In other words, is there any language that uses the same mood to convey ability and possibility? For example, is there a language in which a sentence meaning "He'll be able to do that" and "He might do that" are expressed with the exact same morphemes and syntax, with context (environmental or linguistic) distinguishing the two?
"Ability" and "possibility" are a description of the dichtotomy linguistically known as "alethic modality" vs "epistemic modality". The former relates to the ability to achieve something under certain conditions, the latter to the speaker's extimation that something is likely to have happened. "Could" can index both: "he could be back home at 7 if he hurries up" (alethic) vs "he could be at home since I see his car outside" (epistemic).