The purpose clause is a common kind of adverbial modifier in English. In this book, the standard unbounded-dependency theory of constructions like purpose clauses, outlined within Noam Chomsky's Government and Binding theory (GB), is contrasted with an alternative theoretical characterization of them, worked out within Edwin Williams GB-related theory of thematic roles and argument structure. The central proposal of the alternative theory is that purpose clauses are essentially nonclausal in contrast to the standard fully-clausal analysis. The abundant special properties of purpose clauses, extensively presented and described here, sharply illuminate many of the fundamental assumptions, and limitations of several GB-sub-theories. Among the topics considered are the argument adjunct distinction, the generality of syntactic movement, locality restrictions on filler-gap dependencies, tough-movement, the semantic content of thematic roles, and the quantificational nature and semantics of Control.