I follow Zwicky [Zwicky, A. M., 1985, How to describe inflection, Berkeley Linguistic Society 11.372-86, p. 377] in assuming that an empty affix position is ordinarily the result of the nonapplication of any rule of exponence filling that position: but, like him, I do not exclude the possibility that a rule of exponence might explicitly require a particular affix position to remain empty, e.g. if zero exponence overrides a default rule of affixation.
- Stump (2004), Pag. 126