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That or Which?

A few weeks ago, I did a blog post about relative pronouns, where I shared when to use “that” and when to use “who.” Well, after sharing that post, I received a request to do a writing tip that distinguishes between the use of “that” and “which.” So, today’s tip does just that; see the sentences below and following explanation to learn the difference between these two relative pronouns.

Sentence: The Pearson study, that has 40 questions, was administered in phase 1 of the pilot program.

Edited Sentence: The Pearson study, which has 40 questions, was administered in phase 1 of the pilot program.

Explanation: As a relative pronoun, “that” is always used in a sentence with a “restrictive clause,” which is a clause that is essential to the meaning of the sentence. However, “while” is typically used with a nonrestrictive clauses, or a clause that is nonessential (i.e., it is not needed in a sentence so this type of clause is set off with commas).

In the sentence above, the clause “that has 40 questions” is nonessential; therefore, it is set off from the rest of the sentence with commas. The commas indicate that you can remove the words between them without losing any meaning to the sentence. However, “that” is only used with restrictive clauses, so in the edited sentence, “which” replaces “that.”

When editing your writing, be sure that you only use the relative pronoun “that” when the clause is an essential part of the sentence.

Until next week, happy writing!!!

Dr. V Writing


Author of I'm Not a Writer...I am Just in Graduate School (order your copy at

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