I recently went away to Spain for six weeks over the Christmas holidays, and we (the group) would often find ourselves singing something as we'd walk from one attraction to another. I'd always be singing a harmony part, like a third or a fifth above what everyone else was singing (depending on if they were singing in tune or not ), and very rarely would I sing the tonic. I don't know why, but I tend to avoid the tonic. I'd rather sing those harmony parts than anything else. And the guys on the trip were always saying, "how do you hear that?" How do I hear that? Is it a natural thing, i.e. do I have a natural knack for hearing harmonies? Or is it because I've always listened and sang along to them by choice, and have developed an ear for it?