Plural reference dominance, markedness and semantic categorization in Hiaki pluralia tantum

We provide a description and analysis of “pluralia tantum” (PT) nouns in the Southern Uto-Aztecan language Hiaki (Yaqui, Yoeme, YAQ ISO 639-3). We find that these nouns, which require plural morphosyntactic marking regardless of notional number, fall into several semantic categories. We then model the behavior of number marking in Hiaki using a Distributed Morphology framework. We analyze apparent mismatches in the agreement system that prima facie appear problematic for Corbett’s (2019) Agreement Hierarchy. We propose that they result from a distinction between purely morphological ‘Concord’ features on the noun that can be independent from semantically conditioned ‘Index’ features, taking the Concord/Index distinction from Wechsler and Zlatić (2000, 2003). Index features determine choice of suppletive verbal form, while Concord features control nominal number marking, adjectival and determiner number marking, and the form of anaphoric pronominals. The conclusion is that number-conditioned verbal suppletion is distinct from true verbal agreement. We conclude by discussing whether a frequentist account of the emergence of individual PT nouns might apply in the Hiaki case, i.e. whether plural-reference dominance in these semantic categories might have driven grammaticization of the nominal as a PT noun, and argue against this possibility.