As promised, here is Katharine’s explanation of the who/whom issue in the F.B.I. sentence:
The F.B.I. also arrested two of Mr. Rahim’s associates, whom prosecutors say were involved in the plot.
From: One by One, ISIS Social Media Experts Are Killed as Result of F.B.I. Program
“Whom” sounds wrong to me, and Katharine says it is wrong. The right word is “who.”
|“Who” is the subject form||Who is knocking at my door?||“who” is the subject of the sentence|
|“Whom” is the object form||To whom it may concern||“whom” is the object of “to”|
I was confused by the F.B.I. sentence because, to me, “whom” looked like the object of say (because “whom” refers to “two of Mr. Rahim’s associates”).
But if it was the object of “say,” why did it sound wrong?
It turns out that — and you need a linguist to explain this (at least, I do) — “whom” isn’t the object of say.
The object of “say” is the entire sentence “_______ were involved in the plot.”
“Say” takes a “sentential object“: it takes a sentence as an object.
Other verbs take a simple noun as their object.
I want toast.
“Say” is different.
I said I wanted toast.
In the F.B.I. sentence, “who” is right because “who” is the subject of the sentence “_____ were involved in the plot.”
If that’s confusing, think “they were involved in the plot” versus “them were involved in the plot”:
|They were involved in the plot||Them were involved in the plot|
|Who were involved in the plot||Whom were involved in the plot|
I say he did it.
The object of “say” is “he did it.” Not “he.”
That’s why you don’t write:
I say him did it.
Nor do you write “The F.B.I. also arrested two of Mr. Rahim’s associates, whom prosecutors say were involved in the plot.”