One major English grammar challenge is figuring out when to use either “who” or “whom.” A good number of professional communicators (myself included) have done fairly decent impressions of owls as they glare at their computer screens trying to decide which of these two pronouns sounds right in a particular sentence.

Trouble is, what sounds right and what is right can be very different. So, to help you with this common conundrum, here are the rules.

The Basic Rules
“Who” refers to the subject (one who acts) of a sentence or clause while “whom” is the object (what/or is acted upon). Consider the following sentences:

The woman who volunteered to oversee the festival is experienced in event marketing.

He was the man to whom I spoke last night

In the first sentence, “the woman” acts, that is, “volunteers to oversee.” Therefore, “who” is the appropriate pronoun. In the second sentence, the phrase “I spoke” contains the subject and verb of the sentence. Therefore “the man” is the object of “spoke” in that sentence and so takes the pronoun “whom.”

Subordinate Clause Rules
Things get a little more complicated when the who/whom issue arises in a subordinate clause (a group of related words that includes a subject and a verb but does not provide a complete thought on their own). Take a look at the following examples:

I forgot who won the game last week.

The woman whom he loved has gone away.

In the first sentence, the subordinate clause is “who won the game last week.”  The pronoun “who” is the subject of the verb “won” although the entire clause is the object of the verb “forget.” In the second sentence, “woman” is the object of the verb “loved.”

How to Apply the Rules
Grammar experts suggest that we can determine whether to use “who” or “whom” by substituting the personal pronouns “he/him” or “she/her.” If “he” or “she” is the correct substitution, the proper choice is “who.” If “him” or “her” is appropriate, use “whom.” You may have to slightly alter the word order to see which substitution works:

Sawyer is the man with whom I play golf every Saturday. (I play golf with him.)

The analysts differed as to who they thought might win. (They differed on whether she might win.)

Mignon Fogarty provides a quicker variant in the last paragraph of the Grammar Girl article “Who Versus Whom.”

When to Break the Rules
I started off by saying that what’s grammatically correct and what sounds right can be very different. “Whom do you recommend?” is correct since “whom” is the object of “recommend.”
However, the sentence sounds … off. People just don’t speak like that.

If you’re using informal English in your piece, incorrect grammar sometimes enhances the conversational flow. In fact, MarketingProfs recently wrote about this technique. So when writing informally, you’d use “who do you recommend?”since it sounds better.

Also, when a preposition follows its object, informal English allows for “who” rather than “whom” as in “Who is the gift for?”

That does not mean that the previous who/whom rules are unimportant. You’ll be doing formal pieces, but with the more informal stuff, you have the freedom to make a judicious choice.