Download Presumption and Burden of Proof: IADA Workshop

Elements and Methods of
Argumentation Theory
University of Padua Lecture
Padua, Italy, Dec.1, 2008.
Douglas Walton
Assumption University Chair in
Argumentation Studies
Centre for Research in Reasoning,
Argumentation & Rhetoric (CRRAR)
University of Windsor
What is an Argument?
 An argument is a social and verbal means of trying to
resolve, or at least contend with, a conflict or
difference that has arisen between two parties
engaged in a dialog by eliciting reasons on both sides
(Walton, 2007).
 According to this definition, an argument necessarily
involves a claim that is advanced by one of the
parties, typically a claim that the one party has put
forward as true, and that the other party questions.
 Arguments have premises and conclusions, they can
be of different kinds, they can be stronger or weaker
(have weights), and different standards of proof can
be required of them in different contexts of use.
Deductive Argument
 Premise: Luigi is an Italian soccer player.
 Premise: All Italian soccer players are divers.
 Conclusion: Luigi is a diver.
 It is logically impossible for the premises to be
true and the conclusion false.
 But is the first premise true?
Inductive Argument
 Premise: Luigi is an Italian soccer player.
 Premise: Most Italian soccer players are
divers.
 Conclusion: Probably Luigi is a diver.
 It is improbable for the premises to be true
and the conclusion false.
Wigmore (1931, p. 20) considered arguments of a kind
that are commonly used in collecting evidence in law.
Last week the witness A had a quarrel with the
defendant B, therefore A is probably biased against B.
A was found with a bloody knife in B’s house, therefore
A is probably the murderer of B.
Deductive, Inductive, and the
3rd Type: Abductive?
Clue: Backward Reasoning by Explanation?
Defeasible Reasoning

Birds fly.

Tweety is a bird.

Therefore Tweety flies.
 Subject to exceptions (Tweety = penguin).
 Based on non-absolute generalizations.
 Nonmonotonic: valid arguments can
become invalid by adding premises.
Defeasible Linked Argument
Typical Argumentation Schemes
 Common schemes include such familiar types of argumentation
as argument from lack of knowledge, argument from example,
argument from a rule to a case, argument from a verbal
classification, argument from position to know, argument from
expert opinion, argument from analogy, argument from
precedent, 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.
 In addition to presumptive schemes, it is possible to treat
deductive and inductive forms of argument as schemes.
 All are linked arguments.
Argument from Expert Opinion
 Dr. Phil is an expert in psychology.
 Dr. Phil says that Bob has low self-esteem.
 Therefore Bob has low self-esteem.
Scheme: Arg. from Expert Opinion
 Major Premise: Source E is an expert in domain D
containing proposition A.
 Minor Premise: E asserts that proposition A (in
domain D) is true (false).
 Conclusion: A may plausibly be taken to be true
(false).
Araucaria
 Araucaria is a software tool for analyzing arguments.
It aids a user in reconstructing and diagramming an
argument using a simple point-and-click interface.
The software also supports argumentation schemes,
and provides a user-customizable set of schemes
with which to analyze arguments.
 Once arguments have been analyzed they can be
saved in a portable format called AML, the Argument
Markup Language.
 http://www.computing.dundee.ac.uk/staff/creed/arauc
aria/
Dr. Phil Argument Diagram
Corroborative Expert Opinions
Questionable Example
 This alarming defense spending will lead to
economic disaster. According to Einstein,
heavy defence spending in a country is a sign
of political instability that is not consistent with
sound fiscal policies that can yield lasting
financial recovery from a recession.
 Einstein is cited as an expert.
 But is he an expert in the right field for the
argument?
 Fallacy of argument from authority.
Critical Questions for Scheme


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Expertise Question: How knowledgeable is E as an
expert source?
Field Question: Is E an expert in the field D 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?
Screen Shot of Dr. Phil
Enthymemes
 An enthymeme is an argument with an implicit
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premise or conclusion.
All physicians are college graduates, so all members
of the AMA are college graduates.
MISSING PREMISE: All members of the AMA are
physicians.
Roadside sign: “The bigger the burger, the better the
burger. The burgers are bigger at Burger King.”
MISSING CONCLUSION: The burgers are better at
Burger King.
Argument with Missing Premises
 This example was found on a web site called animal freedom.
 Animals in captivity are freer than in nature because there are
no natural predators to kill them.
 Conclusion: animals in captivity are freer than in nature.
 Explicit Premise: there are no natural predators to kill animals
that are in captivity.
 Implicit Premise: there are natural predators to kill animals that
are in nature.
 Implicit Premise: if animals are in a place where there are no
natural predators to kill them, they are freer than if they are in a
place where there are natural predators to kill them.
Common Knowledge & Commitment
How Arguments are Evaluated
 Burdens of proof and standards of proof, along with
argument weights, determine how to evaluate the
argumentation in a dialog.
 The burden and standard of proof are set at the
opening stage, and depend on the type of dialog.
 In the argumentation stage, each side presents
reasons supporting its view and attacks the opposed
view by raising critical questions and rebuttals.
 The burdens and standards are then applied at the
closing stage to determine which side won and which
lost the dialog.
Some Further Reading
 Douglas Walton, ‘The Three Bases for the
Enthymeme: A Dialogical Theory’, Journal of
Applied Logic, 6, 2008, 361-379.
 Douglas Walton, Fundamentals of Critical
Argumentation, Cambridge, Cambridge
University Press, 2008.
 Douglas Walton, Chris Reed and Fabrizio
Macagno, Argumentation Schemes,
Cambridge, Cambridge University Press,
2008.