The features of the larynx: N-ary or binary?

Multivalued features have generally not been permitted on the classificatory level of representation by generative phonologists. It is found necessary, however, to posit a multivalued scalar feature "glottal width" on the classificatory level of representation in order to provide a satisfactory explanation of the diachronic tone splits conditioned by the phonation type of the syllable-initial consonants among the languages and dialects of the Tai language family in Southeast Asia. The feature "glottal width" consists of a lineraly ordered set of terms along a single physical continuum that extends from the widest open position of the glottis to the fully closed position (i.e. glottal stop). Other proposed sets of laryngeal features are tested against this evidence and found to be inadequate. A binary feature "vibrating" is also proposed within this theoretical framework.