You just can't stop people putting themselves in harm's way. If they're not walking into the buzzsaw they're crashing like bugs into the windshield… As the previously referenced discussion about usage in The Guardian's online pages developed a bit further, a commenter called scherfig responded to Steve Jones's devastating piece of evidence about Mark Twain not obeying Fowler's which/that rule by saying this:
OK, steve, let's forget Mark Twain and Fowler (old hat) and take a giant leap forward to George Orwell in the 30's and 40's. In my opinion, in his essays, the finest writer of the English language ever . Check out his use of English – it is, after all, several decades after Twain and still 70 years ago, and he has actually written sensibly about language (quite a lot).
What Steve immediately did, of course, was to take a relevant piece of Orwell's work and look at it; scherfig, the Orwell fan, astonishingly, had been too lazy to do this. And again his result was total and almost instant annihilation of the opponent.
Here's what Steve wrote to scherfig:
I didn't bring out Mark Twain, Michael did. And it was Fowler who was responsible for the non-rule in the first place.
If you are suggesting that we should copy Orwell, 'the finest writer in the English Language ever' then you'd better jettison your nonsense about 'which' not been used in restrictive relative clauses because his famous essay 'Politics and the English Language' is full of it being used thus, starting with the very first paragraph.
belief that language is a natural growth and not an instrument which we shape for our own purposes.
Did scherfig acknowledge that this was a point against him? Not at all. Not one bit (read for yourself).
What is going on here? People insist that they believe in the fictive rule that which is a mistake at the beginning of a restrictive relative clause; they cite examples of writers they admire, and predict that these writers would never disrespect the rule; they don't look to see, not even at the first page or so; instead they publish their unchecked claim in an online department of a national newspaper; Steve Jones checks their claim quite easily in a minute or two of research and shows that they are just plain wrong; and they refuse to accept that the evidence tells us anything. They move on to suggesting a different author, or change the subject, or post personal insults against the messenger (scherfig tells Steve, who is spot-on relevant and exactly correct, "I have come to the conclusion that you have no idea what you're talking about … you just witter on…", and also accuses Steve of claiming that there are no rules at all).
Linguistics is a very strange business to be in. Matters like what rules or regularities expert users of English are following when they construct relative clauses are not difficult like quantum mechanics is difficult. They are readily settled by inspection of text that anyone could do. And all linguists want to base on such inspection is an accurate description of the language of which the texts are a sample. Linguists believe (and could anyone seriously think otherwise?) that on the whole a correct description of the grammar of a language has to be an account of the rules or regularities that expert users of English follow when they construct sentences. That doesn't mean everything any user writes down is in compliance with the rules — we all make occasional mistakes from inattention. But it does mean that overwhelming evidence concerning a regularity in published English prose should count for something (probably quite a lot) when we're discussing English grammar.
And the overwhelming evidence says that the regularity about English restrictive clauses, in speech as well as published prose, and in cases where the users themselves would say that they were not in error and did not choose their words carelessly, is that they sometimes begin with which (a thing which I have often wondered about), and sometimes begin with that (the thing that I can't understand), and sometimes begin with neither (the thing I want to explain). The evidence is overwhelming. But people can't accept it, and insist it isn't so.
It's like being a chemist and explaining to people that mercury is poisonous and accumulates in the body and causes mental deterioration; and they just keep adding mercury to their food, and eating it and going mad, and claiming that chemists say there should be no food.