Verb-final subject suffixes in Ngwi (West-Coastal Bantu B861, DRC): language-internal innovation or language-external imposition?

This chapter presents a preliminary analysis of the synchronic distribution and diachronic origins of subject suffixes in the West-Coastal Bantu language Ngwi (B861). We describe their present-day use in six different monoverbal affirmative future and past constructions and in one biverbal affirmative construction. Except for subject suffixes, which are highly unusual from a Bantu-centric perspective, monoverbal affirmative past and future constructions in Ngwi are significantly more conservative than aspectual constructions with present-time reference and prefixal subject indexes. Past morphology is inherited from Proto-Bantu, while future morphology is built on the past template with some innovative future-specific forms. In the biverbal affirmative construction, the subject index follows the erstwhile auxiliary, which is undergoing univerbation with the nominalized lexical verb. Even though they could presumably be a recent innovation, we are unable to identify a language-internal source construction from which subject suffixes could have originated in Ngwi. Hence, we speculate that this innovative feature may have a language-external source, possibly first-language imposition from shifters originally speaking a non-Bantu language with subject suffixes. Other features possibly diagnostic of substratum interference in Ngwi include phonemic interior vowels, diphthongization, heterosyllabic vowel sequences, final vowel loss, umlaut, a significantly reshuffled noun class system, and the rise of lability in noncausal/causal alternations.