One mistake I see a lot, and which annoys me to no end, is when writers use “that” when they should use “who.”
They are both relative pronouns, words that introduce a dependent clause that further defines or explains its antecedent. They do the same thing, but “who” is used when the antecedent is a human being. “That” is used for all other antecedents. However, people often use “that” for people; it’s not only incorrect, it’s actually dehumanizing, like calling someone “it.”
The thieves who stole the gemstone are still on the loose. “Thieves” are human beings, so we use “who,” not “that.”
The words that replace nouns are called pronouns. “Words” aren’t people, so we can use “that.”
Now you try. Look for what word the relative pronoun is referring to, and if it’s a person or people, use “who.” Otherwise, use “that.”
The driver ____ caused the wreck will be charged with a crime.
The student ____ earns the highest grade will win a scholarship.
Those are the shoes ____ I want!