``Transformational-Generative theory'' = ``Transformational theory'' = ``Grammatical Theory''
To begin with, the phrase structure tree diagram is written in a labelled bracketed form. The labelled bracketing associated with a terminal string generated by a phrase structure is called a phrase marker.
Phrase structure rules are augmented by context sensitive rules (eg. the agreement between subject and verb, say in The girl runs and The girls run.)
Thus in Transformational grammars sentences are derived from an initial phrase structure (called deep structure - earlier called ``kernel sentence'') by the action of transformational rules to give a derived (surface) structure (see fig. ). Note in this model that that syntax is primary while semantics and phonology are both constructed on the syntactic core - the arrows go outwards only. In the 1970s this model was given the label Interpretive semantics (see sec. ).
Active and passive versions of a sentence would have the same deep structure. A transformational rule can convert an active sentence into a passive one, a positive into a negative or interrogative one. In such an analysis,
What are you looking for? is the ``what-question'' transformation of You are looking for it.; while What are you running for? is a ``why-question'' transformation of You are running.
Ambiguous phrases/ sentences can be shown to have different transformational histories. Flying airplanes can be dangerous may come from Flying airplanes is dangerous or from Flying airplanes are dangerous.
The transformations are structure-dependent i.e., they act on the abstract (phrase-) structural representations of sentences.
Hallmark of Chomsky's approach was rigorous logical and mathematical analysis - which went beyond the simple computational principles outlined by Shannon. Before Chomsky, finite automata theory and recursive function theory had been applied to artificial languages; now they were applied to linguistics. The study of the formal properties and generative capacities of various types of grammar now exists as a branch of mathematical logic. Chomsky has also made original mathematical contributions to the study of formal systems.
Chomsky's theory led to similar formal models in developmental psycholinguistics, computational linguistics, neurolinguistics and in socio- and anthropological linguistics. For neurolinguistics see Eric Lenneberg (1967) Biological Foundations of Language.