Jonathan Kvanvig has an interesting paper on Fitch's knowability paradox in which he argues that the paradox is a puzzle for everyone (not just those who believe that if a proposition is true then it is knowable). The puzzle is one of modal collapse; Fitch's argument shows that:
1. p --> possibly Kp
(if p then it is possible that p is known by some being at some time)
2. p --> Kp
(if p then p is known by some being at some time).
But how come the possibility operator can just disappear like that? Everyone has work to do explaining this, according to Kvanvig.
Thinking about the way the Fitch argument works suggests the following explanation:
Nothing of the form (p and not Kp) is knowable. But given 1, if anything of that form is true, then it is knowable. That's why, if 1 is true, nothing of the form (p and not Kp) is true. And that's why if 1 is true then 2 is true too.
Kvanvig must think there's something unsatisfying about this simple explanation. But what? Do we need further explanation of one or more of the claims it draws upon? I don't think so, but even if we do it could surely be given. More plausible, I think, is the thought that the simple explanation doesn't really explain the disappearance of the possibility operator; it just explains why 2 follows from 1.
If the worry is something like this then it is interesting. What counts as a good explanation of a fact does plausibly depend on (among other things) the way the fact is presented. The thought here would be that presenting the implication of 2 by 1 as a case of surprising modal collapse makes the simple explanation offered above inadequate (even if it is a good-enough explanation of the same fact under a different description).
But I am left with two questions:
A. What exactly is wrong with the simple explanation, considered as an explanation of the modal collapse? What virtue would a satisfying explanation have that this one lacks?
B. If we can answer question A, do we have any reason to think that there will be a good explanation of the modal collapse so described (i.e. an explanation that has the virtue we've identified as lacking in the simple explanation)? Or might it be that the best we can do is explain why 1 implies 2, leaving the fact that 2 takes the form of 1 without the 'possibly' a sort of coincidence?