Movement was first postulated by structuralist linguists who expressed it in terms of discontinuous constituents or displacement.
Movement is the traditional means of explaining discontinuities such as wh-fronting, topicalization, extraposition, scrambling, inversion, and shifting:[3] The a-sentences show canonical word order, and the b-sentences illustrate the discontinuities that movement seeks to explain.
Movement is actually taken to be a process of copying the same constituent in different positions and deleting the phonological features in all but one case.
An analysis of subject-auxiliary inversion that acknowledges rightward movement can dispense with head movement entirely: The analysis shown in those sentences views the subject pronouns someone and she as moving rightward, instead of the auxiliary verbs moving leftward.
Since the pronouns lack dependents (they alone qualify as complete phrases), there would be no reason to assume head movement.
Called locality theory,[9] it is interested in discerning the islands and barriers to movement.
[10] The following tree illustrates the feature passing analysis of a wh-discontinuity in a dependency grammar.
[12] The assumption is that features (=information) associated with what (e.g. noun, direct object) are passed up and down along the catena marked in red.
By examining the nature of catenae like the one in red, the locality constraints on discontinuities can be identified.
In such theories, traces are considered real parts of syntactic structure, detectable in secondary effects they have on the syntax.