This article discusses the effects of variation in the meaning of property concept (PC) lexemes (Dixon 1982) on the form of predicative and comparative constructions. We demonstrate the existence of two kinds of PC lexeme, which differ systematically in how they participate in constructions expressing the truth conditions of PC predication. The first kind of lexeme is used in canonical predicative constructions, the other in predicative constructions that invoke possessive morphology or syntax. The differences between the two classes are observable both within a single language and crosslinguistically. The article argues that the morphosyntactic differences in the behavior of the two lexeme types are predictable from their lexical semantics. Specifically, we argue that some PC lexemes denote mass substances (in a technical sense) and therefore require possessive semantics to achieve the relevant truth conditions. A semantic theory for substance-denoting lexemes is developed, and a compositional analysis of the relevant constructions is presented for Ulwa, an endangered Misumalpan language of Nicaragua. We argue that assuming semantic variation is necessary, since the observed generalizations cannot be captured by extending existing semantic analyses of gradable adjectives to all PC lexemes.