In what circumstance can the word "who" be used to replace "whom"?
Today I read some tips about how to use who/whom in grammar books.
One of the book told me that I should not replace "whom" with "who" if there is a preposition before it. For example: 1. He is the hero of whom we are all proud. 2. Whom did you give the book to?
But in another grammar book, I found a sentence: Here is the man (who,whom,that) you have been looking for. In this sentence，all the three words are correct.
To me this sentence is just similar to the Example 2 and now I am confused. Am I misunderstanding about the grammar tips? I need some advice, thank you!
Let me see if I can simplify this grammar problem for you: The relative pronoun “who” has two cases: subjective (“who”) and objective (“whom”). The confusion arises because sometimes a clause whose subject is “who” (“the man who is my grandfather”) is used as the part of the object of the main clause (“I never met [whom?] the man who is my grandfather.”) When using the phrase “to whom” always use the objective case—“whom.” Whenever, in fact, you are forming a prepositional phrase with this pronoun, use the objective case—“from whom,” “with whom,” “around whom,” etc. The syntax (word order) “To whom are you addressing that letter?” or “Whom are you addressing that letter to?” does not change the rule (because the subject is still “you” in this example.) As for substituting “who” for “whom” or vice versa, I can’t think of a single case where it is grammatically right to do so. If in doubt, you have to break the clauses down into their component parts. Simply put, “who” is the subject of a clause; “whom” is an object of either a clause or a prepositional phrase.