Transcript Argument Visualization Tools for Corroborative Evidence

Argument Visualization Tools for
Corroborative Evidence
2nd International Conference on Evidence Law
and Forensic Science (ICELFS 2009)
Beijing, China, July 25, 2009
Douglas Walton (CRRAR)
University of Windsor
http://www.dougwalton.ca
Defining Corroborative Evidence
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Corroborative evidence can be broadly defined as
any evidence that further supports some evidence
that already exists in a case.
The evidence that is already there can be called the
primary evidence, and the evidence that supports it
can be called the secondary evidence.
What is meant when it is said that the secondary
evidence supports the primary evidence is that the
secondary evidence increases the probative weight
of the primary evidence.
An Example
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A witness testified that she saw the defendant drive
his car into a red car. Subsequent to that a second
witness testified that he saw red paint on the fender
of the defendant’s car on the day after the accident.
In this case both kinds of evidence are based on
testimony.
The primary evidence is the testimony of the first
witness that she saw the defendant drive his car
into the red car.
The secondary, or corroborating evidence, is the
testimony of the second witness that he saw red
paint on the fender of the defendant's car.
Questioning the Definition
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Some would say that the red paint example
is not really a case [strictly speaking] of
corroborative evidence.
Reason: it may not be true that the red paint
evidence increases the probative weight of
the witness testimony evidence.
Still, if both pieces of evidence support the
conclusion that the defendant drove his car
into the red car, the case is [in a broader
sense] one of corroborative evidence.
Two Kinds of Arguments
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In a linked argument, the premises function
together as a reason to support the conclusion.
Example: Bob is an expert on paint matching; Bob
says that this paint sample matches that one;
therefore this paint sample matches that one.
In a convergent argument, each premise is a
separate reason for the conclusion.
Example: A witness testified that she saw the
defendant drive his car into a red car. Subsequent
to that a second witness testified that he saw red
paint on the fender of the defendant’s car on the
day after the accident.
Example of a Linked Argument
This paint sample matches that one.
Bob is an expert on paint
matching.
Bob says that this paint sample
matches that one.
Example of a Convergent Argument
The defendant drove his
car into a red car.
A witness testified that she
saw the defendant drive
his car into a red car.
A second witness testified
that he saw red paint on the
fender of the defendant’s car
on the day after the accident.
A Question about Independence
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In the red paint example [classified as
a convergent argument] is each
premise an independent reason?
Maybe the paint matching evidence
increases the probative weight of the
eyewitness testimony evidence.
This would mean that the one reason
is not independent from the other.
Argument from Expert Opinion
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Major Premise: Source E is an expert in subject domain S containing
proposition A.
Minor Premise: E asserts that proposition A is true (false).
Conclusion: A is true (false).
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Critical Questions for Argument from Expert Opinion
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CQ1: Expertise Question. How credible is E as an expert source?
CQ2: Field Question. Is E an expert in the field that A is in?
CQ3:Opinion Question. What did E assert that implies A?
CQ4: Trustworthiness Question. Is E personally reliable as a source?
CQ5: Consistency Question. Is A consistent with what other experts
assert?
CQ6: Backup Evidence Question. Is E's assertion based on
evidence?
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Argument from Witness Testimony
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Position to Know Premise: Witness W is in position to know whether
A is true or not.
Truth Telling Premise: Witness W is telling the truth (as W knows it).
Statement Premise: Witness W states that A is true (false).
Conclusion: A may be plausibly taken to be true (false).
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Critical Questions for Argument from Witness Testimony
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CQ1: Is what the witness said internally consistent?
CQ2: Is what the witness said consistent with the known facts of the
case (based on evidence apart from what the witness testified to)?
CQ3: Is what the witness said consistent with what other witnesses
have (independently) testified to?
CQ4: Is there a bias that can be attributed to the witness?
CQ5: How plausible is the statement A asserted by the witness?
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Three Ways One Argument Can
Support Another Argument
Example of Argument Support
Araucaria
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Araucaria is a free software tool for analyzing
arguments that helps a user to diagram a given
argument using a point-and-click interface.
The user moves the text of discourse into a box on
a left window of the Araucaria interface, and then
highlights each statement (premise or conclusion).
The user can then draw an arrow representing each
inference from a set of premises to a conclusion.
Araucaria was the first argument visualization tool
to incorporate the use of argumentation schemes.
Araucaria Menu with Critical
Questions
Corroborative Expert Opinion
Evidence in Araucaria
Corroborative Expert Opinion
Evidence in Rationale
Carneades Screen Shot
ArguMed: Two Types of
Corroborative Evidence
Schum (1994): Two Forms of
Corroborative Evidence
Supportive Corroborative
Evidence in BAC Case
Convergent Corroborative
Evidence in BAC Case
Expert Testimony with
Double Counting
Corroborative Expert Opinion
Evidence in Carneades
A Third Category?
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In addition to linked and convergent arguments,
there is a third category called EvAcc arguments.
An evidence accumulating argument is one where
the probative weight of the conclusion increases as
you go from each premise to the next.
Example: in diagnosis of diseases, each premise
indicating the presence of a symptom give only a
small probative weight to the conclusion that the
patient has the disease, but as you go from each
premise to the next the probative weight of the
conclusion increases [step by step].
An Example from MYCIN
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Prem1: The gram stain of the organism is gramneg.
Prem2: The morphology of the organism is rod.
Prem3: The aerobicity of the organism is anaerobic.
Conclusion: There is suggestive evidence that the
identity of the organism is bacteroides.
Each premise gives a small probative weight for the
conclusion, but as you go from each premise to the
next, that probative weight increases until finally the
argument is a “clincher” that gives enough evidence
for a diagnosis.
Classifying EvAcc Arguments
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They seem more like convergent
arguments, because each reason is
independent from the next as evidence.
But they also seem like linked arguments,
because the premises go together in a
cumulative buildup of evidence.
This may be a third category, but how
should it be visually represented?
Hypothesis on How to
Represent EvAcc Arguments
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Maybe EvAcc arguments can be modeled
using standards of proof.
According to this hypothesis, each premise
is a sign, and as each argument from sign is
put forward greater probative weight is
gained.
Finally, the probative weight in support of
the conclusion meets a standard of proof.
Some Useful Resources
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Argument Mapping Software
Araucaria: http://araucaria.computing.dundee.ac.uk/
ArguMed: http://ai.rug.nl~verheij/
Rationale: http://rationale.austhink.com/
Carneades: http://carneades.berlios.de/downloads/
Origins of Evidence Diagramming
John H. Wigmore, The Principles of Judicial Proof, Boston,
Little, Brown and Company, 1913.
Argumentation Schemes
Douglas Walton, Chris Reed and Fabrizio Macagno,
Argumentation Schemes, Cambridge, Cambridge University
Press, 2008.