Language attrition is the loss of linguistic abilities or the regression of specific grammatical properties and overall fluency in linguistic skills. It impacts language use, lexical access, and grammatical integrity. Non-pathological attrition is natural in situations of language contact and bilingualism and can occur in the first, native, language as well as in a second language. As a gradual and dynamic process of accommodation that occurs when bilinguals use the second language extensively, attrition is a highly individualized phenomenon and hard to predict a priori. If attrition eventually happens, it affects individuals differently, with some exhibiting more widespread loss than others. Two factors that determine the extent of language attrition in bilinguals are the availability of input and the age of the individual at the onset of the reduction in input in their native language. An important question is whether attrition mainly occurs at the level of processing or whether it affects actual linguistic competence. Theoretical approaches to attrition have emphasized its relationship with L1 acquisition, the selectivity of attrition by linguistic modules, the effects of language use on memory, and the interplay between the L1 and the L2 along the life span. We still lack understanding of how attrition affects linguistic representations and processing and the external and individual cognitive factors that modulate, predict, or prevent attrition in bilinguals.
Morphological attrition is far more common and extensive in children than in adults and it manifests itself in a variety of ways: morphophonemic leveling, morphological simplification, including omission of required morphology in obligatory contexts, paradigmatic reduction, simplification/reduction of suffixal allomorphy, regularization of irregular forms, and the replacement of synthetic forms for analytic/periphrastic forms. Morphological attrition has often been discussed in the context of language death and language loss at the community level for both child and adult bilinguals. The scant empirical evidence to date seems to indicate that the processes of omission, regularization, and suppletion that are common in attrition occur regardless of the dominant morphological type of a language. Both inflectional and derivational morphology are affected under language attrition and seem to undergo similar processes of reduction and simplification, regardless of the morphological type of the language. Within inflectional morphology, nominal morphology (gender, number, case) is more prone to attrition in the actual number of occurrences than verbal morphology (agreement, tense, aspect, mood), and attrition occurs more rapidly and extensively.