Analyzing the roles of challenge and defense in argumentation.

• Author: Ricco, Robert B.

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). A locution consists of one or more statements or propositions and a specific communicative action the speaker intends to accomplish through them. Arguments feature various types of locution including assertions, concessions, and challenges (van Eemeren and Grootendorst, 1992, pp. 37-40; van Eemeren, Grootendorst, Jackson, and Jacobs, 1993, pp. 25-30). The model proposed here identifies several different kinds of challenge and includes locution types that have not previously been employed in models of argument. These latter consist of direct defenses, indirect defenses, and supporting justifications. Each of the locutions of the model is described at length below. In addition, the proposed model recognizes that moves in an argument may be represented at more than one level of spe ech act (van Eemeren and Grootendorst, 1992; pp. 28-30). Thus a given statement may function as a challenge and a defense at one and the same time.

Like all manner of discourse, arguments may be assumed to follow certain procedural rules. Among other things, these rules spell out the obligations incurred by participants through the various moves available and determine what impact a move has on the burden of proof in an argument (van Eemeren et al., 1996, pp. 263-271; Walton and Krabbe, 1995, pp. 150-152). Although procedural rules are likely to vary somewhat with the type of argument and the nature of the participants, the dialectical model of argument proposed here claims that at least the following two rules are commonly observed in argumentation. Procedural Rule 1 (PR1) holds that the participants in an argument are obligated to provide evidence for the truth or relevance of their statements, the soundness of their inferences, and for other elements of their argument if called upon to do so (van Eemeren and Grootendorst, 1988, 1992, pp. 208 -209; Once, 1975). For this reason, a challenge typically shifts the burden of proof onto the challenged parti cipant who must attempt to satisfy the concerns raised by the challenger. Failure to meet this obligation leaves one open to a charge of evading burden of proof (van Eemeren et al., 1996, pp. 300-306; Walton, 1996a, p. 12) and could result in the neutralization or loss of the challenged element (Rips, 1998; Walton and Krabbe, 1995, pp. 140-154). Procedural Rule 2 (PR2), however, holds that the challenger also incurs an obligation to provide an explanation or rationale for that challenge if requested. Therefore, when challenged, an arguer can respond with a challenge of her own which targets specific statements in the explanation or rationale accompanying the opponent's challenge and this would not represent an inappropriately evasive move (Walton, 1996a, pp. 129-131). Thus the procedural rules of the model allow for a challenge to be used as a defensive move under certain conditions. Challenge is a legitimate defense when it targets the rationale for the opponent's challenge, but not when it is aimed at some other element in the opponent's argument.

The two procedural rules of the model derive, ultimately, from the cooperative principle and the maxims of conversation (Grice, 1975). Thus the maxims of quality, relevance, and manner, for example, obligate the speaker in a conversation to justify the truth, relevance, consistency, logicality, etc., of her contributions if called upon to do so. Argumentation may be thought of as a process of conversational repair (Jacobs, 1987; Jacobs and Jackson, 1982) arising when one or more communicants is unable to arrive at an interpretation of their partner's contributions that convincingly upholds each of the maxims. Argument begins with, and is sustained by, explicit requests that a communicant show how her contributions conform to the maxims (PR1). One demands evidence, for example, that a claim is true or relevant. By the same token, when one questions whether a partner's contributions uphold the maxims, one implies that one genuinely lacks knowledge of how the maxims have been met and can demonstrate this lack i f called upon to do so (PR2).

In addition to procedural rules, another type of rule is of particular importance in accounts of argumentation. These are commitment rules. The totality of statements from an argument that a participant accepts as true or reasonably likely represents that individual's commitment set (Mackenzie, 1990; Rescher, 1977, pp. 20-28; Walton, 1989). Commitments can be statements that are explicit in the discussion or that are merely implied by the explicit statements (Walton and Krabbe, 1995, pp. 124-126). As the argument progresses, statements are either removed from the arguer's commitment set or inserted into it. A set of commitment rules determine which statements go in or out of a commitment set on any given move (Mackenzie, 1990, 1993; Rips, 1998). Some models of argument propose rules that are relatively conservative in nature. Under conservative rules, a statement can only enter one's commitment set if one has asserted or conceded it and statements are only removed through retraction (Rips, 1998). Alternative ly, commitment rules might be fairly liberal such that commitments may also be incurred by failing to challenge an opponent's assertion--silence betokens consent--and commitments may be lost by failing to defend a statement that has been challenged (Rescher, 1977; Walton and Krabbe, 1995, pp. 167-172). The content of each participant's commitment set at any given point in the argument is critical because each arguer is attempting to make their case from within the commitment set of their opponent. Thus each seeks to get certain statements admitted into their opponent's set while blocking other statements from entering their own set.

One problem with strictly conservative accounts of commitment is that they do not seem capable of handling the roles of challenge and defense and they make it unlikely that arguers will reach agreement on key claims (Rips...