What does "whom" mean?

Essentially, who and whom are the question form equivalent of he and him (respectively). They are called interrogative (questioning) pronouns.

He hit whom?
Whom should we follow?

Figuring out who or whom
Notice that the examples above use whom in questions, and in both examples the pronoun (whom) represents the object of the sentence. You can test whether you need a who or a whom by interchanging it with an equivilent subject or object pronoun. Look at the example here:  

Who left the lid off the toothpaste again?
Ahh, [John] did! Typical!

 Whom shall we take off the wedding list?
I know, let's remove he him [Great Uncle Vesper] from the wedding list.

When who or whom act as a relative pronoun.

Distinguishing whether to use who or whom when the sentence needs them as a relative pronoun is where problems can start to occur. We like this example from Grammar-Quizzes.com (opens in new tab)

The woman who called you is here.

The woman (whom) you called is here. (You can leave out whom.)

Here's what we think sometimes happens to make students confused.
Consider these sentences:

Question: Wow! Who made this amazing birthday cake?
Answer: * Me! * Note: Asterisks mean that the sentence has an error.

Question: Oi! Who ate that huge slice of birthday cake?
Answer: (the children point with their fingers)  Him ... it was him!

This everyday speech is very common, but it is not accurate. The answers to those questions should have been:

I — It was I who made this amazing birthday cake .... I made it. 🎂 (and you can see I am proud of myself).

He did, or [It was] he!" as in "It was he who ate that huge piece of birthday cake", or more simply "He ate it".

We are not very strict in New Zealand about making sure that our children know the difference between subject pronouns and object pronouns, so the misunderstanding continues.

Who or whom with prepositions

Sometimes in student writing we see students ending their sentences with a preposition. This isn't wrong, but it is typically a speaking form and therefore is not very formal. Look at these examples.

To whom am I speaking?
To whom should I address this card?

Who am I speaking to?
Who should I address the card to?

It is good in academic essays to use the first of the sentence structures above. Here are some examples of what they might look like in your text.

The community for whom this policy is designed...
The scientists to whom the community is indebted...

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