This Study investigates the syntax of complement and relative clauses in English which lack overt complementizers (clauses without that). The central analytical claim is that these clauses differ in phrase structure from their synonymous counterparts with overt complementizers. In particular, novel evidence from adjunction facts is used to demonstrate that clauses without that are more appropriately analyzed as bare sentences of the category IP rather than CP with a phonologically null head, a proposal which has since been adopted in many economy-driven approaches to phrase structure. This book will be of interest to a broad variety of readers: scholars working in all areas of generative syntax, specialists in English and Germanic syntax, in addition to researchers in non-standard English and Hiberno-English.