This book investigates the systematic correspondences between syntactic structure and semantic interpretation in the domain of predicate-argument relationships. It takes as its starting point the striking effects of nominal argument interpretation on aspectual semantics, pursuing the intuition that these effects are not quirky or exceptional, but are in fact the most visible reflexes of a more pervasive and systematic interaction between the aspectual event structure of a predicate and its arguments. The Scottish Gaelic language is the empirical base of the investigation, as it exhibits a set of predicational structures which interact in a highly visible way with its aspectual system. The book provides a detailed working out of a semantic system of argument classification which moves away from lexically-driven thematic roles in the traditional sense and towards a more constrained, syntactically motivated, set of primitives.