Non-verbal rationality? 2-year-old children, dogs and pigs show unselective responses to unreliability, but to different degrees

Some philosophers argue that reflection is key to rational thinking. By tying reflective thinking to language, they struggle to account for minimally verbal infants and exclude non-human animals. This study assessed processing of undermining defeaters—a basic form of reflective thinking—in 36 two-year-old British children (13 female; Mage = 30.4 months, 98% White), 39 dogs (18 female), and 21 pigs (9 female), tested between 2022 and 2023. Informants acted on two screens: one informant reliably indicated a rewarded location, the other informant did not. Informants switched actions twice, prompting subjects to infer their reliability. Willingness to follow informants’ indications did not differ between reliable and unreliable informants. However, reduced following in later trials suggests a response to uncertainty or an undermining defeater.