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Are You A Brain In A Vat?
November 2, 2008, 1:37 pm
Filed under: Epistemology

Imagine aliens invaded your bedroom and stole your brain while you were sleeping.  Imagine they dumped it into a vat of fluid and hooked it up to electrodes that piped in phony sensory experiences.  Imagine these phony sensory experiences amounted to a coherent simulation of our world.  Imagine that these phony sensory experiences were indistinguishable from normal ones.


With this imaginary situation in view, we can see that perceptual experiences don’t justify our perceptual beliefs. 


Because if they did then our perceptual beliefs while in the vat would be justified.  But those beliefs were false.  They were triggered by the sophisticated tricks of the aliens.


So then we can’t know anything via perception.  


Because perceptual knowledge must be at least justified belief.  But none of our perceptual beliefs are justified.



What’s wrong with this argument?

I think it contains some major misunderstandings about epistemological justification.  First, contrary to the argument, it is perfectly possible for a false belief to be justified.  

It may be that I’m a brain in a vat, but it sure doesn’t seem like it to me.  It seems like I’m sitting down and typing.  (If I’m sitting down and typing then I’m not a brain in vat.)  According to the principle of phenomenal conservatism, if it seems to me that P then I’m at least prima facie justified in believing that P.  I pretty sure that phenomenal conservatism is a necessary truth.  

Anyway, if perceptual beliefs can be justified by perceptual experiences, then the argument dissolves.


Obviously, justified belief is not enough for knowledge.  Truth is also necessary.  And so my beliefs while in the vat do not count as knowledge, even if they are justified.  They aren’t true!  


But what if, by chance, my beliefs while in the vat turned out to be true?  Then they’d be both true and justified.  So would they count as knowledge?


No.  In order to pick out knowledge from mere justified true belief, we have to consider things from an external (i.e. not first person) perspective.  The belief must have been produced by properly functioning cognitive faculties aimed at the production of true belief in an environment conducive to their proper function.  Beliefs so produced are warranted.  You can know something without knowing that your belief is warranted.  What matters is that the belief is in fact warranted.


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