Very early parameter setting and the unique checking constraint: A new explanation of the optional infinitive stage

This paper argues that the traditional view of experience-dependent properties (learned properties) of language as developing late and non-experience-dependent properties as developing early is in fact often wrong. Parameters are set correctly very early (Very Early Parameter-Setting) and properties of inflectional items are also learned very early. On the other hand, some universal properties of language emerge later, presumably under a genetically-driven maturational program. The Optional Infinitive(OI) Stage (Wexler, 1990, 1992, 1994) of grammatical development is explained by the AGR/TNS Omission Model (ATOM) of Schütze and Wexler, (1996). This paper derives this model via a new proposal for a developmental constraint: the Unique Checking Constraint (UCC), which prevents a D-feature on DP from checking more than one D-feature on functional categories, thus forcing either AGR or TNS to be omitted. The Minimalist framework of Chomsky 1995 is assumed — in particular the assumption that a D-feature and not a case feature is the driving force for the Extended Projection Principle. With AGR and TNS both having a D-feature, UCC predicts that finite sentences will not converge. The model also predicts that subjects of OI's will raise to a higher functional projection, even when case is not assigned by INFL, thus solving a traditional problem in the theory of OI's. With natural assumptions on the nature of null-subject languages, the Null-Subjection/Optional Infinitive Correlation of Wexler (1996) is derived from the UCC — that OI's exist in early child language if and only if the adult grammar is not an INFL-licensed null-subject language. Thus the UCC is seen as a fundamental explanatory force for a range of phenomena in early child grammar. Moreover the child data provide strong evidence for the claim that a D-feature motivates the raising of the subject in UG, thus unifying child and adult grammar and demonstrating the usefulness of the investigation of child grammar in the study of UG.