1. He is the man whom I want to talk to.

2. He is the man who I want to talk to.

(Are both OK?

3. He is the man to whom I want to talk.
4. He is the man to who I want to talk.
(#4 is incorrect, right? What about #3?)

#1 and #3 are the correct ones.

#2 is often spoken, even though it's incorrect.

#4 is incorrect, yes.

Both sentences 1 and 2 are grammatically correct and have the same meaning. In both cases, the relative pronoun "whom" and the relative pronoun "who" are used as the object of the verb "to talk to".

Regarding sentences 3 and 4, only sentence 3 is correct. In sentence 3, the preposition "to" is followed by the relative pronoun "whom" because it is used as the object of the preposition "to". However, in sentence 4, the incorrect form "to who" is used. The correct form should be "to whom" since "whom" is the object of the preposition "to".

To determine whether to use "who" or "whom," the general rule is:

- Use "who" when referring to the subject of a sentence or clause.
- Use "whom" when referring to the object of a verb or preposition.

In this case, the correct choice is "whom" because it is the object of the verb "to talk to".