Introduction

In Unit 2, we introduced the phenomena of alternation, which are illustrated mainly by alternations that involve segmental changes. Recall that alternations are the patterns that result from morpheme concatenation such as affixation, compounding, or reduplication. We demonstrated that the phonetic form of a morpheme, whether it is a root, stem, or an affix, can change or alternate, depending on the morpheme(s) it comes in contact with. Such changes generate the alternations where a single morpheme has two or more distinct phonetic forms or pronunciations. We continue the study of tone in this chapter, showing that tones of a morpheme can alternate as a result of morphological processes as well. Just like segmental alternations, tonal changes can manifest in the root, stem, or affix. Moreover, just as segmental alternations may be related to the distributional restrictions on segments, tonal alternation and distribution may be caused by identical constraints. For this reason, we continue to focus on the data from Mende to see whether there is any relation between its tonal distribution and alternation.

The tonal alternation data come from poly-morphemic nouns in Mende. They exhibit a number of tonal changes affecting the roots and the suffixes. We show that some of these changes can be traced back to the distributional restrictions on tone discussed in Chapter 13. The alternation data shed light on the debate regarding the segmental versus autosegmental view of tone. We demonstrate that neither view at the extreme is correct. Though some relations between tones and TBUs (tone-bearing units) are unpredictable and consistent with the segmental view, there exist predictable relations between tones and TBUs. Consequently, tones may be unlinked or floating in underlying representation and the mapping of tones to TBUs can be accomplished by rules, as advocated by the autosegmental analysis.