How to Use That/Which

You can look up words in the dictionary, but you must learn proper usage.

Who knew that two little words in the English language could be so vexing? "That" and "which" may seem interchangeable, but the truth is that each has a unique role in composition. Ask anyone when to use each one, however, and you'll get a different answer every time. Although using that or which incorrectly will not -- in most cases -- muddle your meaning, knowing how to use them correctly will make your writing sophisticated and relentlessly clear.

Things You'll Need

• Computer
• Pen and paper

Instructions

1. Use "that" to introduce a "restrictive clause." A restrictive phrase, as its name suggests, restricts the meaning of the person or thing that came before it -- in other words, it specifically identifies who or what you're talking about. Take a look at this sentence: "I'd like an avocado that is not too ripe." The restrictive clause here, "that is not too ripe," is essential to the sentence's meaning. If you remove it, the meaning changes and loses specificity.

2. Use "which" to introduce a "nonrestrictive clause." A nonrestrictive clause describes the person or thing you're discussing, but it is not essential to the meaning of your sentence. You should be able to remove the "which" clause without altering the meaning. For example: "I like avocados, which have a buttery, nutty taste." If you take out the "which" clause, the meaning of this sentence remains the same -- the speaker still likes avocados just as much as she did before.

3. Understand the punctuation that accompanies that or which. When you use "that," you generally do not use a comma before it: "The dog that I loved the most was a poodle." You should generally use a comma before "which": "Our poodle, which lived to be 16, was the best pet I've ever had." Or, "Our poodle lived for 16 years, which is a long time for a small dog."

4. Understand that this grammar issue can be a very important matter -- this isn't just nitpicking. For example, consider these two sentences: "I love cats that don't scratch rowdy children." "I love cats, which don't scratch rowdy children." Unless this speaker has grown up with super-docile cats, he needs to use "that." Why? Because "that don't scratch rowdy children" identifies the kind of cats he loves. You can't remove the clause from the sentence and retain the sentence's meaning. The second sentence is incorrect for two reasons. First, many cats do scratch rowdy children; the clause "which don't scratch rowdy children" suggests otherwise. Second, the meaning of the sentence changes if you take out the clause: "I love cats" implies that the speaker likes all cats, when the truth is that she likes only those cats that do not scratch rowdy children. A vital meaning of the sentence is at stake here, and it's imperative to use that/which properly.

5. Test your usage of that/which when you revise your work by asking yourself these questions: If I take out the clause, does my sentence's meaning remain the same? If it does, you should use "which." If the meaning changes, use "that." Does the sentence call naturally for a comma? If it does, this might be a signal that you need to use "which."

References

• Grammar Girl: Which Versus That
• Kent College of Law: The Legal Writing Teaching Assistant: Clauses - Restrictive and Nonrestrictive