How far back can a tense like hu, which fails to agree with its subject, be reconstructed in Swahili? Alternatively, do we know which construction it developed from?
This question is based on reading the Wikipedia article on Swahili grammar. That's also where the example comes from.
One of the Swahili tenses, the habitual seems unlike the rest. It a) does not agree with the subject of the clause and b) appears not to have a negative counterpart.
In the sentence below, the absence of agreement on the verb hula obscures whether ng'ombe is singular or plural. I think in Swahili it is normal (or perhaps required?) for the verb not to agree with the direct object when it is a full noun phrase.
Ng'ombe hula nyasi. head(s)-of-cattle HAB-eat grass Cows eat grass
Given that this tense is so different from the others, I'm wondering if we know how it developed or, alternatively, how far back the habitual tense or another tense with similar agreement rules can be reconstructed.