Rationalist fiction (or rational fiction) is a subgenre of speculative fiction that emphasizes consistent world-building and the application of rationality to resolve narrative conflicts. Major news outlets, including The New York Times and The Washington Post, have identified works in the genre as sharing a core focus on human cognitive processes and logical problem-solving. The genre often functions as a "pedagogical fiction," where the narrative intentionally teaches the reader specific mental models or scientific concepts through the characters' actions.
The movement's development is often linked to the 2010 work Harry Potter and the Methods of Rationality (HPMOR) by Eliezer Yudkowsky, which utilized J. K. Rowling's universe to explore cognitive science. While the genre's formalization is associated with the LessWrong community, it draws influence from the Golden Age of Science Fiction and the rigorous world-building traditions of authors like Isaac Asimov. Unlike traditional hard science fiction, which focuses on the accuracy of the physical sciences, rationalist fiction focuses on the accuracy of the cognitive and social sciences.
Rationalist fiction is defined by structural principles that emphasize transparency and logic:
Following HPMOR, the genre expanded into other universes, often under the shorthand label ratfic. This expansion was heavily driven by online serial platforms and community-driven feedback loops. Alexander Wales used the Lex Luthor perspective in The Metropolitan Man to explore existential risk and the logical implications of a nearly omnipotent alien living on Earth. Other works include Mother of Learning, which applied rationalist principles to the "time loop" trope, and qntm's Ra, which reimagined magic as a branch of particle physics discovered in the 1970s.
Mainstream literary works are often categorized as being in dialogue with rationalist fiction due to their focus on credible biology and the mechanics of consciousness. Peter Watts's Blindsight and Ray Nayler's The Mountain in the Sea have been cited by critics at The New York Times, The Guardian, and Slate for their rigorous, logical approach to non-human intelligence. These works are distinguished from typical speculative fiction by their use of scientific paradigms to resolve central mysteries. The genre continues to evolve through collaborative writing and the "rationalist" blogging ecosystem, where tropes are analyzed and refined in real-time.