Actually, S&W is updated frequently and is considered comprehensive.
By whom? Not by me.
I first read it cover to cover about 19 years ago, and I had to memorize it for AP English Comp. But it's a short book with a very clear focus.
In other words - it is 'By whom' not 'by who', always.
That is a real rule. But it can protentially conflict with another rule.
The book is by who wrote it.
You wouldn't say "by whom wrote it," would you? In fact, a pronoun has been elided. The full sentence would be, "The book is by he who wrote it."
You could certainly write, "The book is by him who wrote it." That would fulfill your rule. But now our pronoun and the who in the clause are not in agreement. So we are left with a choice:
The book is by he who wrote it.
The book is by him whom wrote it.
So let's try replacing the who/whom.
The book is by he (he wrote it).
The book is by him (him wrote it).
Clearly, the him/whom is out of place. So clearly, "The book is by him who wrote it," is preferable. The "who" is "the guy who wrote it." When we elide the pronoun, in one case, and clause, in the other, we end up with:
The book is by him.
The book is by who wrote it.
So as you can see, it is "always"
by whom, but since it always
who wrote it, the rules conflict.
Since it far more likely that
It was he who committed hypocrisy.
than
It was hypocrisy who committed him.
I choose
who.
