Effects of age and education on variable but native heritage grammars: Theoretical and empirical implications for the Null Subject Parameter

In this contribution, we investigate the impact of language-internal and language-external factors on the parametrized grammatical domain of (null) subjects in adult Italian heritage speakers (HS, n =16). Based on empirical evidence from correlation analyses comparing these speakers' spontaneous speech to monolingual Italians (n =10), we determine the kind and extent of variation in monolingual and bilingual adult end-state grammars. We will show that there is indeed a significant variation in the null subject production of the HS related to the factors age and education which is, however, constrained to contexts of 1st grammatical person. This observation cannot be taken to represent incomplete acquisition but rather a discourse and possibly situation-related competent behaviour. We propose that end-state HS grammars are characterized by a full grammatical and pragmatic competence, combined with a larger variation of language-externally determined preferences than monolinguals show. This does not call the native end-state competence of HS into question but opens the door for potential changes in future bilingual generations. We further discuss the implications for language acquisition theory and language change in terms of stability.