A range of uses of negative epistemic constructions in German: ICH WEIß NICHT as a resource for dispreferred actions

•Examines German ICH WEIß NICHT ('I don't know') regarding complementation patterns.•Claiming to have no knowledge actually does not mean to have no knowledge.•Fully realized variants display lack of knowledge or reluctance to answer a question.•Reduced variants show tentativeness or potential inadequacy of subsequent utterances.•ICH WEIß NICHT in response to assertions and assessments functions as objection.

Our paper deals with the use of ICH WEIß NICHT ('I don't know') in German talk-in-interaction. Pursuing an Interactional Linguistics approach, we identify different interactional uses of ICH WEIß NICHT and discuss their relationship to variation in argument structure (SV(O), (O)VS, V-only). After ICH WEIß NICHT with full complementation, speakers emphasize their lack of knowledge or display reluctance to answer. In contrast, after variants without an object complement, in contrast, speakers display uncertainty about the truth of the following proposition or about its sufficiency as an answer. Thus, while uses with both subject and object tend to close a sequence or display lack of knowledge, responses without an object, in contrast, function as a prepositioned epistemic hedge or a pragmatic marker framing the following TCU. When ICH WEIß NICHT is used in response to a statement, it indexes disagreement (independently from all complementation patterns).