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head movement

SYNTAX: movement of a head, an X0, out of its projection to another head-position. EXAMPLE: in questions a finite verb may move to C0. In (i) the auxiliary will (an I, see INFL) is moved to C0, leaving a trace in I.

(i) [CP What [C willi] [IP John [I ti] buy]]?
Head movement obeys the Head Movement Constraint.
LIT. Chomsky, N. (1986b)
Rizzi, L. (1990)