pro-constituent (n.)

A term used in later GENERATIVE LINGUISTICS, usually abbreviated to PRO, and analogous to PRO-FORM in other approaches, referring to an ELEMENT which SUBSTITUTES for a LEXICAL item elsewhere in a SENTENCE. The application of the term varies, depending on the grammatical MODEL involved. In GOVERNMENT-BINDING THEORY, for example, the symbol PRO is associated with a BASE-generated SUBJECT of certain INFINITIVES.