Our knowledge of the physical world depends on our perceptual faculties being just about as sensitive as they are. Consider an ideally rational animal, or ideally rational community of inquirers, with only, say, our auditory and proprioceptive faculties. Call it A. It is hard to imagine how A could develop anything we should consider a complete physics. Perhaps I’m wrong – I’m only going on conceivability here – but it sure seems as if the ontology of the theory A would possess at the end of inquiry just could not be the same as any ontology human beings will reach at the end of inquiry.*
A’s theory and ontology would be, in some sense, inadequate. This is because we have all of the evidence A has and more, and A’s theory is inadequate to account for all of our evidence. My intuition is that this inadequacy has some sort of normative force; that is, in some sense, A should adopt a theory that is able to account for our evidence as well as our own completed physics.
Here’s my question: What reason do we have, if any, not to believe that, for all we know, we are in A’s position? More precisely, what reason do we have, if any, not to believe that, for all we know, there is some (perhaps uninstantiated) perceptual faculty, such that our theories should account for the evidence this faculty would furnish for us, were we to have it, in the same sense that A’s theory should account for the evidence furnished by our visual faculties? To be sure, we have pretty good evidence to suspect that none of the animals on Earth have such a perceptual faculty. The question is whether, for all we know, something could have such a faculty, with the world and its contents remaining otherwise entirely as they are.
The only reason I can think of – if it is true – would be furnished by a certain sort of “instrumentalist” meta-ontology. I take instrumentalism to be the view that ontology O is to be preferred over ontology P just in case O is better suited to our purposes than P. Once we have all the evidence in hand, we answer these sorts of “big picture” ontological questions (Carnap might have called them external questions) by recourse to our purposes in theorizing. Suppose our purposes are just to develop a theory with all of the virtues of descriptive adequacy, explanatory power, and simplicity that accounts as well as possible for all of the way things appear to us.** In that case, it is clear that no such troublesome perceptual faculty could exist, because no perceptual faculties other than our own can have any normative bearing on our choice of ontology. Note that this sort of meta-ontology makes it difficult to hold on to the initial intuition I had about A’s epistemic situation – namely, that A should adopt a theory that is able to account for evidence outside of her own perceptual purview. If we think that ontologies are beholden, at last, only to the way things appear to the community of inquiry, then the percepts of outsiders, real or imagined, can have no rational bearing on what exists, in our language.
It’s not clear which I like more – this version of instrumentalism or the offending intuition. Is there some adjudicating evidence that I’ve left out of court? Can anyone point me in the direction of some relevant literature?
* - I’m assuming here that neither we nor A ever experience any sort of divine revelation or anything like that.
** - This description of “our” purposes is really unsatisfactory to me, but I can’t do any better yet. For what it’s worth, it probably beats Carnap in ESO, where he suggests that the purpose for which he uses the language of serious theory is “the purpose of communicating factual knowledge.”