Introducing English Linguistics (Cambridge Introductions to Language and Linguistics)

In brief, the puristic attitude towards language – the idea that there is
an absolute standard of correctness that should be maintained – has its
origin in a natural nostalgic tendency, supplemented and intensified by
social pressures. It is illogical, and impossible to pin down to any firm
base. Purists behave as if there was a vintage year when language
achieved a measure of excellence which we should all strive to maintain.
In fact, there never was such a year. The language of Chaucer’s or
Shakespeare’s time was no better or no worse than that of our own –
just different.