Abstract 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.

中文翻译：

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年龄和教育对可变但本土的文法的影响：空主题参数的理论和经验含义

摘要在这项研究中，我们研究了语言内部和语言外部因素对成年意大利传统母语使用者（空置，n = 16）的参数化语法域（空）的影响。根据相关分析的经验证据，将这些说话者的自发言语与单语意大利语（n = 10）进行比较，我们确定了单语和双语成人最终状态语法变化的种类和程度。我们将显示，与年龄和教育程度相关的HS的空主题产生确实存在显着变化，但是，该变化仅限于第一语法人的语境。这种观察不能被认为代表不完全的习得，而只是一种话语和可能与情况有关的胜任行为。我们提出，最终状态HS语法的特点是具有完整的语法和语用能力，并且与单语者相比，具有更大的语言外部确定偏好变化。这不会使HS的本机最终状态能力受到质疑，但会为将来的双语世代带来潜在的变化。我们从稳定性的角度进一步讨论了语言习得理论和语言变化的含义。