On the basis of five case studies from languages of the American Pacific Northwest, we argue that, at least in the areas of syntax and semantics, a scientific approach to the study of linguistic diversity must be empirically grounded in theoretically informed, hypothesis-driven fieldwork on individual languages. This runs counter to recent high-profile claims that large-scale typology based on the sampling of descriptive grammars yields superior results. We show that only a hypothesis-driven approach makes falsifiable predictions, and only a methodology that yields negative as well as positive evidence can effectively test those predictions. Targeted elicitation is particularly important for languages with a small number of speakers, where statistical analysis of large-scale corpora is impossible. Given that a large proportion of the world’s linguistic diversity is found in such languages, we conclude that formal, hypothesis-driven fieldwork constitutes the best way rapidly and efficiently to document the world’s remaining syntactic and semantic diversity.