Student or Learner
WHat is the difference between the following sentences: 1) I saw him talking to the policeman. 2) I saw him talk to the policeman .
NOT A TEACHER
(1) May I just add a note to the moderator's excellent answer?
(2) Some (repeat: some) speakers might see a difference:
(a) I saw him talking to the cop. = I saw a part of their conversation. Maybe I saw the beginning, maybe the middle, or maybe the end. In any case, I did not see the whole conversation.
(b) I saw him talk to the cop. = I saw the whole conversation.
(c) For example, let's say that the man claims that the cop beat him. And let's say that you are a witness in court. If you saw him talk to the cop, then you will know whether it it is true or false that the police officer beat him (because you saw the whole conversation); if you saw him talking to the police officer, then you saw only a part of their conversation and maybe you were not looking when the police officer had hit the man.
(3) Many teachers give this example for their students to study:
I saw Mona cross the street. = I saw the whole action.
I saw Mona crossing the street. = I saw only a part of her crossing. (Maybe I saw her start; maybe I saw her in the middle of the street; maybe I saw her finish. In any case, I definitely did not see all of the action.)
P.S. Please remember that I AM NOT A TEACHER. If my answer is different from a teacher's answer, the teacher's answer is the correct one.
I agree with TheParser on this one.
I think it's also possible that "I saw him talk to the policeman" could be used by a speaker to suggest that they saw the person concerned initiate a conversation with the policeman.