A few months ago, I wrote about the correct use of “me,” “myself,” and “I,” which is tricky for a lot of people. Knowing when to use “who” and “whom” is tricky too, but you’re in luck, since if you’ve mastered the distinction between objective and subjective case (which helps with those tricky first-person pronouns), the most common cases of “who” and “whom” will be a cinch. (Maybe.)
Recall that we use the subjective case when the pronoun in question is the person performing an action. We use the objective when the person is having an action performed on him or on his behalf. Simply put, “who” is the subject of a sentence, and “whom” is an object. If the person you’re speaking about is performing an action, use “who.” So:
The boy who ate his own shoe had a horrible case of indigestion.
The poor boy, to whom I gave an antacid, thanked me profusely.
In the first example, it is “who” who ate, and so we use the subjective case. In the second sentence, antacid was given to the boy (not by him), and so we use the objective case. Even though the “who” in the first sentence is sort of buried behind the primary subject (“boy”), it relates to the subject doing the action “ate” and so we should use “who.”
As a quick rule of thumb, consider that if the pronoun is used next to the word “to,” it is generally going to require the objective case “whom.” But what about this?:
Whom were you feeding antacid to?
Even though the pronoun in this case occurs at the beginning of the sentence in the customary place of a good strong subject, there’s that pesky “to” at the end of the sentence, which can be rewritten in the following ways:
To whom were you feeding antacid?
You were feeding antacid to whom?
The key here is that the “whom” is the beneficiary or recipient of the action and not the performer of it, and so it is the object and requires the objective case.
Commit that subjective/objective distinction to memory and you’ll be set for most of your writing life, but there is one more dicey scenario I’ll cover (actually there are several, but let’s not get crazy). Linking verbs are verbs that connect a noun (or pronoun) to an attribute. The most common of these is the verb “to be.” In a sentence like “He is tall,” we are basically using the verb as an equals sign. Another such common verb is “seems like,” and there are other variants such as “looks like.” The iron-clad rule of linking verbs is that that if two nouns are being compared as equal or not, they must both be written in the subjective case. Think of the subjective case as a bag of apples and the objective as a bag of oranges. When using linking verbs, you can’t compare one to the other. So then take this sentence:
The pharmacist couldn’t think of who the boy reminded him of but knew the lad could not be Werner Herzog.
We have, basically, “the boy = who,” with “reminded him of” as the linking verb. A lot of people are tempted in such a case to use “whom,” mostly because it’s a complex sentence and “whom” seems appropriately formal and complex itself. Just remember that if the sentence is making an equivalence judgment, you’ll want to use “who.” (It’s the same reason, by the way, that we’re taught to use the stilted “this is he” when answering the telephone — spot that pesky linking verb and observe that the proper sentence uses the subjective case “he” rather than the objective case “him.”)
And now for a little freebie. If people have trouble with “who” and “whom,” they have even more trouble with “whoever” and “whomever.” The same rules apply, and nine times out of ten, you’ll really need “whoever” even if you’re tempted to use “whomever” because it sounds more fancy.
Finally, I’m going to editorialize for a moment and say that I’m not really convinced that this distinction matters a whole lot. The difference between the subjective and objective pronouns causes no semantic confusion, and that tiny little “m” is a small enough change that sentences don’t sound quite as wretched when written incorrectly as when “I” and “me” or “he” and “him” are mixed up. Although I tend to use “who” and “whom” correctly except when using my most informal speech, I think that if this set of rules gives you a headache, you ought to consider just using the subjective case (“who” and “whoever”) and putting the objective aside.