 The idea of defeasibility also showed up in work on the formal theory of argumentation, including Stephen Toulmin’s  The Uses of Argument (Toulmin 1964). Toulmin, building on Hart’s observations, argues for the importance of distinguishing between warrants and rebuttals (Toulmin 1964, 101ff, 143ff). The formal theory of argumentation (van Eemeren et al. 2020; Prakken and Vreeswijk 2002) has proved a fruitful ground for the development of models of defeasible reasoning.