Native Speakers, Interrupted aims to advance our understanding of heritage language development and change. It is argued that heritage language speakers also qualify as potential agents of diachronic language change of the diasporic variety of their language in the language contact situation. Heritage speakers are early bilinguals born with the cognitive ability to learn two or more languages fully and indeed retain native ability in specific grammatical areas of the heritage language due to their early exposure to the language. They are native speakers because exposed to their home language from birth implicitly in a naturalistic setting, in a family environment where the language was spoken. However, insufficient input and infrequent use of the heritage language during late childhood and adolescence interrupts the healthy development of the heritage language, profoundly affecting heritage speakers’ command of specific aspects of their grammar, such as vocabulary, morphosyntax and other linguistic interfaces. What is interrupted in this case is not the language as a whole, as several have proposed, but the individual language acquisition process itself, so that specific aspects of the heritage language, in some individuals, in some languages, and under some circumstances, show significant synchronic variability.

This chapter explores the relationship between language acquisition at the individual level and language change at the macro linguistic level. Given the semantic and pragmatic complexity of DOM cross-linguistically, the question arises as to how DOM is acquired by young children growing up in a monolingual environment. To what extent the semantic and pragmatic principles that guided diachronic developments constrain language development at the individual level? Language contact and bilingualism are often cited as critical factors in linguistic change at the macro-sociolinguistic level. Considering how DOM is acquired by different types of bilinguals and in different bilingual situations is critical to understand the link between language acquisition and language change. How language acquisition at the psycholinguistic level contributes to language change at the sociolinguistic and diachronic level, and the roles that both language internal (individual, cognitive factors) and language external (situational) factors play in the process and outcome of change are considered. Existing studies of DOM in L1 acquisition are discussed, followed by a critical review of studies in L2 and bilingual acquisition and in language change at the sociohistorical level. Monolingual children faithfully replicate the language they hear in the input while bilinguals are affected by dominant language transfer.