"Restrictive wh relatives with non-personal heads have been occurring in impeccable English for about 400 years:"
A date which will live in infamy. (Franklin D. Roosevelt).
When, oh, when did Americans become speakers of "impeccable English"?…particularly their Presidents!!!
I don't think being 'anti-American' is at all helpful. Roosevelt was highly educated, at Harvard I believe.
And I also quoted the King James Bible. Got a problem with that too?
Georgia: "Under what conditions is it acceptable to use "which" instead of "that" to introduce a restrictive relative clause?"
Always use 'that' before a Restrictive clause. Others may dismiss this with an emotive "It's a silly rule".
I am not one of them. The use of 'that' signals to the reader/other person in the conversation that the words to follow SPECIFICALLY IDENTIFY what (noun) you are referring to.
Wake up, Claire! That's one of the arguments against the silly ban on restrictive which-relatives: there can't be any problem about failure to distinguish restrictive versus nonrestrictives (in other ways than via the obligatory commas or intonation difference), because NOBODY suggests that restrictive who-relatives are a mistake. It's only with "which" that anyone has made a fuss about this non-issue.
Also, Claire, you might be interested in this usage note from the Oxford Dictinary:
The general rule in British English is that, in restrictive relative clauses, where the relative clause serves to define or restrict the reference to the particular one described, which can replace that.
I think it's time you brushed up on your grammar, Claire!
Mr. Matthews:
Your emotional outbursts cloud your judgment as to what I was contributing to this discussion. For one thing, your logic that because an American President (or, to cover all basis as I look at the logic you employ, "Americans") says something, proves….PROVES your point, needs to be challenged.
Dictionaries now take into account that people, such as yourself (and those less interested in the beauty of the English language sculptured over the centuries) are of the opinion that 'anything goes' and don't discriminate.
I Do see the importance of the difference and say so. You seem to feel a need to attack me for saying so!