Wo has a post up criticising my views on conceptual disagreement. I won’t summarise the complaint, because you can head over there for that. Instead a few quick responses.
First, I think this passage contains a mistaken step. (See his post for the explanation of the numbering.)
Note that reason (5) probably collapses into reason (4) if ideal rationality suffices to find out which classes are natural to what degree. At any rate, (5) is covered by (4) together with (3) if ideal rationality and sufficient information about our world in principle suffice to know facts about naturalness. So if (5) is really meant to be an additional explanation, degrees of naturalness must be neither a priori knowable nor a posteriori knowable: they must be altogether unknowable.
I agree with the first two sentences, but not the third. And here’s why. I think that ideal rationality does not guarantee knowledge of facts about naturalness, especially when we’re dealing with moral concepts. But that does not mean those facts are not knowable. It just means that failure to know them is not a failure of rationality. If the concepts are moral concepts, it might be a moral failing.
Let’s go back to the case that motivates a lot of this. A and B disagree about whether in a particular thought-experiment, what C does is right or wrong. I claim that facts about what the moral concepts really are, facts that are partially constituted by facts about naturalness, are relevant to determining who’s right here and who’s wrong. Let’s say A, who thinks what C does is wrong, is herself wrong and B is right. I claim A can be wrong despite knowing all the relevant facts and being perfectly rational if A lacks appropriate moral insight – a failing I don’t think is comfortably described as a failure of rationality. (Though see Michael Smith for a contrasting view.) That doesn’t mean that B can’t know that what C does is right. Moral insight might increase knowledge without, I think, lack of moral insight, or distorted moral ‘sight’ being a failure of rationality.
There’s a parallel here to philosophy of mind. You don’t want to endorse the following cheap argument for mysterianism. Lots of smart people disagree about consciousness. In all probability they will keep disagreeing. Therefore the facts about consciousness are unknowable. The problem, of course, is that even if perfectly rational people disagree, it might still be the case that, due in effect to epistemic luck, the one’s who are right know the true story. That’s the same as what I think is going on in ethics.
Even if my theory needed semantic inscrutability, I don’t think it would be as bad as Wo makes it out to be, for three reasons.
First, the epistemic theory of vagueness needs exactly the kind of semantic inscrutability that my theory allegedly does, and it seems that’s not an objection to the epistemic theory of vagueness. The best objections, I think (and this is going to be a partisan observation) are to the underlying metaphysics behind the epistemic theory, not to its epistemology.
Second, the example involving “cat” Wo gives seems uncomfortably similar to examples like “fish” where we have let facts about naturalness override pre-theoretical intuitions. The benefit of having terms lock onto stable kinds is a communicative benefit, so it can override intuitions. (It is possibly important here that although natural kinds do not impress themselves so vividly on the mind that all rational persons are aware of them, they are scrutable. So maybe this just amounts to the main point.)
Third, the example Wo gives just about has to be underdescribed because of Kripkenstein worries. I think that unless we use naturalness in our theory of menal content, in which case the worries about scrutability for linguistic content that Wo raises will reappear for mental content, then it is just impossible to have intuitions about all possible cases. In which case a predicate, which unless classical semantics is on holiday applies or doesn’t apply in every case, can’t match intuitions about 100% of cases. So I’m not sure how to really understand Wo’s case, and all the ways I have of understanding it involve appeals back to naturalness.