A study of Emai, an Edoid language of south-central Nigeria, focuses on the system of constraints governing tonal processes. Specifically, it examines the ways in which general processes of low tone raising and high tone lowering are realized in domains constructed by verbs and by preverbal auxiliary and adverbial constituents. Sequentially ordered in some environments, these processes are constrained on one hand by expression of aspectual and polarity categories, ultimately making tonal pattern dependent on an agreement category preceding the verb, and on the other hand, by an inflectional category incorporating deontic modality particles and the imperative mood. For each of these processes, the operational syntactic domains and positions of application are examined. Domains range from the verb phrase itself to the inflectional preverbal phrase within which syllabically-defined constituents also become relevant. The study concludes by postulating a single category underlying deontic modality and imperative constructions. The underlying notion is that Emai facts can be accounted for by positing rules of maximal generality and then factoring them into domains of varying syntactic complexity. Contains nine references. (MSE)