This dissertation contributes to the growing tradition of work in which detailed exploration of understudied languages informs formal semantic and syntactic theory and probes the tension between crosslinguistic grammatical variation and crosslinguistic commonality in communicative goals. The dissertation focuses on two topics in Navajo (Diné Bizaad): (i) attitudes of 'thinking' and 'desiring' and (ii) the expression of adjectival meaning and degree constructions. The first part of the dissertation presents the methodological and linguistic background for the rest of the dissertation. Chapter 1 discusses the project of crosslinguistic semantic research and fieldwork methodology. Chapter 2 gives a broad introduction to the Navajo language and the literature which has explored it. The second part of the dissertation focuses on the expression of attitudes in Navajo. Chapter 3 presents an empirically rich description of the morphological, syntactic, and semantic characteristics of Navajo sentences that report distinct attitudes of 'thinking' and 'desiring' despite containing the same attitude verb, nisin Chapter 4 argues that the meaning of the embedded clause --- not nisin --- determines what attitude is reported. The exploration of Navajo is guided by investigation of English and German attitude reports begun by Kratzer (2006, 2013a) and developed by Moulton (2009, 2015). These authors develop a fully compositional account that presents an alternative to familiar verb-driven analyses of attitude reports; in their account, key aspects of the semantics of attitude reports come from material in the embedded clause. It is argued here that Navajo is a limiting case within the empirical landscape explored by Kratzer and Moulton, in which the attitude verb only determines the attitude holder. The third part of the dissertation (Chapter 5) builds on work published as Bogal-Allbritten (2013) and investigates the syntax and semantics of Navajo adjectival expressions and degree constructions, e.g. comparative and equative constructions. Chapter 5 argues that while all Navajo adjectival expressions have the same semantic type, their syntactic structure differs depending on the morphology they bear. The proposed syntactic heterogeneity explains differences in degree constructions which contain adjectival expressions of different morphological shapes.