Based on an exhaustive search of published sources and the author's firsthand fieldwork, Concreteness in Grammar explores the role of phonological form in the noun class systems of the Arapesh languages spoken in Papua New Guinea. Linguists have long known that from plays a critical role alongside semantics in the classification of lexical items. In Arapesh, virtually every possible final ending of a noun is represented in the paradigm of noun class and agreement markers, reflecting an interpenetration of sound structure and grammar that many would disallow as wildly unconstrained. In this book, Lise Dobrin describes these formal patterns in order to reveal their naturalness and elegance, establishing their place in a typology of noun class systems and drawing out their significance for theories of grammatical architecture. A rigorous study of an endangered language, Concreteness in Grammar revisits the definition of a morpheme and looks at unusual language patterns to reveal the naturalness of grammar.