‘That’ vs. ‘Which’: Easy tips for determining when to use each word

For many writers, deciding between the two is among the most confusing language conventions. Here’s some quick advice to make that decision easier.

Recently, I edited a lengthy article written by a fairly experienced author. The article was well written, but there was one problem—”that” and “which” were used incorrectly in most sentences. This is hardly surprising; in my experience knowing when to use “that” versus when to use “which” is one of the most confusing usage issues.

The reason for the confusion?

Those who try to explain their use invariably launch into an explanation using terms such as relative pronouns, subordinate clauses, restrictive clauses, and nonrestrictive clauses. If you’re not asleep after this explanation, then you’re more confused than ever.

I am now going to explain the use of “which” and “that” without using any of these sedating, bewildering terms. But I warn you, this is a tough one. Keep your wits about you.

“That” and “which” are pronouns used to introduce clauses in a sentence. Their use allows writers to combine sentences and avoid choppy prose. For example:

• Our customers were confused by the instructions. + They were not written very clearly. = The instructions, which were not written very clearly, confused our customers.

• The article was clearly plagiarized. + It was removed from the publication. = The article that was clearly plagiarized was removed from the publication.

The confusion sets in when it comes to deciding which pronoun to use—”that” or “which.” They are not interchangeable. And they should certainly never be mixed for the sake of word variation.

One way of deciding whether to use “that” or “which” is to determine if the clause in question can be omitted without changing the meaning of the sentence. If the clause can be omitted, use “which.” If the clause cannot be omitted, use “that.”

“The article that was clearly plagiarized was removed from the publication.”

“That” is used in this sentence because “that was clearly plagiarized” tells the reader which article was removed: The one that was plagiarized.

“The instructions, which were not written very clearly, confused our customers.”

In this case, “which” is used in this sentence because you can remove the clause “which were not written very clearly” without changing the meaning of the sentence. Another way to remember which word to use—always use “that” unless you could justifiably place a comma before the clause. “Which” always mandates the use of a comma.

“The fact that he could not write, which was apparent to anyone who read his work, seemed to escape him.”

You need a comma after the word “write,” so use “which.”

This is all seems fairly straightforward. However, many writers (including me) are often confused when it comes to deciding whether a clause is necessary. This is most likely the result of over-thinking. But that’s an issue we can tackle in another post.

A version of this story first appeared on the author’s blog Impertinent Remarks.

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