Accepted by

This thesis examines certaln issues of tonal phonology within the theory of lexical phonology. Tonal ph~nomena require the enrich-ment of the lexical framework to include a post-lexical phonetic component. This component is shown to playa crucial role in account-ing for the array of phenomena known as downdrift/downstep. By separating phonological processes from phonetic processes, and by distinguishing between two classes of phonological processes-- namely, those that apply lexically and those that apply post-lexically-- we move towards an understanding of why particular tonal rules exhibit the properties that they do. For example, phonological constraints on autosegmental linkings may hold of rules applying lexically, but not of rules applying post-lexically-- or such constraints may hold of rules applying lexically and post-lexically, but not phonetically. The role of underspecification in tonal phonology is investigated