Traditional approaches to verbal periphrasis (compound tenses) treat auxiliary verbs as lexical items that enter syntactic derivation like any other lexical item, via Selection/Merge. An alternative view is that auxiliary verbs are inserted into a previously built structure (e.g., Bach 1967, Arregi 2000, Embick 2000, Cowper 2010, Bjorkman 2011, Arregi and Klecha 2015). Arguments for the insertion approach include auxiliaries’ last-resort distribution and the fact that, in many languages, auxiliaries are not systematically associated with a given inflectional category (Bjorkman’s (2011) “overflow” distribution). Here, I argue against the insertion approach. I demonstrate that the overflow pattern and last-resort distribution follow from Cyclic Selection (Pietraszko 2017)—a Merge counterpart of Cyclic Agree (Béjar and Rezac 2009). I also show that the insertion approach makes wrong predictions about compound tenses in Swahili, a language with overflow periphrasis. Under my approach, an auxiliary verb is a verbal head externally merged as a specifier of a functional head, such as T. It then undergoes m-merger with that head, instantiating an External-Merge version of Matushansky’s (2006) conception of head movement.
We propose a theory of head displacement that replaces traditional Head Movement and Lowering with a single syntactic operation of Generalized Head Movement. We argue that upward and downward head displacement have the same syntactic properties: cyclicity, Mirror Principle effects, feeding upward head displacement, and being blocked in the same syntactic configurations. We also study the interaction of head displacement and other syntactic operations, arguing that claimed differences between upward and downward displacement are either spurious or follow directly from our account. Finally, we show that our theory correctly predicts the attested crosslinguistic variation in verb and inflection doubling in predicate clefts.