Some omissions seem to be causes. For example, suppose Barry promises to water Alice’s plant, doesn’t water it, and that the plant then dries up and dies. Barry’s not watering the plant – his omitting to water the plant – caused its death. But there is reason to believe that if omissions are ever causes, then there is far more causation by omission than we ordinarily think. In other words, there is reason to think the following thesis true.