- Who is a subject pronoun — use it when the person is doing the action (like he/she/they).
- Whom is an object pronoun — use it when the person receives the action (like him/her/them).
- The fastest test: rephrase the sentence with "he" or "him." If "he" fits, use who. If "him" fits, use whom.
- In casual speech, "who" often replaces "whom," but formal writing still distinguishes them — especially after a preposition.
- Do not confuse whose (possessive) with who's (contraction of "who is" or "who has").
The Grammar Mistake That Haunts Professional Writing
"Who should I contact?" "Whom should I contact?" Most English speakers pause at this choice, if they notice it at all. The who/whom distinction has been fading from casual conversation for decades, yet it still appears in formal emails, cover letters, academic papers, and legal documents. Using the wrong form can make an otherwise polished piece of writing look careless.
The good news is that the rule is simple once you strip away the grammatical jargon. You do not need to diagram sentences or memorize Latin case systems. You only need to know whether the person you are talking about is performing an action or receiving one. Everything else follows from that.
This guide gives you a practical, modern framework for choosing between who and whom. We will cover the substitution test, common exceptions, formal versus informal usage, and the difference between whose and who's. By the end, you will be able to decide in seconds — and know when the choice actually matters.
The One-Rule Explanation
Who and whom are both pronouns that refer to people. The difference is their grammatical role:
- Who = subject pronoun (the doer of the action).
- Whom = object pronoun (the receiver of the action).
English Grammar Zone puts it plainly: who functions as a subject pronoun, while whom functions as an object pronoun. If you can replace the word with he, she, or they, use who. If you can replace it with him, her, or them, use whom.
Here are two quick examples:
- "Who called?" → "She called." → Use who.
- "Whom did you call?" → "I called her." → Use whom.
That is the entire rule. The rest is just practice and knowing the handful of situations where usage has shifted.
The Substitution Test: Your Fastest Decision Tool
When you are unsure which pronoun to use, rephrase the sentence as a statement and substitute a personal pronoun. This method works for questions and for relative clauses.
| Original | Rephrased | Substitute | Correct Choice |
|---|---|---|---|
| ___ wrote this report? | ___ wrote this report. | He wrote it. | Who |
| ___ should we invite? | We should invite ___. | Invite him. | Whom |
| The manager ___ hired us is leaving. | ___ hired us. | She hired us. | who |
| The manager ___ we thanked is leaving. | We thanked ___. | We thanked her. | whom |
| ___ did you give it to? | You gave it to ___. | To him. | Whom |
The "M-test" is another useful memory aid. Whom ends in "m," just like him and them. If the answer would use him or them, the question uses whom.
Who in Action
Use who whenever the pronoun is the subject of a verb — the one doing something.
Questions
- Who sent this email?
- Who is responsible for the deadline?
- Who discovered penicillin?
Relative Clauses
- The engineer who designed the bridge won an award.
- Students who study regularly tend to perform better.
- Anyone who wants to join is welcome.
In each case, the who is performing the action: designing, studying, wanting. If you rephrase, you would use he, she, or they.
Whom in Action
Use whom whenever the pronoun is the object of a verb or preposition — the one receiving the action.
As the Object of a Verb
- Whom did the committee select? (The committee selected her.)
- The candidate whom we interviewed has accepted the offer. (We interviewed him.)
- The professor whom everyone admires just published a book. (Everyone admires her.)
After a Preposition
This is where whom is most firmly preserved in modern English. When a preposition comes directly before the pronoun, whom is required in formal writing.
- To whom it may concern.
- With whom did you attend the meeting?
- The colleague from whom I borrowed the book is on vacation.
Improving Your English notes that many native speakers would say "Who did you go with?" instead of "With whom did you go?" The informal version is widely accepted in speech, but the formal version is still expected in business letters, academic writing, and professional reports.
Common Mistakes and How to Avoid Them
Using "Who" After a Preposition in Formal Writing
Incorrect in formal contexts: "To who should I address this?" Correct: "To whom should I address this?"
Overusing "Whom" to Sound Sophisticated
Incorrect: "The person whom called yesterday left a message." Correct: "The person who called yesterday left a message." Reason: "Called" needs a subject, so who is correct.
Confusing "Whose" and "Who's"
Whose is the possessive form. Who's is a contraction of "who is" or "who has."
- Whose laptop is this?
- Who's coming to the meeting? (Who is coming?)
- Who's seen the report? (Who has seen it?)
If you can expand the word to "who is" or "who has," use who's. Otherwise, use whose.
Formal vs Informal Usage
English Grammar Zone documents a clear long-term trend: whom has been declining in everyday speech since the mid-20th century and is now largely confined to formal writing and fixed expressions. Linguists predict it may eventually disappear from ordinary use except in phrases like "To whom it may concern."
What does this mean for you? In texts, Slack messages, and casual conversation, "Who did you invite?" is fine. In a cover letter, grant application, or legal brief, use "Whom did you invite?" or restructure to avoid the issue: "Who did you invite?" is acceptable in most semi-formal contexts, but "Whom did you invite?" is safer when formality matters.
Professional writing is especially important now that AI tools generate so much text. A model can produce fluent prose, but it will not save you from a misplaced whom in a high-stakes document. For more on language precision, see our guide to affect vs effect.
Who and Whom in Real-World Contexts
The who/whom distinction shows up differently depending on where you write. Knowing the register of your audience helps you decide whether the formal form is worth using.
Business Email
In professional correspondence, especially with unknown recipients, "To whom it may concern" remains the standard opening. Using "To who it may concern" signals carelessness. In the body of the email, however, "Who should I contact?" is generally accepted because it sounds natural and the grammatical error is less glaring.
Academic Writing
Essays, theses, and research papers maintain the traditional distinction. Reviewers and editors may flag "who" used as an object in formal prose. When in doubt, apply the substitution test and err on the side of "whom."
Fiction and Dialogue
Characters in novels rarely say "whom" unless they are meant to sound stiff, old-fashioned, or highly educated. Most contemporary fiction uses "who" in dialogue even when "whom" would be technically correct, because that reflects how people actually speak.
Journalism
News outlets generally prefer natural, accessible language. You will see "who" used for both subject and object in most articles, with "whom" reserved for direct quotes, formal titles, or fixed phrases. The Associated Press style does not require "whom" in every grammatically correct position.
Legal and Government Documents
Legal writing preserves the distinction most carefully. Contracts, regulations, and court filings use "whom" after prepositions and as the object of verbs. Precision in these documents can have real consequences, so the conservative choice is usually the right one.
Quick Reference Cheat Sheet
Print this or bookmark it for your next writing session:
- Who = subject = he/she/they = doer.
- Whom = object = him/her/them = receiver.
- Whose = possession = his/her/their.
- Who's = who is / who has.
- After a preposition in formal writing, use whom.
- In casual speech, who is often acceptable for both.
The who/whom distinction is not about being pedantic. It is about clarity and register. Use the right form when the situation demands precision, and do not stress about it when you are chatting with friends. Grammar exists to serve communication, not the other way around.
"The perfect is the enemy of the good." — Voltaire (a useful reminder for grammar decisions too)
Frequently Asked Questions
When should I use who vs whom?
Use "who" when the pronoun is the subject of the verb (the doer). Use "whom" when it is the object of the verb or preposition (the receiver). Test by substituting "he" or "him": if "he" fits, use "who"; if "him" fits, use "whom."
Is whom still used in modern English?
Yes, but mostly in formal writing and fixed expressions such as "To whom it may concern." In casual speech and informal writing, "who" has largely replaced "whom."
What's the difference between whose and who's?
"Whose" shows possession, like "his" or "her." "Who's" is a contraction of "who is" or "who has." If you can expand it to "who is" or "who has," use "who's."
Can I use who instead of whom?
In informal contexts, yes. In formal writing — especially after a preposition — "whom" is still preferred. Avoid "preposition + who" constructions such as "to who" in formal English.
How do I test which one is correct?
Rephrase the sentence and substitute "he" or "him." If "he" works, use "who." If "him" works, use "whom." For example, "Whom did you see?" works because the answer is "I saw him."
Is "To whom it may concern" correct?
Yes. "Whom" is the object of the preposition "to," so the formal construction is correct. It remains one of the most common surviving uses of "whom" in business English.
What about "Who did you see?" vs "Whom did you see?"
Technically, "Whom did you see?" is correct because "whom" is the object of "see." However, "Who did you see?" is so common in everyday speech that it is widely accepted outside formal writing.
Does the who/whom rule apply to animals?
Traditionally, "who" and "whom" refer to people, while "that" or "which" refer to animals and things. Modern usage is more flexible, and "who" is increasingly accepted for pets or animals with human-like qualities.