We know there are parts of the body operating that are not within control of your consciousness. When your heart is pumping blood the process is not dictated by your brain (consciousness). You can move your arm whenever you want, but that motion is commanded by the brain. We understand the brain to be an organ in the same way the heart is an organ. Both serve a purpose in our anatomy and both follow natural processes. The difference is we understand far more about the heart than we do the brain.
If the brain is an organ that we do not fully understand isn’t it suspicious that it is the one organ on which free will depends? Now of course a complex structure (such as the brain) is where we would expect to find free will if it did exist, but keep in mind emotions were once credited to the processes of the heart. Neuroscience reveals more and more about how the brain works and now that we’ve discovered more about the brain it is claimed that instead of total free will we have partial free will. This idea is known as Compatibilism.
To claim there is free will is to claim that consciousness is derived from something outside of natural law. To claim partial free will (Compatibilism) is to claim that the processes of the brain give us some freedom to move around within the confines of natural law. But as our understanding of the brain increases, I predict that these “freedoms” will show to be just as natural and predictable as all the other bodies processes. The adherents of free will have had to admit that we lack free will in some areas. This is irrefutable in the case of the subconscious. We all admit that certain thoughts and actions dictated by the brain are outside your control. It is likely that the rest of consciousness will show itself to be just as lacking in volition.
The only logical conclusion one can make with a naturalist view of the world is that there simply is no free will. It is of course possible that consciousness exists outside of the physical realm but that is a metaphysical claim and cannot be tested. I would refer anyone making that argument to look up the analogy known as Russell’s teapot (or the celestial teapot). Metaphysical claims have no business in this discussion until we have good reasons to believe there are things outside the physical realm. Our reasoning and logic are based on observable patterns we see in the natural world and these patterns reflect a physical world lacking any evidence for metaphysical claims. To claim you have free will is to claim that the molecules which make up your brain matter obey you and not the laws of nature.