Early emerging probabilistic estimates govern judgments about possibility

The complex probabilistic properties of specific events determine the number or range of possible outcomes they can produce (i.e., outcome entropy). Do humans use estimates of outcome entropy for real-world events to reason about what is possible? We test whether adults (N=106) and children (N=368) use such estimates to constrain their judgments about outcomes for complex, real-world events including paint mixing and skin-color inheritance. Here we show that adults’ and children’s judgments reflect awareness of outcome entropy, such that fewer outcomes are deemed possible for deterministic events than probabilistic ones. Evidence of this sophisticated capacity appears between four and five years of age. Taken together, the results suggest that outcome entropy is a fundamental and early emerging factor in human reasoning about what is possible.