Acquiring the syntactic constraints on auxiliary change under restructuring in L2 Italian: Implications for the Interface Hypothesis

This paper reports the findings of an experiment into the syntactic constraints on auxiliary change under restructuring in Italian L2 grammars which are possibly at the end state. Its aim is to test the prediction of the original version of the Interface Hypothesis that narrow syntactic properties are fully acquirable in the L2. In Italian restructuring constructions with embedded unaccusatives, the change of auxiliary from avere (‘have’) to essere (‘be’) is either optional or obligatory depending on clitic presence and placement. A group of highly proficient L1 Croatian adult L2 learners of Italian and a group of adult Italian native speakers used Magnitude Estimation to express their auxiliary preferences in restructuring constructions with embedded unaccusatives. The L2 learners were shown not to know when auxiliary change is optional and when obligatory. Such findings are not consistent with the version of the Interface Hypothesis tested. Possible reasons for the incomplete acquisition of the phenomenon under scrutiny are discussed in the paper.