Changes

The basic idea of a generative grammar is to provide a set of rules which are capable of generating all possible grammatical sentences in some language; the rules also constrain generation so that only grammatical sentences are generated. The rules can also be used in reverse to parse a sentence and check if it is grammatical.

The basic idea of a generative grammar is to provide a set of rules which are capable of generating all possible grammatical sentences in some language; the rules also constrain generation so that only grammatical sentences are generated. The rules can also be used in reverse to parse a sentence and check if it is grammatical.

==Simple example==

==Example of a very simple generative grammar==

The very simple example here is based on one by David Crystal.

This very simple example can handle only a tiny subset of English and should not be taken seriously as a guide to English grammar or vocabulary. It is based on an example by David Crystal.

<ref>{{cite book  

<ref>{{cite book  

| last = Crystal  

| last = Crystal  

| isbn = 978052126438

| isbn = 978052126438

| pages = page 97

| pages = page 97

}}</ref> The symbol "->" means "can be replaced by".  When there are several items on the right hand side separated by commas, any one of these items can be selected.

}}</ref>  

  ''Sentence''  ->  ''NounPhrase'' ''VerbPhrase''

  ''NounPhrase'' ->  ''Determiner'' ''Noun''

 

  ''VerbPhrase'' ->  ''Verb'' ''NounPhrase''

  ''Sentence''  ->  ''NounPhrase'' ''VerbPhrase''        # A ''Sentence'' consists of a ''NounPhrase'' followed by a ''VerbPhrase''

  ''Determiner'' ->  '''a''', '''the'''

  ''NounPhrase'' ->  ''Determiner'' ''Noun''              # A ''NounPhrase'' consists of a ''Determiner'' followed by a ''Noun''

  ''Noun''      ->  '''boy''', '''girl''', '''dog'''

  ''VerbPhrase'' ->  ''Verb'' ''NounPhrase''              # A ''VerbPhrase'' consists of a ''Verb'' followed by a ''NounPhrase''

  ''Verb''      ->  '''chased''', '''heard''', '''saw'''

  ''Determiner'' ->  '''a''', '''the'''                        # A ''Determiner''  is either '''a''' or '''the'''

  ''Noun''      ->  '''boy''', '''girl''', '''dog'''               # A ''Noun'' is one of: '''boy''' or '''girl''' or '''dog''' 

  ''Verb''      ->  '''chased''', '''heard''', '''saw'''            # A ''Verb'' is one of: '''chased''' or '''heard''' or '''saw'''

By making appropriate substitutions we can generate such sentences as:

By making appropriate substitutions we can generate such sentences as:

:The girl heard the dog.

:The girl heard the dog.

:The boy saw a girl.

:The boy saw a girl.

==Chomsky hierarchy==

==Chomsky hierarchy==