A student once told me that she chose the who/whom answer on quizzes by deciding which one she thought was correct and then marking the other one.   She had decided that she would never learn the difference and that she would always be wrong.  Enough!  Let’s get to the root of the problem.

When talking about the difference between I and me, I said that the pronoun changes its form according to its use in the sentence.  The same is true for who/whom and whoever/whomever.

WHO is always used as the subject of a verb.

•  “Who is the major suspect?”  “He is the suspect who is at the top of our list.”   Whether the verb is the main verb in the sentence or a verb in another part of the sentence, the subject of the verb is always who.
• "We need a President who will help us solve our problems."

WHOM is used as the object of a verb.  

The problem is that “whom” does not follow the verb in subject/verb/object order as in “Kevin likes me.”  The order is object/subject/verb.  Here are some examples:

• "Whom did you see at the Cape?"   See is the verb, and the person doing the seeing is you.
• "We need a friend whom we trust."   We is the subject of the verbs need and trust. 

WHOM is used after prepositions.  A preposition is simply a word that links a
noun or pronoun to a sentence. 

• With whom is the contractor meeting?  Is meeting is the verb, and its subject is the contractor.    
• To whom were you referring?   Were referring is the verb, and its subject is you. 

Technical stuff:  Case indicates how the pronoun is used in a sentence.  Nominative is the subject of a sentence or follows the verb “to be.”  Objective case is the object of the action of verbs and prepositions.

Nominative case                              Objective case

who, whoever                                  whom, whomever