The study considers the syntax of German infinitive constructions, with the concepts of subject potential (control/raising) and the coherence of dominating verbs being drawn upon as fundamental criteria for the investigation. After an introduction to the phenomena involved and a discussion of the seminal work done by Gunnar Bech on this topic, a formal analysis method for optional and obligatory coherence in various classes of verb (control verbs, semi modals, modals) is presented within the framework of a declarative grammar theory (HPSG - Head-driven Phrase Structure Grammar). The approach includes analysis of passivization and a discussion of the scope of nominal and verbal operators.