|E.B. White, spinning in his grave.|
For restrictive clauses -- those with a crucial bit of definition -- the preferred word is that.
Robert Lane Green, an international correspondent for The Economist, is a descriptivist in matters of the language and so he thinks the title of this post is just swell.
To pick on Strunk and White, they prescribe a rule on “which” and “that” to introduce relative clauses: “which” must introduce a “nonrestrictive” relative clause (a mere extra bit of information). Only “that” can introduce a “restrictive” clause (a crucial bit of definition). You agree with White that “The lawn mower which is broken is in the garage” should have “that,” not “which.” However, even White doesn’t agree with White. As the linguist Geoff Pullum noticed, White used “which” in the “wrong” way in his essay “Death of a Pig”: “the premature expiration of a pig is, I soon discovered, a departure which the community marks solemnly on its calendar.” White would probably say he slipped. I’d console him; no, he didn’t. It’s a fine sentence from a fine American writer.Green is a frequent contributor to The Economist's excellent blog on writing, Johnson, but, heavens man, are you going to take on Strunk and White and risk a lightning strike?
Furthermore, in the afterlife you'll have to deal with Miss Schindler, who taught me grammar in the eighth grade and who taught my father before me and who would have given me a resounding slap on the shoulder had I confused which and that.
Which I didn't.