ARGUMENTATION METHODS OF ARGUMENT RECONSTRUCTION

Douglas WaltonCRRAR

FMAR, Konstanz, Sept. 21, 2012

Argumentation Schemes• The current problem with trying to evaluate plausible reasoning using

systems of weights with numerical values is that there can be many ways of doing this.

• Argumentation takes the approach of using forms of argument that have now been identified that represent different kinds of plausible reasoning called argumentation schemes.

• Argumentation schemes sometimes appear similar to the forms of arguments we are familiar with in deductive logic, like modus ponens or syllogistic argument forms.

• But the most common ones (a) represent defeasible, plausible arguments that depend on common understanding of the way things can normally be expected to go in a kind of case familiar to speaker and hearer, and (b) depend on warrants that are generalizations that hold only subject to exceptions.

Matching Critical Questions

• Each argumentation scheme has a matching set of critical questions, and the scheme, used in conjunction with the questions, is the device for identifying, analyzing and evaluating the argument.

• Defeasible argumentation schemes with critical questions are used in the formal systems for modeling legal argumentation ASPIC+ and Carneades.

• Over 60 schemes are set out in (Walton, Reed and Macagno, 2008), and some of them have been used in empirical studies to identify arguments in everyday in political discourse and legal texts (argument mining).

Argument from Expert Opinion

• Major Premise: Source E is an expert in field F containing proposition A.

• Minor Premise: E asserts that proposition A (in field F) is true (false).

• Conclusion: A may plausibly be taken to be true (false).

Six Basic Critical Questions

• Expertise Question: How credible is E as an expert source?

• Field Question: Is E an expert in the field F that A is in?• Opinion Question: What did E assert that implies A?• Trustworthiness Question: Is E personally reliable as a

source?• Consistency Question: Is A consistent with what other

experts assert?• Backup Evidence Question: Is E’s assertion based on

evidence?

Forensics of Fine Art Example

• According to Martin Kemp, a professor at Oxford who is an expert on the forensics of fine art a portrait of a young woman in Renaissance dress, originally sold for about $20,000 in 1998, is an undiscovered masterwork of Leonardo da Vinci possibly worth more than $100 million.

• The fine details of the drawing were examined by Kemp’s expert eye. He found tiny marks and techniques in the painting consistent with the works of Leonardo.

Expert Kemp

• Martin Kemp is Emeritus Professor of the History of Art at Oxford University.He was trained in Natural Sciences and Art History at Cambridge University and the Courtauld Institute, London. He was British Academy Wolfson Research Professor (1993-98).

• He has taught at the universities of Glasgow and St. Andrews. He has held visiting posts in Princeton, New York, North Carolina and Los Angeles.

Carbon Dating Evidence

• The young woman in the portrait is identified as Bianca Sforza, the daughter of da Vinci's patron Ludovico Sforza, the Duke of Milan.

• Carbon dating showed the vellum, or animal skin on which the portrait was painted, is consistent with the time of da Vinci's work.

• However forgers often use old material to try to deceive art experts.

Corroborating Evidence

• Another expert, Pascal Cotte, uses a special camera to examine the painting and identifies left-handed brushstrokes of a kind consistent with the painting technique of Leonardo.

• Cotte found evidence of knife marks on the vellum, suggesting someone might have cut the portrait out as a single page of a book.

• A book is found in the national Library of Poland, the history of the Sforza family, and Cotte matched three holes in the portrait with the stitching in the book. It is a perfect match.

Expert Cotte

• Pascal Cotte is an engineer who developed a tool that enables the in-depth study of fine art paintings to reveal the true pigments for viewing and analysis without touching or damaging the paintings.

• He is the founder of Lumiere Technologies, a company in Paris that offers this service to museums to authenticate, restore and reproduce masterpieces of fine art.

Scheme with Implicit Premise

• Major Premise: Source E is an expert in subject domain S containing proposition A.

• Minor Premise: E asserts that proposition A (in domain S) is true (false).

• Conditional Premise: If source E is an expert in a subject domain S containing proposition A, and E asserts that proposition A is true (false), then A may plausibly be taken to be true (false).

• Conclusion: A may plausibly be taken to be true (false).

Explaining the Fallacy

• Because this version of the scheme has the modus ponens form, some might think argument from expert opinion can be modeled as deductively valid (closed; monotonic).

• This would be a great error, according to the analysis of the argumentum ad verecundiam fallacy given in (Walton, 1997, ch. 8).

• On that analysis, “fallacious cases occur where what is basically a presumptive and defeasible form of argument is presented in an absolutistic and final manner in a dialogue” (p. 230).

The Trouble with Experts

Experts are often wrong.In the recent stock meltdown, we discovered that some of our most important experts – our financial gurus - didn’t know much at all. Dutch artist John Myatt used house paint and KY jelly to forge the works of Great Masters. He managed to fool top art critics and museums for eight years before he was finally caught.

Pollock’s Red Light Example• Pollock (1995, 41) offered the following argument as an example. • Premise 1: This object looks red to me. • Premise 2: When an object looks red, then (normally, but subject to exceptions) it is red. • Conclusion: This object is red. • This argument is defeasible, since even objects that are not red look

red when illuminated by a red light. • Nevertheless, it is an argument that can be justifiably held to hold

tentatively, and give a reason to accept its conclusion, if there is no evidence that the situation is exceptional.

Argument from Perception

• Rather than seeing the argumentation in Pollock’s red light example as an inductive form of reasoning, it can be represented using the scheme for argument from perception (Walton, Reed and Macagno, 2008, 345).

• MAJOR PREMISE: To have a φ image (an image of a perceptible property) is a prima facie reason to believe that the circumstances exemplify φ.

• MINOR PREMISE: Person P has a φ image (an image of a perceptible property)

• CONCLUSION: It is reasonable to believe that φ is the case

Critical Questions

• CQ1: Are there circumstances giving a reason to think that P’s having a φ image may not be a reliable indicator of φ?

• CQ2: Are there other images that P has that suggest that P’s having a φ image may not be a reliable indicator of φ?

• CQ3: What test has been made, if any, that would confirm that P’s having a φ image is a reliable indicator of φ?

CQ1 Modeled as an Exception

CQ1: Are there circumstances giving a reason to think that P’s having a φ image may not be a reliable indicator of φ?

How Carneades Evaluates It

This object is red.

This object looks red to me.

When an object looks red then it is red.

This object is illuminated by a red light.

+ARGUMENT FROM

PERCEPTION

−

The circumstances are such that looking red is not a reliable indicator of being red. +

This object is red.

This object looks red to me.

When an object looks red then it is red.

This object is illuminated by a red light.

+ARGUMENT FROM

PERCEPTION

−

The circumstances are such that looking red is not a reliable indicator of being red. +

Precedent and Analogy• The basis for deciding whether one case is a precedent for another in law

is that it is based on an underlying argument from analogy (Walton, D., Similarity, Precedent and Argument from Analogy Artificial Intelligence and Law, 18 (3), 2010, 217-246) .

• But how is a case where a man sued a company because there was a decomposed snail in his beer bottle similar to a case where a man tried to sue because of a defective Buick automobile?

• My answer: there is something about the common sequence of events that makes the one case similar to the other.

• First the plaintiff bought some product that he assumed was the normal product he expected, and he thought therefore that the product was reasonably safe to use. Then something in the product turned out to be defective, and when he used the product this defect caused some harm that impacted badly on his health.

Script Common to Both Cases

Scheme for Argument from Analogy

• In the basic scheme for argument from analogy, a similarity between two cases where a proposition A holds in the one case can shift a weight of evidence from one case to the other.

• The following basic scheme (Walton, Reed and Macagno, 2008, 315) represents this version of the structure of argument from analogy.

• Similarity Premise: Generally, case C1 is similar to

case C2.

• Base Premise: A is true (false) in case C1.

• Conclusion: A is true (false) in case C2.

Script as the Basis of the SimilarityPremise in Argument from Analogy

CQs for Argument from Analogy

• CQ1: Are there particular respects in which C1 and C2 are different that would tend to undermine the force of the similarity cited?

• CQ2: Are there particular respects in which C1 and C2 are similar that would tend to further support the force of the similarity cited?

• CQ3: Is A the right conclusion to be drawn in C1?

• CQ4: Is there some other case C3 that is also similar to C1, but in which some conclusion other than A should be drawn?

Analogy Scheme with Implicit Premise

• Similarity Premise: Case C1 is similar to case C2.

• Base Premise: A is true (false) in case C1.

• Implicit Conditional Premise: If case C1 is similar to case C2, and A is true (false) in case C1, then A is true (false) in case C2 [material conditional: no exceptions].

• Conclusion: A is true (false) in case C2.

Is it Deductive?

• Once again, as in the case of argument from expert opinion, the argument from analogy becomes a fallacious argument when construed in this closed (nonmonotonic) way.

• Argument from analogy has to be defeasible and open to case-based critical questioning and counter-arguments as new information comes in.

• Otherwise it is ossified, fixed in an unduly restrictive (closed) way that makes it not open to refutation.

Case-Based Reasoning

• CATO (Aleven, 1997) is based on factors representing respects in which a case is similar to or different from another one (questions CQ1 and CQ2 ).

• This can happen in case-based reasoning when some factors support the argument while others detract from it.

• In case-based reasoning argument from analogy is a defeasible form of argument in which further evidence can be introduced that can go against or even defeat the argument.

• To weigh the arguments on each side, we have to consider the factors on each side, and determine which factors are more “on-point”, or relevant.

Version 2 and Modus Ponens

• If you look at version 2 you can see that the argument has something like a modus ponens structure as an inference. It looks like the form called defeasible modus ponens.

• Verheij (2001, p. 232) proposed that defeasible argumentation schemes fit a form of argument he called modus non excipiens: as a rule, if P then Q; P; it is not the case that there is an exception to the rule that if P then Q; therefore Q.

DMP

• This form of argument can be used for evaluating defeasible inferences like the Tweety argument: If Tweety is a bird, Tweety flies; Tweety is a bird; therefore Tweety flies.

• This form of argument was called defeasible modus ponens (DMP) by Walton (2002).

• An example (Copi and Cohen, 1998, p. 363) also illustrates DMP: if he has a good lawyer then he will be acquitted; he has a good lawyer; therefore he will be acquitted.

Binary DMP Form• The binary DMP form of argument has the following structure,

where A1, A2,…, An is a set of assumptions, E1, E2,…, En is set of exceptions, and B is a proposition.

[(A1, A2,…, An) & (E1, E2,…, En)] => B

A1, A2,…, An

E1, E2,…, En

------------------------- B • There are two different kinds of prerequisites, the assumptions,

including the ordinary premises, and the exceptions, that have to be met for the conclusion to be defeasibly inferred.

Research on Other Schemes

• Even though in this paper evidence has been presented to show that the scheme for argument from expert opinion has this DMP form, it remains to be seen how many of the other schemes share it.

• Some of them, for example the scheme for argument from lack of evidence, also called the argument from ignorance, does not have this form (Caminada, 2008).

• It has a defeasible modus tollens form of argument. Also, some of the other schemes are more complex, and apparently need a separate study.

Conclusion

• It has also been argued that the general logical DMP form is not itself an argumentation scheme, but is better seen as a general logical category of reasoning into which the schemes fit.

• Prakken (2010) also noted that some of the arguments categorized as argumentation schemes in the argumentation literature do not really seem to be schemes in narrower sense applicable to many of the other schemes.

• Instead, they appear to be more general categories of reasoning.

ReferencesCaminada, M. (2008). On the Issue of Contraposition of Defeasible Rules. Computational Models of Argument: Proceedings of COMMA 2008. Ed. P. Besnard, S. Doutre and A. Hunter. Amsterdam: IOS Press, 109-115.Gordon, T. F. (2010). The Carneades Argumentation Support System, Dialectics, Dialogue and Argumentation, ed. C. Reed and C. W. Tindale, London: College Publications.Prakken, H. (2010).On the Nature of Argument Schemes. Dialectics, Dialogue and Argumentation, ed. Chris Reed and Christopher W. Tindale, London: College Publications, 167-185.Reed, C. and Walton, D. (2003). Diagramming, Argumentation Schemes and Critical Questions, Anyone Who Has a View: Theoretical Contributions to the Study of Argumentation, ed. F. H. van Eemeren, J. A. Blair, C. A. Willard and A. Snoek Henkemans. Dordrecht: Kluwer, 195-211.Verheij, B. (2001). Legal Decision Making as Dialectical Theory Construction with Argumentation Schemes, The 8th International Conference on Artificial Intelligence and Law: Proceedings of the Conference, New York Association for Computing Machinery, 225-236. Available at http://www.ai.rug.nl/~verheij/publications.htm.Walton, D. Appeal to Expert Opinion. University Park: Penn State Press, 1997.Walton D. and Gordon, T. F. (2005). Critical Questions in Computational Models of Legal Argument, Argumentation in Artificial Intelligence and Law, IAAIL Workshop Series, ed. Dunne, P. E. and T. J. M. Bench-Capon. Nijmegen: Wolf Legal Publishers, 103-111.Walton, D., Reed, C. and Macagno, F. (2008). Argumentation Schemes, Cambridge: Cambridge University Press.