What Language Do You Think In??

Question: What language do you think in?? I think in English. Anything thing I say in my mind can be transferred right on to paper, because everything comes out in complete words (except for the times that I'm confused). Most of the time, the language that you think in is the language that you speak the most or know the most. So, what language did cavemen think in? They didn't speak completely even when they were old. They used pictures. Well, we don't have all information, so I guess I can't say I'm perfectly right. But thats something I think about everyday.
I used to think that I could predict what I was going to say or type even if I'm not talking about it. Why did I think this?? Because, when i type (and as I am typing right now) I say the words (in my mind or aloud) exactly, I repeat EXACTLY, as I type them. Strange? I don't think so, probably happens to everyone. Thats how I study, too. I write/type all the information that I need to know so that my brain remembers it. If you study this or something, please explain.
Why did I start thinking of this all of a sudden? I was reading an article online about synesthesia. This is a disease where something someone says to you, you think in a color. For example, if I say number one and you see a color in your mind right away, then you're synesthete. Here is the article.