TRANSFORMATIONAL GRAMMAR

The transformational grammar was a theory of how grammatical knowledge is represented and processed in the brain. Developed by Noam Chomsky in the1960's, the transformational grammar consisted of:

1. Two levels of representation of the structure of sentences: an underlying, more abstract form, termed 'deep structure', and the actual form of the sentence produced, called 'surface structure'. Deep structure is represented in the form of a heirarchical tree diagram, or "phrase structure tree,"* depicting the abstract grammatical relationships between the words and phrases within a sentence.
   
2. A system of formal rules specifiying how deep structures are to be transformed into surface structures.
   

Consider the two sentences "Steven wrote a book on language" and "A book on language was written by Steven." Chomsky held that there is a deeper grammatical structure from which both these sentences are derived. The transformational grammar provides an characterization of this common form and how it is manipulated to produce actual sentences. Or take the sentence "Who will John see." This corresponds to its surface structure. According to the transformational grammar, we form this sentence by unconsciously applying transformation rules to the underlying deep structure given in the phrase structure tree of the form "John will see who." In this particular case, the transformation rule applied is termed "Wh-movement."*
The transformational grammar formed the basis for many subsequent theories of human grammatical knowledge. Since Chomsky's original presentation, many different theories have emerged. Although current theories differ significantly from the original, the notion of a transformation remains a central element in most models.


http://www.class.uh.edu/cogsci/Lang/Entries/transformational_grammar.html