ABA+: Assumption-Based Argumentation with Preferences

We present ABA+, a new approach to handling preferences in a well known structured argumentation formalism, Assumption-Based Argumentation (ABA). In ABA+, preference information given over assumptions is incorporated directly into the attack relation, thus resulting in attack reversal. ABA+ conservatively extends ABA and exhibits various desirable features regarding relationship among argumentation semantics as well as preference handling. We also introduce Weak Contraposition, a principle concerning reasoning with rules and preferences that relaxes the standard principle of contraposition, while guaranteeing additional desirable features for ABA+.