kp), where ◊SKi refers to one of a finite or infinite list of skeptical scenarios (one of which is our SK). Since the skeptic is forced to accept the antecedent of this premise, and □(◊SK & ◊SK1) ⇔ (□◊SK & □◊SK1) is a theorem in S5, we can get at the same conclusion as in the original argument.
To be precise, wA is not a skeptical scenario in the above-used sense, since empirical propositions are true in this world (or so we hope). Nonetheless, it does not alter the fact that ◊SK and ~Kp are both true in wABS, and the truth of ~Kp is ensured by the fact that wABS and wA are indistinguishable.
Chalmers 2002, p. 149
It should be noted that this replacement affects the structure of the skeptic’s argument as well, as she has to start (as her major premise) with: ~K(~◊SK) ⊃ ~Kp.
Indeed, the LD scenario is superior to the BIV in this respect: while the BIV argument shows that we have no empirical knowledge in our own world, the LD scenario would validate the impossibility of such knowledge.
Just to mention one example, Nozick’s (1981) tracking theory seems to be a good illustration of my point: his reliance on non-closure is the price he paid for avoiding the skeptic.
References
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Marton, P. Calling the Skeptic’s Bluff: Brains, Vats, and Irrelevance. Philosophia 47, 477–488 (2019). https://doi.org/10.1007/s11406-018-9982-9
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DOI: https://doi.org/10.1007/s11406-018-9982-9