Who, whom, that and which are all relative pronouns — they link one phrase or clause to another. Unfortunately, they are easy to mix up. When you’re unsure, you can often “hear” the correct pronoun by reading the sentence out loud. However, if this doesn’t work, you have to take a closer look at the rules.
Rule 1: Who and whom refer to people. That and which refer to groups of things.
- Wrong: Karen is the one that finished the report.
- Right: Karen is the one who finished the report.
Rule 2: Use whom when referring to the object and use who when referring to the subject of a sentence.
- Wrong: Whom wrote this email?
- Right: Who wrote this email? (The subject performed this action, so this sentence requires a subject pronoun.)
- Wrong: Who did you invite to the lunch?
- Right: Whom did you invite to the lunch? (The object received this action, so the sentence requires an object pronoun.)
Rule 3: That introduces essential clauses while which introduces nonessential clauses.
- Wrong: We do not completely believe his claims which indicate a total economic recovery in three months.
- Right: We do not completely believe his claims that indicate a total economic recovery in three months. (This is an essential clause.)
- Right: We do not complete believe his claims, which indicate a total economic recovery will take place in three months. (The second clause is nonessential.)
Rule 4: Whoever, whomever and whichever are compounds, and should follow the same rules as other relative pronouns.
- Right: I will examine whichever report arrives first.
- Right: Whoever designed this presentation is very talented.
With practice, it becomes easier to determine the correct pronoun to use, making your writing clearer and more effective.
- Subject pronouns vs object pronouns (englishelxnb1.wordpress.com)
- Who vs. Which vs. That (grammarbook.com)