A key challenge for agent architectures and programming paradigms is to account for defeasible reasoning over mental attitudes and to provide associated conflict resolution mechanisms. A growing body of work is looking to address these challenges by proposing argumentation based approaches to agent defeasible and practical reasoning. This work conforms to Dung’s seminal argumentation semantics. In this paper we review our previous work in which we extend Dung’s semantics to allow for inclusion of arguments that express preferences between other arguments. In this way we account for the fact that preference information required to resolve conflicts is itself defeasible and may be conflicting. We then propose the extended semantics as a semantics for agent defeasible and practical reasoning, and substantiate this claim by showing how our semantics can characterise, and indeed provide a framework for extending, existing approaches to agent reasoning over beliefs, goals, and actions...