Differentiating "could" from "should": Developmental changes in modal cognition.

Young children have difficulty in distinguishing events that violate physical laws (impossible events) from those that violate mere physical regularities (improbable events). They judge both as "impossible." Young children also have difficulty in distinguishing events that violate moral laws (immoral events) from events that violate mere social regularities (unconventional events). They judge both as "wrong." In this set of studies, we explored the possibility that both difficulties arise from a more general deficit in modal cognition, or the way in which children represent and reason about possibilities. Participants (80 children aged 3-10years and 101 adults) were shown impossible, improbable, unconventional, and immoral events and were asked to judge whether the events could occur in real life and whether they would be okay to do. Preschool-aged children not only had difficulty distinguishing law-violating events from regularity-violating events but also had difficulty distinguishing the two modal questions themselves, judging physically abnormal events (e.g., floating in the air) as immoral and judging socially abnormal events (e.g., lying to a parent) as impossible. These findings were replicated in a second study where participants (74 children and 78 adults) judged whether the events under consideration would require magic (a specific consequence of impossibility) or would require punishment (a specific consequence of impermissibility). Our findings imply that young children's modal representations clearly distinguish abnormal events from ordinary events but do not clearly distinguish different types of abnormal events from each other. That is, the distinction between whether an event could occur and whether an event should occur must be learned.