Wh-movement as copying and deletion

we make the implicit assumption that a moving head (e.g Similarly to how an inverted auxiliary) leaves a null copy of itself in the position from which it moves, a moved wh-expression leaves a copy at its extraction site (that is, in the position from which it is extracted extracted/moved). Previously, throughout the 1970s and 1980s, it was thought that moving constituents left a trail traces in the positions from which they move (informally denoted as t), and traces of nominally moved in certain ways, constituents were compared to pronouns the highest component of the chain (i.e. the moved constituent) was said to be the head of the movement chain, and the lowest member was considered to be the foot of the movement chain A trace is considered a full copy (rather than a pronominal copy) of a moved element in Chomsky's more modern copy theory of movement. Informally, however, the null copies left behind by movement will be referred to as traces or trace copies in later sections and chapters.