The formal syntax for licensing parenthetical verb clauses

This study examines the formal syntax (distributional, configurational and computational properties) of parenthetical verb clauses (henceforth PVCs) in Moroccan Arabic (henceforth MA), which include a first-person subject (denoting speaker) and a cognitive verb such as: think, believe, suppose, guess. These are a sub-set of the speaker-oriented parentheticals of Reinhart (1983), and they denote the attitudes and the point of view of the speaker regarding the validity of the proposition expressed in the host structure they attach to. The examination and analysis of the distributional properties of PVCs provides new empirical insights into the constraints that are at play in licensing the clausal attachment of PVCs to their host structures. It shows that the occurrence of PVCs in the clausal structure of MA is disallowed in 21 types of syntactic contexts, and that the seemingly free distribution of PVCs is not actually free. PVCs' clausal attachment is shown to be a main clause phenomenon that is sensitive to the clausal makeup of the left periphery in the host structure, more specifically to the availability of an aboutness TopicP functional projection and a realis assertion ForceP functional projection. This configurational constraint is further reduced to an Agree-based feature-valuing computational requirement for the licensing of PVCs. I propose an Agree-based unifying account that derives the TopicP and the ForceP constraints from an underlying syntax-discourse interface constraint, viz., a constraint on how a PVC is required to have its unvalued discourse features Agree-valued by TopicP and ForceP functional projections in the host structure. I supply two sets of empirical evidence to support this unifying account. The first set of evidence draws on the selective (in)sensitivity of the clausal attachment of the PVC to the realization of different types of topic NPs in the left periphery of the host structure. The second set of evidence draws on the dependency between the force of the PVC and the matrix clause. This approach is shown to be able to account, with zero stipulations, for the fact that indexical shifting is blocked in the presence of a PVC structure.