The word “who” has a more sophisticated looking sibling, “whom”. While they are used in the same way and look almost identical, one cannot replace the other. Whom is not the grown-up version of who, ready to be used when you want to speak English like an adult. They both refer to a specific set of answers that could be given to the questions they are used in.
If you can answer a question with he, she, or they, use who. If your options are him, her, or them, use whom. You can remember this rule by the “-m” in him and them: if the response could end in “-m”, use whom instead of who.
You might have to rearrange your sentence a little to find which of the two applies:
Who/~~Whom~~ knows this? → He knows this. ~~Him knows this.~~
Who/~~Whom~~ owns this car? → She owns this car. ~~Her owns this car.~~
~~Who~~/Whom can I ask? → ~~I can ask he.~~ I can ask him.
~~Who~~/Whom does this car belong to? → ~~This car belongs to she.~~ This car belongs to her.
The grammatically correct response tells us which word to use when phrasing the question.
When in doubt, it is fair and safe to avoid whom. It is common for people to only use who in practice, as whom sounds very formal. Sticking to who will usually not sound out of place, while using whom incorrectly will. Overusing whom, particularly when using it incorrectly, can seem desperate to appear sophisticated.
In formal settings, using whom according to the rule laid out here is appropriate. In informal settings, or when unsure if whom applies, sticking to who is perfectly acceptable.
All lessons in this course
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