[This is part of a series of defectivity case studies.]

Harris (1969:114) observes that the Spanish verbs agredir ‘to attack’ and aguerrir ‘to harden’ are defective in certain inflectional forms. Gorman & Yang (2019:180), consulting various Spanish dictionaries, expand this list to include abolir ‘to abolish’, arrecir(se) ‘to freeze’, aterir(se) ‘to freeze’, colorir ‘to color/dye’, descolorir ‘to discolor/bleach’, despavorir ‘to fear’, empedernir ‘to harden’, preterir ‘to ignore’, and tra(n)sgredir ‘to transgress’.

All of the defective Spanish verbs appeear to belong to the 3rd (-ir) conjugation, which is the smallest of the three and characterized by extensive irregularity. including raising and/or diphthongization of mid e, o to i, u and to ie, ue, respectively. For instance, the verb dormir ‘to sleep’ (along with the minimally different morir ‘to die’) undergoes diphthongization to ue when stress falls on the stem (e.g., duermo ‘I sleep’) and raising in various desinence-stressed forms (e.g., durmamos ‘we would sleep’). According to  Maiden & O’Neill (2010), it is exactly these forms which would show stem vowel changes which are defective (e.g., in the paradigm of abolir), though this claim ought to be verified with native speakers.

Harris has long argued that these stem changes are limited to stems bearing abstract phonemes. In his 1969 book, stems which undergo diphthongization bear an abstract feature +D; in his 1985 paper, a similar distinction between diphthongizing and non-alternating stem mid vowels is marked using moraic prespecification. The apparent raising of stem mid vowels is analyzed as a dissimilatory lowering of an underlying [+high] vowel, but since there are some stems which do not lower (e.g., vivir/vivo ‘to live/I live’), similar magic (i.e., abstract specifications) is likely called for. In contrast, I understand Bybee & Pardo (1981) and Albright et al. (2001) as arguing that these stem changes are locally predictable, conditioned by nearby segments.¹ Albright (2003) suggests that competition between these locally predictable conditioning factors is responsible for defectivity.

Gorman & Yang (2019) argue that, on the basis of a Tolerance Principle analysis, that there are no productive generalizations for 3rd conjugation mid vowel stem verbs in Spanish, if diphthongization and raising are viewed as competitors to a “no change” analysis.² In support of this, they note that children acquiring Spanish as their first language only very rarely produce incorrect stem changes in the 3rd conjugation. This suggests that during production, they may be “picking and choosing” verbs for which they have already acquired the relevant inflectional patterns.

Endnotes

1. Of course their arguments are largely limited to adult nonce word studies. I consider this inherently dubious for reasons discussed by Schütze (2005).
2. They claim “no change” is productive in both the 1st and 2nd conjugations. In support of this they note that diphthongization is commonly underapplied in these conjugations by children acquiring Spanish as their first language.

References

Albright, A., Andrade, A., and Hayes, B. 2001. Segmental environments of Spanish diphthongization. UCLA Working Papers in Linguistics 7: 117-151.
Albright, A. 2003. A quantitative study of Spanish paradigm gaps. In Proceedings of the 22th West Coast Conference on Formal Linguistics, pages 1-14.
Bybee, J. L. and Pardo, E. 1981. On lexical and morphological conditioning of alternations: a nonce-prob e experiment with Spanish verbs. Linguistics 19: 937-968.
Gorman, K. and Yang, C. 2019. When nobody wins. In F. Rainer, F. Gardani, H. C. Luschützky and W. U. Dressler (ed.). Competition in Inflection and Word Formation, pages 169-193. Springer.
Harris, J. W. 1969. Spanish Phonology. MIT Press.
Harris, J. W. 1985. Spanish diphthongisation and stress: a paradox resolved. Phonology 2: 31-45.
Maiden, M. and O’Neill, P. 2010. On morphomic defectiveness: evidence from the Romance languages of the Iberian peninsula. In M. Baerman, G. G. Corbett, and D. Brown (ed)., Defective Paradigms: Missing Forms and What They Tell Us, pages 103-124. Oxford University Press.
Schütze, C. 2005. Thinking about what we are asking speakers to do. In S. Kepser and M. Reis (ed.), Linguistic Evidence: Empirical, Theoretical, and Computational Perspectives, pages 457-485. Mouton de Gruyter.