Argument Schemes and the Evaluation of Presumptive Reasoning

The pertinence of Toulmin and Perelman/Olbrechts-Tyteca for informal logic

“…Correspondingly, argument schemes are the genus of which patterns of deductively valid argument forms and schemes for defeasible arguments are species. Some of the recent theoretical work in informal logic and its applications, especially by douglas Walton, has focused on the study of various argument schemes, on the connection between argumentation schemes and informal fallacies, and on the application of argument scheme theory to legal reasoning and to artificial intelligence (see Walton 1996Walton , 2008Blair 1999Blair , 2000Blair , 2001Pinto 1999Pinto , 2001Godden and Walton 2007;and Walton, Reed and Macagno 2008). The concept of argument schemes is also something that connects Toulmin with Perelman and Olbrechts-Tyteca, and to a discussion of their influence on informal logic I now turn.…”

“…On the other hand, Robert Pinto (1999Pinto ( , 2000 has argued that the idea of a probative argument scheme that is a kind of an analogue of a deductively valid argument form is misconceived. According to Pinto the normative question is whether a given use of an argument scheme is cogent on that occasion, not whether there are argument schemes with normative force.…”

Good Reasoning on the Toulmin Model

“…The type of exceptional circumstance that shows the conclusion to be incorrect may be said to override (Pinto, 1999) or rebut (Pollock, 1970) the warrant; a standard example is the circumstance that a bird is a penguin, which overrides the warrant that birds fly (since penguins do not fly). The type of exceptional circumstance that shows the warrant to be inapplicable even though the conclusion may nevertheless be correct, may be said to undermine (Pinto, 1999) or undercut (Pollock, 1970) the warrant; a standard example due to Pollock (1995) is the undermining of the warrant that things that look red are red by the circumstance that the object one is looking at is illuminated by a red light. If one is not justified in assuming that a warrant lacks defeaters in a particular case, then one's conclusion about that case is obviously unjustified.…”

Defeasibility in Judicial Opinion: Logical or Procedural?

“…Here, it will have to be determined which legal rule(s) ought to trump the other(s), and fundamental legal principles like justice and fairness may apply. In this way, legal arguments may be rebutted (Pollock, 1970) or overridden (Pinto, 2001) by stronger arguments for opposite conclusions.…”

“…In this way, legal arguments may be undercut (Pollock, 1970) or undermined (Pinto, 2001) by operative facts which defeat the inference at work in the argument. Thus, MacCormick (1995, p. 103) describes all legal rules as only "ordinarily necessary and presumptively sufficient.…”