forum 1, week of Jan 8, Dretske
"suppose knowing something is excluding *relevant* alternatives to it. What could *relevant* mean?" Dretske would probably say that a relevant alternative to something you know would be information that would prove your knowledge false if it was true. For example: A relevant alternative that you are excluding in order to know that the zebras in the zoo are in fact zebras is that they are painted mules. I think that a relevant alternative to a situation should have some evidence for its possibility for it to be considered a real alternative. By this I mean one does not normally actively exclude the fact that what one is looking at is just an imitation of what it looks like. Why shouldn't the zebras be zebras? This thought normally does not even cross our minds unless we have been reading too much philosophy. For Dretske's example to be a relevant alternative I would have to see something like black and white house paint in the zebra pen. That would at least give me a reason for considering the possibility that things might not be as they appear. There are usually relevant alternatives to many things we think we know. Evidence that shows us we may be wrong but that we decide to exclude because it is not strong enough to change our minds. In short, "relevant" just means "less-likely". There is a reason to believe in this alternative, the fact that something is "possible" should not make it a faire contender for an alternative to our knowledge.
I agree with this idea that relevant alternatives should be supported by some kind of empirical evidence. If one were to take seriously any possible alternative then there would be very little one could claim to actually know. Even a priori knowledge could be questioned if one were to believe that there was some kind of evil demon operating solely to trick them. If empirical evidence were not enough to give us true knowledge, then one would be forced to say that 'I think that' or 'It is likely that' the zebras are not painted mules. I do not think that this particular example can be dealt with by saying it is a problem of semantics. I think one can say that they literally know that the zebras are zebras by applying these standards of empirical evidence to rule out alternatives, such as painted mules.
I agree that there would be very little one could claim to actually know, IF we have to consider all possible alternatives. However, one fundamental problem is that empirical evidence may or may not be enough to give us true knowledge, depending on the notion of evidence used. Yes, there is no consensus yet on what the heavily-used concept of evidence is! Besides, what are these standards of empirical evidence that you have in mind? Are they related at all to the definition of "evidence" given by Richard Royall and Steven Goodman? (e.g., see http://www.ncbi.nlm.nih.gov/pubmed/3189634 or http://www.botany.wisc.edu/courses/botany_940/06EvidEvol/powerpoints/Evidence.pdf)
I agree. Dretske's examples of relevance seem self-defeating at times. The Zebra case is especially troubling because it involves intentional deception in a case where there is usually no intent to deceive. The Zebra-painter is almost as evil as Descartes' demons. The reliance on this sort of example is emblematic of a deeper problem in his theory in that it it is too exclusive and unnecessarily limits knowledge to a subset of what we usually define knowledge to include. Too much error-avoidance leads to unnecessary ignorance.