Abstract
This dissertation investigates the nature of tone sandhi by focusing on the issue of unpredictable tone sandhi operation directionalities that has being attracting much attention lately. Based on data of five Chinese dialects, including Tianjin, Boshan, Sixian-Hakka, Chengdu and Beijing Mandarin, and the Kuki-Chin language of Hakha-Lai, an intriguing correlation between tone sandhi operation directionalities and normal vs. misapplications is found. In the tone sandhi patterns that are direction-sensitive, target-to-trigger rule application directionality would produce misapplication outputs (outputs with tonal changes that are not properly conditioned (i.e., overapplication) or failure of tonal changes when properly conditioned (i.e., underapplication)), while trigger-to-target directionality would produce outputs of normal application (outputs with tonal changes that are properly conditioned). It is argued in this dissertation that over- and underapplications in tone sandhi, like those observed in reduplications and paradigms, are identity effects. They are forced by the desire for a tonal output to be more like a tonal base it prosodically relates to. The desire to achieve identity (captured by the output-to-output correspondence constraint) forces tone sandhi to operate in the target-to-trigger direction, leading to misapplications. Prosodically related outputs would however sometimes fail to correspond. If preserving identity would produce forms that contain highly marked sequences (captured by the markedness constraints) or forms that involve tonal changes taking place at the prominent position (captured by the positional faithfulness constraint), the desire for identity would be sacrificed. In that case, tone sandhi operates in the reverse direction and the resultant outputs are those of normal application. Thus, the directionalities are predictable through the interactions of the markedness constraint/positional faithfulness constraint and the output-to-output correspondence constraints, where the markedness constraint/positional faithfulness constraint must dominate the output-to-output correspondence constraint. The investigation of the issue of directionality discloses an important feature of tone sandhi. In tone sandhi, identity preservation between prosodically related outputs is important. The output-to-output correspondence relation may force a tonal output to deviate from the canonical surface patterns of the language, so that it becomes more like a tonal base to which it prosodically relates. Identity preservation is highly respected in tone sandhi, unless this would produce forms that are highly marked or forms that involve tonal changes in the wrong position.