When I was an undergrad in college, I was a philosophy minor. I spent countless hours debating ideas about things like free will. My final paper was a 60 page rebuttal to what I thought was a sloppy argument against free will. Now, it's been more years since I wrote that than I care to admit - and I still keep seeing the same kind of sloppy arguments, that I argue are ultimately circular, because they're hiding their conclusion in their premises.
There's an argument against free will that I find pretty compelling. I don't agree with it, but I do think that it's a solid argument:
Everything in our experience of the universe ultimately comes down to physics. Every phenomenon that we can observe is, ultimately, the result of particles interacting according to basic physical laws. Thermodynamics is the ultimate, fundamental ruler of the universe: everything that we observe is a result of a thermodynamic process. There are no exceptions to that.
Our brain is just another physical device. It's another complex system made of an astonishing number of tiny particles, interacting in amazingly complicated ways. But ultimately, it's particles interacting the way that particles interact. Our behavior is an emergent phenomenon, but ultimately, we don't have any ability to make choice, because there's no mechanism that allows us free choice. Our choice is determined by the physical interactions, and our consciousness of those results is just a side-effect of that.
If you want to argue that free will doesn't exist, that argument is rock solid.
But for some reason, people constantly come up with other arguments - in fact, much weaker arguments that come from what I call sloppy dualism. Dualism is the philosophical position that says that a conscious being has two different parts: a physical part, and a non-physical part. In classical terms, you've got a body which is physical, and a mind/soul which is non-physical.
In this kind of argument, you rely on that implicit assumption of dualism, essentially asserting that whatever physical process we can observe isn't really you, and that therefore by observing any physical process of decision-making, you infer that you didn't really make the decision.
And indeed, this is starting to happen. As the early results of scientific brain experiments are showing, our minds appear to be making decisions before we're actually aware of them — and at times by a significant degree. It's a disturbing observation that has led some neuroscientists to conclude that we're less in control of our choices than we think — at least as far as some basic movements and tasks are concerned.
This is something that I've seen a lot lately: when you do things like functional MRI, you can find that our brains settled on a decision before we consciously became aware of making the choice.
Why do I call it sloppy dualism? Because it's based on the idea that somehow the piece of our brain that makes the decision is different from the part of our brain that is our consciousness.
If our brain is our mind, then everything that's going on in our brain is part of our mind. Taking a piece of our brain, saying "Whoops, that piece of your brain isn't you, so when it made the decision, it was deciding for you instead of it being you deciding.
By starting with the assumption that the physical process of decision-making we can observe is something different from your conscious choice of the decision, this kind of argument is building the conclusion into the premises.
If you don't start with the assumption of sloppy dualism, then this whole argument says nothing. If we don't separate our brain from our mind, then this whole experiment says nothing about the question of free will. It says a lot of very interesting things about how our brain works: it shows that there are multiple levels to our minds, and that we can observe those different levels in how our brains function. That's a fascinating thing to know! But does it say anything about whether we can really make choices? No.