Proceedings of the Annual Meeting of the Cognitive Science Society

Modal concepts—representations of possibility, necessity, and impossibility—play a central role in human thought. Some argue that these are uniquely human and dependent on modal language, whereas others propose earlier developmental and evolutionary emergences. Recent success by rhesus macaques on a modified 3-cup task supports the latter view. Here, three-year-old children (N =144), who struggle with modal words, completed equivalent modified 3-cup tasks across three experiments. When preserving most features of the original 3-cup task—contrasting a guaranteed reward with a possible reward or its absence—children mirrored macaque performance and did not exceed chance. However, children successfully preferred a guaranteed reward to a possible reward or non-reward. A follow-up experiment confirmed that our paradigms did not bias participants towards the guaranteed side. Although this pattern broadly paralleled macaques, evidence for a between-experiments difference in performance was weaker, likely reflecting different primary constraints on 3-year-olds' modal reasoning abilities.