Deep structure
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In linguistics, and especially the study of syntax, the deep structure of a linguistic expression is a theoretical construct that seeks to unify several related observed forms. For example, the sentences "Pat loves Chris" and "Chris is loved by Pat" mean roughly the same thing and use similar words. Some linguists have tried to account for this similarity by positing that these two sentences are distinct surface forms that were derived from an unobservable common source, the so-called deep structure underlying both sentences.
The concept of deep structure plays an important role in transformational grammar. 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. Since some transformations are optional and/or can be applied non-deterministically, the same deep structure can give rise to several distinct surface forms. 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 transformational grammar).
It is tempting to regard deep structures as representing meanings and surface structures as representing sentences expressing those meanings, but this is not the concept described by Noam Chomsky. Rather, a sentence more closely corresponds to a deep structure paired with the surface structure derived from it, with an additional phonetic structure obtained from processing of the surface structure. In the traditional theory, sentences with identical deep structures have to have more or less identical meanings, but the reverse is not true: there is nothing to prevent synonomous sentences having different deep stuctures (e.g. "John admires Bill" and "John looks up to Bill", if we allow that "admire" and "look up to" are actually synonyms).
The "surface" appeal of the deep structure concept soon led people from unrelated fields (architecture, music, politics) to use the term to express various concepts in their own work. In common usage, the term is often used as a synonym for Universal Grammar — the constraints which Chomsky claims govern the overall forms of linguistic expression available to the human species. This is probably due to the importance of deep structure in Chomsky's earlier work on Universal Grammar, though his concept of Universal Grammar is logically independent of any particular theoretical construct, including deep structure.
References
- Noam Chomsky (1957). Syntactic Structures. Mouton.
- Noam Chomsky (1965). Aspects of the Theory of Syntax. MIT Press.
- Noam Chomsky (1981). Lectures on Government and Binding. Mouton.
- Noam Chomsky (1986). Barriers. Linguistic Inquiry Monographs. MIT Press.
- C. S. Lee (1985) has described musical meter in terms of deep structure (Middleton 1990, p. 211). See also chord progression#Rewrite rules.