[Part III. Interactions between segments and features, Acoustic and aerodynamic factors in the interaction of features]
This paper presents an account of the physical factors responsible for crosslinguistically common patterns of co-occurrence between values of the features [voice] and [nasal]. Specifically, it offers explanations for why nasals are typically voiced and why voiced obstruents are often accompanied by nasalization, or in terms of features, why [+voice] and [+nasal] co-occur so often and in such a variety of ways. First, it addresses the <i>acoustic-auditory</i> factors responsible for glottal vibration favoring the perceptibility of nasalization. Second, it examines the <i>aerodynamic</i> factors responsible for nasality facilitating glottal vibration. In particular, it suggests that nasal leakage is a maneuver to facilitate voicing in the stop and to preserve the voicing contrast. The paper also argues that if the interaction between the two features can be explained by phonetic principles, then there is no need to encode the patterns of co-occurrence as redundancy rules or constraints in universal grammar. Furthermore, phonological representations that assign the nasal valve and the larynx to separate nodes cannot capture the interaction between nasality and voicing and the co-occurrence patterns.