Day 195: Use which to begin non-restrictive phrases, not that.

Mistakes using that and which are probably the most common grammar problems we fix. This tip will deal with using which correctly.

To understand how to use which, you need to understand nonrestrictive phrases. A non-restrictive phrase provides additional information about some noun. The information is not essential for the reader to know which thing you are describing. It can be removed from the sentence, and the reader will still know what you are talking about. Consider this sentence.

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“Legal counsel approved the brief, which was well written.”

In this sentence, we already know which brief we are discussing. The information “which was well written” provides an additional description of “brief.” The phrase is not essential to the meaning. Thus, “which was well written” is a non-restrictive phrase.

Remember to set the non-restrictive phrase apart from the rest of the sentence with commas. If you forget the commas, your grammar check may suggest adding them. Be careful, though. The real problem may be that you don’t need which but that.

For example, if we had written

“Legal counsel approved the brief that was well written,”

then we know that legal counsel considered multiple briefs but only approved the well-written one. “That was well written” is a restrictive phrase because it tells us which brief was approved.

As you can see, that and which communicate different information. Using the correct word helps you communicate accurately.

Here’s the simple rule. If the reader already knows which one, use which. If you need to tell the reader which one, use that.