Abstract In language acquisition, children assume that syntax and semantics reliably map onto each other, and they use these mappings to guide their inferences about novel word meanings: For instance, at the lexical level, nouns should name objects and verbs name events, and at the clausal level, syntactic arguments should match semantic roles. This review focuses on two cases where canonical mappings are broken—first, nouns that name event concepts (e.g., “a nap”) and second, light verb constructions that do not neatly map syntactic arguments onto semantic roles (e.g., “give a kiss”). We discuss the challenges involved in their acquisition, review evidence that suggests a close connection between them, and highlight outstanding questions.