Multiple sources of competence underlying the comprehension of inconsistencies: a developmental investigation.

How do children know the sentence "the glass is empty and not empty" is inconsistent? One possibility is that they are sensitive to the formal structure of the sentences and know that a proposition and its negation cannot be jointly true. Alternatively, they could represent the 2 state of affairs referred to and realize that these are incommensurate, that is, that a glass cannot simultaneously be empty and contain something. In 2 studies, the authors investigated how children (N = 186; ages 4-8) acquire competence to notice inconsistencies. The authors found that children could determine that 2 states of affairs were incommensurate before being able to determine that statements of the form p and not-p were inconsistent. The results demonstrate that competence in understanding inconsistent relations depends on (a) the ability to represent 2 states of affairs and (b) the ability to process negation in the context of an inconsistency. The authors discuss these results in relation to sources of competence that may underlie the assessment of such simple inconsistencies.