 Black, an evil neurosurgeon, wishes to see Smith dead but is unwilling to do the deed himself. Knowing that Mary Jones also despises Smith and will have a single good opportunity to kill him, Black inserts a mechanism into Jones’s brain that enables Black to monitor and to control Jones’s neurological activity. If the activity in Jones’s brain suggests that she is on the verge of deciding not to kill Smith when the opportunity arises, Black’s mechanism will intervene and cause Jones to decide to commit the murder. On the other hand, if Jones decides to murder Smith on her own, the mechanism will not intervene. It will merely monitor but will not affect her neurological function. Now suppose that when the occasion arises, Jones decides to kill Smith without any “help” from Black’s mechanism. In the judgment of Frankfurt and most others, Jones is morally responsible for her act. Nonetheless, it appears that she is unable to do otherwise since if she had attempted to do so, she would have been thwarted by Black’s device.