Open Access

This article examines a recurrent format that speakers use for defining ordinary expressions or technical terms. Drawing on data from four different languages - Flemish, French, German, and Italian - it focuses on definitions in which a definiendum is first followed by a negative definitional component (‘definiendum is not X’), and then by a positive definitional component (‘definiendum is Y’). The analysis shows that by employing this format, speakers display sensitivity towards a potential meaning of the definiendum that recipients could have taken to be valid. By negating this meaning, speakers discard this possible, yet unintended understanding. The format serves three distinct interactional purposes: (a) it is used for argumentation, e.g. in discussions and political debates, (b) it works as a resource for imparting knowledge, e.g. in expert talk and instructions, and (c) it is employed, in ordinary conversation, for securing the addressee's correct understanding of a possibly problematic expression. The findings contribute to our understanding of how epistemic claims and displays relate to the turn-constructional and sequential organization of talk. They also show that the much quoted ‘problem of meaning’ is, first and foremost, a participant's problem.