A recent letter to the editor in my morning paper contained the following:
You can imagine my horror to see a guest writer with a PhD., division chair, and professor of English at the university level write the following sentence: “Sad, but whom to blame?”
The subject of the sentence would clearly have been “who.” The linking verb, “is,” and the infinitive at the end should have been a clue.
The time has probably come for English speakers to drop whom from their vocabularies altogether or at least refrain from criticizing its use in the speech and writing of others.
The letter-writer has this much right: who is a subject form and whom is an object form.
When this pronoun is the subject of a main verb, the correct form to use is who:
Who is chairman of the bake sale? (subject of the verb “is”)
When the pronoun is the object of a main verb or the object of a preposition, the correct form to use is whom:
Whom did you appoint troop leader? (object of the verb “did appoint”)
To whom did you send the invitation? (object of the preposition “to”)
Now for the usage that horrified the letter-writer: “Sad, but whom to blame?”
This group of words is not a sentence. It is a sentence fragment. And it does not contain “the linking verb is.”
The phrase does not contain a main verb of any kind. It is made up of an adjective (sad), a conjunction (but), a pronoun (whom), and an infinitive (to blame).
The rule about using who as the subject of a main verb does not apply to this phrase.
Although whom can never be the subject of the main verb in a clause, it can be the subject of an infinitive: “Sad, but whom to blame?”
In this instance, whom is the subject of the infinitive “to blame.” The college professor was correct.