Dretske and CohenDretske is a fan of the Relevant Alternatives Theory. He thinks it does a good job of explaining his Gadwell duck/grebe case. In that case, you see a bird that has all the markings of a Gadwell duck--and in fact it is a Gadwell duck. Do you know that it is? Dretske says that depends on whether there are relevant alternatives to its being a Gadwell duck. For example, one alternative hypothesis might be that there is a species of grebe around which has the same markings. (A grebe is a kind of bird that looks like a duck but isn't.) If that is a relevant alternative, Dretske thinks, then you don't know that the bird you see is a Gadwell duck. But if it's not a relevant alternative, then you can know.
Dretske gives a similar kind of case in another paper, "Epistemic Operators." (This paper is on reserve in Robbins Library.) In that case, you're at the zoo, and in the pen in front of you is a striped horse-like animal. The sign on the pen says "Zebra." Do you know that the animal is a zebra? (Assume that in fact it is a zebra.) Dretske says: Well, what about the possibility that it's just a mule painted to look like a zebra? Do you really know that the animal is not a cleverly-disguised mule? You may have some reason to believe that it's not a cleverly-disguised mule. (Zoos don't typically try to fool people like that.) But your evidence doesn't seem to be good enough to know that it's not a cleverly-disguised mule. You haven't made any special tests, or anything like that. So Dretske thinks you don't know it. But he still wants to say that, so long as the mule hypothesis is not a relevant alternative, you can know that the animal in the pen is a zebra.
What Makes an Alternative Relevant?Now what determines whether some possibility is a relevant alternative or not? Does the subject have to know about the grebe possibility for it to be relevant? Or is it enough if there is a suspicious ornithologist poking around in the neighborhood, who thinks there are grebes like that in the area? What if there is no ornithologist but some people think there is? What if there really are look-alike grebes in the area but no one knows that there are? In which of these cases is the grebe possibility a relevant alternative?
There are different kinds of stories one can tell about this.
Relevant Alternatives Theory and ClosureRecall the Closure Principles about knowledge that we discussed earlier. For example:
If you know that P, and you know that P logically entails not-Q, then you have to know (or at least be able to know) not-Q too.At first glance it looks like the Relevant Alternatives Theorist will be rejecting Closure. Closure tells us that you have to know to be false everything which is (or which you know to be) an alternative to P; whereas the Relevant Alternatives Theorist says you only have to know to be false those alternatives which are relevant.
And sure enough, Dretske's version of the Relevant Alternatives Theory does reject Closure. This comes out more in Dretske's paper "Epistemic Operators."
For example, Dretske claims that you can know that the animal in the pen is a zebra on the basis of evidence which does not enable you to know that the animal isn't a cleverly-disguised mule. So here we have a counter-example to Closure:
Dretske thinks that knowledge is closed under some known entailments. For example, he thinks that if you know that P&Q, then you know that P. (P&Q logically entails that P.) He just thinks that Closure fails when it's a matter of knowing P, and knowing that P entails not-Q, but Q is not at the moment a relevant alternative to P. In such a case, Dretske thinks, you can know P even if you're not in a position to know not-Q. You can know it's a zebra in the pen even if you're not in a position to know it's not a clerverly-disguised mule. But if the possibility of its being a cleverly-disguised mule were to become relevant, then since you can't rule it out you would no longer count as knowing that it's a zebra in the pen.
However, matters are not so straightforward. After all, it's somewhat odd to deny Closure. It's odd to say that you could know that P, and know that P entails not-Q, but not be able to put these together and draw the conclusion that not-Q.
If you hold a Contextualist version of the Relevant Alternatives Theory, then you might be able to retain some kind of Closure Principle.
According to the Contextualist, Norm can say "Caesar knew he had hands" and Skepty can say "Caesar did not know he had hands," and they need not be disagreeing. They might both be right. It's just that what they mean by "X knew he had hands" is different, since the sets of relevant alternatives are different.
Similarly, when you say "I know I have hands" and the skeptic says "You don't know you're not dreaming," the Contextualist can say you're speaking in different contexts, with different sets of relevant alternatives. It's as if Tom were to say "I'm Tom" and Jerry were to say "I'm not Tom." There's no conflict there, just a difference in context.
With this in mind, the Contextualist can go on to insist that Closure holds within any single context. In any given single context, you either know that you have hands and that you're not dreaming, or you don't know that you're not dreaming and you don't know that you have hands, either. If dreaming is a relevant alternative, then you don't know either of these things. But if dreaming is not relevant, then you can know that you have hands, and you can also know that you're not merely dreaming.
So it looks like one can be a Contextualist and still accept the Closure Principle, after all.
Does the Relevant Alternatives Theorist Beg the Question Against the Skeptic?How satisfactory a reply to the skeptic does a Relevant Alternatives Theory really give us? The skeptic will just say, "You're begging the question against me, in claiming that my skeptical possibilities are irrelevant and don't need to be ruled out, if you're to count as having perceptual knowledge."
However, as Cohen points out in "Skepticism, Relevance and Relativity," the Relevant Alternatives Theorist can reply back to the skeptic: "Why should we accept your account of which alternatives are relevant and which are irrelevant? You're just begging the question against common sense, in claiming that those alternatives are relevant to the question whether we know."
We seem to have reached a stand-off. Both sides claim that the other side begs the question. How might this stand-off be resolved?
Well, we should distinguish two different sorts of anti-skeptical projects we might be engaged in.
A Problem for ContextualismOne natural way to think about the Contextualist's story is as follows. We have evidence for believing various things. And some of the things we beleive are true. But if your evidence for P is very slight, that won't be enough for you to know that P, even if P happens to be true. So we have the question: how much evidence does it take for a true belief to count as knowledge?
Now the Contextualist will answer this question by saying, "That depends upon the context." In some contexts, having evidence that makes P 99% likely might be good enough for you to know that P. In other contexts, e.g., when we're thinking about lotteries and so on, 99% might not be good enough.
What the skeptic tends to do is to get us into contexts where the bar for knowledge is very high. The Contextualist acknowledges that in contexts of that sort we don't count as having knowledge. But he says that we shouldn't lose sight of the fact that in other, ordinary contexts, where the bar for knowledge is lower, our evidence might very well be good enough for us to count as knowing.
That story does have some plausibility to it. But the problem is that it requires you to have some evidence against the skeptic's possibilities. In ordinary contexts, that evidence should be good enough to know those possibilities don't obtain; though in skeptical contexts the bar is higher and there the evidence isn't good enough for knowledge.
But do we any evidence against the skeptic's possibilities? What is our evidence that we're not in the Matrix, or not being deceived by evil demons? We would be having exactly the same experiences even if those possibilities were true. So it's not clear whether we even have any evidence at all that those possibilities don't obtain. (This is a point the Blumenfelds made, earlier.)
We need to think more about how the skeptic's arguments bear on issues about evidence and justification, not just knowledge. And we need to think about the relations between justification and knowledge. That is what we'll turn to next in the course.