Models of Persuasion Dialogue

This chapter1 reviews formal dialogue systems for persuasion. In persuasion dialogues two or more participants try to resolve a conflict of opinion, each trying to persuade the other participants to adopt their point of view. Dialogue systems for persuasion regulate how such dialogues can be conducted and what their outcome is. Good dialogue systems ensure that conflicts of view can be resolved in a fair and effective way (6). The term ‘persuasion dialogue’ was coined by Walton (13) as part of his influential classification of dialogues into six types according to their goal. While persuasion aims to resolve a difference of opinion, negotiation tries to resolve a conflict of interest by reaching a deal, information seeking aims at transferring information, deliberationdeliberation wants to reach a decision on a course of action, inquiry is aimed at “growth of knowledge and agreement” and quarrel is the verbal substitute of a fight. This classification leaves room for shifts of dialogues of one type to another. In particular, other types of dialogues can shift to persuasion when a conflict of opinion arises. For example, in information-seeking a conflict of opinion could arise on the credibility of a source of information, in deliberation the participants may disagree about likely effects of plans or actions and in negotiation they may disagree about the reasons why a proposal is in one’s interest. The formal study of dialogue systems for persuasion was initiated by Hamblin (5). Initially, the topic was studied only within philosophical logic and argumentation theory (15; 7), but later several fields of computer science also became interested in this topic. In general AI the embedding of nonmonotonic logic in models of persuasion dialogue was seen as a way to deal with resource-bounded reasoning (6; 2), while in AI & Law persuasion was seen as an appropriate model of legal