Toulmin’s Jurisprudential Model, Inductive Probabilty, and Computation

1. The Toulmin Model and Assessing Connection Adequ acy Stephen Toulmin has established a connection between legal reasoning and a general theory of argument through his jurisprudential model of "the layout of arguments." In introducing this model in The Uses of Argument, he seeks to reject the Aristotelian (mathematical/geometrical/syllogistic) model of argument structure, which analyses arguments as syllogisms with minor premise, major premise, conclusion, in favor of a more complex model representing distinctly greater functional diversity among the elements constituting an argument. The distinctions are modelled on those made in jurisprudence in analysing the types of propositions that may enter into a legal argument or the types of questions one may raise about those propositions. The model is intended as a generalization of these distinctions, applicable to arguments in general. The Toulmin model, as is well known, involves six different elements. Any argument will seek to establish some claim. The facts presented to support or justify that claim are the data. Propositions purporting to show or explain the legitimacy of the step from the data to the claim, corresponding to rules or inference−licenses, are warrants. Different warrants involve different degrees of force. As Toulmin points out, in some cases, given the data, the warrant authorizes accepting the claim "unequivocally" while on others one can accept the claim only "tentatively" or with "qualifications." In the former case, "these warrants entitle us...to qualify our conclusion with the adverb ‘necessarily’;" in the latter "other modal qualifiers, such as ‘probably’ and ‘presumably’ are in place." (1958, pp. 100−101) Such modal qualifiers are a further element in arguments, besides claims data, and warrants. The excep− tions or qualifications——rebuttals as Toulmin calls them——are a further element in arguments. Finally, one may question not just whether a given warrant is applicable in a given case but whether the warrant is acceptable in general or at all. "Standing behind our warrants,...there will normally be other assurances, without which the warrants themselves would possess neither authority nor currency——these other things we may refer to as the backing...of the warrants." (1958, p. 103) Such backing then constitutes a still further type of element in arguments. Toulmin pictures how these six elements fit together through the following diagram: