In Western Armenian, verbs obligatorily contain a root, one of three theme vowels, and an inflectional suffix. Theme vowels are ornamental morphs whose presence and quality are determined jointly by the root, the verbalizer v, and Voice. The choice of theme vowel is partly governed by transitivity but also shows arbitrariness, which is root-conditioned. The appearance of theme vowels correlates with the presence of verbal semantics and morphosyntactic structure, including Voice. Data from lexical causatives and from subordinate compounds show that theme vowels cannot be identified either with verbalizers or with Voice, but their information is distributed among both of these and the root.