Proto-Indo-European language
By Edwin Francis Bryant
[W]e know there was a Proto-Indo-European language; we do not know to what extent our reconstructions approximate it.
By R. M. W. Dixon
What has always filled me with wonder is the assurance with which many historical linguists assign a date to their reconstructed proto-language. . . .
We are told that Proto-Indo-European was spoken about 6,000 years ago. What is know with a fair degree of certainty is the time between proto-Indo-Aryan and the modern Inclo-Aryan languages—something in the order of 3,000 years. But how can anyone tell that the development from proto-Indo-European to proto-Indo-Aryan took another 3,000 years? . . .
Languages are known to change at different rates. There is no way of knowing how long it took to go from the presumed homogeneity of proto-Indo-European to the linguistic diversity of proto-Indo-Iranian, proto-Celtic, proto-Germanic, etc. The changes could have been rapid or slow. We simply don't know. . . .
Why couldn't proto-lndo-European have been spoken about 10,500 years ago? . . . The received opinion of a date of around 6000 BP for proto-Indo-European . . . is an ingrained one. I have found this a difficult matter to get specialists to even discuss. Yet it does seem to be a house of cards.
By Stefan Zimmer
It must be stressed, and cannot be said often enough, that whatever date is given for 'PIE,' it is necessarily no more than pure speculation.
Every attempt, then, to give absolute dates for Proto-Indo-European (or dates for alleged different stages of'PIE') is either based on the speculative identification of an archaeological culture with the speakers of the 'language of the PIE's' or on what may be called 'intelligent guesses,' deliberations of probability and feelings of appropriateness. ...
The first type of proposal is usually contested by fellow archaeologists and doubted by linguists, the second, being purely subjective because objective arguments simply do not exist, is bound to remain noncommittal. As is easily to be seen, many dates of both types have found their way to an often far too skeptical public.
It is therefore historically irresponsible for the linguist to speak of Proto-Indo-European in the 4th millennium, and linguistically meaningless for the archaeologist to argue about 'Proto-Indo-Europeans' living somewhere before ca 2500 B.C.