This article contributes to a better understanding of dystopia’s practical aims by offering a critical defense of what Gregory Claeys calls the “Atwood Principle.” Derived from the writings of Canadian author Margaret Atwood, it establishes a yardstick for separating speculative fiction from science fiction. I argue that, rather than elevating it to the status of a genre definer, the Atwood Principle should be vindicated in terms of a heuristic device for contextually identifying the central mechanism underpinning dystopias: warning through extrapolation. The real challenge, then, is how to make sense of the complex functioning of extrapolation. Instead of viewing it in mechanistic terms, my suggestion is to envisage extrapolation as a dynamic process involving both realism and estrangement. I illustrate this through a contrast between two kinds of stories about the current climate emergency: cautionary and post-cautionary tales of the Anthropocene.