I tend to agree with Sam Harris in that free will is an illusion. If you don’t know what thought is going to arise next (and you don’t), how can you think you’re the author and not the narrator? Free choice would mean deciding which thought to have ad infinitum. Consider Charles Whitman, The Texas Tower Sniper, who shot and killed several people in 1966. He left a note (he knew he’d be killed) saying that he believed there was something physically wrong in his brain, causing him to have homicidal thoughts. An autopsy revealed a large brain tumor pressing on an area associated with feelings of anger and violence. If your thoughts can be affected by the physical structure of your brain (in fact, some believe it is the changing of the physical structure of the brain that enables memory and consciousness), then free will is tentative, indeed.