So you just opened this email. Interesting. Did you have the choice not to? Of course. But you did. Did somebody somewhere already know that you were going to open it? Thought experiment: Imagine an all-knowing demon that has, stored in his memory, all the past of the entire universe. Imagine I said ;) Would that demon be able to predict precisely whether or not you'd have opened that email?
Did you answer yes? Congratulations, you believe in practical unpredictability. Did you answer No? Interesting, you believe in absolute unpredictability. The Practical kind entails that the universe is deterministic: If we know the state of the universe down to the smallest entity - and yes, inclusive even of probabilistic quantum events, smartass reader - and know the nature of all interactions, we can predict precisely what the future will look like. Absolute unpredictability means there is something in the fabric of the universe that is fundamentally unpredictable. I personally don't believe so.
Now, this ultimately leads us to Free Will. If the universe is deterministic and the same past - exact same past - causes the same future, this means a criminal did what he did because of his past. He couldn't help it. This past caused this behaviour and he couldn't have escaped it in any way. Extra step: His very thoughts about his Free Will were caused by his past experiences!
One might draw a conclusion at this point: The above entails that Free Will is an illusion. But then again, it doesn't. Let me explain. Say you drank and drove and killed a cat :( cat killer! No matter whether unpredictability is practical or absolute and your past (abusive father, tough week etc.) has led you to become an irresponsible alcoholic, locally, at the scale of a given day, you chose to drink and drive and killed an animal. You are responsible for that choice. In other terms, in the larger scheme of things, a scheme of events (again - abusive father, tough week etc.) led you to do what you did. However, on a smaller scale, you made that choice. At that scale - and it is the one where society operates - you did enjoy free will and will enjoy tonight's dinner in prison. Confusion stems from us making a bigger deal of what "free" means as we envision it as ultimate or absolute freedom. But freedom could also operate in the context of a deterministic world! See Impossible Family? Good morning :)