Good and Bad Grammar

There still remains a usage of the term grammar that we have not mentioned, in instances such as; she wrote me a nice letter,but her grammar was awful. Here the speaker is passing  a judgement on someone’s use of language. He is evaluating a piece of english usage againts some supposed norm, called ‘good english’or correct english. The norm is usually what is called ‘standard english’ or educated english usage.

            The use of double negation (They didn’t have none), for example : is not intrinsically ‘bad grammar’ it merely represent a non-standard english usage. Double negation may not be appropriate in the english of public communication, but in more casual or intimate circumstances among certain groups of english speakers it may well constitute a normal feature of english grammar (Jackson,1985:2)