On the productivity of length-based alternations in Xhosa noun class prefixes

Noun classes in isiXhosa are each associated with specific prefixes on the noun stem. Some of these noun class prefixes exhibit length-based allomorphy: they take one form before multisyllabic stems and a different, longer form before stems that are monosyllabic. Specifically, classes 5 and 11 alternate between V- and VlV- shapes, and class 10 alternates between iin- and izin-. We use a wug test paradigm to test whether speakers apply these alternations productively in unfamiliar nonce words. We compare the results of several experiments, including both in-person and web-based tasks. Experiment results suggest that on the whole the prefix alternations are productive and therefore must be factored in to the synchronic (morpho)phonology of Xhosa. At the same time, not all speakers apply the alternations to wug items with 100% systematicity; rates of alternation vary by speaker, are different across online vs in-person tasks, are different for different noun class pairs and are sensitive to the ‘direction’ of the task (i.e. forming plurals vs forming singulars). This variability, in tandem with the existence of exceptional counter-examples, suggests that the pattern contains some inherent gradience or noise. Surprisingly, our experiments reveal an unexpected systematicity in the treatment of words that are inferred to be names. Altogether, these results contribute to growing our understanding of noun class systems in Bantu languages, including how they are represented in the mental grammar and how they are psycholinguistically processed.