Weekly Grammar: That Versus Which

I'm glad to finally have this grammar rule cleared up! How do you know when to use that or which in a sentence? Does it really make any difference? Yes, and it's not difficult, as long as you can identify a restrictive clause. I'm going to borrow the example in the book Grammar Girl's Quick and Dirty Tips for Better Writing:

Gems that sparkle often elicit forgiveness.

"The words that sparkle restrict the kind of gems you're talking about. Without them, the meaning of the sentence would change. Without them, you would be saying that all gems elicit forgiveness, not just the gems that sparkle." (p. 42)

A non-restrictive element in a sentence is additional information that can be eliminated without changing the meaning of the sentence. Again, I'll use the example in the book:

Diamonds, which are expensive, often elicit forgiveness.

"Leaving out the words which are expensive doesn't change the meaning of the sentence. Also note that the phrase is surrounded by commas." (p. 43)