"Argument Structure" is a contribution to linguistics at the interface between lexical syntax and lexical semantics. It formulates an original and highly predictive theory of argument structure that accounts for a large number of syntactic phenomena, and it should interest linguists who focus on the nature and form of linguistic representation as well as psychologists who study the acquisition and use of language. The main analytical focus is on passives, nominals, psychological predicates, and the theory of external arguments. Grimshaw suggests that, contrary to the prevailing view, argument structure is in fact structured: it encodes prominence relations among arguments that reflect both their thematic and their aspectual properties. The prominence relations support a new theory of external arguments with far-reaching consequences for the syntactic behaviour of predicates and the nature of cross-categorical variation in argument structure.