This chapter presents a more fine-grained analysis of why and how DOM vulnerability may have become more prevalent in Spanish than in Hindi and Romanian at the individual level. Specifically, linking language acquisition, language attrition and diachronic language change, it addresses the question of the potential relationship between the I-language of the heritage speakers and the E-language of the first-generation immigrants, who are often the heritage speakers’ main source of input. It presents follow-up studies of DOM in Spanish-speaking bilingual children and adults and their mothers and the results are not consistent with direct transmission of DOM omission from the first to the second-generation (the heritage speakers). It is suggested that that second-generation heritage speakers, who have as much difficulty mastering the morphology of their heritage language as typical L2 learners, can also change the grammars of the parental generation and be the innovators in the Spanish variety spoken in the United States.

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.

In this chapter challenge cases to Knowledge Counter-Closure discussed so far are distinguished from cases of transmission failure and easy knowledge. I explain how these challenge cases work and argue that Knowledge Counter-Closure can be replaced by a plausible principle phrased in terms of justification, rather than knowledge. I then discuss Murphy's claim that inferential knowledge can arise from unjustified belief and from non-belief. I close the chapter by showing that rejecting Knowledge Counter-Closure avoids substantial costs.