In this study, the problem of non-uniqueness in phonology is reviewed against the more recently developed notions of 'simplicity metric' and 'partially specified matrices' within the distinctive feature framework. The discussions center around the well-known case of the indeterminate phonemicization of the Mandarin palatalized obstruent series [t□, t□', □]. As an application of the new notions to the Mandarin data appears to yield different results, it seems warranted to conclude that the problem of non-uniqueness in phonology, as first observed by Chao, still remains unresolved.