This thesis is a study of clause architecture within a theory of generative grammar. It discusses four major syntactic hypotheses that have crucial bearing on the design of phrase structure: the Agreement-based Case theory, the internal subject hypothesis , the uniform three-level X-bar theory, and a hypothesis about string vacuous head movement. ;After the introductory chapter, Chapter 2 through Chapter 4 discuss object positions in three typologically and genetically different languages, i.e. English, Zarma, and Japanese. It is argued that they (...) all possess Agreement Phrases for objects . A consideration of learnability suggests that the presence of AGRoP in these languages, particularly in Japanese, is not learnable from the data available to children. Thus, it is highly likely that UG is so construed that every language has AGR . ;Chapter 5 turns to subject positions. There is conflicting evidence regarding the base-position of the external argument. Some data indicate that the external argument originates in a position lower than its surface position. Other data suggest that its base-position is outside AGRoP which dominates the main verb and the internal arguments. If the ISH is correct in that all arguments of a predicate category originate within the maximal projection of this category, then the apparently contradicting data suggest that there are two verbs, hence two VPs, in a single clause . One verb is above AGRoP, and the other is below AGRoP. The so-called external argument is an argument of the upper V, and "internal arguments" are arguments of the lower V. ;Chapter 6 is concerned with X-bar theory. It is argued, contrary to the wide held view, that some functional categories allow more than one specifier position within their projections , and that the X-bar schema as such is not a part of Universal Grammar. ;Chapter 7 discusses string vacuous verb raising in head final languages. In particular, evidence is presented for overt verb raising in Japanese. Its consequences are also explored to various aspects of syntactic theory. (shrink)