Some commentators (van Cleve, possibly but I need to check) think that McDowell is committed to a kind of infallibilism. Because McDowell says that the evidence someone has for her beliefs in the good case are better than what she would have in the bad on the grounds that only subjects in the good case have knowledge, some take him to be committed to the view that among the conditions necessary for knowledge is that the possession of evidence or reasons that the subject could have only in the good case. Because of this, some might take McDowell to be saying that it is impossible for the truth of a belief to be the only thing that distinguishes a good case of perceptual knowledge from the bad case. In turn, this suggests that his view is that a perceptual belief constitutes knowledge only if based on something that is incompatible with the falsity of that belief.
Does that mean that McDowell subscribes to the infallibilist view that S can know p only if S’s basis for believing p is incompatible with ~p? He might, but epistemological disjunctivism as such does not entail infallibilism. At least, I hope it doesn’t. Infallibilism leads to skepticism. It might not lead to a skepticism concerning perceptual knowledge, but it leads to skepticism concerning induction. (Actually, I think he denies this. But, well, c'mon!) If knowledge is possible only when we have infallible grounds for our beliefs, the external world skeptic might be wrong but I cannot see how the inductive skeptic could be.
Okay, so is McDowell committed to infallibilism? According to fallibilism:
(F) It is possible for a subject to know that p is the case on the basis of evidence or grounds that do not entail that p.
If fallibilism is true, subjects in the good and bad case could have just the same evidence or reasons for believing p, but one of these subjects will be mistaken in believing p. But, then it seems that the difference between the good and bad case will be ‘blankly external’ to the subjects in these cases. So, either there can be differences in epistemic standing that are blankly external to the subjects in the good and bad case or infallibilism is true and knowledge based on non-entailing grounds or evidence is impossible. If the former is true, we do not need experiential disjunctivism to understand how perceptual knowledge is possible. If the latter is true, we trade one skeptical problem for another.
While I am not entirely convinced that this response is sufficient (or necessary), McDowell could say this. One problem with the objection is that it assumes that p could be blankly external to the subject who knows p. Why would the truth of her belief be blankly external to her? Sure, you might say that the falsity of the mistaken subject’s belief is blankly external to her. Why can’t McDowell acknowledge this as a possibility and say that if someone is in the dark, there will be matters blankly external to her that explain why she believes p without knowing p? How much do you have to know to be ignorant?
From Epistemological to Experiential Disjunctivism
I take it that one of McDowell's arguments for experiential disjunctivism is contained in this passage:
The root idea is that one’s epistemic standing … cannot intelligibly be constituted, even in part, by matters blankly external to how it is with one subjectively. For how could such matters be other than beyond one’s ken? And how could matters beyond one’s ken make any difference to one’s epistemic standing?
If you endorse epistemological disjunctivism but think that experience embraces the same things in perception and hallucination, you end up having to say that facts blankly external to the subject are responsible for the superior epistemic standing of that subject’s beliefs in the good case when compared to the beliefs in the bad.
The response I offered on McDowell’s behalf earlier to the charge that his view led to a kind of infallibilism that came with skeptical consequences should work here if it worked earlier. The difference between the good case and bad will not be blankly external to the subject in the good case. Because she knows p, she knows something that rules out the possibility that she’s the one in the bad case. How could a fact known to her directly on the basis of observation be blankly external to her? How could it matter to her that the difference between her and someone else who is ignorant is a difference lost on the subject who is in the dark about a great many things? If McDowell insists that the difference between the good and bad case cannot be a difference that is blankly external to the subject in the bad case, it seems he is committed to the rather odd view that there is something available to the subject in the bad case that would allow her (in principle, perhaps) to work out her epistemic predicament. If he rests content with the much more modest principle that the difference between the good and bad case cannot be 'blankly external' to the subject in the good case, I guess I'd say that the truth isn't blankly external when you know the truth.