Assume that sensory experience has no propositional or semantic content. Further assume that Hume has developed two reliable dispositions. He has learned to discriminate colors from each other, and he has also formed the reliable disposition to believe in any color experience that the object in question is not the missing shade of blue. Thus, in every sensory experience involving color, Hume is disposed to form two beliefs, one identifying the particular color in question and the other denying that the object is the missing shade of blue.
After years of experience never having encountered the missing shade of blue, Hume finally finds an object that is the missing shade of blue, and upon seeing it, Hume believes that the object is the missing shade of blue.
My question is how to explain Hume’s justification for this belief. If we appeal only to his reliable dispositions, it looks like there are two competing dispositions. One disposition, a highly reliable one, inclines him to believe that the object is not the missing shade of blue. Another disposition, also highly reliable, inclines him to identify the particular color the object is, which in this case is the missing shade of blue. If we could appeal to some content of the experience itself, it would easy to explain why we favor the latter disposition over the former in accounting for the justification of Hume’s belief. But we are assuming that experiences have no content, so we can’t do that. Notice further that each disposition is perfectly general, and that each can be replaced in a given case with more specific dispositions: upon seeing a magenta flower, Hume is disposed to believe that it is magenta and that it is not the missing shade of blue, etc. (I point this out to try to block the attempt to see this problem as just a version of the generality problem for reliabilism.) So, without appeal to content, what reasons could a theorist have for preferring one of the dispositions in question to the other?