I. Introduction II. The Semantic Properties of PRO III. Previous Approaches to Control 2.1. Movement Approaches to Control (Chomsky (2000, 2001), Radford (2004)), and others) 2.2. A Deletion Approach to Control (Kim 2010) IV. Problems 4.1. Implicit Arguments 4.2. Event Control and Ambiguous Control V. The Linking Theory as an Alternative VI. Controllers and Thematic Roles VII. Conclusion