The present study, using Japanese and Ryukyuan verbal morphology as its primary database, argues that evidence from the syntactic branch of the grammar and evidence from the phonological branch of the grammar converge on the conclusion that, while inflectional morphology is fully syntactic, derivational morphology has properties that militate against a syntactic treatment. The boundary between grammar and lexicon, then, falls at the boundary between inflection and derivation, rendering morphology “split” between syntactic and nonsyntactic subparts.