When do you use who vs. whom? Our language is changing, and it's becoming more appropriate to use "who" all over the place. But the basic rule is that "who" is the subject form ("Who is calling, please?") and "whom" is the object form ("Whom did you see in the garden?") The only thing to remember is to never use "whom" as a subject ("Whom is calling?" is ungrammatical).
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