Nobody quite knows why speech and language change. It may be that this has something to do with the movement of populations. As adults travel and return they bring back new words. As people migrate they bring their first languages with them. And they may pass some of this on to their children as they learn the language of the host community.

Icelandic with very little population movement, with very little immigration and no history of foreign wars, has changed only a little since the sagas were written 800 years ago. But it has changed. It may be that single individuals can exercise a linguistic effect.

Britain, and especially London, is at the opposite extreme of openness to external effects on speech and language. London was a major recruiting ground for the soldiers of colonisation.

Charles Dickens represents the speech of working class Londoners, often known as Cockney, saying V as W, saying very good as werry good. Phonetically, the W sound, known as a ‘glide’ has become a fricative. But this had disappeared at least by the 1930s when Cockney was being strongly influenced by the Yiddish of Jewish refugees, first from Czarist Russia, and then the Nazis. Cockney is now being replaced by a new variety, influenced by Bangladeshi immigrants from the 1970s and 1980s. The speech of the children is English, but a new variety.

English, as spoken today in London, is different from the English of Charles Dickens, and proportionately more so from that of William Shakespeare, and even more so from that of Geoffrey Chaucer. The Old English of King Alfred 1,200 years ago was plainly a different language.

In major European and North American cities with large proportions of young speakers from families where the first language is different from the majority language there is a constant stream of new terms from minority heritages, consciously or otherwise. Some of these get copied.

As William Labov (1994 and 2001) shows in ongoing research in the USA today, some of the prime movers of one sort of change are feisty, thirty-something, well-connected, working-class women.

When English puritan colonists settled in North America, assuming that they had rights to everything they found, their English started to sound different from the English of the country they had left. They had new sorts of contact with rival settlers from France and Spain, with native Americans, and with slaves. And their situation was quite different.

To a degree it is possible to reconstruct what English at different stages may have sounded like. But the rate and scale of language change sets a limit on how far back linguistic reconstruction can go. It is generally, though not universally, believed that it is not possible to trace back the history of a language more than around 9 or 10.000 years.

Some populations stay in the same place. Others move – for all sorts of reasons, to overcome some natural disaster, to find more food, to find new resources, to escape deprivation, oppression, or starvation, or to colonise and exploit others.

A lexicon, with anything from 20 to 100,000 entries is almost certainly unique to the individual speaker. And lexicons and pronunciations change as new groups form and define their identity by their speech and language. Are these dialects? How different do they have to become to be called languages? Max Weinreich, a linguist who specialised in the study of Yiddish is said to have said in Yiddish, “A language is a dialect with an army and navy”.

In brief

As populations move, so does speech and language. If there is enough change even within a single life-time to get in the way of easy understanding, for children learning to talk there is an obvious need to take account of differences in the speech and language of parents, grand-parents, great grand-parents, which may diverge more and more with each generation. So however the system of speech and language acquisition works, it has to be able to adjust to change. Children may vary in their ability to ignore these divergences. This ability (or the lack of it) may be relevant to some developmental issues.

The notion of perfect English is a myth. It is not definable.