Do Monkeys and Young Children Understand Exclusive "Or" Relations? A Commentary on Ferrigno et al. (2021)

Ferrigno et al. (2021) claim to provide evidence that monkeys can reason through the disjunctive syllogism (given A or B, not A, therefore B) and conclude that monkeys therefore understand logical "or" relations. Yet their data fail to provide evidence that the baboons they tested understood the exclusive "or" relations in the experimental task. For two mutually exclusive possibilities-A or B-the monkeys appeared to infer that B was true when A was shown to be false, but they failed to infer that B was false when A was shown to be true. In our own research, we recently found an identical response pattern in 2.5- to 4-year-old children, whereas 5-year-olds demonstrated that they could make both inferences. The monkeys' and younger children's responses are instead consistent with an incorrect understanding of A and B as having an inclusive "or" relation. Only the older children provided compelling evidence of representing the exclusive "or" relation between A and B.