M.F.
Some of this has been said by previous posters, but just to articulate a little more - your son is hitting as a way of communicating that he is upset/frustrated/angry/etc. Even though he is very articulate for his age, that doesn't mean that he has learned that when you are angry, etc. you need to handle it with words, not with hitting. He is advanced verbally, but not emotionally. Plus, it is very developmentally appropriate for 2 year olds not to want to share. So, if you put him in a time out, what you are doing is telling him that it is not right for him to feel angry/frustrated/etc. Instead, you want to give him the message that when you are angry, you talk about it. When he hits, you say something like, "We don't hit. I can see that you are frustrated because you want to play with your sister's toy. Let's find a toy for you." Yes, you will have to do this a million times, but he eventually will get it. Also, you might see that eventually his sister might even offer the toy to him because he asked nicely. Just remember, you are teaching him the right way to deal with things. He needs to learn this just like anything else.