I think I have seen this question a few times before, but I have never read a specific answer. Before I knew any quantum mechanics, I assumed that if you knew enough information about a system, you could predict how it would be at any point in time, and therefore complex things like human decisions, which we have no reason to believe are anything more than (fundamentally) chemical reactions, could be predicted if enough information was known. Since then I have learned of HUP and Bell's theorem, which I think I am right in saying means that any prediction is only an approximation to some level of accuracy (though I have also read that QED keeps agreeing with experiment the more accurate they go, so I am not entirely sure about this). As I understand it, HUP says that we can never know precisely the conditions of any system (which combined with chaos theory means we cannot predict precisely what will happen in a system, in terms of individual particles), and Bell's theorem says that there aren't any hidden variables "governing" all of the particles in the system. Please correct me if I have said anything that is wrong. My question specifically is this: do HUP and Bell's theorem rule out determinism? Or is it not possible to say? I am not entirely sure about all of the different types of hidden variables that there are and which ones Bell's theorem rule out (like local or non-local etc, I don't know how many there are or even what they really mean), but surely these two theorems combined should mean that determinism cannot be correct. However I still see some very clever people arguing in favor of determinism from time to time, so I was hoping that someone could clear it up for me. :) Thanks in advance.