Transcript Visualization Tools, Argumentation Schemes and Expert Opinion Evidence in Law Douglas Walton University of Winnipeg, Canada Thomas F.

Visualization Tools, Argumentation Schemes and Expert
Opinion Evidence in Law
Douglas Walton
University of Winnipeg, Canada
Thomas F. Gordon
Fraunhofer FOKUS, Berlin, Germany
January 28, 2007
Outline
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The two main tools used in argumentation theory are the formal models of
dialogue (of different types) and the schemes.
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Question: how can argumentation schemes best be used in argument
visualization technology?
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Question: how much of the dialogue stuff can be put on argumentation
diagrams with schemes without making the system too complex for the
user?
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Discussion restricted to two argument visualization systems, Araucaria and
Carneades, and to one scheme, argument from expert opinion.
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Argument from expert opinion put forward as an example of an existing
argumentation scheme that may need to be modified for legal use.
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Three version of this scheme discussed.
Introductory
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In argumentation theory, arguments are identified, analyzed and evaluated
by means of argumentation schemes representing stereotypical kinds of
ordinary reasoning.
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The scheme is a form of argument (normative) that can be applied to a
particular argument in a given text of discourse.
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The most interesting schemes at the moment are the defeasible ones that
represent plausible reasoning, rather than deductive or inductive reasoning.
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Each scheme has a special set of critical questions matching it. An
argument is evaluated using the critical questions.
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The argument holds as plausible unless critically questioned or attacked by
an opposing argument.
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But there may be different ways different critical questions do this.
Argumentation Schemes
Common schemes include such familiar types of argumentation as
argument from sign, argument from example, argument from commitment,
argument from a verbal classification, argument from position to know,
argument from analogy, argument from precedent, argument from a rule to a
case, argument from correlation to cause, practical reasoning, abductive
reasoning, argument from gradualism, and the slippery slope argument.
Other schemes that have been studied include argument from waste (also
called sunk costs argument), argument from temporal persistence and
argument from appearance. These schemes are called presumptive or
defeasible, meaning that they can fail in some instances, for example by the
asking of critical questions. They represent arguments that are “necessary
but dangerous” (WilliamTwining).
Scheme for Argument from Appearance
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Major premise: If the object looks x then the object is x.
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Minor premise: The object looks x.
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Better explanation exception: there is a better explanation for the object's
appearance.
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Conclusion: The object is x.
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Example (Pollock): This object looks red, therefore it is red. But a better
explanation of why it looks red may be that it is illuminated by a red light. If
this is known to be the case, it is an exception.
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Example (Prakken): This object looks like an affidavit, therefore (plausibly) it
is an affidavit.
Pollock’s Red Light Example in Carneades
Another Argumentation Scheme
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Scheme for 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).
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The Six Basic Critical Questions
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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?
Argument from Expert Opinion with Scheme and Generalization
Problem with Representing Critical Questions
What Happens When the Respondent Asks a Critical Question?
Two Kinds of Questions
1. When the credibility critical question is asked, the burden shifts to the
proponent to answer it. If no answer is given, the proponent’s argument
fails.
2. When the trustworthiness critical question is asked, something else is
needed to make the burden of proof shift to the other side. To make the
proponent’s argument fail, the respondent needs to support the critical
question with further argument. For example, the questioner might offer
evidence that the expert is biased. Such evidence would cast doubt on
the assumption that the expert is trustworthy.
The Credibility Question as a Rebutter in Araucaria
The Trustworthiness Question as an Undercutter in Araucaria
The Carneades Solution (Basic Idea)
Arguments have four kinds of premises:
Ordinary premises – for the minor and major premises of schemes.
Assumptions – for critical questions to be answered by the
proponent.
Exceptions – for critical questions to be answered by a respondent.
Negative Premises – like ordinary premises except that the
proponent must prove that the statement is not the case.
Modeling Critical Questions with Carneades
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When instantiating an argumentation scheme, each critical question is
modeled as an assumption or an exception.
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Modeling the critical question as an assumption places the burden of proof
on the proponent, but only after the respondent has made an issue out of its
statement. So long as the statement is undisputed, the assumption holds.
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Modeling the critical question as an exception places the burden of proof on
the respondent. Even after the respondent has made an issue out of the
exception’s statement, the exception continues to hold until sufficient
arguments have been asserted to make the statement acceptable, given its
proof standard.
Syntax of Argument from Expert Opinion in Carneades
(argument arg-1
(scheme argument-from-expert-opinion)
(premises
(domain e d)
(asserted e a)
(within a d)
(assuming (credible e))
(assuming (based-on-evidence (asserted e a)))
(unless (not (trustworthy e)))
(unless (not (consistent-with-other-experts e))))
(conclusion (pro a)))
Argument from Expert Opinion in Carneades
Bias Allegation Supporting Trustworthiness Question in Carneades
Version 1 of Legal Argument from Expert Opinion
Ordinary Premise 1: E is an expert in knowledge domain D.
Ordinary Premise 2: E said that statement S is true.
Assumption 1: S is in D.
Assumption 2: E has depth of knowledge in D.
Conclusion: S may plausibly be taken to be true.
Problem: Assumption 2 seems to add nothing new (as stated), merely
repeating ordinary premise 1. What’s the difference?
Version 2 of Legal Argument from Expert Opinion
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Ordinary Premise 1: E is an expert in knowledge domain D.
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Ordinary Premise 2: E said the sentence S*.
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Ordinary Premise 3: S is a reasonable interpretation of S*.
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Assumption 1: S is in D.
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Assumption 2: The knowledge of E about D is deep enough to know about
S.
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Assumption 3: E’s testimony about S* is based on his own careful analysis
of the evidence in the case.
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Exception 1: S is inconsistent with what other experts say.
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Exception 2: E is not trustworthy.
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Conclusion: S may plausibly be taken to be true.
Version 2 of Argument from Expert Opinion
Ordinary Premise 1: E is an expert in knowledge domain D.
Ordinary Premise 2: E said the sentence S*.
Ordinary Premise: S is a reasonable interpretation of S*.
Assumption 1: S is in D.
Assumption 2: The knowledge of E about D is deep enough to know about S.
Assumption 3: E’s testimony S* is based on his own careful analysis of
evidence in this case.
Exception 1: S is inconsistent with what other experts in D say.
Exception 2: E is not trustworthy.
Conclusion: S may plausibly be taken to be true.
Conclusions
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Both Araucaria and Carneades can be used to model arguments from
expert opinion in a way useful for visualization of evidence in law.
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Araucaria has many useful features, but appears limited in how well it can
deal with critical questions with different burdens of proof.
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There are three versions of the argumentation scheme for argument from
expert opinion that might be adaptable to law.
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It appears that the argumentation scheme for argument from expert opinion
can best be modeled in law using version 2.
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Carneades is especially suitable to using version 2 of the scheme for
argument from expert opinion in law.
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The lessons learned with this scheme apply to other schemes, like the
scheme for argument from appearance, and so forth.