Quirks of English

--for those who speak English as their second language or who just want to improve their writing

(Text-only version of Quirks of English)

which or that

Although that and which are both relative pronouns that refer to nouns, their usage depends on whether the phrase that they introduce is restrictive or nonrestrictive.

Restrictive phrases are necessary to the meaning of the sentence. They are not set off by commas. Although they can be introduced by that, which, or who, many authors and editors prefer to avoid ambiguity by using only that and who to introduce restrictive phrases:

• The coho salmon that John caught in the Chagrin River near Daniel's Park weighed nearly 12 pounds.

The meaning of a sentence changes if a restrictive phrase is omitted:

• The coho salmon weighed nearly 12 pounds.

Which coho salmon?

Nonrestrictive phrases, on the other hand, may add to the meaning of a sentence, but they are not essential to it. They are never introduced by that, and they should always be set off by commas. (If the phrase ends the sentence, a comma precedes the phrase. If the phrase is in the middle of the sentence, commas precede and follow it.)

• Mature coho salmon, which range in weight from 5 to 20 pounds, are plentiful in the Chagrin River during their annual migration.

Here, the phrase "which range in length from 5 to 20 pounds" is nonrestrictive, and its omission does not change the central meaning of the sentence:

• Mature coho salmon are plentiful in the Chagrin River during their annual migration.

Often, whether or not a phrase is restrictive or nonrestrictive depends on the author's intended meaning. If coho salmon have this size range in the Chagrin River but different size ranges elsewhere, the sentence would need a restrictive phrase introduced by a restrictive relative pronoun:

• Mature coho salmon that range in weight from 5 to 20 pounds are plentiful in the Chagrin River during their annual migration.

Here, the author leaves open the possibility that an expert fishermen could hook a 20-pound coho in the Chagrin.

When two or more which's or that's appear in the same sentence, use at least one of each to improve the readability of the sentence:

• John caught the coho salmon that weighed 12 pounds which had wriggled off Frank's hook last week.

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Last updated: 1/20/2009