The study of complementation has received considerable attention in generative studies. Following Rosenbaum's (1967) pioneering study of the English complement system, there are extensive studies by Lakoff (1965), Ross (1967), Perlmutter (1971) and a large number of publications. More recent detailed studies are Emonds (1970) and Bresnan (1972) . These studies have increased enormously the body of factual knowledge about the complement system of English, and about the phenomenon of complementation in general. As a consequence there are a number of empirical hypotheses about the structure of human languages which must now be tested against facts of different languages. Of these hypotheses, perhaps the most interesting is that the grammars of all languages make use of the principle of the transformational cycle. Testing this hypothesis constitutes one of the main concerns of the present book. Furthermore, these studies have also raised numerous interesting empirical issues of great importance for linguistic theory, most of which are still awaiting fresh evidence from different languages in order to be settled. This study is directed towards resolving some of these issues by adducing relevent data, primarily from Portuguese.