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When do I use which or that in a sentence?

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4 Answers

Let me give you two examples to explain the correct usage of "which" and "that."

1. We recently installed new siding on our house, which was flooded last month.

Use "which" when the information in your subordinate clause ("which was flooded last month") is non-essential to the meaning of the sentence. If you took away the subordinate clause, the reader would still know what house you are referring to.

2. I returned the book that I bought last night.

You should use "that" when the information directly following it is essential to understanding the sentence. Without "that I bought last night," the reader wouldn't know which book you are talking about.

The way I remember it is by thinking of "that" as a tight knot within a sentence and "which" as a looser bow.

When I attended the University of Phoenix, we had a grammar checker called WritePoint.  Whenever I used the word "which" in a sentence, it would make a note explaining in scholarly writing, "that" was preferable to "which," and if "that" could be substituted for "which" without changing the meaning of the sentence, replace "which" with "that." 

Absolutely! Also keep in mind that you don't necessarily always use a comma when using "which", so keep your sentence structures in mind!

I agree with Rebecca and resound with her conclusion that even though it seems random, that and which are consistent in sentences. Simply, if you are doubting the use of that or which... remember that a "a witch is a ditch". (once you understand that, it'll stick!)


That's a great way to remember it Jonathan!

"A which is a ditch" -- Beautiful!

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