That Standard English is one dialect among many is an empirical fact which presupposes the view that the English language consists of the sum of all its varieties in past and present use. Present-day Standard English evolved from one of the Middle English dialects. It carries the greatest prestige as the standard written form of the language for very good reasons. But from the linguistic point of view, its undeniable superiority is not intrinsic, but historically and socially determined.
The differences between Standard English and the regional dialects are minimal in relation to the whole vocabulary and grammar of the language, and they are also arbitrary. For example, why does Standard English require 'himself', not 'hisself', to match 'myself' and 'yourself', like some of the dialects? Why has it not made the past tense of 'be' regular: I were, you were, he were, we were, etc, or alternatively, I was, you was, he was, we was, etc, like some of the dialects? Why do Standard English speakers say 'aren't I?' but never 'I aren't'?
The answer to these examples does not lie in any superior logic in Standard English. It simply happens that the dialects, including the one that has become Standard English, have changed in different ways. It is axiomatic that living languages are in a constant state of change.
A belief that Standard English is one dialect among many in no way implies that it should not be properly taught in schools. However, as a quid pro quo, the regional dialects should be understood as the 'non-standard' varieties of English and worthy of serious objective study, not pejoratively labelled as 'sub-standard', 'incorrect' or 'corrupt'.
The writer is a former chief examiner of A-level English language for the London BoardReuse content