The Past

I'm not sure how much of this weeks reading I understand. It seems like nothing has a set response and neither free will nor determinism reign in the universe. What really confused me in particular is that "another way to think of compatibilism is to question the assumption of the past being 'fixed' in some way" (6). How can you question that which has already happened? I don't get it. What I do understand is thoughts about different outcomes. If the situation were slightly different, then we would have chosen differently and we would not be in the same situation as the present. How, though, does that say anything about the flexibility of the past? Are they trying to say that things could have gone differently? That seems to fall under common sense...but maybe it doesn't? I don't know. It's a good thing that we only have class twice this week, I think this subject is going to be just as exhausting as altruism.