(NP = Noun Phrase and AUX = Auxiliary) In the 1970s, by the time of the Extended Standard Theory, following Joseph Emonds's work on structure preservation, transformations came to be viewed as holding over trees.
By the end of government and binding theory, in the late 1980s, transformations were no longer structure-changing operations at all; instead, they added information to already existing trees by copying constituents.
In the Extended Standard Theory and government and binding theory, GTs were abandoned in favor of recursive phrase structure rules, but they are still present in tree-adjoining grammar as the Substitution and Adjunction operations, and have recently reemerged in mainstream generative grammar in Minimalism, as the operations Merge and Move.
[6] His general position on the context-dependency of natural language has held up, though his specific examples of the inadequacy of CFGs in terms of their weak generative capacity were disproved.
[7][8] Using a term such as "transformation" may give the impression that theories of transformational generative grammar are intended as a model of the processes by which the human mind constructs and understands sentences, but Chomsky clearly stated that a generative grammar models only the knowledge that underlies the human ability to speak and understand, arguing that because most of that knowledge is innate, a baby can have a large body of knowledge about the structure of language in general and so need to learn only the idiosyncratic features of the language(s) to which it is exposed.
[11] But such sentences manifest a linguistic problem that is distinct from that posed by meaningful but ungrammatical (non)-sentences such as "man the bit sandwich the", the meaning of which is fairly clear, but which no native speaker would accept as well-formed.
[12] Chomsky noted the obvious fact that when people speak in the real world, they often make linguistic errors, such as starting a sentence and then abandoning it midway through.
A grammar that achieves explanatory adequacy has the additional property that it gives insight into the mind's underlying linguistic structures.
Chomsky argued that even though linguists were still a long way from constructing descriptively adequate grammars, progress in descriptive adequacy would come only if linguists held explanatory adequacy as their goal: real insight into individual languages' structure can be gained only by comparative study of a wide range of languages, on the assumption that they are all cut from the same cloth.
[citation needed] Chomsky developed transformational grammar in the late 1950s, drawing on older work including that of the structuralists.
[13][2] Its central ideas are maintained to varying degrees in present-day approaches to syntax such as Minimalism, while others such as Combinatory categorial grammar are distinctly non-transformational.