I remember watching this interview with philosopher Daniel Dennett - he's a smart guy. They were talking about consciousness and the interviewer was claiming that this is one of the things you can only probe "from the inside" - subjectively - and that's related to the concept of a soul. However Dennett was arguing that, at least in principle, you can learn everything about another person's mind, thoughts and everything by studying his brain. And you can, in principle, understand what it is to be him, to feel his feelings and so on. Trivial, but somehow difficult to accept...
Anyway, I'd like to read some of Dennett's books, too!