The Wall Street Journal recently ran an article about the reportedly horrendous grammar that has become in the norm in the workplace.

The response was huge: Hundreds of commenters logged on to say that our language is in a state of catastrophic decline. A couple were astute enough to note that this seeming "decline" emerged from a shortsighted view of the constant evolution of language — the same process through which the words and grammar conventions we hold dear were born in the first place.

But those voices were drowned out by readers who seemed certain that the English language had achieved perfection at the exact moment they were learning about it, and that every change since has been an abomination.

The response was so large that the Wall Street Journal's website followed up with an article about the response itself, plus a grammar quiz for readers. The 22-question quiz, supplied by Jack Appleman, of the Monroe, N.Y., company Successful Business Writing, covered a surprisingly narrow range of grammar issues, with five questions dedicated to possessives, three on the difference between "affect" and "effect," and another three asking about the difference between "principle" and "principal."

The most interesting thing about the quiz lay in its three questions about "that" versus "which." These questions included "Reports that/which are marked 'priority' must be reviewed quickly" and "The book is a reference guide that/which covers the entire industry." For either of these questions, if you chose "which," you got it wrong.

A few readers commented that the "that-vs.-which" questions were the only ones they missed. No doubt, some will take the lesson to heart, never again cavalierly using their ear to choose between "that" and "which." That's unfortunate, because in fact, the quiz's author was wrong.

Had this been a test on Associated Press or Chicago editing style, the questions would have been fine. In both these styles, "which" should not be used to introduce restrictive clauses.

A restrictive clause is one that narrows down the range of possible subjects. For example, if I say, "The reports must be reviewed quickly," I'm talking about a wide range of reports. But if I say, "The reports that are marked 'priority' must be reviewed quickly," I'm talking about a smaller set of reports — only the ones marked "priority."

Therefore, the clause introduced with "that" is restrictive, literally restricting the range of things referred to by the noun.

Compare that to "The reports, which are marked 'priority,' must be reviewed quickly." This sentence suggests that all the reports are marked priority anyway. So they must all be reviewed quickly.

That's an example of a nonrestrictive clause, in which the stuff introduced by "which" doesn't narrow down the subject and can be lifted right out of the sentence without any loss of specificity.

In both AP and Chicago styles, "which" should introduce only nonrestrictive clauses. For restrictive clauses, these styles say, the only correct choice is "that." Thus, to them, "Reports which are marked 'priority' must be reviewed quickly" is wrong.

But this is not a grammar rule. It's a style convention — an American style convention. And it illustrates the real heroes in distinguishing restrictive from nonrestrictive clauses: commas.

"You can use either 'which' or 'that' to introduce a restrictive clauses," notes Merriam-Webster's Dictionary of English Usage. "The grounds for your choice should be stylistic."

Personally, I don't think the style guides should mention this issue at all. It's not a rule. It's just a common practice.

American speakers usually opt for "that" to introduce restrictive clauses naturally anyway. So why tell people they should do something they're already doing when the alternative isn't even an error?

By discussing this matter, the style guides clearly do more harm than good.

JUNE CASAGRANDE is the author of "It Was the Best of Sentences, It Was the Worst of Sentences." She can be reached at JuneTCN@aol.com.