Fall 2002

Theory of Knowledge Goldman's 'Discrimination and Perceptual Knowledge'

Goldman offers a theory of perceptual knowledge which has elements in common with the relevant alternatives theories we've looked at already. However, Goldman's theory has an important new element as well.

According to the theories we've looked at so far, eliminating an alternative Q, or "ruling that alternative out," turned on what sort of evidence you have against Q. Goldman rejects this assumption. He says you don't need to have evidence against Q to eliminate it; it suffices if you're able to perceptually discriminate the situation in which P obtains from the one in which Q obtains.

Suppose there are two twins, Judy and Trudy. Suppose moreover that you're usually able to tell them apart. You don't know how you do it, but when you're confronted with one of the twins, you're usually right in your beliefs about which twin it is. You may not be aware of any evidence you use to tell the two apart. Instead, there are subtle differences in their faces and the way they walk that your brain picks up and processes, without any conscious intervention or assistance from you. The details of these cognitive mechanisms are hidden from you. For all you can tell, you just end up with beliefs about which twin is which, and these beliefs tend to be reliable. They're right much more often than not. In such a case, you're able to perceptually discriminate between Judy and Trudy although you're not in conscious possession of any evidence which distinguishes between them.

The view Goldman wants to defend says the following:

• Whether you have perceptual knowledge that P is a matter of whether you can reliably discriminate P from its alternatives.

• You don't have to discriminate P from all its alternatives, but only from the relevant alternatives.

• Reliably discriminating P from certain alternatives doesn't require you to have evidence telling against those alternatives. It only requires you to have cognitive mechanisms which tend to produce correct beliefs about whether P or the alternatives obtain.

• As in the Judy/Trudy case, you don't have to know how you discriminate P from its alternatives; nor do you have to know that the method you use is reliable. There just has to be some method, and it just has to be reliable.

So the basic idea of Goldman's view will be this: if you truly believe that P on the basis of your perceptual experiences, then you perceptually know that P, unless there's some alternative to P which is both relevant and which you can't reliably discriminate from P.

Because of its focus on what you can reliably discriminate rather than on what sorts of evidence you have, Goldman's view counts as an externalist account of (perceptual) knowledge. We'll discuss this more below.

Goldman's Two Analyses

Goldman's first attempt to capture his basic idea goes as follows:

This analysis seems to capture Goldman's basic idea in many cases. For example, suppose S looks out the window of his car and sees a barn. S forms the true belief that there's a barn. One alternative would be the hypothesis that it's just an empty field. However, if that alternative obtained, then S would have different experiences and so he would no longer believe that there's a barn. Hence, S is able to discriminate this alternative from what believes to be true. Another alternative might be that it's not a barn but just a barn facade. If this alternative obtained, then we can suppose that S would have the same experiences he's now having, and so he would still believe that there's a barn. Hence, S is not able to discriminate this alternative from what he believes to be true. If this alternative is a relevant one, then S won't count as knowing that there's a barn. However, if the only relevant alternatives are like the empty field alternative, then since S is able to discriminate them from what he believes to be true, his belief will count as knowledge.

So far, so good. Goldman's analysis captures the basic idea he wants to base his account of knowledge on. However, there are some problem cases that Goldman's first analysis delivers the wrong result for.

Suppose S sees a dachshund, and that S is able to reliably discriminate dachshunds from larger animals like German Shepherds and wolves. However, we suppose that S is not able to tell German Shepherds and wolves apart very well. Now suppose that there are lots of wolves running around, so the possibility that what S sees is a wolf is a relevant alternative to its being a dachshund. Intuitively, S still knows that what he sees is a dachshund, since he's able to reliably discriminate dachshunds from wolves. So far, so good. But now suppose that S looks at the dachshund and forms the true perceptual belief, "That's a dog." Does this belief count as knowledge? Intuitively, it would. The fact that S mistakes some dogs (German Shepherds) for wolves shouldn't show that S can't know that this dog (which looks nothing like a German Shepherd) is a dog. So the intuitively correct thing to say is that S knows that the creature he sees is a dog, even though there are some other dogs which he can't tell apart from wolves.

Goldman's first analysis doesn't deliver this result though. Goldman's first analysis tells us that S's belief "That's a dog"doesn't count as knowledge, since there's a relevant alternative--the possibility that it's a wolf--and if that alternative obtained, we can suppose that S would confuse the wolf for a German Shepherd and so still hold the belief "That's a dog." So according to the first analysis, S's doesn't know the dachshund he sees to be a dog.

What's gone wrong? If the wolf alternative obtained, S would still believe "That's a dog" but he'd believe it on the basis of different experiences. Perhaps that's the problem. The fact that S confuses wolves with some dogs, ones that look very different, ought not to show that S can't know that the dachshund he sees is a dog.

As things stand, Goldman requires there to be no alternative Q such that, if it obtained, S would continue to form the belief that P for any reason. That's what gets him in trouble with the dachshund case. If S were seeing a wolf instead, S would still believe "That's a dog" but he'd believe it on the basis of very different experiences. Perhaps Goldman should say instead that there is no alternative Q such that, if it obtained, S would continue to form the belief that P by the same method, or on the basis of the same sorts of experiences. If there are relevant alternatives to P in which S has the same belief and the same experiences, then S doesn't know that P.

This gives us Goldman's second analysis:

Call a possibility "perceptually equivalent" to P for S just in case the experiences it would produce in S are exactly the same as the experiences that P produces. (Or, if the experiences differ, they do so in respects that are ignored by the mechanisms that produced S's belief that P.) With this notion, we can restate the last condition in Goldman's analysis as follows:

Compare Goldman's summation of his account:

This second analysis solves the dachshund problem. If the wolf-alternative obtained, S would still form the belief "That's a dog," but he wouldn't form it by the same method. He would form it on the basis of very different experiences. So we get the intuitively correct result: the relevance of the wolf-alternative doesn't prevent S from knowing the dachshund he sees to be a dog.

There are further problems of detail that Goldman considers on pp. 788-9, but we don't need to go into them here.

Why Goldman's Account Is So Novel

Because of its focus on what you can reliably discriminate rather than on what sorts of evidence you have, Goldman's view is very different from traditional accounts of knowledge.

On Goldman's view, whether your true beliefs count as knowledge doesn't depend on what evidence you're conscious of having, or on any other facts about your belief that are open to your introspective, self-reflective consciousness. It depends on how your beliefs were caused, and whether they were caused in a way that's reliable.

Call an account of some epistemological state internalist when it says that the presence or absence of the state depends on facts which are "internally available" to you, that is, knowable on the basis of introspection and reflection. Call an account of some epistemological state externalist when it says that the presence or absence of the state depends on facts which aren't "internally available" to you. There can be internalist or externalist accounts of knowledge, of justification, and of various related notions.

Now, everybody says that whether your beliefs count as knowledge depends in part on whether they're true; and whether your beliefs are true is something that might not be detectable just on the basis of introspection and reflection. So to that extent, everybody has an externalist theory of knowledge. But traditionally, philosophers have mostly thought that truth is the only externalist component of knowledge. They have assumed that all of the other features which go towards making true beliefs count as knowledge are "internally available."

Goldman's view rejects this traditional assumption. On Goldman's view, whether your true beliefs count as knowledge depends on facts about the beliefs (how they were caused, how reliable the mechanisms which caused them are, etc.) which aren't "internally available" to you. When people talk about externalist theories of knowledge, they're usually thinking of views like this one.

Suppose there's someone out there who's a psychological duplicate of you. He has all the same beliefs, thoughts, experiences, and memories as you have. Everything which you can tell about yourself on the basis of introspection and reflection, is also true of him (and like you, he can tell that it's true of him on the basis of introspection and reflection). Call such a person an internal epistemic duplicate of you.

On the traditional accounts of knowledge, if you had a belief which counted as knowledge, and your duplicate had the same belief, and his belief was also true, then his belief would have to count as knowledge too. On the traditional accounts, there can be no difference in epistemic status between internal epistemic duplicates, unless their beliefs differed in truth-value. The truth-value is the only external feature.

On Goldman's account, however, your true belief might count as knowledge, whereas your duplicate's true belief fails to count as knowledge, because his belief was not produced in the same reliable way that yours was. This is a difference between you and your duplicate, but it's not an "internally available" difference. So on this view, there are other external features besides the truth-value of your belief which can make a difference to whether you know.

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