I see mix-ups between that and which all the time at work, so I figured it was time to explain the difference in a Writing Wednesday post! Contrary to popular belief, the words are not interchangeable and there are specific times when you should use them.
Let's start with the differences in the phrases they introduce:
- That: The word that should be used as part of a restrictive clause. In other words, that should be used in a phrase that is absolutely essential to the meaning of the sentence. For example, in the sentence I love sharing books that inspire me to be better, removing that and the phrase following it changes the meaning.
- Which: Think of which as part of a parenthetical or non-essential phrase. Which needs to be preceded by a comma as well — and the phrase it introduces can be removed from the sentence without changing its meaning. Here's an example: Dogs, which bark and jump up on people, often scare Lindsay. If you removed the nonrestrictive clause that begins with the word which, the sentence would still make sense (and in this case it is also still true; I am definitely afraid of dogs).
It sounds easy on paper, but the questions usually start coming when people use which in place of that. So here are two easy questions you can ask yourself every time you see which and are wondering if it's in the right place:
- Does it introduce a phrase that includes non-essential information (i.e. traits that most people associate with dogs)?
- Does it have a comma in front of it and after the phrase it introduces (since non-essential phrases need to be set off from the rest of the sentence with commas)?
If you answer "yes" to those questions, leave that sentence alone. If you answer "no," time to take a closer look at the sentence and use that instead. And when in doubt, keep the cheesy graphic at the top of this post in mind. :)
Was that explanation helpful? Do you have trouble remembering the difference between that and which?