[2] American linguist Sydney Lamb wrote in 1975 that Chomsky "probably [borrowed] the term from Hockett".
[5] In early transformational syntax, deep structures are derivation trees of a context-free language.
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".
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.