Comparing decisions on the basis of a bipolar typology of arguments

Arguments play two types of roles w.r.t. decision, namely helping to select an alternative, or to explain a choice. Until now, the various attempts at formalizing argument-based decision making have relied only on one type of arguments, in favor of or against alternatives. The paper proposes a systematic typology that identifies eight types of arguments, some of them being weaker than others. First the setting emphasizes the bipolar nature of the evaluation of decision results by making an explicit distinction between prioritized goals to be pursued, and prioritized rejections that are stumbling blocks to be avoided. This is the basis for an argumentative framework for decision. Each decision is supported by arguments emphasizing its positive consequences in terms of goals certainly satisfied, goals possibly satisfied, rejections certainly avoided and rejections possibly avoided. A decision can also be attacked by arguments emphasizing its negative consequences in terms of certainly or possibly missed goals, or rejections certainly or possibly led to by that decision. The logical properties of this framework are studied. The richness of the proposed typology makes it possible to partition the set of alternatives into four classes, giving thus a status to decisions, which may be recommended, discommended, controversial or neutral. Each class may be refined into sub-classes taking advantage of the strengths of the different types of arguments. This typology is also helpful from an explanation point of view for being able to use the right type of arguments depending on the context. The paper also presents a preliminary investigation on decision principles that can be used for comparing decisions. Three classes of principles can be considered: unipolar, bipolar or non-polar principles depending on whether i) only arguments pro or only arguments cons, or ii) both types, or iii) an aggregation of them into a meta-argument are used.