This article uses a conversation analytic framework to describe a type of wh-question used to challenge a prior utterance, specifically to challenge the basis for or right to do an action done by the prior utterance. These wh-questions are able to do challenging because, rather than asking for new information, they are used to convey a strong epistemic stance of the questioner, a negative assertion. The utterances are designed as requests for an account for a prior claim or action, but (...) by conveying a negative assertion, they suggest that there is no adequate account available and, thus, that there are no grounds for the prior claim or action. The use of these questions in institutional settings can display participants' orientation to institutional goals, norms and roles, showing that institutional roles can thus be enacted, and goals accomplished, by means of practices of talk which are not, themselves, institutionally specific. (shrink)