Like the problem of consciousness, questions concerning free will are nearly impossible to answer because they require a vantage at least one level removed from that of reality in order to definitively prove. By no means is the following thought experiment from the philosopher Harry Frankfurt a proof, but it demonstrates that what is probably most important to human free will is the assumption of moral responsibility, not the ability to choose from a set of alternatives. This weakens the force of the determinist's position against proponents of the common sense view of free will.
>Donald is a Democrat and is likely to vote for the Democrats; in fact, only in one particular circumstance will he not: that is, if he thinks about the prospects of immediate American defeat in Iraq just prior to voting. Ms White, a representative of the Democratic Party, wants to ensure that Donald votes Democratic, so she secretly plants a device in Donald's head that, if activated, will force him to vote Democratic. Not wishing to reveal her presence unnecessarily, Ms White plans to activate the device only if Donald thinks about the Iraq War prior to voting. As things happen, Donald does not think about Iraq prior to voting, so Ms White thus sees no reason to activate the device, and Donald votes Democratic of his own accord. Apparently, Donald is responsible for voting Democratic although, owing to Ms. White's device, he lacks freedom to do otherwise.
"If Frankfurt is correct in suggesting both that Donald is morally responsible for voting Democratic and that he is not free to do otherwise, moral responsibility, in general, does not require that an agent have the freedom to do otherwise. Thus, even if causal determinism is true, and even if determinism removes the freedom to do otherwise, there is no reason to doubt that people can still be morally responsible for their behavior."
This seems obvious after the fact, because intent is so essential to human behavior. It's not enough that a person choose a certain way. His intentions would also have to be in agreement with the act.
https://en.wikipedia.org/wiki/Frankfurt_cases