That vs. Which

Have you ever started writing a sentence only to get half way though, then wonder if “that” or “which” is the appropriate word to use to link the first part of the sentence to the rest?

Both “that” and “which” are relative pronouns, but they are used slightly differently.

According to The Chicago Manual of Style—the go-to style guide for writers and editors—”that” is used restrictively to narrow a category or identify a particular item (e.g., The large tree that is next to the school has my favourite blossoms in the spring).

Whereas “which” is used non-restrictively—not to narrow a class or identify a particular item, but to add additional or supplementary information about an item that has already been identified (e.g., The large tree by the school, which has my favourite blossoms in the spring, will be cut down tomorrow). When used non-restrictively, “which” is almost always preceded by a comma, a parenthesis, or a dash.

It is best to use “which” restrictively only when it is preceded by a preposition (e.g., The situation in which we found ourselves).

Of course, there always seems to be exceptions in the English language.

Here are two:

1)    If “that” appears twice in close proximity in the sentence, “which” can be substituted:  

eg., They can’t always avoid making that sound which makes my skin crawl

Or, you can change the first “that” to “the”:

eg., They can’t always avoid making the sound that makes my skin crawl. (I like this sentence better.)

2)    To correct for euphony (so the sentence sounds better):

eg., She had to move from the flat that her ex-boyfriend owned.

Corrected to:

eg., She had to move from the flat which her ex-boyfriend owned.

Or, you can just remove “that” altogether:

eg., She had to move from the flat her ex-boyfriend owned.