Speakers of a language recognise the grammatical sentences of their language and know how the words in a grammatical sentence must be ordered and grouped. All speakers are capable of producing and understanding an unlimited number of nwe sentences never before spoken or heard. They also recognise ambiguities, know when different sentences mean the seme thing, and correctly preceive the grammatical relations in a sentence such as subject and direct object. This kind of knowledge is accounted for in the grammar by the rules of syntax.
Sentence have structure that can be represented by phrase structure trees containing syntactic categories. Such a representation reveals the linear order of words, and the constituency of each syntactic category. Syntactic categoies are either phrasal categories, such as NP and VP, which can be decomposed into other syntactic categories, or lexical categories, such as noun and verb, which correspond to the words of the language.
A linguistic grammar is a formally stated, explicit description of the mental grammar or speaker's linguistic competence. Phrase structure rules characterise the basic phrase structure tree of the language, the deep structures, and include fact regarding syntactic constituency such as a noun phrase may be a determiner followed by a noun, but never (in English) a noun followed by a determiner.
In phrase structure rules a category that appears on the left side of rule may also occur on the right side. Such rules allow the same syntactic category to appear repeatedly in a phrase structure tree, which reflects a speaker's ability to produce sentences without length limitations.
The lexicon represents the knowledge speakers have about the vocabulary of their language, including the syntactic catrgory of word and what elements may occur together, expressed as subcategorisation restrictions.
Transformational rules are also used to account for the movement of Aux or wh- words to the beginning of interrogative sentence, and other systematic structural relationships that occur among the sentence structures of the language.
To capture the knowledge speakers have about the syntax of their language, the grammar requires, at a minimum, phrase structure rules, a lexicon richly endowed with speakers knowledge about individual words, and a set of transformational rules describing the structure-dependent patterning that occurs throughout the language.
