On that we might agree
Merriam-Webster’s Dictionary of English Usage describes where things stand on the controversy at the moment: “You can use either which or that to introduce a restrictive clause—the grounds for your choice should be stylistic—and which to introduce a nonrestrictive clause.”
Like the brothers Fowler, I think that it would be beneficial for writers to follow a general practice of using that to introduce restrictive clauses and which to introduce nonrestrictive clauses. Though some writers on grammar and usage would like to call that a rule, it is a suggestion. I recommend it as a stylistic preference.
One reason for my preference is the increasing tendency for writers to revive the archaic use of that to introduce nonrestrictive clauses. I see dozens of examples a week in reporters’ copy. While it’s usually possible for the reader to puzzle out the intended meaning, it is neither precise nor elegant.
Professor Pullum’s urbanity and good humor are not always imitated.
Someone named Stephen Jones commented on the “I’m just a simple country boy” passage in my post: “'Ah'm just a poor country boy.' Then go back and look after the cows! Copy editors are supposed to know English grammar and usage, not some petty prejudices they were mistaught at Grade School.”
Someone else named Peter Seibel commented similarly at his blog: “Why is it that English grammar is one of the few fields where what we learned in fifth and sixth grade is considered state of the art? I doubt the Sun’s assistant managing editor in charge of political reporting would explain the paper’s approach to election coverage by saying: ‘I’m just a simple country boy from Kentucky who learned about U.S. politics in Mr. Bobbie Smith’s fifth- and sixth-grade Social Studies classes at Elizaville Elementary School.’”
Messrs. Jones and Seibel offer a valuable reminder to writers and editors that there will always be some readers for whom an explanation of irony will be necessary.