'We know our will is free and there's an end on't'. Dr. Johnson's words express a widely held intuition about free will, namely that our actions are the effects of our choices and decisions, and these choices and decisions are not the effects of antecedent causes. At least for some of our actions, the causal chain begins with conscious deliberation about what to do. It is this intuition that informs our attitudes to wrongdoing and justifies the belief that wrongdoers should be punished because this is what they deserve. However, we also know that we live in a world in which events have...