The 'proper' way of speaking and writing is really
just a matter of what's fashionable:
“I wish you was here,” John Adams wrote to Abigail from France in 1778. Abigail had written to John two years earlier worried that “you was poisond at New York.” You was turns up quite regularly in their correspondence. It was acceptable English to John and Abigail – as was at New York, which would have been preferable to in New York.
Thus when linguists observe that language always changes, we do not mean only that Old English became Modern English far back in the mists of time, nor are we referring merely to the ever changing nature of slang. Even educated people’s sense of what it is to speak elegantly changes from century to century.
Previous post on linguistic pedantry
here.