David Crystal expressed the view in ‘Rediscover Grammar’ that ‘all varieties of the [English] language have an intrinsic value and interest’. This is taken by some to mean ‘anything goes’, but, as he said on his blog in reply to the British broadcaster John Humphrys,
. . . no linguist would ever say such a stupid thing – it goes totally against the principles of linguistics . . . it is the kind of glib phrase that people who don’t like linguists claim they say.
One commentator has described recognizing the linguistic validity of nonstandard varieties as a trahison des clercs, (‘a compromise of intellectual integrity by writers, artists, and thinkers’ – OED), but those who celebrate the diversity of English do not thereby undervalue its standard variety. Standard English (SE) enhances our career prospects, widens our social, intellectual and cultural horizons and makes us more likely to be taken seriously when we wish to pursue an argument, make a complaint or write to the newspapers. To deny that advantage in particular to those from underprivileged backgrounds is to contribute to the perpetuation of social inequality. It is certainly not, as some might still maintain, to inhibit creativity. Most major works of English literature have been written in the conventional language of their time.
There is broad agreement (but not universal agreement, see below) about what SE is. I give my own brief definition here, and you can read what others more qualified have said about it here. If you want to take it further, I provide a number of sources, including, a lecture by Peter Trudgill in which he offers this balanced view:
It is clear, however, that Standard English is not “a language” in any meaningful sense of this term. Standard English, whatever it is, is less than a language, since it is only one variety of English among many. Standard English may be the most important variety of English, in all sorts of ways: it is the variety of English normally used in writing, especially printing; it is the variety associated with the education system in all the English-speaking countries of the world, and is therefore the variety spoken by those who are often referred to as “educated people”; and it is the variety taught to non-native learners. But most native speakers of English in the world are native speakers of some nonstandard variety of the language, and English . . . can be described . . . as consisting of an autonomous standardised variety together with all the nonstandard varieties which are heteronomous with respect to it. Standard English is thus not the English language.
If anyone in the UK wants a quick and easy indication of what SE is, I would point them in the direction of George Alagiah reading the Six O’Clock News on BBC1. If you can imagine him including a particular word or construction in his reading of the news, then it’s probably Standard English. If you can’t, it probably isn’t. It is important to point out, however, that SE is a dialect, not an accent. Its predominant features are its grammar and vocabulary. It can be spoken with any accent.
While there may be broad agreement about what SE is, there is nevertheless some debate about particular points. Some of the variants can be dealt with by distinguishing between formal and informal language, as in the use of ‘who’ and ‘whom’. Others are no more than shibboleths, as described in ‘The Cambridge Guide to English Usage’:
The insistence on ‘different from’, the avoidance of split infinitives, and the preservation of the subjunctive are planks in the party platform, endorsed without any critical thought about their basis in contemporary English. More damagingly, they are made the touchstones of ‘correct’ English, to which everyone must adhere or be damned.
It is hard to imagine anything in the field of linguistics being clearer than the fact that Standard English, the prestige syntactic dialect of the whole global family of English dialects, has preposition stranding, singular antecedent uses of “they”, infinitival constructions with an adjunct between “to” and the verb, and so on — and has had them for literally hundreds of years.
I mention these causes of disagreement, not to provoke a discussion of them here, but to show that such variation within a single dialect (for that, as Peter Trudgill has shown, is what SE is) is to be considered separately from differences between SE and other dialects. ‘My wife and I went to the pub’ is clearly SE. ‘Me and the wife went down the boozer’ equally clearly is not. More examples of the differences are available from The British Library, which has a number of recordings of British regional dialects. One includes the West Country examples
if we’d ever spoke to the teachers like they do speak to the teachers today
mother did come and get us out of bed
In the first, SE would form the past participle as spoken, and omit do before speak. (Some might also want as in place of like. That’s another usage in SE over which there is disagreement.) In the second, SE would omit did and use the past tense of come (came) and the past tense of get (got).
Nonstandard dialects are often seen as corruptions of ‘correct’ English, but there are no grounds for this view. SE is as it is because of historical accident. Nonstandard dialects are as grammatical as SE and it’s hard to see how they wouldn’t be. Without an internally consistent grammar, communication is impossible.
Multilingualism is normal for the speakers of many languages. In the same way, there is no reason why we shouldn’t be multidialectal in our own language, switching from one to the other as the occasion requires, and this is what many of us actually do. SE has enormous political, economic and social prestige, and we are at a great disadvantage if we cannot read, write, speak and understand it. But the majority of native speakers don’t use it in their everyday lives. In our speech, and in our informal writing, most of us use nonstandard language, at least occasionally. As the authors of ‘Linguistics: An Introduction’ have written:
. . . the speech of most people is, at least in some respects, variable, combining, for example, both standard and non-standard sounds, words or grammatical structures.
There is nothing to be ashamed of in that, and nothing to condemn.