Agree, agreement dissociation and subject ellipsis. Towards a new characterization of the Null Subject Parameter

Abstract This paper offers a new characterization of the Null Subject Parameter (NSP). I contend that the NSP must be modeled referring to two main properties of the Agree /agreement systems: (i) presence/absence of abstract Agree , and (ii) presence/absence of agreement dissociation at PF. The first property results in the division between radical argument ellipsis languages of the Japanese type and consistent null subject languages of the Spanish type, including languages like Central Trentino, i.e., languages with some obligatory clitic subjects but with rich agreement and free inversion. The second property results in the division between consistent null subject languages and consistent non-null subject ones. The agreement dissociation hypothesis also accounts for the partial null subject type, which characterizes languages like Brazilian Portuguese that have impoverished agreement expansion at PF (perhaps, only for number features). From a theoretical point of view, this study focuses on the agreement dissociation property showing why abstract Agree cannot guarantee subject ellipsis even in those perplexing cases in which it produces enough agreement distinctions at PF. The reason is that only an expanded agreement morpheme adjoined to the T 0 node can serve as a licit antecedent for ellipsis of a subject D 0 head at PF. Therefore, the theory derives the bimorphemic principle in Koeneman and Zeijlstra (Koeneman, Olaf & Hedde Zeijlstra. 2021. Pro-drop and the morphological structure of inflection. Ms. Available at: https://www.heddezeijlstra.org/bio ) without further ado, i.e., the observation that null subject properties correlate with a bimorphemic T 0 node expressing tense and agreement separately.