Page 322 - Practical English Usage 3ed - Michael Swan, Oxford

kinds of English (2): correctness 309
6 What kind of English should learners study?
For most learners, the best model is one or other of the two main standard varieties: British or American English. Neither of these is 'better' than the other, and they are both used and understood worldwide. The differences are generally unimportant: for details, see 51.
7 international English
As English is used more and more as a language of international communication, it seems possible that a new form of international English may develop. This could be a 'super-standard', with characteristics of both British and American English. International English could turn out to be simpler in some ways than the modern standard varieties, without some of their less important grammatical complications. It will be interesting to see what happens.
309 kinds of English (2): correctness
When people say that somebody's language is 'not correct', they may mean several different things.
1 slips and mistakes
People sometimes make slips of the tongue when they are talking. He works in Wildlife Conversation - I mean Conservation.
Somebody can use a word wrongly because he or she is unsure of its meaning, or confuses it with another word.
You're being very authoritative. (meaning 'authoritarian') And many people have trouble with spelling and punctuation.
The firm has doubled it's profits this year. (should be its profits)
Foreign learners may also make mistakes with points of grammar that do not cause problems for native speakers.
I could not understanding the lecture. (instead of I could not understand . ..)
2 dialect forms
Many people think that dialects are corrupt versions of the standard language, and that dialect forms are mistakes, made by ignorant people who have not learnt correct grammar. In fact, this is not at all true (see 308.2): dialects have their own systematic - but different - grammars. Teachers in British schools often tell children whose dialects have multiple negation, for example, that they are making mistakes if they say things like lain't done nothing, because 'two negatives make a positive' (so lain't done nothing is supposed to mean 'I have done something'). This is not, of course, the case: in the child's dialect, the sentence means 'I haven't done anything'. And if 'two negatives make a positive', then the teacher oUght to be quite happy if the child says 'I ain't done nothing to nobody', since logically three negatives must make a negative! Dialect forms are not, therefore, incorrect in themselves. They are, however, out of place in styles where only the standard language is normally used. It would be inappropriate - in fact, incorrect - to use I wants, he don't or a double negative in a school essay, a job application, a newspaper article or
a speech at a business conference.
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