Who and Whom in formal English
English learners are sometimes confused when using who and whom. Who and whom are pronouns used in questions or in relative clauses.
In formal English who is used to replace a subject, while whom is used to replace an object.
Who
Who is a subjective pronoun.
Examples:
Leila is the teacher. -- (Leila is the subject of the sentence.)
→ Who is the teacher?
→ Leila, who is the English teacher, will give a talk about human rights.
The senators supported the president. --(The senators is the subject of the sentence.)
→ Who supported the president?
→ The senators who supported the president are happy with the new bill.
Whom
Whom is used to replace an object.
Examples:
You have met Alan. -- (Alan is the object of the sentence.)
→ Whom have you met?
→ This is Alan, whom I believe you have already met.
Nancy can ask her husband for help . -- (her husband is the object of the sentence.)
→ Whom can she ask for help?
→ Her husband whom she can ask for help is on a trip.
Who and whom in informal English
While in traditional grammar who is used as a subjective pronoun and whom as an objective pronoun, as it is explained above, in informal English, the normal practice is to use who in both cases (as subjective and objective pronouns), thus replacing whom in the contexts where the latter was traditionally used.
Examples:
• Whom did you offer the book to? (Formal English)
• Who did you offer the book to? (Informal English)
Subject: Who and Whom 
Mon Oct 12, 2015 10:27 pm
