As of yesterday I have completed my series of defectivity case studies, at least for the time being. From these I propose the following tentative taxonomy:
- Pure allomorphic competition (including “stem change”, stress shift, etc.): English, Polish, Russian (1 2), Greek, Spanish, Hungarian
- Morpho-metrical constraints: Chaha, Kinande
- Morpho-phonotactic constraints: Icelandic, Norwegian, Swedish
It is not clear to me whether three categories are really needed. In both of the latter two, here seems to be some tight phonotactic constraint on inflectional variants which results in ungrammaticality and defectivity if not satisfied. In the two cases from Africa, these constraints are of a metrical nature and impact many lexemes; in the cases from Scandinavia, they concern stem-final consonant clusters and possible mutations to them. And this looks a lot like the case of Russian verbs. This just leaves Tagalog, which I think has simply been misanalyzed, and Turkish, where the only defective lexemes are a handful of subminimal borrowings.
I am aware of two other cases of interest: (various stages of) Sanskrit (Stump 2010) and Latvian. These are phenomenologically quite different from the ones I’ve discussed so far: both involve gaps in the paradigms of inflected pronouns. I do not find gaps in the distribution of functional elements to be nearly as shocking as the failure of, say, an otherwise unobjectionable Russian or Spanish verb to have a 1sg. form. I should mention that the constraint against contracting n’t to am in standard English (see Yang 2017:§3 and references therein) is also possibly an example of this form; I suppose it depends on whether or not n’t is really an inflectional affix or not.
References
Stump, G. 2010. Interactions between defectiveness and syncretism. In M. Baerman, G. G. Corbett, and D. Brown (ed.), Defective Paradigms: Missing Forms and What They Tell Us, pages 181-210. Oxford University Press.
Yang, C. 2017. How to wake up irregular (and speechless). In C. Bowern, L. Horn, and R. Zanuttini (ed.), On Looking into Words (and Beyond), pages 211-233. Language Science Press.