The role of epistemic reasoning in mutual exclusivity inferences

When encountering a novel word, adults and children as young as 12 months old often reason that it refers to a novel object rather than one with an existing name - making a 'mutual exclusivity inference.' We explored the mechanism of this inference, aiming to differentiate between three hypotheses: whether mutual exclusivity arises due to reasoning about a specific speaker's knowledge, projection of one's own egocentric knowledge, or reasoning generally about the conventionality of labels. Adults and 3.5-5-year-old children in our experiment heard a label being either taught or invented on the spot. They were then asked to decide what another label, produced by a speaker who was absent during the first label's introduction, referred to. Our results revealed that adults and older children made more mutual exclusivity inferences when the first label was taught compared to when it was invented. Additionally, they were more likely to exclude the previously-labeled object in the referential choice if they judged that the speaker also knew the label, regardless of how the label was introduced. Both adults and older children also showed sensitivity to the speaker's explicit statements of knowledge, excluding an object that the speaker explicitly stated that he did not know the name of from their referential choice. These results suggested that adults and older children reasoned about a specific speaker's knowledge of labels in order to make mutual exclusivity inferences, likely in the form of a Gricean inference where they reasoned about possible alternative utterances a speaker could have said.