Características del clima social del aula

In Syntactic Structures (1957:24), Chomsky suggests that “the simplest type of grammar which, with a finite amount of apparatus, can generate

an infinite number of sentences” is a finite state (or Markov-process) grammar. While finite-state grammar is not a serious candidate for an

adequate grammar and has rarely been proposed as a model for

describing a syntactic system, it does merit some consideration.

A finite-state grammar is a grammar that is an abstract device but one

that may be viewed as a kind of machine. Such a machine defines a language as the set of sentences produced from the initial state to the final state. The machine has a finite number of states and the capacity to

change from one state to another as it registers different symbols

(words). A machine defining a language this way automatically follows

a sequence of operations programmed into it. The set of sentences

produced by the machine defines a finite state language and the machine producing that set of sentences is called finite state grammar. A finite state grammar may be extended by altering the operations the machine is programmed to carry out. These are based on the view that sentences are generated by means of a series of choices made from ‘left-to-right’:

that is to say, after the first, or leftmost element has been chosen, every

subsequent choice is determined by the immediately preceding elements. According to this conception of syntactic structure, a sentence

like:

1. This man has brought some bread.

Might be generated as follows: The word this would be selected for the

first position from a list of all the words capable of occurring at the beginning of English sentences. Then, man would be selected as one of

the words possible after this; has as one of the words that can occur after this and man; and so on. If we had selected that instead of this for the first position, the subsequent choices would have been unaffected:

ENG 221 AN INTRODUCTION TO SYNTACTIC MODELS

That man has brought some bread.

Is an equally acceptable sentence. On the other hand, if we had first selected those or these, we should then have to select words like men for

the second position, followed by words like have for the third position – the possibilities for the fourth and subsequent positions being as before.

And if we had selected the initially, we could continue with either man and has or men and have.

One way of representing graphically what has just been said in words is

by means of the state diagram shown below. (This is slightly more complicated than the one Chomsky gives on p.19 of Syntactic Structures).

Fig.1: State Diagram

The diagram may be interpreted as follows: we can think of the grammar as a machine, or device, which moves through a finite number

of internal ‘states’ as it passes from the initial state (‘start’) to the final

state (‘stop’) in the generation of sentences. When it has produced a

word (from the set of words given as possible for that ‘state’) the

grammar then ‘switches’ to a new state as determined by the arrows.

Any sequence of words that can be generated in this way is thereby defined to be grammatical (in terms of the grammar represented by the

diagram).

The grammar illustrated in the diagram above will generate of course

only a finite number of sentences. It can be extended, however, by allowing the device to ‘loop’ back to the same or some previous state at

ENG 221 AN INTRODUCTION TO SYNTACTIC MODELS

particular points of choice. For example, we could add ‘loops’ between

{this, that, the, same, a,…} and {man, bread, book,…} and between {these, those, the, some,…} and {men, books…} making possible the selection of one or more elements from the set {awful, fat, big,…}, and

thus the generation of sentences beginning:

That awful man…

That big fat man…

Some big fat awful men…

The grammar could also be extended in an obvious way to allow for the generation of compound sentences like (3):

2. That man has brought us some bread and this beautiful girl has eaten the cheese.

Sentences such as this are still very simple in structure; and it would clearly be a complicated matter, even if it were possible, to construct a

finite state grammar capable of generating a large and representative sample of the sentences of English. It would be observed, for example,

that we had to put the both with this, that, etc., and with these, those, etc.

We should also have to put {awful, fat, big, etc.} in several different places because this awful man and these awful men but not *these awful man and *this awful men are acceptable. Problems of this kind would

multiply very quickly if we seriously set about the task of writing a

finite state grammar for English; and the conception of syntactic structure that underlies this model of description has little to recommend

it other than its formal simplicity. But Chomsky proved that our

rejection of finite state grammar as a satisfactory model for the

description of a natural language is more solidly based than it would be if it rested solely upon considerations of practical complexity and our

intuitions as to how certain grammatical phenomena ought to be described. He demonstrated the inadequacy of finite state grammars by

pointing out that there are certain regular processes of sentence formation in English that cannot be accounted for at all, no matter how

clumsy or counter-intuitive an analysis we are prepared to tolerate,

within the framework of finite state grammar.

SELF ASSESSMENT EXERCISE 1 1. Define ‘finite state’ grammar.

2. To what extent is finite state grammar adequate in accounting for all and only the sentences of English?

ENG 221 AN INTRODUCTION TO SYNTACTIC MODELS