The aim of this essay is to present a phonological analysis of Lushai, a Tibeto-Burman language spoken in the Mizoram province of India, in terms of componential features applying as mutation rules to the morphophonological level. An analysis of this nature becomes possible if the concepts of phonological extension systems and redundancy-free representations are introduced. Alongside with the phonemic aspect, a semantic analysis of morpheme structure is required yielding the smallest significant units at different morphological or syntactic levels. Though based on criteria implying concepts like rule, underlying representation, and so forth, of the standard theory of generative phonology, this essay tries to implement the concepts of phoneme on the phonemic, and of morphophoneme on the morphophonological levels, and to bring about a methodologically sound classification of phonological rules.