Naturalism is the belief that nothing exists outside of the natural world. Many people denote that if naturalism is true (which I believe is the case) that the laws that govern the universe are what make everything happen. That everything which happens in the universe is a physical play out through time. And that means everything single thing, including our conscious thought and decision-making. That these happenings aren’t some magical exceptions to the physics of the universe. In such a natural universe, things such as “free will” just don’t make sense. If our decisions are tied to the physical processes of the universe, then we only have a say in them in so far as the physical processes output what we will say about them. In other words, what we think, feel, say, and do are all an output of how the universe is playing out (both large scale and small scale processes).
And even if we accept that some events don’t have a cause (e.g. certain interpretations of quantum mechanics), those un-caused events are just part of the physical process that we still have no control over.
Though I agree with such analysis for various reasons, I think the incoherence of free will has a much wider reach. In other words, we don’t have to accept a naturalistic worldview to understand that free will doesn’t make any sense what-so-ever.
We just need to understand that an event (something “happening”) must either have a cause (be an output of something that already exists), or not have a cause (just happen – not the output of anything in existence). These are the only two possibilities for events. Not just “naturalistic” events, but any event. A so-called “supernatural” event simply can’t escape this dichotomy.