“That” vs. “Which”

19 Nov 2009


Today, one of our most grammar-savvy clients emailed us with a question.

She asked:
If a sentence says, ‘A policy (that/which) protects the merchant against penalties… ’ should you use ‘that’ or ‘which’? And why?

I wasn’t 100 percent sure I knew the right answer. I was pretty sure. Mostly sure. But not totally sure. And, truthfully, I couldn’t have explained my choice, other than one just, well… sounded better. I figured there was probably a better reason than that. And I was right.

According to the AP Stylebook (shameless plug – I love, love, love this site – it’s ideal for answering little grammar questions like this), in our client’s case, the answer is “that.”

“That” and “which” are used in essential and nonessential clauses. The one you choose depends on the type of clause.

A nonessential clause is exactly what it sounds like. It’s not essential to the sentence. A nonessential clause contains good information, and it adds detail to your writing, but you could take it out if you were, say, trying to cut your word count or get right to the point. Nonessential clauses are usually set off with commas.

When you’re dealing with a nonessential clause, use “which.”

The policy, which will be effective starting December 2nd, will protect merchants against penalties due to customer error.

You could take out the nonessential clause (everything inside the commas), and the meaning of the sentence wouldn’t change:
The policy will protect merchants against penalties due to customer error.

This sentence is about what the policy does – not when it’s effective.

If you’re working with an essential clause, use “that.”


The policy that protects merchants against customer fraud helped Roy avoid penalties for accepting the stolen credit card.

In this case, we’re talking about the type of policy that helped Roy. Take the essential clause out, and the meaning of the sentence changes, too.

So, there you go.

Have any other grammar questions? We’ll be happy to answer them.

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