Deep structure and surface structure

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) deep structure. Chomsky coined and popularized the terms "deep structure" and "surface structure" in the early 1960s. American linguist Sydney Lamb wrote in 1975 that Chomsky "probably [borrowed] the term from Hockett". American linguist Charles Hockett first used the dichotomous pair "deep grammar" vs "surface grammar" in his 1958 book titled A Course in Modern Linguistics. Chomsky first referred to these Hockettian concepts in his 1962 paper The Logical Basis of Linguistic Theory (later published as Current Issues in Linguistic Theory in 1964). In it Chomsky noted that "the difference between observational and descriptive adequacy is related to the distinction drawn by Hockett (1958) between 'surface grammar' and 'deep grammar', and he is unquestionably correct in noting that modern linguistics is largely confined in scope to the former." In early transformational syntax, deep structures are derivation trees of a context-free language. These trees are then transformed by a sequence of tree rewriting operations ("transformations") into surface structures. The terminal yield of a surface structure tree, the surface form, is then predicted to be a grammatical sentence of the language being studied. The role and significance of deep structure changed a great deal as Chomsky developed his theories, and since the mid-1990s deep structure no longer features at all (see minimalist program).