Editing Transformational grammar (section)

===Transformations===
Transformations are rules that map a deep structure to a surface structure. For example, a typical transformation in TG is [[subject-auxiliary inversion]] (SAI). That rule takes as its input a declarative sentence with an auxiliary, such as "John has eaten all the heirloom tomatoes", and transforms it into "Has John eaten all the heirloom tomatoes?" In the original formulation (Chomsky 1957), those rules held over strings of terminals, constituent symbols or both.

:X NP AUX Y   <math>\Rightarrow</math>      X AUX NP Y

(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.

The earliest conceptions of transformations were that they were construction-specific devices. For example, there was a transformation that turned active sentences into passive ones. A different transformation raised embedded subjects into main clause subject position in sentences such as "John seems to have gone", and a third reordered arguments in the dative alternation. With the shift from rules to principles and constraints in the 1970s, those construction-specific transformations morphed into general rules (all the examples just mentioned are instances of NP movement), which eventually changed into the single general rule [[Move α|move alpha]] or Move.

Transformations actually come in two types: the post-deep structure kind mentioned above, which are string- or structure-changing, and generalized transformations (GTs). GTs were originally proposed in the earliest forms of generative grammar (such as in Chomsky 1957). They take small structures, either atomic or generated by other rules, and combine them. For example, the generalized transformation of embedding would take the kernel "Dave said X" and the kernel "Dan likes smoking" and combine them into "Dave said Dan likes smoking." GTs are thus structure-building rather than structure-changing. 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.

In generative [[phonology]], another form of transformation is the [[phonological rule]], which describes a mapping between an [[underlying representation]] (the [[phoneme]]) and the surface form that is articulated during [[Spoken language|natural speech]].<ref>{{cite book|last=Goldsmith|first=John A|title=The Handbook of Phonological Theory|publisher=Blackwell Publishers|year=1995|isbn=1-4051-5768-2|editor=John A. Goldsmith|series=Blackwell Handbooks in Linguistics|page=2|chapter=Phonological Theory|author-link=John Goldsmith (linguist)}}</ref>

====Mathematical representation====
An important feature of all transformational grammars is that they are more powerful than [[context-free grammar]]s.<ref>{{cite journal|last=Peters|first=Stanley|author2=R. Ritchie|year=1973|title=On the generative power of transformational grammars|url=http://www.cs.utoronto.ca/~gpenn/csc2517/peters-ritchie73.pdf|journal=Information Sciences|volume=6|pages=49–83|doi=10.1016/0020-0255(73)90027-3}}</ref> Chomsky formalized this idea in the [[Chomsky hierarchy]]. He argued that it is impossible to describe the structure of natural languages with context-free grammars.<ref>{{cite journal|last=Chomsky|first=Noam|year=1956|title=Three models for the description of language|url=http://www.chomsky.info/articles/195609--.pdf|url-status=dead|journal=IRE Transactions on Information Theory|volume=2|issue=3|pages=113–124|doi=10.1109/TIT.1956.1056813|s2cid=19519474 |archive-url=https://web.archive.org/web/20100919021754/http://chomsky.info/articles/195609--.pdf|archive-date=2010-09-19}}</ref> 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.<ref>{{cite journal|last=Shieber|first=Stuart|year=1985|title=Evidence against the context-freeness of natural language|url=http://www.eecs.harvard.edu/~shieber/Biblio/Papers/shieber85.pdf|journal=Linguistics and Philosophy|volume=8|issue=3|pages=333–343|doi=10.1007/BF00630917|s2cid=222277837}}</ref><ref>{{cite journal|last=Pullum|first=Geoffrey K.|author2=Gerald Gazdar|year=1982|title=Natural languages and context-free languages|journal=Linguistics and Philosophy|volume=4|issue=4|pages=471–504|doi=10.1007/BF00360802|s2cid=189881482}}</ref>