Toulmin's Rhetorical Logic: What's the Warrant for Warrants?

Introduction

Argument, on virtually any model, is a movement, from reasons to claims; the basic problem for argument theory lies in distinguishing, in general terms, between legitimate and illegitimate moves. Stephen Toulmin's distinctive account is intended to be a procedural account of argument, as an alternative to the usual formalization of reasoning. A theory of reasoning must define a principle that allows movement; in formal logic this principle is represented by the material conditional.¹ Toulmin claimed, in The Uses of Argument (1958), that not all argument was reducible to logic. He offered an alternative to the material or formal conditional; he envisaged a different inference principle, which he called a warrant. He insisted that warrants, rather than being abstractions like conditionals, were bounded by institutional and disciplinary constraints, contextual boundaries he called fields. As Foss, Foss, and Trapp summarize, "the warrant assesses whether or not the trip from grounds to claim is a legitimate one" (131)—within those institutional and disciplinary constraints.

In a sense, Toulmin is subtly moving ninety degrees from the classical tradition of logic. In classical logic, the term Aristotle uses to describe the character of logical inference in the syllogism, anagkhaios, is usually translated as necessary, but it might also be rendered as constrained or compulsory; in a valid syllogism the reasoner "needs to" draw the conclusion. In contrast, in a Toulmin argument, she is allowed to draw the conclusion. A warrant, normally, is permission to do something, and that permission is conditional.² The common use of the term "warrant" in law is the prototype: a warrant to search a home is permission to search it. In many secondary texts on Toulmin's model, the warrant is called an "inference license."³

Despite the innovation of Toulmin's response to classical logic and the popularity of his model for argumentation theory, a problem still remains: Scholars are not in agreement on what a warrant is or how to identify it, either theoretically or for purposes of teaching and criticism. If our understanding of warrants remains unclear, we have made no progress in understanding argument from the innovative position that Toulmin makes possible. There is a substantial body of work on Toulmin as an intellectual figure and on the Toulmin model as a critical and pedagogical tool. But while this literature offers little help in clarifying the nature of warrants, it represents the bulk of interpretive literature on Toulmin.

The usual story about Toulmin—endorsed by supporters like Brockreide and Ehninger (1960) as well as detractors like Castaneda (1960) is that The Uses of Argument is an attempt to drive a wedge between argument and logic, for better or worse. His admirers (in speech communication) saw him as liberating the multiple possibilities of argumentation from the manacles of a simple-minded formalism, while detractors (in philosophy) thought he had given up on a notion of reason foundational to Western philosophy. We regard both camps as somewhat mistaken.

It is difficult to accept claims that Toulmin writes to undermine logic when Uses fails to even address the contemporary theories of logic. While the reigning conception of logic at the time was the first-order predicate calculus (FOPC),⁴ Toulmin does not address his criticisms to it, instead focusing his attention on syllogisms. As Castaneda notes in his contemporary review of Uses, "It should be remarked at the outset that Toulmin ignores the progress of logic in the last 120 years; he nowhere discusses anything but syllogisms" (1960, 281). Lukasiewicz had recently shown (1952) that the FOPC was not only equivalent to but more powerful than the traditional syllogistic, and so if Toulmin had intended to undermine the sovereignty of the FOPC in particular, he could have done so explicitly.⁵ So casting Toulmin as the enemy of logic seems not quite right.⁶

Yet the fans of Toulmin are not quite right either. Toulmin's work is richer and more complex than recognized by those who use it merely to justify a turn away from formalism. Toulmin is more than just the philosopher who gives blessing to...