Perceived similarity explains beliefs about possibility

No one has ever performed a successful brain transplant or traveled the Milky Way, but people often see these events as within the realm of possibility. Across six preregistered experiments (N = 1,472) we explore whether American adults' beliefs about possibility are driven by perceptions of similarity to known events. We find that people's confidence in the possibility of hypothetical future events is strongly predicted by how similar they think the events are to events that have already happened. We find that perceived similarity explains possibility ratings better than how desirable people think the events are, or how morally good or bad they think it would be to accomplish them. We also show that similarity to past events is a better predictor of people's beliefs about future possibilities than counterfactual similarity or similarity to events in fiction. We find mixed evidence regarding whether prompting participants to consider similarity shifts their beliefs about possibility. Our findings suggest that people may reflexively use memories of known events to guide their inferences about what is possible. (PsycInfo Database Record (c) 2025 APA, all rights reserved).