After some work I have given up on having a clever inheritance system for aspect in my Nuuchahnulth grammar. But I want to run this by other grammar engineers to see if I am missing something. Below is my current understanding of the morphology and perfective/imperfective split of Nuuchahnulth verbal aspect.
There are some obvious generalizations here: Anything that is graduative can become perfective, for instance. Initially I had a hierarchy where that bottom row of perfective forms inherited from the graduative and the other aspect, and specified in the lexical rules that anything graduative could undergo perfective morphology (and the inheritance would sort out what the full aspect was).
But this doesn’t quite work because I need (for other components of the grammar) to distinguish between perfective and imperfective aspect types. There are two aspect forms that are perfective—the momentaneous and the inceptive—which can become imperfective through the application of the graduative template, and then perfective again through the perfective (or “momentaneous”) morpheme being reapplied. I don’t think there’s a way to have an inheritance hierarchy that both captures the generalization about graduative forms becoming imperfective that also is able to group the bottom row of *-graduative-perfective forms with the momentaneous and inceptive. I’ve torn out the clever hierarchy and just have all the forms listed here, and each node separately inherits from a perfective or imperfective type. I want to check with other engineers that there is no clever way of generalizing over the perfective/imperfective hierarchy together with the morphological pathway of verbal aspect that I’m missing.