That's the way to do it | Mind your language | Media | guardian.co.uk

Some writing gurus say there's no need to distinguish between the use of which and that, but I disagree. Using those words correctly can aid reader understanding and reduce reader confusion. And, important for the writer, using them correctly is not hard to do.

This article explains the difference well. Rather than summarizing its key points, I recommend reading it.

But here's how I describe use of those words in Garbl's Editorial Style Manual (it also describes when to use who or whom in place of that, though the confusing choice of who or whom is explained in another link):

that, which, who, whom That is the defining, or restrictive, pronoun for essential clauses: The camera that is broken is in the shop (tells which one). Which is the nondefining, or nonrestrictive, pronoun for nonessential clauses: The camera, which is broken, is in the shop (adds a fact about the only camera in question).

In the examples above, note the correct use of commas: Which clauses are always set off with commas (or sometimes dashes or parentheses), and that clauses aren't. Essential that clauses cannot be cut without changing the meaning of a sentence. Don't set off an essential clause from the rest of a sentence with commas. Nonessential which clauses can be dropped without altering the meaning. Set off a nonessential clause with commas.

James J. Kilpatrick, The Writer's Art, 1984: "Rule of thumb: If the qualifying phrase is set off by commas, use which; if not, use that."

In addition, that is the preferred pronoun to introduce clauses that refer to an inanimate object: Greg remodeled the house that burned down Friday. Which is the only acceptable pronoun to introduce a nonessential clause that refers to an inanimate object: The house, which Greg remodeled, burned down Friday.

When an essential or nonessential clause refers to a human being or something with human qualities (such as a family), introduce it with who or whom. That -- but not which -- also may be used to refer to human beings, as well as inanimate objects. Don't use commas if the clause is essential to the meaning. Use them if it is not. See who, whom.

Theodore M. Bernstein, The Careful Writer, 1977: "Which normally refers to things, who to persons, and that to either persons or things."

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This article is featured in today's (July 18) Garbl's Style: Write Choices -- available at the Editorial Style tab above and by email subscription.