"If removing the words that follow would change the meaning of the sentence, use "that." Otherwise, "which" is fine." (Text above copyright Mignon Fogarty, Grammar Girl)
|
Restrictive Elements
A restrictive element is part of a sentence you can’t get rid of because it specifically restricts the noun. Here’s an example from Grammar Girl's post:
Dogs that bark scare me.
The words “that bark” restrict the kind of dog we’re talking about. Without those words, the meaning of the sentence changes: we’d be saying all dogs are scary, not only the ones that bark. Note that restrictive elements are not surrounded by commas.
Nonrestrictive Elements
On the other hand, a nonrestrictive element can be left out without changing the meaning of the sentence. A nonrestrictive element simply provides additional information.
Dogs, which bark, are scary.
Leaving out the words “which bark” doesn’t change the meaning of the sentence. With or without those words, we know that dogs are scary. Nonrestrictive elements are surrounded by commas. I think of it this way: you could grab both commas, pick up the element, and throw it out of your sentence, and it would still make sense.
Knowing which word to use with restrictive or nonrestrictive clauses isn't the big issue. It's more important to know how to properly use commas with those clauses.
Compare these two sentences:
Dogs which bark are scary. vs. Dogs, which bark, are scary. |
The only difference between these two sentences is the addition of commas, which bound the expression that can be removed, leaving the meaning of the rest of the sentence intact: Dogs are scary.
Knowing whether to use "which" or "that" is fine, but I believe it's more important to pay attention to the proper use of commas surrounding nonrestrictive clauses. The commas, more than the choice of "which" or "that," makes the difference.
What do you think?