Directionality of Disyllabic Tone Sandhi across Chinese Dialects is Conditioned by Phonetically-Grounded Structural Simplicity

Despite various work which aimed to identify the phonetic and structural underpinning of tone sandhi directionality, the underlying mechanism that governs tone sandhi remains unknown. We note that the two widely discussed properties of tone sandhi, their phonetic grounds and directionality, correspond to two types of cognitive biases widely investigated in segmental phonology, namely substantive bias and structural bias respectively. This study examines structural simplicity and phonetic naturalness of tone sandhi patterns across seventeen Chinese varieties. Based on a structure-based analysis, we show that tone sandhi patterns are overwhelmingly uni-directional (i.e. structurally simple) either throughout a sandhi system or within each grammatical category. Crucially, uni-directionality is largely right-dominant, which could be attributed to its phonetic grounding. We argue that structural simplicity grounded on phonetic substance better captures tone sandhi asymmetries and such phonetically-grounded structural simplicity bias is reflected in the asymmetries of Chinese tone sandhi directionality.