'That' and 'which'

Posted by June on June 30, 2025
LABELS: GRAMMAR, THAT VS. WHICH

Here’s a little reminder about “that” and “which”: Editing styles have some strict rules on their usage, but they’re not universal grammar rules, just a style thing.

Here’s the rule, according to the Associated Press Stylebook and the Chicago Manual of Style: “which” can’t be used for restrictive clauses. Only “that” can introduce restrictive clauses.

Restrictive clauses narrow down the things they refer to. Compare:

The hats that have feathers sell the best

with

The hats, which have feathers, sell the best.

In the first example, the clause beginning with “that” actually narrows down which hats we’re talking about. Only the ones that have feathers are being discussed. In the second example, all the hats are being referred to. The “which” clause lets us know that they all have feathers.

So a restrictive clause restricts — narrows down or specifies — its subject. A nonrestrictive clause does not: It can be lifted right out of the sentence without losing specificity of your subject.

And AP and Chicago agree that you can’t use “which” for a restrictive clause. 

“The hats which have feathers sell the best.” That, according to the style guides, is wrong because the clause is supposed to be restrictive. How do we know that the writer meant this clause to be restrictive? The lack of commas. Commas set off nonrestrictive information. To the lack of commas around the clause makes it restrictive.

There’s some logic at the heart of the style rule: Most American English speakers usually use “which” only for nonrestrictive clauses, leaving the other job to “that.” You can also see that keeping these two separate can clear up the potential ambiguity of sentences like “The hats which have feathers will sell best.” (That is, if you doubt the writer’s punctuation skills, you couldn’t be sure whether she meant only the hats that have feathers sell best or whether she meant all the hats sell better than other merchandise and oh, by the way, they all have feathers.)

But unless you’re editing in one of those two styles, you don’t have to worry about this. In my experience, most people manage “that” and “which” clauses well, leaving no question as to what they meant.