This project investigates the grammatical properties of two genetically unrelated indigenous languages spoken in the southwest. Due to contact over hundreds of years the languages share grammatical features, in particular, complex morphological process (that is, the way that words are formed), especially when talking about pluralities of individuals or events. These grammatical features are only rarely found in human languages. Understanding these processes will thus allow fundamental contributions to language sciences. By studying how words are formed in these languages, and through this complex case, the project will sharpen linguistic and psychological theories of word formation, as well as how words are processed and stored in the brain. Additionally, the project provides educational opportunities for graduate students and post-doctoral researchers to train in field linguistics, language documentation, and language revitalization. The two languages mark plurality, pluractionality, and plural agreement using complex morphological systems that are typologically rare, and which provide an ideal opportunity for studying the semantics-morphology interface. After documenting these systems, the research team will use the resulting data to make the following fundamental contributions to language science: (i) draw bounds on how semantic composition works below the level of the word; (ii) sharpen morphological theories of the paradigm; (iii) compare competing theories of suppletion; and (iv) consider the implications for how complex morphological systems diffuse areally. These questions will be investigated through elicitation, both structured and semi-structured, over a three-year period. The result will be the richest set of data on plurality and pluractionality for this linguistic region and will allow researchers around the world to investigate novel questions about how words work in human languages. Concrete results of the project include research publications, as well as a publicly shared corpus with semantic and morphological annotations. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.