Ordinary thought distinguishes two kinds of incapacity: I might lack (say) the brute strength to accomplish some task, or I might just not know how to do it. Is this an important (deep, principled) distinction? If so, what is its basis? (What justifies counting some abilities, but not others, as constituting a kind of knowledge?)
It doesn't just seem to be the difference between physical vs. mental incapacities, since even the latter (e.g. working memory limitations) may be intuitively classified as brute incapacities. Nor does the distinction seem to rest on differences in how the capacity may be acquired: practicing the piano does not seem obviously different in kind from lifting weights, though only the former is thought to yield procedural knowledge. Perhaps we need to combine several conditions, but then the resulting classification starts to look a bit ad hoc.
I feel like I must be missing something obvious here. Any thoughts?