TRANSFORMATIONAL GRAMMARS

Further research revealed great generality, mathematical elegance, and wide applicability of generative grammars. They became used not only for description of natural languages, but also for specification of formal languages, such as those used in mathematical logic, pattern recognition, and programming languages. A new branch of science called mathematical linguistics (in its narrow meaning) arose from these studies.

During the next three decades after the rise of mathematical linguistics, much effort was devoted to improve its tools for it to better correspond to facts of natural languages. At the beginning, this research stemmed from the basic ideas of Chomsky and was very close to them.

However, it soon became evident that the direct application of simple context-free grammars to the description of natural languages encounters great difficulties. Under the pressure of purely linguistic facts and with the aim to better accommodate the formal tools to natural languages, Chomsky proposed the so-calledtransformational grammars. They were mainly English-oriented and explained how to construct an interrogative or negative sentence from the corresponding affirmative one, how to transform the sentence in active voice to its passive voice equivalent, etc.

For example, an interrogative sentence such as Does John see Mary? does not allow a nested representation as the one shown on page 37 since the two words does and see obviously form a single entity to which the word John does not belong. Chomsky’s proposal for the description of its structure consisted in

(a) description of the structure of some “normal” sentence that does permit the nested representation plus

(b) description of a process of obtaining the sentence in question from such a “normal” sentence by its transformation.

Namely, to construct the interrogative sentence from a “normal” sentence “John sees Mary.”, it is necessary

(1) to replace the period with the question mark (*John sees Mary?),

(2) to transform the personal verb form see into a word combination does see (*John does see Mary?), and finally

(3) to move the word does to the beginning of the sentence (Does John see Mary?), the latter operation leading to the “violation” of the nested structure.

This is shown in the following figure:

S

Nested:

John

N

does see

V

Mary

N

VP

?

 

Not nested:		Does		John	N	see	V	Mary	N	?

 

A transformational grammar is a set of rules for such insertions, permutations, movements, and corresponding grammatical changes. Such a set of transformational rules functions like a program. It takes as its input a string constructed according to some context-free grammar and produces a transformed string.

The application of transformational grammars to various phenomena of natural languages proved to be rather complicated. The theory has lost its mathematical elegance, though it did not acquire much of additional explanatory capacity.