Deep structure and surface structure (also D-structure and S-structure although those abbreviated forms are sometimes used with distinct meanings) are concepts used in linguistics, specifically in the study of syntax in the Chomskyan tradition of transformational generative grammar.
The deep structure of a linguistic expression is a theoretical construct that seeks to unify several related structures. For example, the sentences "Pat loves Chris" and "Chris is loved by Pat" mean roughly the same thing and use similar words. Some linguists, Chomsky in particular, have tried to account for this similarity by positing that these two sentences are distinct surface forms that derive from a common (or very similar[1]) deep structure.
- ^ In the first formulations of transformational grammar, active and passive pairs had identical deep structures. As the theory developed, it became necessary to mark whether a sentence was active or passive in the deep structure itself, with the result that active/passive pairs had almost-but-not-quite identical deep structures.