Bi-Unique Relations and the Maturation of Grammatical Principles

The purpose of this paper is to argue for a maturational schedule in language development involving the gradual reformulation of UG-determined biunique relations. We investigate an early stage (about 2;0) in child Italian which shows object agreement with a participle for lexical objects, a phenomenon not attested in standard adult Italian. We provide an analysis for participle agreement in adult Italian, based on Spec-Head agreement. We then argue that the child analyzes participle phrases with direct objects as APs, rather than as transitive VPs, resulting in an extension of Spec-Head agreement to the relations between the participle and its object. This error on the part of the child, we argue, derives from the existence in the child's grammar of the maturationally-determined Unique External Argument Proto Principle (UEAPP), requiring every predicative element to have its own unique subject. Independent evidence for UEAPP is provided by the confirmed prediction that children in the object agreement stage do not use unergative verbs in the passato prossimo. Additional evidence from early Polish further confirms our analysis, and we further show that the null subject stage in child language follows from UEAPP. We conclude by outlining the maturational schedule we propose.