Saturday, October 23, 2004

Skepticism Overview

Note: I wrote the following essay in my Epistemology and Metaphysics exam earlier this year. So it lacks footnotes/references and may be a bit scruffy in places (we were only given an hour per essay, after all). But I quite like it still, so thought I'd type it up here - with some minor editing, including the addition of hyperlinks. I don't recall the exact question, but it was something along the lines of "What is skepticism, and what rational responses can be made to it?"


Skepticism is the thesis that we cannot obtain genuine knowledge - that even our most basic beliefs about the world are epistemically unjustified. The basis for such an extreme claim is found in the apparent impossibility of ruling out various skeptical scenarios or hypotheses which are inconsistent with our everyday beliefs. For example, it seems possible that we could be brains in vats (BIVs), being 'fed' experiences by a mad scientist electrically stimulating our brains in such a way as to give rise to the exact same phenomenal experiences that we usually assume are caused by reality. The skeptic argues that because we are unable to distinguish the BIV scenario from Realism, we are not justified in assuming either one to be the case. Instead, the skeptic argues, the rational thing to do is suspend belief.

In everyday life, this strikes us as a rather implausible suggestion. As the Humean response goes, we are 'natural-born believers'. No matter the philosophical force of skepticism, it is of little practical import. Many philosophers, however, have thought that we can actually beat skepticism on its own terms. Various rational responses have been made to try to refute the skeptic's argument.

As the skeptic's argument is based on the empirical indiscernibility of Realism from Anti-Realism, the most obvious response would be to try to find an a priori reason for preferring the former. Most of these attempts fail - for example, we cannot assign probabilities to these cases. Nor can we say Realism is necessarily any simpler or more parsimonious.

Some have suggested a semantic response, however. Hilary Putnam argues that when an envatted person says "there is a tree", they speak the truth - given what they mean by 'there' and 'tree' (something like "a tree in-the-image").

Putnam advocates a form of anti-Realism here, but we need not follow him in that respect. David Chalmers has a similar response which sees the "matrix" (the world the envatted people think they occupy) as a genuinely real world in itself. He offers a complete metaphysical analysis of it, arguing that it is a world whereby:
(1) It is computational at the most fundamental level of reality;
(2) Inhabitants' minds exist outside of physical space-time, but interact with physical processes;
(3) Physical reality was created by beings outside of (the matrix's) space-time.
This nullifies the skeptical power of the BIV hypothesis, for we can say that envatted people still have largely true beliefs about their world.

Alternatively, if one is dissatisfied by the a priori responses, one must look elsewhere than foundationalist internalism for epistemic justification.

One possible alternative is coherentism. Here, a belief is said to be justified to the extent that it coheres with our other beliefs. Since we are 'natural born believers', and perception causes (though does not itself justify) us to have beliefs about the natural world, it follows that Realism - as a general framework - coheres better with our existing beliefs, than does anti-Realism. We are thus justified in rejecting the BIV hypothesis, due to the incoherence it would bring to our wider belief system.

However, coherentism cannot judge between equally-coherent alternative systems. So the BIV-believer could always insist that his own beliefs are perfectly coherent (and thus justified) - even though they may clash with ours. Coherentism forces a sort of neutrality, then. If we want to go on the offensive, and argue that common-sense / Realist beliefs are not merely justified, but epistemically obligatory, then we will require the philosophical power of epistemic externalism.

According to externalism, justification arises in part from conditions external to the agent. That is, a belief could be justified without the agent subjectively realising that this was so. This instantly overcomes the skeptic's arguments, for the indiscernibility problem becomes irrelevant.

Reliabilism, for example, merely requires that a justified belief be one which was formed by a reliable process. Now, we may not be aware of whether perception is reliable. But, nevertheless, there is some fact of the matter. If it is reliable, then my beliefs about the world will (according to Reliabilism) be justified.

Contextualism is another popular response to skepticism. It suggests that the standards required for knowledge vary according to context - so although we may not know we are not BIVs according to 'high standards' contexts, we can, contextualists claim, know our everyday beliefs based on the 'lower standards' appropriate in those contexts.

The problem with such a response is that if we are foundationalist internalists, then there is no possible evidence to recommend common-sense Realism over the BIV hypothesis. This means that no matter how low the standards are set, we can still never have justification for our everyday beliefs. For contextualism to be any use at all, it must work in tandem with one of the previously discussed solutions - most usually, externalism. (A common answr is the 'relevant alternatives' view, whereby we only need to rule out alternatives that are relevant to the present context. This is at heart an externalist theory though, since 'relevance' is an appeal to factors external to the agent.)

Perhaps the most impressive such fusion is Keith DeRose's mix of contextualism and possible-worlds externalism. The core idea is that S's belief that P is justified to the extent to which it satisfies the condition S believes that P iff P is true in close possible worlds. The justification is stronger, the more close possible worlds there are where this condition holds; that is, where S's belief "tracks the truth" (as Nozick put it) through those worlds.

DeRose's contextualist twist is that the 'strength' of justification required for knowledge will vary according to context. Our belief that we are not BIVs is very strong, for it is accurate in all nearby possible worlds. The closest world in which we are mistaken (i.e. the BIV world) is a very distant one indeed!

So there are several different rational responses one could make to the skeptic. Skepticism demonstrates that an a posteriori, foundationalist, internalist view of knowledge about reality is untenable. We can thus overcome the objection by denying any one of the three conditions. We need a response which is either a priori, coherentist, or externalist in nature.


  1. "Our belief that we are not BIVs is very strong, for it is accurate in all nearby possible worlds. The closest world in which we are mistaken (i.e. the BIV world) is a very distant one indeed!"

    How is this not question-begging? Why can't the skeptic just say "You're mistaken, sir. You're a BIV. And in all nearby possible worlds, you're a BIV who is similarly mistaken"? 

    Posted by Blar

  2. "How is this not question-begging?"

    Suppose the BIV hypothesis (or something similar) is true, so we have false beliefs. That instantly violates a necessary condition for knowledge, so we don't have knowledge (of those beliefs) in such a situation. There's nothing more to say here, so it's not a situation worth considering. The interesting question is what happens if our beliefs are actually true.

    So let's now suppose we have true beliefs about the external world. Whether they amount to knowledge depends upon whether those true beliefs of ours are also justified.

    Most forms of externalism suggest that if our belief that we are not BIVs is (objectively) true, then we will be justified in believing this, even if we lack subjective evidence. This is an important and interesting claim, and it doesn't beg any questions.

    Note that the skeptic doesn't actually believe we're BIVs. The question is whether we are justified in ruling the hypothesis out. The skeptic brings up the BIV hypothesis to cast (internal/subjective) doubt, not to try to convert us to a new dogma. If he met someone who actually believed in BIVs, the skeptic would be appalled, and likely ask, "But how can you be sure that you're not perceiving external reality?"

    Again, the question here is about justification, not truth. The skeptic should be willing to grant the truth of Realism (even if merely for the sake of argument), so long as we do not assume that we KNOW this truth. So it's not question-begging for the externalist to assume that our beliefs are true, in order to show that it then follows that they are (or would be) justified.

    But it does mean that it ends up being a conditional justification (which I may have failed to make clear before). If the external world is real, then we know about it. If it is not, then of course we don't. That's about as good a result as an anti-skeptic could possibly hope for. 

    Posted by Richard

  3. I think that this is basically how you've summarized DeRose's argument:

    If a skeptic accepts, first, that your belief that you are not a BIV is true in this world and would continue to track the truth in all nearby possible worlds, and second, that knowledge is belief that is true in the actual world and tracks the truth in all nearby possible worlds, then the skeptic will be forced to accept that you know that you are not a BIV.

    As a response to skepticism, that doesn't seem to be much stronger than this argument:

    If a skeptic accepts, first, that your belief that you are not a BIV is true, and second, that knowledge is true belief, then the skeptic will be forced to accept that you know that you are not a BIV.

    In both arguments, it seems that the skeptic has to assume all of the important points as premises. 

    Posted by Blar

  4. Well, they're of the same logical form. But the problem with the second argument is that nobody thinks that knowledge is merely true belief. But if that theory were correct, then yes, it would overcome skepticism. (After all, the "knowledge = true belief" theory is just a very extreme form of externalism.) Or, to put it more subjectively: if we found that theory plausible, then we would have reason to not be so concerned by the skeptic.

    So the difference is that possible-worlds externalism is a more plausible theory of knowledge. We have more reason to accept that premise as true. (We are not forced to accept it of course, but it would at least not be unreasonable of us to do so.)

    "In both arguments, it seems that the skeptic has to assume all of the important points as premises."

    Well, as I said before, assuming the truth of our beliefs (in this context) is not an important point. You can always discharge the assumption by turning it into a conditional: if these beliefs are true, then we know them. That's sufficient to show how we could have knowledge (it doesn't definitively prove that we DO have knowledge, but that's besides the point).

    So that just leaves the assumption that our chosen theory of knowledge is correct. Which again, we can get around by conditionalising. If externalism about justification is correct, then we can obtain knowledge. That's true - even the skeptic would have to concede that much. He might not think externalism is true, but that's his problem.

    Bear in mind that our aim here is not to persuade the skeptic; that seems to be what you're focussing on, but I think it's an unproductive way of looking at the problem. Instead, we should be trying to convince ourselves.

    The skeptic provides a challenge: to explain how we could possibly know anything about the external world. There are many possible responses, as I outlined in my essay above. You point out that the skeptic might not accept the given explanation, but I don't see why that matters. My aim is not to prove to the skeptic that we have knowledge. (I think that's where you've misunderstood me.) Instead, it is merely to explain how it is that we could have knowledge in the face of the skeptic's argument.

    Hope that clears things up a bit :) 

    Posted by Richard


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