There are interesting parallels between (i) the Dasgupta/Maudlin interaction on inexpressible ignorance, and (ii) a better-known debate in the contemporary philosophical literature—
., that regarding whether one can proffer a linguistic response to philosophical scepticism. Famously, Putnam argued that, since brains-in-vats can only ever refer to vat-facsimiles of real-world objects, they can never articulate the sceptical problem—and so, the issue is dissolved (see Putnam, 1981, for the original source, and McKinsey, 2018, for an elegant summary of notable responses). In reaction to this, Nagel maintained that the argument is too quick: perhaps brains-in-vats are simply inexpressibly ignorant of real-world facts—“Instead I must say, ‘Perhaps I can’t even think the truth about what I am, because I lack the necessary concepts and my circumstances make it impossible for me to acquire them!’” (Nagel, 1986, p. 73)—; or perhaps one can make use of non-referring terms to articulate the sceptical scenario—“I can use a term which fails to refer, provided I have a conception of the conditions under which it would refer” (Nagel, 1986, p. 72).
Transparently, in these debates, Dasgupta parallels Nagel, insofar as the latter is to be read as endorsing the possibility of inexpressible ignorance—but who parallels Putnam? If one reads Putnam as stating that, because brains-in-vats are inexpressibly ignorant of real-world objects, they are in fact not ignorant of anything at all, then it would seem to be Dasgupta’s final reading of Maudlin in Dasgupta (2015a) who is the appropriate analogue here.
Note, though, that if what we have said in the foregoing subsections is correct, then the response that Maudlin himself (rather than Dasgutpa’s reading of Maudlin) would proffer to the sceptical problem is a little different. Suppose, to make the parallel with static shifts more explicit, that we consider various different sceptical scenarios, in which the data supplied to the brain-in-vat is the same, but the real-world facts are altered. Call these “sceptical shift scenarios.” Then, on our first reading of Maudlin presented in §1.4.1.2, he would argue that these shifted worlds are genuinely distinct, and there are real-world facts of which we are inexpressibly ignorant, but that there is no epistemological problem, because we can identify indexically which of this class of worlds is our own. On our second reading of Maudlin......, he would argue that there is in fact no inexpressible ignorance at all, for we can refer indexically to real-world objects.
Are either of these responses plausible in the sceptical shift scenario? In our view no, for one cannot identify indexically real-world objects as one can identify indexically one’s own position—the situation is more analogous to the kinematic shift, or to the cases of gauge transformations in electromagnetism .... than to the static shift. There is, however, one disanalogy between the sceptical shift scenarios and these latter two cases: in the sceptical case, if Putnam is correct, we are inexpressibly ignorant of the real-world facts; whereas in the latter two cases, we are expressibly ignorant. This difference stands in spite of the fact that we cannot identify indexically our world in either case.
Where, then, does this leave us? If Putnam is the analogue of Dasgupta’s Maudlin, and (one aspect of) Nagel is the analogue of Dasgupta, then Maudlin himself finds neither a straightforward nor plausible parallel in the sceptical case—for it is not possible for a brain-in-vat to identify indexically real-world facts or objects in sceptical shift scenarios; this blocks both of our own readings of Maudlin in this context.
