Acquisition of Object Clitics in Child Polish: Evidence for D-Linking Marta Tryzna American University of the Middle East 1 Introduction Following Wexler, Gavarr´ o & Torrens (2003), two patterns of object clitic acquisition in child language have been identified, based on the presence of clitic-past participle agreement in a given language. Languages with object clitic-past participle agreement (Catalan, French, Italian) involve a clitic omission stage (Schaeffer 2000, Wexler, Gavarr´o, & Torrens 2003), while languages without clitic-past participle agreement (Spanish, Greek) are characterized by early object clitics in child grammar (Wexler, Gavarr´ o & Torrens 2003, Tsakali & Wexler 2003). Due to the observed split, Wexler et al. (2003) hypothesized that clitic production in child grammar is regulated by the Unique Checking Constraint (UCC), which prevents the D-feature on the DP from being checked twice. The UCC, initially proposed to account for Root Infinitives (i.e. non-finite forms used as main verbs) in child language, works as follows. First, based on the Minimalist Pro- gram (Chomsky 1995), syntactic operations such as argument DP movement are motivated by feature checking. Upward movement of a DP can be triggered by the need to check features which are associated with certain functional projections. One such feature is the D(eterminer)-feature associated with both the DP and functional projections. In particu- lar, if the D-feature is [-Interpretable], it is checked once and subsequently deleted, while a [+Interpretable] D-feature does not get checked and remains in the derivation until LF. A [-Interpretable] feature cannot remain unchecked, as this would cause the derivation to crash, which explains why in adult syntax the uninterpretable features in all functional projections must be checked. Second, the UCC stipulates that, in child syntax, the D-feature of a DP can only check against one functional category (hence unique checking). Thus, if a derivation contains more than one functional projection with a [-Interpretable] D-feature, for example tense (TNS) and subject agreement (AGRS), in adult grammar the subject DP must raise to check off against the D-features of both TNS and AGRS. This operation requires two instances of checking, which are problematic for a child, as stipulated by the UCC. In order to prevent the derivation from crashing (i.e. no unchecked uninterpretable features in the derivation), a particular functional projection (either TNS or AGR) is deleted from the representation. LSO Working Papers in Linguistics 8: 71-84. Proceedings of WIGL 2010. 71