Converbs are essentially verb forms that have some form of adverbial use. In some way one could also say they are "cases for verbs". They often mark things such as "condition on which the main verb depends", "action that was enabled by the predicate", "action that enabled the predicate", "... preceded ...", "... followed ...", "... coincided with ...", etc. There is a lot of possibilities with converbs, and I may write a post going into some of that later on.
However, let's think a bit about the relationship between the converb and the main verb. We can divide all sentences in the world into two types:
- No converb is present.
- One or more converbs are present.
We can imagine a system with a handful of different converbs, maybe the following:
- in order to
- as a result of
- until the end of
- from the end of
- temporarily doing
What if a clause with no converb usually does not mark its predicate verb with the usual finite markers, but with one particular converb's forms, thus giving us a slightly "ergative-like" pattern, where "normal verb inflections" are ergative, and that particular converb is "absolutive"? Maybe there can be two converbs that can have that "absolutive" role, with a differential morphology thing going: maybe "simultaneous" usually just means "happens", whereas "temporarily" means "habitually or on-and-off".
We can consider other factors also that trigger which pattern is used: maybe some persons take the regular finite verb, or inanimates take some of the converbs for predicates except if there's some "real" converb present?