ABSTRACT
An abstract element in surface structure, which, as a phonologically empty category, syntactically represents the logical subject of an infinitive ( projection principle). Infinitival clauses are treated as whole sentences on the basis of the abstract representation of the subject by PRO ( complementizer). In contrast to the empty category marked by pro, the PRO element is always ungoverned, i.e. it occupies a position which no case-bearing NP could occupy. The distribution and semantic content of PRO is governed by the theory of control.
