island (n.)

A term originally used in TRANSFORMATIONAL GRAMMAR to refer to a structure out of which CONSTITUENTS cannot be moved by any MOVEMENT RULE; more generally, a constituent across whose boundary certain relations between two ELEMENTS cannot be held. For example, the constituents of a RELATIVE CLAUSE cannot be moved out of the clause: in the sentence I saw the person who bought my car, the relative-clause constituents cannot be moved to other positions in the sentence without producing an unacceptable sentence (e.g. *What did I see the person who brought?). Other structures which may have been proposed as islands are NOUN-COMPLEMENT clauses (e.g. The fact that Mary was angry surprised me), SUBJECT noun clauses (e.g. What she told me was this), co-ordinate structures (e.g. I saw Jules and Jim), DEFINITE NPs (e.g. I read the story about Jim), ADJUNCT phrases (e.g. I read the book after she wrote the book), and constructions to which the A-OVER-A principle applies. The island condition in X-BAR SYNTAX asserts that constituents can be extracted out of complement phrases, but not out of subject/ADJUNCT phrases (the CONDITION ON EXTRACTION DOMAIN).