Abstract
Preference is a key concept in argumentation to represent the comparative strength of arguments. In abstract argumentation, it is represented by an ordinal comparative, or by a numerical function. In this chapter, we study the role of comparative preference in abstract argumentation, and numerical preferences are studied in an accompanying chapter. This chapter consists of two parts. In the first part, we survey four reductions discussed in the literature to provide semantics to preference-based argumentation frameworks, and we present ten principles for such semantics. Some of these principles have been mentioned in the literature before, and some of them are new. We provide a complete analysis for the four Dung semantics, based on these four reductions and the ten principles. In the second part of the chapter, we give an outlook of the various open research challenges concerning preference in abstract argumentation. We discuss alternative semantics not based on reductions, principles in the context of symmetric attack, the relation to structured argumentation, and the dynamics of preference and argumentation.