A relative pronoun connects a dependent, or relative, clause to an independent clause. According to Claire Cook, such pronouns “introduce clauses modifying the words they stand for” (viii). Cook notes that the relative pronoun “[w]ho refers to a person, which to a thing, and that to either” (151).
I pointed out the barista who had kindly fixed me an herbal tea.
In this example, the clause “who had kindly fixed me an herbal tea” is dependent, meaning that it is grammatically incomplete and is linked to the preceding independent, or grammatically complete, clause “I pointed out the barista.” The dependent clause is attached to the independent clause by the pronoun who, which stands for “the barista.”
I finally emptied the suitcase that had lost one of its front wheels.
The relative pronoun that stands, in this example, for the inanimate noun the suitcase.
A Misunderstanding about That
There is a common belief that the relative pronoun that cannot refer to a person, but this belief is a misunderstanding. As noted above, Cook clearly supports the use of that to refer to a person.
There’s the good Samaritan that helped carry my shopping.
An Inanimate Noun That Implies a Person
You may be tempted to use the relative pronoun who when the noun it refers to is inanimate but implies a person. In such cases, follow Cook’s rule: inanimate nouns take that, not who.
I need to find a source that understands linear algebra.
Although the noun source in this example suggests a person, one who “understands linear algebra,” the noun denotes an inanimate object.
An Inanimate Noun That Implies a Group of People
What about when an inanimate noun implies a group of people? As before, use the pronoun that to refer to the noun.
I met with the cohort that received the highest score on the standardized test.
Individuals, not groups, usually take standardized tests, so cohort may not be your preferred noun in this example. If you wish to mention the test takers explicitly and to use the pronoun who, then revise the sentence:
I met with the students who received the highest score on the standardized test.
Animals and Other Beings
In casual contexts, writers sometimes refer to animals using the relative pronoun who.
Dolly is the fish who keeps bumping up against the glass.
But in formal academic prose, use the pronoun that to refer to animals, following the guidance of the The Chicago Manual of Style (“Relative Pronouns”).
Readers don’t encounter Moby Dick, the whale that gives the novel its name, until they are well into the story.
Living beings other than animals also take the pronoun that.
Streptococcus pyogenes is the bacterium that causes strep throat.
Cook, Claire Kehrwald. Line by Line: How to Edit Your Own Writing. Modern Language Association of America, 1985.
“Relative Pronouns Defined.” The Chicago Manual of Style, 17th ed., 2017, www.chicagomanualofstyle.org/book/ed17/part2/ch05/psec056.html.