Edward Sapir (18841939). Language: An Introduction to the Study of Speech. 1921.
we indulge our sneaking desire for the forbidden locution by the use of the who in certain twilight cases in which we can cover up our fault by a bit of unconscious special pleading. Imagine that some one drops the remark when you are not listening attentively, John Smith is coming to-night. You have not caught the name and ask, not Whom did you say? but Who did you say? There is likely to be a little hesitation in the choice of the form, but the precedent of usages like Whom did you see? will probably not seem quite strong enough to induce a Whom did you say? Not quite relevant enough, the grammarian may remark, for a sentence like Who did you say? is not strictly analogous to Whom did you see? or Whom did you mean? It is rather an abbreviated form of some such sentence as Who, did you say, is coming to-night? This is the special pleading that I have referred to, and it has a certain logic on its side. Yet the case is more hollow than the grammarian thinks it to be, for in reply to such a query as Youre a good hand at bridge, John, arent you? John, a little taken aback, might mutter Did you say me? hardly Did you say I? Yet the logic for the latter (Did you say I was a good hand at bridge?) is evident. The real point is that there is not enough vitality in the whom to carry it over such little difficulties as a me can compass without a thought. The proportion I:me=he:him=who:whom is logically and historically sound, but psychologically shaky. Whom did you see? is correct, but there is something false about its correctness.
It is worth looking into the reason for our curious