The Proper Usage of Which and That in Clauses

When to Use "Which" or "That"

Choosing the proper use of which and that is a common question, often resulting in a grammatical error that can change the meaning of your sentence, and has implications with proper punctuation usage. This is a brief explanation of when to use which and that. Several examples are included.

The confusion between which and that arises when introducing clauses in a sentence. Which can be used when introducing nonrestrictive clauses. Nonrestrictive clauses tell you something about the proceeding subject, but do not effect the meaning of the subject or sentence. That is only used with restrictive clauses. Restrictive clauses limit the meaning of the subject and sentence; they are necessary for the intended meaning.

You should include a comma around the clause when using which (nonrestrictive clauses), and should not include a comma around the clause when using that (restrictive clauses).

In Summary

Which:

• Use with an unrestrictive clause (a clause not necessary for the sentence or its subjects meaning)
• Surround the clause with commas, the first one immediately before which, the second at the end of the clause (if at the end of a sentence, one before "which" with no second comma - you'll use a period instead)

That:

• Use with a restrictive clause (a clause necessary for the sentence or its subjects meaning)
• Do not use commas before "that" or to surround the the clause

Examples of When to Use "Which" or "That"

A few examples of using that:

The books that cover theoretical concepts are challenging reads.

That is specifying that a particular type of books, books covering theoretical concepts, are challenging reads. "That" is correct because "that covers theoretical concepts" is required for the meaning of the sentence; those particular book are a challenging read. Using "which" would be incorrect because it would make the clause unrestrictive, which would change the meaning of the sentence.​

Books that were given to me by my grandfather mean a lot to me.

This sentence is saying that particular books, the ones given by your grandfather, mean a lot. "Which" is incorrect because it changes the meaning of the sentence; using "which" suggests the books mean a lot and happen to be given by the grandfather, and that books in general mean a lot. Using "that" implies the books mean a lot because they were given by the grandfather.​

A few examples of using which:

Stephen King's On Writing, which I got as a gift from my Aunt, has improved my writing skills.

This sentence is saying that Stephen King's book, On Writing, has improved your writing skills, and your aunt happened to give it to you. Using "which" is correct because "which I got as a gift from my Aunt" is unnecessary to the meaning of the sentence - it's extra information. Using "that" would be incorrect because it should be used in restrictive clauses; using "that" in this sentence would imply that it helped because it was from your Aunt, or that that particular copy was somehow special (changing the meaning of the subject).

Reading, which I enjoy, improves both cognitive function and imagination.

This sentence is saying reading improves cognitive function and imagination, and happens to be something you enjoy. Using "which" is correct because "which is something I enjoy" is added information that is not requirement for the sentence to retain its primary meaning; if you removed the clause, the basic meaning of the sentence would remain. Using "that" (without commas) would change the meaning of the sentence to mean that only the reading you enjoy improves cognitive function and imagination.
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One final comparison:

Books that smell good remind me of home.

This sentence means that good-smelling books remind you of home because they smell good. "That smell good" is a requirement for the meaning of the subject or sentence.

Books, which smell good, remind me of home.

This sentence means that books remind you of home, and that all books smell good. "Which smells good" isn't necessary for the meaning of the subject or sentence because this sentence is saying that, in general, books remind you of home.​

See how the meaning of the sentence changes? Usually there is a clear intended meaning; however, in some sentences like the one above, both uses of that and which are grammatically correct and have different, yet equally acceptable, meanings. If you're still having trouble with the proper use, ask yourself what exactly you're trying to say.

Note

If you have any questions about the proper usage feel free to ask a question in our Word Mechanics Forum. If there are any errors in this grammar explanation, please mention it in the comments or contact us. If you can improve, clarify, or expand upon this explanation, feel free to do so.