Problems with regard to the analysis of argumentative partly discourse arise from definitorial disconformity. In this article, Informal argument is taken as the primary definition to study the basic structure of argument from a fragment of an Agatha Christie novel. Bilmes' account of the notions of Formulation (F) and Decision (D+/D-) are adapted to describe the relations of opposition which are displayed in informal argument. The minimal structure of argument is represented by the formula F/D-/D-, in which F is a (...) speaker's personal composition of a ‘fact’, the first D- is the disconfirming uptake of it by another speaker and the second D- is the completing disconfirming uptake by the initial speaker. Some of the speaker's possibilities to initiate an argument by expressing a Formulation are explored, as well as the social and cultural norms which play a role in argument-initiation and the concepts of ‘win’ and ‘loss’. (shrink)