Transformational grammar

Transformational grammar is a broad term describing grammars (usually those of natural languages) which have been developed in a Chomskyan tradition. The term is usually synonymous with the slightly more specific transformational generative grammar. This article concentrates heavily on Chomsky and Chomsky-related aspects of this topic. This is justifiable to some degree considering his importance in the field, but it would be nice to have a more balanced view.

In the 1950s and 1960s, Chomsky developed the idea that each sentence in a language had two levels of representation - a deep structure[?] and a surface structure[?]. The deep structure was a direct representation of the semantics of a sentence, and was mapped onto the surface structure (which followed the phonetic form of the sentence very closely) via transformations. There is a common misunderstanding that Deep Structure was supposed to be the same across all languages (see Universal Grammar), but this was not in fact suggested. However, Chomsky did hope that there would be considerable similarities between the Deep Structures of different languages, and that these structures would reveal properties common to all languages which were concealed by their Surface Structures.

Though transformations continue to be important in Chomsky's current theories, he has now abandoned the notion of Deep Structure and Surface Structure. Initially, two additional levels of representation were introduced (LF - Logical Form, and PF - Phonetic Form), and in the 1990s, Chomsky sketched out a new theory of grammar known as Minimalism, in which Deep Structure and Surface Structure no longer featured, and PF and LF remained as the only levels of representation. PF and LF are not really analogous to DS and SS in the early theory, however.

To complicate the understanding of Chomsky's original theories further, the precise meaning of Deep Structure and Surface Structure has changed over time - by the 1970s, the two were normally referred to simply as D-Structure and S-Structure, and D-Structure bore increasingly less resemblance to the Deep Structure of the 1960s. In particular, the idea that the meaning of a sentence was determined by its Deep Structure was dropped, and LF took over this role.

Terms such as "transformation" can give the impression that theories of transformational grammar are intended as a model for the processes through which the human mind constructs and understands sentences. Chomsky is clear that this is not in fact the case: the theory models only the knowledge which underlies the human ability to construct sentences. One of the most important of Chomsky's ideas is that most of this knowledge is innate[?], and that all languages conform to a set of principles, while differing only in the values of certain parameters (and of course raw vocabulary). Therefore, a baby can have a large number of expectations about the structure of language in general, and need only deduce the values of the various parameters for the language(s) it is learning. Chomsky was not the first person to suggest that all languages had certain fundamental things in common (he quotes philosophers writing several centuries ago who had the same basic idea), but he helped to make the innateness theory fashionable after a period dominated by more behaviorist attitudes towards language. More importantly, he made concrete and technically sophisticated proposals about the structure of language, and made important decisions about how the quality of any given theory of language should be evaluated.

Early on, Chomsky introduced two central ideas about how the structure of language should be studied. The first was the distinction between competence and performance. Chomsky noted that when speaking in the real world, people often make linguistic errors (e.g. starting a sentence and then abandoning it midway through). He argued that these errors in linguistic performance were irrelevant to the study of linguistic competence (the knowledge which allows people to construct and understand grammatical sentences). The second idea related to the evaluation of theories of grammar. Chomsky made a distinction between grammars which achieved descriptive adequacy, and those which went further and achieved explanatory adequacy. A descriptively adequate grammar for a particular language describes the set of grammatical sentences in that language, whereas an grammar which achieves explanatory adequacy gives an insight into the universal properties of language which result from the innate linguistic structures in the human mind. Therefore, if a grammar has explanatory adequacy, it must be able to explain the various grammatical nuances of the languages of the world as relatively minor variations in the universal pattern of human language. Chomsky argued that, even though linguists were still a long way from constructing descriptively adequate grammars, progress in terms of descriptive adequacy would only come if linguists held explanatory adequacy as their goal.

Chomsky went against the prevailing viewpoint amongst linguists in the first half of the 20th Century by suggesting that the notion of a "grammatical" and "ungrammatical" sentence could be defined in a meaningful way. An extreme behaviorist linguist would argue that language can only be studied through recordings or transcriptions of actual speech, the role of the linguist being to look for patterns in such observed speech. Chomsky argued that the intuition of a native speaker is enough to define a sentence as either grammatical or ungrammatical, i.e. if a native English speaker finds it difficult or impossible to understand a particular string of English words, it can be said that the string of words is ungrammatical. This was a significant philosophical development in the study of language because it allowed theories to be tested in a reasonably rigorous way - if a theory predicts a sentence to be grammatical and a native speaker does not regard it as grammatical, there is a fault in the theory.

Returning to the more general mathematical notion of a grammar, an important feature of all transformational grammars is that they are more powerful than context free grammars. This idea was formalized by Chomsky in the Chomsky hierarchy. It is now generally accepted that it is impossible to describe the structure of natural languages using context free grammars (at least if these descriptions are to be judged on vaguely Chomskyan criteria).