One of the big things that historians and archaeologists believed in the past was that there had been a series of 'invasions' of Britain - hordes of invaders sweeping in from the Continent and overwhelming the more 'primitive' society living here with their greater numbers and better weapons technology. Then it began to be recognised that, actually, there is very little archaeological evidence for invasions. Now genetics has taught us that while we know that there were movements of people into Britain after the Last Glacial Maximum (when Britain was uninhabitable), the 'invasions' were largely movements of cultures, not the movement of large numbers of people, and not extermination of the previous populations. The hordes of Angles, Saxons and Jutes, who were supposed to have slaughtered the Celtic Britons, and extinguished their language just didn't exist.
But, there is a problem inherent in this. English is a West Germanic language, and, as far as is known, the language in Britain at the time of the Roman Invasion was Brittonic, or Brythonic, a Celtic language that is the ancestor of the Celtic languages Welsh, Cornish and Breton. As we now know that while there were Anglo Saxons arriving in Britain in the Dark Ages (450 - 650 CE), these were not in vast numbers. Not enough?to extinguish the Brittonic language, so why is all the evidence that is left of it in England a few toponyms (place names) - in particular, river names such as Avon and Esk/Usk? The question, then, is what happened to the Brythonic language if it wasn't a massive invasion that slaughtered the vast majority of the Britons and stamped out their language? People don't just stop talking a language. After the Norman invasion the English didn't start speaking French - yes, they took on Norman French words, but the basic grammar of the language, and most of the really key words are still descended from Anglo-Saxon.
There are a number of possibilities, which I intend to return to in later posts.
This book proposes that there were sufficient Anglo Saxons that arrived to have their own settlements, and that they were more of a ruling class than the existing natives of the area - perhaps they would have had more weapons than the local? Then these two groups, the local Brittonic speakers, and the speakers of Anglo-Saxon lived in the same area in parallel. The Saxons largely spoke Old English, the Celts spoke Brythonic. The Celtic language acted as substrate to the English, and caused a number of grammatical changes in it. Effectively, Old English was a pidgin of Anglo Saxon and Brythonic, that developed into the Creole of Modern English. There are certainly a number of pieces of evidence for this in the structure of English (and in earlier regional variations of English - under the influence of local Celtic speakers).
For one researcher Theo Vennemann, if a Celtic form of English varies from Standard English or if an English form varies from other Germanic languages, then it is due to a Celtic substratum. There are some interesting examples discussed, including:
There are other examples given as well. It is certainly an interesting theory, that hopefully will yield more information with more research. I will return to the issue of "Why do we speak English?" in my notes on Stephen Oppenheimer's "the Origins of the British".