Opacity condition

Opacity Condition is a condition which is in effect a reinterpretation of the Specified Subject Condition as a condition on anaphors (including NP-traces). It is the precursor of condition A of the binding theory. The Opacity Condition states that

(i) An anaphor cannot be free in the domain of the subject of beta, beta minimal (beta = NP, S')

Links
Utrecht Lexicon of Linguistics