Analyzing the Roles of Challenge and Defense in Argumentation

The reasoning employed by participants in everyday, informal arguments is, to varying degrees, dialogical or dialectical in nature (Blair and Johnson, 1987; van Eemeren et al., 1996, pp. 2-5; Rips, 1998). That is, arguments do not consist of two relatively distinct lines of reasoning constructed independently of one another. Arguers cannot simply derive or demonstrate their thesis (Parsons, 1996). They must convince an opponent who may be attempting to support their own counter-thesis and who is free to raise objections. Each of the two opposing lines of reasoning in an argument engenders a critical awareness of the other and develops in response to the other (Missimer, 1994; Salmon and Zeitz, 1995). The reasoning of arguers reflects multiple concerns-supporting a thesis, subjecting the opponent's claims to critical doubt, and anticipating and defending against objections raised with respect to one's own claims (Walton, 1985; 1989). Subjecting claims to critical doubt occurs through the use of challenges (Salmon and Zeitz, 1995). Challenges may call into question the acceptability of a statement, the connection between a statement and the claim it is meant to support, or any number of other aspects of an argument (Brandt, Quiroz, and Apotheloz, 1991; Freeman, 1991, pp. 36-46). Advancing a challenge typically shifts the burden of proof in an argument and participants are then under some obligation to respond to a challenge by conceding the point or offering a defense (Bailenson and Rips, 1996; Rescher, 1977, pp. 20-28; Walton, 1996a). Particular forms of challenge call for specific lines of defense. As such, challenges made to an arguer's contributions over the course of an argument may be said to drive the construction and articulation of that arguer's line of reasoning (Apotheloz, Brandt, and Quiroz, 1993; Muntigl and Turnbull, 1998; Salmon and Zeitz, 1995; Rescher, 1977, pp. 9-14; Rips, 1998). Some challenges are also accompanied by su pporting justification consisting of one or more statements backing up the challenge (Salmon and Zeitz, 1995). Thus challenges may represent an important source of new assertions in an argument both by way of the defensive moves they motivate and through the rationale or justification supporting the challenge. The present paper offers an analysis of the roles that challenge and defense play in informal argumentation. The analysis is then applied to argumentative exchanges from internet discussion groups. DIALECTICAL MODEL OF ARGUMENT The analysis of challenge and defense presented here proceeds from a dialectical model of argument (van Eemeren et al. 1996, pp. 246-273; Walton and Krabbe, 1995). In a dialectical model, argumentation is modeled as a unique type of dialogue or discourse having game-like properties (Mackenzie, 1985; Walton, 1989, 1998, pp. 6-7) including a methodical and strategic exchange of moves in which the participants take turns. Arguments are initiated by some conflict or difference of opinion as regards an issue. One participant advances a thesis and this is subsequently disputed by the second participant. This act of disagreement may be represented as the posing of a counter-thesis which is either contradictory or contrary to the thesis (Walton, 1989). The goal of each participant in an argument is to justify or demonstrate their thesis by using only statements acceptable to their opponent--so as to persuade or convince them--while at the same time avoiding concession of statements that would enable the opponent to establish her thesis (Walton, 1985, 1989). The use of challenge is important in avoiding concession of a statement while the use of defense is critical to gaining acceptance for a statement (Mackenzie, 1990; Rips, 1998; Walton and Krabbe, 1995). In recognition of the fact that arguments typically take place within and through discourse, dialectical models represent the individual moves in an argument as speech acts or locutions (Jacobs, 1987, 1989; Jacobs and Jackson, 1982). …