That, Which, and Who—Making Sense of Relative Pronouns
by Stephen Dolainski
What are Relative Pronouns?
That, which, and who are relative pronouns. A relative pronoun introduces a group of words called a relative clause. A relative clause provides additional information about a noun in a sentence.
That and which introduce different kinds of relative clauses. Who is used when the clause refers to a person or people.
When to Use That
Use that to introduce a group of words that give very important information about a noun.
When that follows a noun, it introduces information that’s essential, or necessary, to the meaning of the noun and the sentence. This essential group of words is called a restrictive clause or an essential clause. A restrictive clause helps explain or define the meaning of the noun it follows. If the restrictive clause is removed from the sentence, the noun will be left incomplete and the sentence will lose meaning.
Examine this sentence:
An automobile that gets good gas mileage is the Honda Civic.
Try removing the restrictive clause that gets good gas mileage from the sentence. What are you left with?—An automobile is the Honda Civic. Without the restrictive clause some very important (essential) information about the noun automobile is missing. The sentence has lost its full meaning.
When to Use Which
Which generally introduces a relative clause that does not provide essential information.
A relative clause that only adds extra, or nonessential, information is called a nonrestrictive clause. A nonrestrictive clause does not define the noun as a restrictive clause does. A nonrestrictive clause provides some extra descriptive information about the noun. These extra descriptive words can be removed from the sentence without losing any meaning.
Examine this sentence:
Lake Superior, which is the deepest of the Great Lakes, is the largest freshwater lake in the world.
The nonrestrictive clause which is the deepest of the Great Lakes adds extra information about the noun Lake Superior. The nonrestrictive clause can be removed from the sentence without a loss of meaning because what’s left—Lake Superior is the largest freshwater lake in the world—makes perfect sense by itself.
When to Use the Relative Pronoun Who
As a relative pronoun, who is used to introduce a relative clause about a person or people. Who replaces that and which when the reference is to a person or people. Here are two examples:
restrictive relative clause
High-school students who want to design computer software should go to college.
nonrestrictive relative clause
The high-school student, who wants to design computer software, should go to college.
Comma Caution with Relative Clauses
Use commas to enclose or set off nonrestrictive clauses introduced by which or who.
Nonrestrictive Clauses Are Set Off with Commas:
This blue shirt, which my mother gave me, is my favorite shirt.
The opera singer married a translator, who works for the United Nations.
Restrictive Clauses Are Not Set Off with Commas
I got two blue shirts for my birthday. The blue shirt that my sister gave me is too small, but the blue shirt that my brother gave me fits fine.
The opera singer married the translator who works for the United Nations, not the translator who works for the World Bank.
Learn more about pronouns and ways to avoid other common grammar mistakes in Grammar Traps: A Handbook of the 20 Most Common Grammar Mistakes and How to Avoid Them, by Stephen Dolainski.
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