In a similar vein, Hume argues that determinism is essential for the concept of free will to exist, I believe. I think the argument is that if our actions aren't controlled by our thoughts, then they're controlled by a random diceroll of bizarreness from another ontological dimension without meaning to us. I used fanciful terms to describe that, of course, but essentially its saying that since our physical thoughts are what matter to us and are what are associated with free will traditionally, the traditional concept of free will depends on physical determinism once we accept that we are not magic ghost angel souls in human bodies.

For will to cause things to happen determinism must be true, since wills are physical things.