According to Chomsky (1965),
a scientific grammar should be observationally, descriptively and explanatorily
adequate. A TG grammar must account for all and only grammatical sentences.
To him a grammar as the tacit shared knowledge of all speakers is a system
of finite rules by which an infinite number of sentences can be generated.
The task for the linguist is to describe adequately this system of rules
and explain how they work. Chomsky (1965) constructs a theoretical model
to account for the mental process of speaking, which can be diagrammed
as follows:
The model known as the standard theory has been revised again and again
since it was proposed. Hard to confirm as it is, the model is the first
attempt to explain what the mental process of speaking is like. According
to this model, we select words from the lexicon (our mental dictionary)
and string them together, following phrase structure rules. The sentence
structure at this stage is the deep structure, which will be further manipulated
according to transformation rules. The actual form of the sentence is
the surface structure, which is represented phonetically in speech or
orthographically in writing. If this model is correct, then writing a
TG grammar of a language means working out two sets of rules which are
followed by speakers of the language.
