Lasnik, H. & Sobin, N. Natural Language & Linguistic Theory (2000) 18: 343. doi:10.1023/A:1006322600501
It is commonly assumed that the English interrogative/relative pronounwhom is parallel to him and them in manifesting objective pronominal Case. We argue instead that whom is not Case-marked along with these pronouns. Rather, its Case marking follows a different paradigm. Whom in modern English derives from a set of extra-grammatical rules called 'grammatical viruses'. Speakers call upon such rules to check Case and (possibly) agreement features which the normal system of syntax cannot check, but which prestige usage demands. Sentences with whom are typical of sentences resulting from grammatical viruses. Such virus-licensed products have a 'prestige' status, they are not typical of child language, and theintuitions about their use are strikingly different from intuitions about the use of other grammatical elements that they are traditionally claimed to work along the lines of. In the latter instance, intuitions about the use of whom differ markedly from intuitions about the use of ACC personal pronouns.
A common rule for determining whether “who” or “whom” isright is to substitute “she” for “who”, and “her” for “whom”,and see which sounds the better. Take the sentence, “He met awoman who they said was an actress”. Now if “who” is correctthen “she” can be used in its place. Let us try it. “He met a womanshe they said was an actress”. That instantly rings false. It can't beright. Hence the proper usage is “whom”.
In certain cases grammatical correctness must often be subordinated to aconsideration of taste. For instance, suppose that same person had met aman whom they said was a street cleaner. The word “whom” is too austereto use in connection with a lowly worker, like a street cleaner, and its use is known as False Admiration or Pathetic Fallacy. Thurber (1931, p. 101) discussed.