Deductivism as an interpretive strategy: a reply to Groarke's recent defense of reconstructive deductivism.

• Author: Godden, David M.

1--INTRODUCTION

Debates concerning deductivism seem to be a hallmark of the informal logic tradition. The very first issues of the Informal Logic Newsletter, published in the late 1970s, were the site of a sustained debate concerning whether inductive arguments could be distinguished categorically from deductive arguments and, if so, how (Fohr, 1980a, 1980b; Govier, 1980a; Hitchcock, 1980; Johnson, 1980; Weddle, 1979, 1980). (1) At the time, the prevailing view was that deductive and inductive marked kinds of arguments. This prevailing opinion was challenged by Hitchcock (1980) who, following Skyrms (1986, pp. 6-13), proposed that "we regard the distinction between deductive and inductive as a broad and exhaustive distinction between types of validity" (p. 9). This proposal that inductive and deductive are "standard[s] for appraising arguments" (Govier, 1980b, p. 4) has been adopted subsequently by many theorists. For instance, Machina (1985) has argued that "inductive logic [like deductive logic] will be defined by reference to its central concepts and rules" and not in relation to a special set of arguments (p. 578). (Johnson [2000, ch. 3], on the other hand, seems content to continue to use the categories inductive and deductive to mark kinds of arguments.) It also has been argued that additional evaluative standards of argument, e.g., conductive and analogical (Govier, 1980b, p. 3), must be included in any comprehensive theory of argument evaluation.

In the context of this discussion, many questions regarding the role that deduction should play in our theories of argument remain unanswered. Among these is the question whether and how deduction can provide a basis for the interpretation of argument. This essay considers attempts to defend deductivism as a reconstructive thesis as they have appeared in recent informal logic and argumentation theory literatures. These attempts are primarily Groarke's (1992, 1995, 1999, 2002), and I consider them to be representative of the kinds of arguments that could be offered in defense of reconstructive deductivism. The essay begins with the observation that deductivism can be formulated as an evaluative and as a reconstructive (or interpretive) thesis, and some initial observations concerning the relationship between these two theses. I note that one way of defending deductivism as an interpretive thesis is to assert the correctness of deductivism as an evaluative thesis (section 2). Against this, I argue that there are pluralities of nonequivalent standards of evidence against which arguments can be evaluated, and that not all of these are reducible to the standard of deductive validity (sections 3-5). Therefore, the correctness of deductivism as an evaluative thesis cannot justify deductivism as an interpretive thesis. I then consider and reject alternative attempts to defend reconstructive deductivism by recourse to theories about the proper semantics of indicator words and the commitments of arguers (section 6). In place of these approaches, I argue that the interpretation of arguments as deductive must be justified on grounds that involve considerations that are not exclusively evaluative, including contextual and situational features of arguments as well as psychological facts about arguers. In particular I argue that, to interpret an argument correctly as deductive, it must be established that the arguer is, or ought to be, aiming at the deductive standard of evidence. I conclude (in section 7) that deductivism as an evaluative thesis can and should be justified independently of deductivism as an interpretive thesis.

2--DEDUCTIVISM

There is some question how the thesis of deductivism should be understood. On one hand, sometimes deductivism is presented as an evaluative thesis, i.e., that [D1] "all good arguments are deductively valid" (Groarke, 1992, p. 113). (2) This is a thesis about the proper standards of evidence by which arguments should be evaluated. Presumably it means that the only acceptable link between an argument's premises and its conclusion is that in which it is not logically possible for the conclusion to be false given the truth of the premises. The only good arguments are those for which no counterexample can be found, irrespective of the plausibility of that counterexample. Defenders of deductivism are quick to add that deductivism includes not only formal but material validity. Formal validity is explained in terms of the form or structure of the argument such that any substitution instance of a valid argument form will be a valid argument. Material validity is explained in terms of the meanings of the nonlogical terms of the argument. (3)

The word deductivism, though, is not al ways used to mark this thesis about the standards by which arguments should be evaluated. Sometimes deductivism is construed as the interpretive thesis that [D2] "natural language arguments should be understood as attempts to formulate deductive arguments" (Groarke, 1999, p. 2). This is a thesis about how natural language arguments should be understood, interpreted, or modelled. Indeed, it sometimes is stated explicitly as such: "I understand deductivism as the view that ordinary arguments are best analyzed as deductive inferences" (Groarke, 1995, p. 139).

I am concerned primarily with deductivism as an interpretive thesis [D2] (although, as I will note momentarily, the two theses are related). Before proceeding to my own consideration of deductivism, I would like to recognize those objections that typically are raised against it. The standard objections to deductivism (as identified by Groarke [1992] and Gerritsen [1994] and attributed to authors like Govier [1987]) are three: (i) deductivism does not permit differing degrees of evidential support between premises and conclusions; (ii) deductivism either fails to provide an account of fallacies, or provides an incorrect account of fallacies; and finally (iii) deductivism does not provide a defensible interpretive strategy for describing the structure of natural language arguments.

Given my concern with deductivism as an interpretive strategy [D2], I am interested primarily in the third objection. However, in the sections that follow I deal directly with the first objection, which challenges deductivism as an evaluative thesis [D1]. (4) The reason for this is that the correctness of deductivism as an evaluative thesis can be invoked as a reason for its acceptability as an interpretive strategy. Clearly, if [D1] were true--that is, if the only acceptable standard of evidence was embodied in the rules of deduction--then [D2] would follow as a consequence. So, any discussion of deductivism as an interpretive thesis must consider deductivism as an evaluative thesis.

3--DEDUCTIVISM AS AN EVALUATIVE THESIS

One way, then, to justify deductivism as an interpretive thesis is to assert deductivism as an evaluative thesis. Govier (1987) observes: "The crucial point of deductivism is that anything less than a relation of entailment between premises and conclusion is unsatisfactory. On this theory there are absolutely no degrees or kinds of logical support" (p. 23). (5) In this respect, deductivism asks of any argument two questions: (i) are the premises of the argument true (or, perhaps, acceptable)? and (ii) does the conclusion follow from the premises? (Govier, 1987, p. 23)

Another way of asking this second question is: Do the premises give us (as epistemic agents) rational grounds for asserting or adopting the conclusion? Asking the question this way highlights two features of the rational structure of arguments. First, reasons are understood in a practical sense as reasons for either asserting or assenting to some claim or belief. To assert a claim is to put it forth as having met some relevant epistemic standard (e.g., truth or acceptability). To adopt a claim is to accept it as having met some similar standard. Second, our notion of a reason is explained in terms of evidence. The standards with which we evaluate arguments are standards of evidence. Taken together, these standards constitute and exemplify our concept of evidence, and when they change, so can our concept of evidence.

Deductivism upholds the standard of validity. Informally, an argument is valid if and only if it is not logically possible for the conclusion to be false given the truth of the premises (Groarke, 1992, p. 113). That is, the assumption that all of the premises of an argument are true is inconsistent with the assumption that its conclusion is false; it results in a (formal or material) contradiction. Groarke rightly points out that this standard should not be equated with formal validity; material validity will do just as nicely. (6) Groarke (1999) also rebuts accounts of deductivism that "confuse this notion of necessity [i.e., necessary entailment] with the notion that the conclusion of a deductive argument is necessarily true if the premises are true" (p. 3; cf. 1995, pp. 139-140). The concept of necessity embodied in deductivism does not imply that the conclusion is necessarily true; rather "it implies that the conclusion of a deductive argument must be as certain as its premises. A deductive argument should therefore be described as 'certainty preserving' rather than 'certainty establishing'" (Groarke, 1999, p. 3). (7)

4--STANDARDS OF EVIDENCE

Groarke's point, above, is well-taken, but his correction of these "widespread misconceptions" does not achieve his theoretical goals. Groarke (1999) goes on to infer that a purely deductive account of the link between premise and conclusion can be used to represent and preserve relations other than truth or certainty (pp. 4-5). To see his mistake, we first must acknowledge that there are a variety of nonequivalent standards of evidence. Rhetorically, arguments can be evaluated purely with respect to their effectiveness in eliciting assent to, or acceptance of, a conclusion. In a...