Datapoint Fanakalo/Ability verb and epistemic possibility
Some grammars, e.g. Opperman 1967, give azi as a future marker as well (i.e. epistemic certainty). I used to think this is a misanalysis, arising from confusing azi 'to know' with future particle zo (often reduced to clitic z). But given that I found an authentic sentence with negative future with azi (see Example 54), maybe there's something in the idea of future deriving from Zulu azi 'to know, be able' as much as from Zulu auxiliary future marker zo.
For epistemic possibility the "perhaps" reading is not possible; but a contextual reading of the other sort proposed is just about possible.
Values 
Ability verb cannot express epistemic possibility
- Example 61-53:
-
Yena yazi ga bala.Yenaheyazknowgainfbala.writeHe can write. OR: He knows (how) to write.
- Example 61-54:
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Kusasa mina ai yazi khona khaya.KusasatomorrowminaIainegyazibe.ablekhonabe.lockhaya.houseI won't be home tomorrow. OR: I can't be at home tomorrow. OR: I am unable to be at home tomorrow.
- Confidence:
- Certain