The Hard Way
The correct use of who and whom, like all personal pronouns, depends on how the pronoun functions in the sentence. Pronouns either function as the subject of the verb or the object of the verb. The difficulty of who and whom, unlike other personal pronouns, is that it’s not easy to see how who or whom functions.
The Easy Way
By using a three-step process you can avoid the need to understand all this grammar jargon in the previous paragraph. Let’s use this example to see how this process works:
Intelligent citizens will vote for whoever they think is best qualified.
Here are the three simple steps:
Step 1. Begin with the words that follow who or whom to find the gap. With our example, we’d be left with:
they think is best qualified.
Step 2. Plug the gap with either he/she or him/her, whichever one makes sense, and we get:
they think he is best qualified.
Step 3. Use a simple substitution:
he/she = who
him/her = whom
him/her = whom
