Logical Concepts of (Im)possibility Guide Young Children's Decision-Making

The human capacity for rational decisions hinges on modal judgment: the discernment of what could, has to, or cannot happen. This ability was proposed to be a late outcome of human cognitive development, contingent on the mastery of linguistic structures. Here, we show that preschool-age children are capable of sophisticated forms of modal judgment. In two experiments, 96 children (aged 34-65 months) helped an agent attain a benefit or avoid harm. Consistent with logical distinctions, we found that children perform best when faced with choices that cross the logical categories of necessity, possibility, and impossibility, while they struggle with choices only differing in probability. Our results reveal that preschoolers spontaneously recruit logical concepts required for modal judgment, which likely predates modal language. Summary Rational plans and decisions under uncertainty hinge on modal judgment: the discernment between goals that are attainable, unattainable, or guaranteed. It has been proposed that modal concepts are not available prior to the age of 4 years and the acquisition of modal words like "can" and "have to." In a novel paradigm, we found that preschoolers successfully make one-shot decisions between options that cross logical categories (i.e., necessity vs. possibility, possibility vs. impossibility). In contrast, 3-year-olds struggled when asked to compare probabilities within the same category (i.e., highly probable possibility vs. improbable possibility). Our findings reveal that young children have a logical understanding of modal categories that emerges spontaneously to guide their decisions and predates the mastery of modal language.