 One important branch of medieval logic developed in treatises called De obligationibus dealt, roughly speaking, with how an increasing set of true and false propositions might remain coherent in a disputation. According to thirteenth-century rules, a false present tense statement could be accepted as a starting point only if it was taken to refer to a moment of time different from the actual one. Scotus deleted this rule, based on the Aristotelian axiom of the necessity of the present, and later theories accepted the Scotist revision. In this new form, obligations logic could be regarded as a theory of how to analyze possible states of affairs and their mutual relationships. These discussions influenced the philosophical theory of counterfactual conditionals (Yrjönsuuri 1994, 2001; Gelber 2004; Dutilh Novaes 2007).