Short sketch #1: Case system with ergative detail

A language with a somewhat latinate case system, say nominative, genitive, accusative, dative, ablative.

This language descends from a clearly ergative stage, where the ergative case, as in many ergative languages, was identical to the genitive. The indefinite and the intransitive subject are both in the nominative. However, definite third person transitive subjects still are marked by the genitive, except for the pronouns.

The genitive/nominative distinction has carried over to the third person pronouns, but in the pronominal system, a genitive subject is obviative and a nominative one proximative. Genitive 1st and 2nd person subjects tend to mark seriousness.

The accusative is used to mark the object of verbs deemed not beneficial to the first or the second person, sometimes even a third person of personal relevance to either; the pragmatics and sociolinguistics of when the first or second person is relevant are slightly complicated. Beneficial or neutral objects tend to be marked with the dative.

The verb has the following set of forms: [singular, plural] x [1st, 2nd, 3rd] + [3rd II], where II just serves to disambiguate it from the explicitly 3rd person singular one; 3rd person II is used both with singular and plural indefinite subjects, some definite subjects under some circumstances, as well as with subjectless verbs. It has a smaller set of TAM-distinctions than the other persons, and cannot combine with auxiliaries to the same extent either.