Complementizer selection and the properties of complement clauses in German

Complement clauses in German can have a lexical complementizer when they are finite, but they must not have one when they are non-finite. I will argue that this distribution follows from the referential properties of the sentential complement. According to Grimshaw, only referential categories extend to functional projections. The status marker zu in German infinitival complements can be shown to block reference. Thus, non-finite complement clauses with zu do not project a left periphery and cannot host a complementizer.