The overarching goal of this dissertation is to advance our understanding of linguistic tone and the role it plays in the organization of morphological systems. This topic is explored through a typological study, a case study, and a comparative study.
The first study presents a typology of tonal exponence, couched within an Abstractive Word-and-Paradigm approach to morphology. It builds on previous studies on exponence typology by extending it to the study of tone, and explores deviations from form-function isomorphism, polyfunctionality, morphomic distributions, paradigmatic layers, and inflectional class organization. It is argued that the attested diversity of form-function mappings constitutes an empirical argument for a paradigm-based view of morphology, where the range of encoding strategies are treated as equivalent, as opposed to choosing form-function isomorphism as the theoretical ‘ideal’.
The second study contributes to the documentation of tone and morphology in Tira (Heiban; Sudan), a previously understudied language. It is shown how tonal and non-tonal exponents interact in distinguishing verb forms in Tira. The system exhibits complexity of exponence in the sense that there is non-isomorphism between form and function; the meaning of the verb forms is distributed across different markers. It is argued that to understand the nature of the system, both the syntagmatic and the paradigmatic dimension need to be addressed, and an analysis is proposed by identifying a set of implicative relations, zones of interpredictability, and principal parts.
The third study is a comparative morphological study of the West Heiban languages Tira and Moro. It presents novel data illustrating subject and object marking on verbs in Tira and compares this to previously published works on Moro and the Central Heiban languages. Based on similarities and differences across the verb systems, Moro is argued to be innovative in several areas, and a series of diachronic developments are proposed to account for these facts. It is proposed that Moro has undergone a tonally conditioned constructional change whereby prefixed object markers became suffixes in verb forms associated with a specific tone pattern. This shows that tone may play an active role in language change and contribute to the reorganization of constructions.
