SYNTAX: element whose reference cannot usually be determined (but see anaphoric epithet) anaphorically in the sense of the binding theory and as such is distinguished from anaphors and pronominals. R-expressions are also distinguished from quantificational noun phrases and predicative NPs in that they must be in an A-position in LF. With respect to A-binding, variables - either wh-traces or traces of QR - count as R-expressions. R-expressions are not to be confused with referential expressions. With respect to binding theory, R-expressions obey condition C, which says that they must be A-free. This explains the illformedness of (ii) and (iii) (see Strong Crossover).
(ii) * hei thinks that Johni is a fool (iii) * whoi does hei like ti