ABSTRACT
This chapter analyzes data collected in interpretation and production tasks, in which the author searched for evidence that the adult second language (L2) learner can successfully reset the Null-Subject or 'Pro-drop' Parameter (NSP). It also argues that the data shows evidence that adult Spanish L2 learners initially transfer the NSP setting of their L1 to the L2, resulting in the error phenomena observed in many pedagogical works. Over time, there is a shift to a null-subject grammar that is like that of native speakers of Spanish. The parameters of Universal Grammar (UG) are the language-particular instantiations of universal principles that individuate the grammars of specific languages. The Critical Period hypothesis gives a biological explanation for the lack of success of the adult learner. Null-subject languages like Spanish and Italian have a well-known cluster of related syntactic and morphological properties that distinguish them from non-null-subject languages.
