Deep structure and surface structure

Deep structure and surface structure (also D-structure and S-structure, although these 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.

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).

It is tempting to regard deep structures as representing meanings and surface structures as representing sentences that express those meanings, but this is not the concept of deep structure favoured by Chomsky. Rather, a sentence more closely corresponds to a deep structure paired with the surface structure derived from it, with an additional phonetic form obtained from processing of the surface structure. It has been variously suggested that the interpretation of a sentence is determined by its deep structure alone, by a combination of its deep and surface structures, or by some other level of representation altogether (Logical Form), as argued in 1977 by Chomsky's student Robert May. Chomsky may have tentatively entertained the first of these ideas in the early 1960s, but quickly moved away from it to the second, and finally the third. Throughout the 1960s and 1970s, the generative semantics movement put up a vigorous defence of the first option, sparking an acrimonious debate, the "Linguistics Wars".

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