The words which and that have confused scholars since English was invented. Here’s an easy tool to help you decide which to use. Hey, I just used one!
You know that you’re not supposed to end a sentence with a preposition. We don’t say “that’s the movie I went to.” Instead, you could say “that’s the movie I saw.” You know that basic rule, so we won’t talk about it any further. That’s an easy one.
But when to use that and when to use which when writing a good sentence is much more difficult. According to Michael Quinion at WorldWideWords, it’s a question of restricting a noun.
The word that restricts the noun to which it refers. The car that is blue just got in a crash. That sentence tells us that there can only be one car, the blue one. That is a restrictive use of the word that.
The word which doesn’t restrict the noun. The car, which is blue, just got in a crash. There must be more than one car because the word which was used to describe which car was in the crash. The noun is not restricted.
Quinion’s advice is to not get compulsive over the proper word to use. He suggests that your writing will be better if you simply follow your gut feeling.
Here’s the one-better I can add: notice the difference in the structure of the two sentences:
-The dog that was older won the contest.
-The dog, which was older, won the contest.
In the first sentence we are saying that it was the older dog who won the race. The emphasis in the sentence is on the age of the dog. In the second sentence we are saying it was the dog who won the race and he happened to be older. The dog’s age is parenthetical. It’s so non-essential, in fact, that it is set off by commas.
Here’s an easy rule:
-use the word that when the noun to which it refers needs to be explained: the car that was blue, the dog that was old, the house that was sold.
-use the word which when you are illustrating the noun, explaining it in more detail: the dog, which was older, the car, which was blue, the house, which was a two-storey.
If the clause is critical to the meaning of the sentence, use that. If the clause if parenthetical or illustrative, use which.
One more piece of the puzzle – consider these sentences:
-My goal in writing this article was to provide a rule that you could use with a degree of confidence.
-It is nice to have a rule which allows you to write well.
In the first sentence the word that is a strong, singular item. The one rule that you could use.
In the second sentence the word which is less strident, indicating that there may be more than one rule which you could use.
If your sentence is more authoritative, perhaps that is a better word than which, as which tends to be more tenuous. Don’t forget that using the word that is more singular and structurally related to the noun than which, which tends to be more pluralistic and related, perhaps, to a variety of nouns.
In the end, perhaps Mr. Quinon is correct – use the word that seems easiest to use. The issue, of course, is all about the flow of your writing. Choose the word that flows best with your paragraph. Or the word which flows best with your paragraph.
And here’s the good news: there is absolutely no consensus upon which usage is correct – no matter which word you choose you’ll scholars ready to support you!
You can learn more about the fascinating world of words at World Wide Words.