Copy Editor’s Corner | Which vs. That
According to Chicago Manual of Style and The AP Stylebook, that should be used in restrictive clauses and which in nonrestrictive clauses. A restrictive clause is essential to the meaning of the sentence, and a nonrestrictive clause — you guessed it — is not.
Now, the dictionary is hardly a definitive style guide (sorry, Noah Webster), but we want to cover our bases: Both Merriam-Webster and American Heritage state that it’s perfectly acceptable to use which in restrictive clauses.
As copy editors, however, we prefer to follow the more specific guidelines laid out in the stylebooks. Here are some examples of proper usage:
Shannon grew up in Fergus Falls, which is often mistaken for International Falls.
(The nonrestrictive clause is “which is often mistaken for International Falls.” If it were removed, you would still know where Shannon grew up.)
The rental car, which has great gas mileage, is due back tomorrow.
I want a cookbook that has nutrition information.
(The restrictive clause is “that has nutrition information.” It would be hard to give your friend the cookbook she really wants without it.)
Paul went to the store that sells his favorite organic peanut butter.