Parasitic gap

Parasitic gap is an empty category which is licensed by the occurrence of another empty category in the sentence. Thus in a sentence like

(i) which books did you file t without reading e

the operator which is interpreted not only as binder of the direct object t of file, but also as licenser of the direct object e of reading. Evidence that the gap in the adjunct clause is really 'parasitic', i.e. that we do not have something like a 'double trace' configuration, is provided by the pair of sentences in (ii) and (iii) (Kearney (1983), cited in Chomsky 1986b).

(ii)   which books about himself did John file t [before Mary read e] (iii) *	which books about herself did John file t [before Mary read e]

Since a moved wh-phrase can be interpreted as if it were in its base-position (see reconstruction), an anaphor in it may be bound as if it were in the wh-phrase's base-position. From the fact that the anaphor in these examples can only be bound by the subject of the matrix clause (John) and not by the subject of the adjunct clause (Mary), we can conclude that the wh-phrase can only have been moved from t, not from e. Also see operator movement, chain composition, empty operator.

Links
Utrecht Lexicon of Linguistics

Other languages
German parasitäre Lücke, Schmarotzerlücke