Natural and unnatural patterns of sound change?

Sound changes that occur in different languages have been considered more natural than those that do not. Because natural sound changes have been shown to have a phonetic basis, less common outcomes in the exact same context have been considered phonetically anomalous. This paper argues that sound changes that appear to be very different from one another, even opposite, may arise from small variations in the magnitude or coordination of consecutive segments, and from adjustments operating along different dimensions directed to achieve the same functional goal. This argument is supported by experimental evidence on (i) fricative weakening and epenthetic stops in fricative-nasal sequences, (ii) postnasal voicing and devoicing, and (iii) adjustments of different articulatory parameters (e.g., velic leakage, larynx lowering, tongue body lowering) to facilitate sustaining voicing during a stop closure. The data suggest that small differences in the way languages implement their target sounds may give rise to qualitatively different patterns, but the same phonetic principles may be used to explain both common and less common patterns of change.