This is one of those questions that is both fascinating and frustrating at the same time.
One big issue is what is even means to have free will. To say it means having the ability to act without the constraints of necessity or fate is problematic: what does 'necessity' mean? how about 'fate'? Both seem problematic.
One question that has already appeared here is whether free will and determinism can be reconciled. I think there is such a possibility. So, when *I* make a decision to act a certain way, we could say that I have free will if I *could* have made a different decision. But such a different decision would mean that 'I' felt differently, so the actual question is whether 'I' could have made a different decision if I had felt like it or if I had wanted to.
But that is an opening for determinism. For me to 'feel like it' would mean the constraints are at least slightly different, which would mean *even in a deterministic system* that the results could be different.
But we are not all the way there yet. We would have questions about free will if the *reason* I felt different was something external instead of something 'within me'. If there was a puppet master manipulating me into action and the *decision* comes not from me, but from the puppet master, then we could say that free will is violated.
Also, we don't expect that there is *always* free will. For example, if I fall out of an airplane, I do not have the 'free will' to not fall. I am subject to the law of gravity and no amount of will can change that. But, again, this is similar to the puppet master (gravity, in this case) over-ruling my desires.
So, let's get an example going to clarify things. Suppose that I am putting on my shoes and I decide to put on my left shoe before I put on my right shoe. For convenience, we can also assume that
they are equally far from me so they are just as easy to reach.
The *decision* happens within *my* brain. In other words, *I* am the one that made the decision. If my mental (brain) state had been slightly different, I may well have made a different decision. Furthermore, any changes in the scenario would only affect my decision *if* they affected my mental state. So, it definitely seems to me that *I* am making the decision and if I had felt differently, I could have made a different decision. That seems like free will to me. But it is all consistent with strict determinism.
The point is that any decision happens in an incredibly complex situation involving an incredibly complex human brain. MOST of the variables that actually affect the decision happen inside that brain (at least in enough cases to be relevant). And that means that *I* have made the decision and could have made a different one if I had wanted to (different brain state). And that means we have 'free will' in at least some sense even in a deterministic setting.
Now, those who don't like this conclusion should say *exactly* what you think 'free will' should mean. Do you really expect nothing in our past to affect our decisions? That would be pure randomness. So *of course* our history affects our decisions! But that doesn't mean *we* aren't the one making them!