whom - Can a phrase be the object of a clause and how would its subject change?

Take the sentence:

I speak all over to whoever will listen.

...at first blush, I thought, "Ah — whoever should be whomever."

However, I then noted that in the phrase "whoever will listen", whoever is correct.

I think the central issue is that if the sentence had ended without the "...will listen" then it would be correctly stated, "I speak all over to whomever." As it is, it seems like the last part of the sentence ("whoever will listen") ends up being the object of the 'to' rather than the single word: 'whoever'.

Is this sentence grammatically correct, and why?

Answer

According to The McGraw-Hill Handbook of English Grammar and Usage, "whoever" is correct.

Although we see "to whoever", it is correct because "whoever" is not the object of the preposition "to". The object of the preposition is the entire noun clause "whoever will listen". And because "whoever", as you point out, is the subject of "will listen", it is written in the subjective case.

The McGraw-Hill Handbook gives the following example:

We will sell it to whoever bids the highest.

We will sell it to whomever bids the highest.

The Handbook declares the first sentence to be correct.