Abstract
AbstractMorphological defectiveness is a situation in which an inflected or derived word is expected in a language but no word with that meaning exists. It is thus a kind of absolute ungrammaticality or ineffability. In the context of the productive nature of morphology, gaps in inflectional and derivational paradigms seem anomalous – situations in which the grammar fails. Investigating the absence of a morphological form raises definitional and methodological issues, but the diverse causes of gaps allow insight into various aspects of morphological structure. Structural causes include phonotactic ill‐formedness, indeterminate allomorphy, anti‐allomorphy effects (lexical conservatism), and homophony avoidance, among others. Gaps also can arise in the context of lexicalization, inflectional loss and borrowing. At the same time, structural properties that the defective words in a language have in common often are also shared with non‐defective words. This raises the question of why defectiveness occurs instead of a structural repair or some other gap‐filling form. The frequent inadequacy of structural factors for predicting which words are defective suggests the need for a closer examination of the causes of defectiveness, in particular attention to mechanistic explanation. This includes processes involved in learning and change.