Why is there a difference between using "at" and "to"? Why can I not holler to someone or talk at someone? Further, why do we chat with someone? Why do the prepositions change with each verb?
You can also holler to someone. In that case, the person you are hollering to is typically far away. You are trying to send a message across a great distance, so you must holler.
Hollering at someone is simply yelling at them, i.e., talking loudly.
What's more, you can talk at someone. In this case, the communication is typically one-sided: you are talking, whether or not the other person wants to hear you or is listening.
When at is used (with holler, yell, talk,..., even whisper) there is often a sense of aggression. The point is to be heard, typically loudly, and not necessarily to communicate or to be listened to.
(As @AndriyM noted in a comment, the same difference applies to, for example, throw to versus throw at.)
The choice between "to" and "at" (and a few others), when communicating vocally with another human, basically has to do with whether you have their attention and interest.
If you are carrying on a normal conversation, you are talking to the other person (and they are talking to you). (Note that you can also talk with them, implying two-way communications.)
When, however, a parent is telling a teenager something the teenager doesn't want to hear, and thus the teenager is tuning it out, the parent is talking at the teenager.
When yelling the same applies, except that one might yell at some stranger on the street to warn them that a car is coming. In this case they're not intentionally ignoring you, but you do not yet have their attention/interest.
On the other hand, if your friend Bill is standing on that hill over there, facing you and listening, and you are trying to tell him something, you may yell (or shout or holler) to him, simply because if you talk in a normal voice he won't be able to hear you.
Each verb licenses specific prepositional phrases as complements. They are all different, and there is no logic behind it.
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