Use who when the pronoun is the subject of its clause. Use whom for an object when you want the formal form. In everyday English, who is common in object questions such as Who did you invite?
Try the they/them test
- Who sent the invitation? Rearrange it as They sent the invitation. They is the subject, so use who.
- Whom did you invite? Rearrange it as You invited them. Them is the object, so whom is the formal choice.
- To whom should I give the invitation? In formal writing, whom is usual directly after a preposition such as to.
Find the clause that sets the role
In Who do you think sent the invitation?, start with They sent the invitation. The pronoun belongs to sent as its subject. The same check works in a relative clause, as in the neighbor who sent the invitation.
